Thermo-responsive engineering of Greencrete blocks: a foundational study toward waste-based next-generation concrete

Thermo-responsive engineering of Greencrete blocks: a foundational study toward waste-based next-generation concrete | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Thermo-responsive engineering of Greencrete blocks: a foundational study toward waste-based next-generation concrete Muhammad Ali Fardoush Siddquy, Zakaria Hossain, Md Yachin Islam This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7381327/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 05 Apr, 2026 Read the published version in Discover Sustainability → Version 1 posted 12 You are reading this latest preprint version Abstract The relentless surge in the global population and urbanization is intensifying demands on the construction sector, underscoring the urgent need for sustainable masonry solutions with reduced environmental footprints. This study systematically investigated the structural, physical, and microstructural performance of soil, rice husk ash (RHA), and ordinary Portland cement (OPC) composite Greencrete blocks, focusing on two different curing conditions: 24°C with humidity and 30°C without moisture. Sixteen compositional matrices were prepared, focusing on low- and medium-RHA systems (0%, 5%, 10%, and 15% RHA; 0%, 8%, 10%, and 12% OPC), and subjected to qualitative evaluations—namely, bulk density, water absorption, compressive strength, and energy-dispersive X-ray spectroscopy (EDS) coupled with enhanced scanning electron microscopy (SEM). The results revealed that the water absorption of the 5RHA12C sample at 24°C was 30.65%, which increased to 32% at 30°C—indicating a more porous structure. Additionally, the density changed significantly, from 1301.50 kg/m³ at 24°C to 1301.99 kg/m³ at 30°C. This result proves that an appropriate ratio of rice husk ash to cement and slow curing improves the durability and performance of the resulting Greencrete blocks. However, the same sample exhibited the highest compressive strength of 2.83 MPa at 24°C and 3.39 MPa at 30°C, which is in direct contrast to the other results. SEM‒EDS analysis revealed that RHA and OPC formed a dense and homogeneous calcium silicate hydrate (C–S–H) gel matrix under different temperature and humidity conditions, resulting in increased compressive strength and durability. Overall, the study presents strong empirical support for the use of agro-industrial waste, such as RHA, in the production of low-carbon, climate-resilient masonry units. The results align with the Sustainable Development Goals (SDGs 11 and 12) and lay the foundation for next-generation concrete research, with an emphasis on long-term performance and environmental assessment under field conditions. Greencrete blocks Rice husk ash (RHA) Sustainable masonry Compressive strength Curing conditions Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 Figure 14 Figure 15 Figure 16 Figure 17 Figure 18 Figure 19 Figure 20 Figure 21 Figure 22 Introduction The global population is projected to reach 8.2 billion in 2024 and is expected to continue growing for the next 50 to 60 years. The United Nations estimates that the world population will peak at 10.3 billion by the middle of the 2080s [ 1 ]. In 1950, only 30% of the global population lived in urban areas. However, due to increasing industrialization, infrastructure development, and economic opportunities, the urban population rose to 55% by 2018. If this trend continues, approximately 68% of the world’s population will reside in cities by 2050 [ 2 ]. In addition to population growth, urbanization, defined by the expansion of built-up areas, has accelerated significantly [ 3 ]. Numerous studies have established that urbanization has a broad range of environmental and socioeconomic impacts, including the depletion of local resources, the degradation of landscapes and ecosystems, and increased greenhouse gas emissions that contribute to climate change. [ 4 , 5 , 6 ]. Bricks have long been an essential material associated with urbanization, and archaeological evidence suggests that burnt bricks were foundational to early urban centers and that the demand for burnt clay bricks remains strong due to their durability, affordability, and widespread availability [ 7 ]. Globally, approximately 1,500 billion burnt clay bricks are produced annually, with approximately 87% of production, approximately 1,300 billion bricks concentrated in Asia. This industry consumes more than 3.13 billion cubic meters of clay each year, contributing to severe land degradation [ 8 , 9 ]. Furthermore, brick kilns in Asia alone consume approximately 110 million tonnes of coal annually, with each brick emitting approximately 0.41 kg of CO₂, resulting in the brick industry accounting for approximately 2.7% of global carbon emissions [ 10 ]. In response, the construction industry is transitioning toward more sustainable building materials. A significant innovation in this transition is the development of unfired or compressed earth bricks (CEBs), also known as Greencrete blocks. Greencrete, a modified term for green concrete, has developed over decades through efforts to incorporate industrial and agricultural waste into concrete production, aiming to enhance performance, reduce environmental impact, and lower costs. Defined as any material with a lower carbon footprint and specific energy content than conventional OPC concrete, Greencrete is vital for meeting future construction needs while conserving natural resources [ 11 ]. These blocks utilize locally sourced soil, stabilized with minimal cement and pozzolanic agro-industrial by-products such as rice husk ash (RHA). The performance of stabilized CEBs depends on several parameters, including the soil gradation, water content, compressive strength, and the type and proportion of stabilizers used [ 12 ]. The high silica content in RHA reacts with calcium hydroxide during cement hydration, forming calcium silicate hydrate (C-S-H) compounds. These compounds enhance the structural integrity of the bricks, making them stronger and more durable. Consequently, RHA is an environmentally friendly and cost-effective soil stabilizer [ 13 ], with the potential to reduce carbon emissions by up to 80% compared with conventional fired bricks [ 14 ]. In 2024/25, global rice production reached 535.8 million tonnes, representing an increase of 13.7 million tonnes from the previous year [ 15 , 16 ]. Japan alone produces approximately 7.3 million tonnes of rice annually, generating approximately 2 million tonnes of rice husks—most of which remain underutilized and present significant waste management challenges [ 17 ]. Rice husks constitute 20 to 22% of the rice's total weight of rice, with approximately 25% of the husks converted to ash upon incineration [ 18 , 19 ]. Due to its high silica and pozzolanic content, RHA has been extensively studied as a next-generation material in sustainable construction [ 20 , 21 , 22 , 23 ]. Moreover, recent advancements have incorporated carbon capture, utilization, and storage (CCUS) technologies into cementitious systems. Through O₂-curing and mineral carbonation, captured CO₂ reacts with calcium hydroxide to form stable calcium carbonate (CaCO₃), which not only improves the performance of the material but also enhances long-term carbon sequestration [ 24 ]. This shift, from traditional burnt bricks to CCUS-enabled Greencrete, embodies the circular economy approach and the evolution of low-carbon construction technologies aligned with net-zero emission goals [ 25 ]. Traditional burnt bricks exhibit compressive strengths ranging from 10.27 MPa to 19.71 MPa, densities between 1549 kg/m³ and 1989 kg/m³, and water absorption rates ranging from 10–18% [ 26 ]. In one study, bricks containing 2.5% RHA achieved a compressive strength of 16.21 MPa, with a density of 1549 kg/m³ and 14.5% water absorption [ 27 ]. These results indicate the potential of RHA for developing lightweight and sustainable bricks with acceptable performance characteristics. Several investigations have confirmed that 5 to 15% RHA substitution improves the compressive strength, with 10% RHA frequently yielding optimal results. Additionally, RHA reduces water absorption and enhances long-term durability [ 28 , 29 , 30 ]. Nevertheless, in addition to composition, the curing environment, particularly temperature and humidity, plays a decisive role in influencing brick quality. Studies have demonstrated that controlled curing at 24°C with a relative humidity ≥ 90% accelerates the hydration process of RHA-cement-soil blocks, increasing density and compressive strength while minimizing porosity [ 31 ]. In contrast, ambient curing at room temperature (approximately 30°C) slows hydration, resulting in increased porosity, reduced durability, and decreased mechanical performance [ 32 ]. Controlled curing at 24°C (RH > 90%) ensures sufficient internal moisture, promotes complete hydration and reduces microcracks, which leads to strength that is 30% greater than that of ambient-cured samples after 7 days. Water absorption rates typically remain between 16% and 18%, and overall durability improves by 25–30%. Autoclave curing, involving elevated temperature and pressure, has also been shown to increase the compressive strength by 65–85% while reducing water absorption from 18–8% [ 33 , 34 , 35 ]. Recent research has demonstrated that the curing environment, particularly temperature and humidity, substantially influences the physical, mechanical, and environmental performance of unfired bricks manufactured with soil, rice husk ash (RHA), and cement. Accordingly, a comparative investigation of controlled curing conditions (24°C, relative humidity ≥ 90%) versus ambient room temperature curing (30°C, natural humidity) is both pertinent and essential. This study seeks to address existing knowledge deficiencies by empirically evaluating the performance of Greencrete blocks under these two distinct curing regimes. Despite evident environmental and performance advantages associated with Greencrete and CCUS concrete-enabled materials, their large-scale implementation remains constrained due to gaps in scientific understanding and the absence of standardized methodologies. Most extant studies predominantly focus on material-level properties without thoroughly examining curing dynamics, carbon sequestration potential, and lifecycle performance. Furthermore, the thermal responsiveness of waste-derived Greencrete materials remains largely unexplored. To bridge these gaps, this research conducts a comprehensive experimental analysis of the thermal responsiveness of Greencrete blocks composed of soil, RHA, and cement. A comparative assessment evaluates key performance indicators—including compressive strength, water absorption, and bulk density—under controlled (24°C, RH ≥ 90%) and ambient (30°C) curing environments at 28 days. The findings aim to elucidate the influence of curing parameters on hydration kinetics, thereby supporting the development of climate-responsive, low-carbon construction materials in alignment with global sustainability objectives. Materials and methods Materials Soil In this study, the expansive soil used for Greencrete block-making was collected from the Handa area of Tsu city, Mie Prefecture, Japan, approximately 22 km from Mie University. This location was chosen because of the naturally weak, expansive, and poorly consolidated nature of the soil, which presents geotechnical challenges. The representative samples were collected via a systematic soil sampling method, following standard geotechnical procedures. The soil under investigation is classified as A-7–5(5) according to the American Association of State Highway and Transportation Officials (AASHTO) classification system, which typically represents a highly plastic clayey soil with poor drainage characteristics [ 35 ]. The samples for testing were prepared via the air-drying method according to the JIS A 1201:2020 standard. In this method, the soil is dried in a shaded area under normal ambient conditions until it reaches a constant mass, ensuring that the physical properties of the soil remain unchanged. The grain size distribution of the soil was subsequently determined via sieve and hydrometer analyses as per JIS A 1204:2020. Notably, this standard aligns with the internationally recognized International Organization for Standardization, ISO 17892-4:2016 standard. The test results revealed that the soil particle sizes ranged from 0.001 mm to 2.0 mm, indicating a predominantly fine-grained soil. The analysis is presented in Fig. 3 . On the other hand, tests according to JIS A 1205:2020 determined the soil's liquid limit (58.21%), plastic limit (31.05%), sand content (6.2%), silt content (52.56%), and clay content (41.24%), as shown in Table 1 . Additionally, energy dispersive X-ray spectroscopy (EDS) analysis revealed that the soil contained 91.10% silica, 4.35% carbon dioxide (CO₂), 2.40% potassium oxide (K₂O), and 0.57% calcium oxide (CaO). On scientific grounds, this soil is considered suitable for stabilization [ 13 , 36 ]. Rice husk ash In this study, rice husk ash (RHA) with a high silica content of 93.30% was obtained from Make Integrated Technology Co., Ltd., Osaka, Japan. The supplier also provided the material's composition. A high silica level was achieved by burning the rice husk in a computer-controlled incinerator at 650–700°C for 27 hours. The particle size of this RHA ranged from 0.07 to 0.3 mm (as shown in Fig. 3 ), with a specific gravity of 1.47 and a loss on ignition of 4.00–6.00% [ 13 ]. Among the chemical components, this RHA contains 93.30% silica (SiO₂), 4.49% potassium oxide (K₂O), 0.82% calcium oxide (CaO), 0.43% phosphorus pentoxide (P₂O₅), 0.06% iron oxide (Fe₂O₃), 0.04% alumina (Al₂O₃), and 0.86% other compounds. According to research, RHA is 100% effective for making hollow blocks and is widely acclaimed as an eco-friendly construction material owing to its physio-chemical properties and specific gravity [ 35 , 36 ]. Portland cement Ordinary Portland cement (OPC) was used in minimal amounts in this study, primarily to activate the pozzolanic reaction by providing calcium oxide ions, which help bind the materials together. As shown in Table 4, the physical and chemical properties of OPC enable it to act effectively as an activator and binder. The cement itself contains alite (Ca₃SiO₅), which is the main phase responsible for the early and high strength of Portland cement. The decision to use the minimum required dosage of OPC in this study was driven by the aim of reducing cement consumption, increasing durability, and taking advantage of the ready market availability of OPC and its effectiveness as an amorphous SiO₂ activator in pozzolanic systems [ 32 , 33 ]. Table 1 Major properties of OPC [ 13 , 35 , 36 ]. Property Value Specific Gravity, g/cm 3 3.15 Specific surface area, m 2 /kg 340 Loss of Ignition, % < 4 Initial setting time, minutes 170 Final setting time, minutes 255 28-day compressive strength, MPa 33–53 Calcium Oxide (CaO), % 63.40 Silica (SiO 2 ), % 21.60 Iron Oxide (Fe 2 O 3 ), % 5.35 Alumina (Al 2 O 3 ), % 4.45 Sulfur trioxide (SO 3 ), % 1.92 Magnesium oxide (MgO), % 1.65 Potassium Oxide (K 2 O), % 0.22 Sodium oxide (Na 2 O), % 0.11 Magnesium oxide (MgO), % 1.65 Sample Preparation In this study, 16 different mix proportions Greencrete block samples were prepared separately via an established process. For each of the three sample types, 1000 g of clay, cement, or RHA was used to make the blocks. The specific proportions used for mixing and production of the samples are given in Table 2 . Each mixture was labeled with an identifier (Control to 15RHA12C) for statistical analysis and performance evaluation. The preparation of samples followed the JIS R 5201:2015 standard, with the procedure schematically presented in Fig. 5 . Table 2 Parametric study of the soil, RHA, and cement. Mix types Index Material types (% by weight) Soil, % RHA, % Cement, % Water, % Soil Control 100 0 0 30 Soil + 8% 0RHA8C 100 0 8 32 Soil + 10% Cement 0RHA10C 100 0 10 32.5 Soil + 12% Cement 0RHA12C 100 0 12 33 Soil + 5% RHA 5RHA0C 100 5 0 33 Soil + 5% RHA + 8% Cement 5RHA8C 100 5 8 34 Soil + 5% RHA + 10% Cement 5RHA10C 100 5 10 35 Soil + 5% RHA + 12% Cement 5RHA12C 100 5 12 36 Soil + 10% RHA + 0% Cement 10RHA0C 100 10 0 36 Soil + 10% RHA + 8% Cement 10RHA8C 100 10 8 35 Soil + 10% RHA + 10% Cement 10RHA10C 100 10 10 36 Soil + 10% RHA + 12% Cement 10RHA12C 100 10 12 37 Soil + 15% RHA + 0% Cement 15RHA0C 100 15 0 39 Soil + 15% RHA + 8% Cement 15RHA8C 100 15 8 38 Soil + 15% RHA + 10% Cement 15RHA10C 100 15 10 39 Soil + 15% RHA + 12% Cement 15RHA12C 100 15 12 40 First, the raw materials were thoroughly mixed manually in a container until a homogeneous mixture was obtained. To ensure adequate plasticity and adhesion, 30 to 40% of the total dry weight of the ingredients was mixed with water to prepare the clay paste so that the paste could be easily placed and shaped in the mold by hand. This method resembles the traditional clay paste preparation for making common burnt clay building bricks in the Indian subcontinent. As per Indian Standard IS 1077 (1992), 20–30% water by weight is recommended for the preparation of common burnt clay building bricks [ 37 ]. In this study, the use of RHA required slightly more water to produce a similar type of mortar. In this study, 100% clay was used to make the control samples. Additionally, in the preparation of the other samples, higher doses of RHA, 5%, 10%, and 15%, were selected than those reported in previous studies [ 18 , 35 , 36 ]. This is consistent with the use of RHA in existing studies [ 17 , 39 ]. In this study, 8%, 10%, and 12% cement was also mixed with RHA, so that the combined pozzolanic reaction of these two components would ensure an optimal ratio of Ca⁺ ions. Moreover, the use of a minimal amount of cement in construction materials and the incorporation of RHA as a replacement enhance both environmental protection and material efficiency. Curing After removal from the mold, the Greencrete blocks were cured for 28 days in two different ways. Among them, one set was cured in a room at 30°C without any humidity to represent natural conditions, allowing sufficient strength and durability to be achieved quickly, which is consistent with existing research [ 40 ]. The curing process shown in Fig. 7 (a) was carried out following the basic requirements of the Japanese Industrial Standard A 1132:2020, which meets the international standard ISO 1920-3:2004. Another batch of sample bricks was cured at 24 ± 2°C and 50–90% humidity in a chamber for 28 days, as shown in Fig. 7 (b), where the basic requirements of JIS A 1132:2020 were also followed. A similar method has been followed for sample curing in other studies [ 13 , 17 , 35 , 36 ]. This integrated and consistent sample preparation process ensures that all samples provide comparable quality, repeatability, and reliable test results. Testing method Bulk density The density of the Greencrete block samples, which are shown in Fig. 8 (a) and (b), was evaluated following the procedures outlined in American Society for Testing and Materials (ASTM) C67/C67M [ 41 ] or an equivalent standardized methodology. The bulk density was subsequently calculated via Eq. (1), ensuring consistency with established analytical frameworks for masonry materials. ρ = mv (1) where ρ = bulk density m = mass v = volume Water Absorption Test The evaluation of the water absorption properties of the Greencrete block samples was conducted via the standardized methodology prescribed in JIS R 1250:2011 (ISO 10545-3 ) , which specifies the fundamental procedure for water absorption testing, as shown in Fig. 9 . The oven-absorption percentage was subsequently computed via Eq. 2, ensuring methodological consistency and accuracy. The dry mass (M₁) and saturated mass (M₁A) of each sample were precisely measured, and the water a = M 1A - M 1 M 1 ×100 (2) where a = water absorption (%) M 1 = dry weight of the bricks (g) M 1A = saturated weight of the bricks (g) Compressive strength test The compressive strength assessment of the brick samples was performed via a universal testing machine, the schematic diagram in Fig. 8 , adhering to the guidelines specified in JIS R 1250:2011, or an equivalent standardized test protocol. The peak load sustained by each sample during the test was meticulously recorded, and the corresponding compressive strength values were derived via Eq. 3, ensuring alignment with established mechanical evaluation criteria. C = w a N/mm 2 =w a ×1000 MPa (3) where c = compressive strength w = maximum load a = initial cross-sectional surface area Microstructural study Particle size distribution of soil is a vital physical property that directly affects soil texture classification, while the chemical composition of soil is another key characteristic to consider when understanding its physical properties. The scanning electron microscope (SEM) uses the wave properties of electrons to magnify surface details, making it a versatile tool for analyzing soil particles and solid materials, especially in dispersive soils, due to its high resolution. SEM is a highly adaptable instrument used to examine and analyze the microstructure and properties of solid objects [ 42 , 43 ]. Its main advantage for examining Greencrete block samples is its ability to produce high-resolution images of material microstructure. To adhesive carbon tape, ensuring that the exposed surfaces accurately represent the brick's in-situ structure. prepare for analysis, a cross-sectional segment of the brick was mounted on a stub with double-sided The instrument used in this study, to observe the topographical features of the samples on a micro-scale, SEM images are produced using an ultra-high-resolution JEOL JSM-IT200, is a research-grade scanning electron microscope known for its user-friendly interface, compact ergonomic design, and versatility. It offers high-resolution imaging with spatial resolution down to approximately 3 nm at 30 kV in high vacuum mode and supports accelerating voltages (SED) from 0.5 to 30 kV, as shown in Fig. 9 . The SEM features both high vacuum and low vacuum modes, allowing observation of non-conductive samples without the need for conductive coatings. On the other hand, SEM is equipped with secondary and backscattered electron detectors and an integrated energy dispersive X-ray spectrometer (EDS) for real-time elemental analysis, including spectral mapping, line scanning, and automatic drift compensation. This SEM-EDX method is used to detect the presence and amount of chemical elements in brick samples during microscopy inspection based on atomic number, although it cannot distinguish between ionized and free atoms. Results and discussion Bulk density The structural compactness of Greencrete block is an important indicator of mechanical performance and durability, which is significantly affected by the interaction of RHA, OPC, and curing conditions. Studies have shown that RHA is rich in amorphous silica, and its addition helps reduce the density of bricks because of its low specific gravity, high internal porosity, and thinning effect on the binder matrix [ 20 , 44 ]. This density reduction is particularly evident when the amount of RHA exceeds 10%, which leads to an increase in voids and disruption of particle packing [ 45 ]. Conversely, when balanced with high OPC content—especially under 24°C curing conditions, the high silica content [SiO₂] in RHA reacts with calcium hydroxide [Ca(OH)₂], produced by OPC hydration, to form C–S–H (calcium silicate hydrate). This synergistic pozzolanic reaction densifies and strengthens the microstructure of bricks or concrete, thereby increasing density and compressive strength [ 46 , 47 ]. According to Fig. 12 , samples made with 15% RHA and 12% cement presented a bulk density of 1298.99 kg/m³ when cured in a humidity-controlled chamber at 24°C, whereas at 30°C, the bulk density was only 1110.48 kg/m³. This indicates that a higher curing temperature accelerated initial water evaporation and inhibited hydrolysis and silica reactions [ 48 ]. Silica hydrolysis and pozzolanic reactions are slowed or inhibited due to a lack of sufficient water and time, which prevents proper interaction between SiO₂ and Ca(OH)₂ [ 49 ]. The same trend was observed for mixtures such as 10% RHA and 12% cement and 10% RHA and 10% cement, which achieved bulk densities of 1299.44 and 1246.75 kg/m³, respectively, under 24°C curing. These results reveal the thermal sensitivity of the hydration dynamics and particle interlocking processes. Notably, at relatively high curing temperatures (30°C or above) and with high RHA contents, the hydration and C–S–H formation in bricks are disrupted, resulting in density irregularities and structural weaknesses [ 50 ]. Furthermore, under moist curing conditions, mixtures containing 10–15% RHA and 10–12% OPC result in the lowest porosity in the matrix, with densely packed particles attributable to micropore bonding and volume‒filler effects [ 51 ]. When combined with optimized curing protocols, RHA-cement blocks can match or exceed traditional fired clay bricks in terms of density and performance, without high energy consumption or soil surface degradation. These results align with the sustainable construction goals outlined in SDG 11 and SDG 12 and support the transition toward net-zero construction materials [ 52 ]. Water absorption In this study, the water absorption behaviour of Greencrete block at two curing temperatures and humidity levels was examined, revealing important insights into pore development and binder interactions in low-carbon masonry. The results demonstrate a distinct relationship between the RHA content, cement dosage, and curing temperature in controlling capillary pores that govern water absorption. In these studies, during the water absorption test, the samples were made with only clay dissolved in water. The same properties were observed in the sample bricks made without cement and mixed with RHA in different proportions (5%, 10% and 15%). Without the addition of RHA, simply increasing the cement content from 8–12% gradually increased the water absorption from 31.5–34.8% at 30°C, as shown in Fig. 13 , suggesting the possibility of capillary voids being blocked during initial hydration [ 53 ]. With 5% RHA incorporation, mixed effects were observed: 5% RHA and 8% cement, and 5% RHA and 10% cement presented moderate absorption (35.5% and 34.3%, respectively), whereas 5% RHA and 12% cement significantly decreased to 32%, probably due to improved filler-packing effects and pozzolanic refinement of the pore structure, which is consistent with the results of recent studies [ 29 ]. However, at the 10% and 15% replacement levels, the role of RHA became more evident. The 10% RHA group exhibited the highest average absorption (38 to 40%) at both temperatures, suggesting that the additional RHA may increase the matrix porosity due to its high amount of unburned carbon and irregular particle morphology [ 29 , 53 ]. Interestingly, the blocks made with 10% RHA and 12% cement absorbed 40.5% of the water, and the bocks made with 10% RHA and 8% cement absorbed 38.7% of the water, which was only a slight improvement compared with each other, indicating that cement addition alone could not completely reduce the increased pore volume associated with high RHA content. Notably, the water absorption values at 24°C in the controlled curing chamber were reflected in the relative trend compared with those at 30°C, but were slightly lower, confirming the effect of higher curing temperatures on increasing hydration kinetics, and confirming the relative absorption trend in some recent studies [ 54 , 55 ]. The 15% RHA series further highlights the complex interplay of binder dilution and hydration control. 15% RHA and 8% cement, and 15% RHA and 10% cement showed very high absorption 47.7% and 46.3%, respectively, whereas 15% RHA and 12% cement presented an abnormal value of 1298.99%, which emphasizes the need for moisture control protocols during sample conditioning. In line with the proposed pore system instability theory, such excessive absorption could also indicate uncontrolled pore coordination, caused by insufficient cementitious matrix formation. Nevertheless, even when exogenous factors are excluded, the overall data suggest that a significant balance in the cement dosage is required to stabilize the RHA microstructure above 5%. Comparative analysis across temperature bands confirms that 30°C curing leads to slightly greater absorption than 24°C curing does, a phenomenon attributed to rapid hydration and capillary channel development under thermal acceleration. Furthermore, the trend validates the dual function of RHA as both a pozzolanic additive and an internal curing agent when used within the optimal range (~ 5%) [ 56 ]. Overall, this study highlights the importance of finely ground RHA–cement blends for adjusting the water absorption properties of unfired eco-bricks. This highlights that moderate RHA inclusion (≤ 5%), when adequately balanced with the cement content, synergistically improves pore packing and reduces capillary action. In contrast, excessive RHA (≥ 10%) without adequate cement fails to achieve microstructural densification. These results support broader efforts to develop green masonry materials through agro-waste evaluation, as per SDG 12. Compressive strength The compressive strength of Greencrete block is an important parameter to ensure structural applications and durability, especially when incorporating durable materials such as RHA. This study explored the variation in the compressive strength of block made with different RHA and cement ratios at 30°C and 24°C in a humidity-controlled chamber. The results demonstrate a nonlinear relationship between binder composition and mechanical performance, which is significantly affected by both pozzolanic reactivity and curing kinetics. According to Fig. 14 , the 5% RHA series exhibited higher compressive strengths, with the 5% RHA and 12% cement samples achieving 3.67 MPa at 30°C and 2.83 MPa at 24°C, much higher than those of the control brick (2.05 MPa). This increase in strength is attributed to the synergistic effect of the cementitious matrix from RHA and reactive silica, which increases calcium silicate hydrate (C–S–H) gel formation and densifies the microstructure [ 57 ]. Adding up to the optimum limit of RHA (~ 5%) increases the pozzolanic activity, fills the voids, and refines the pore networks, thereby improving the compressive strength [ 13 ]. However, the strength decreases significantly at higher RHA contents (10% and 15%) unless adequately compensated by cement. For example, 15% RHA and 8% cement achieved only 0.68 MPa at 30°C and 0.81 MPa at 24°C, which is consistent with the literature that excess ash increases porosity and disrupts matrix continuity [ 30 ]. The samples cured at 30°C and 24°C presented compressive strengths of 0.95 MPa and 2.61 MPa, respectively. Rapid hydration at higher temperatures results in an unconventional structure with additional pores or microcracks, which reduces the compressive strength. On the other hand, at lower curing temperatures (24°C) with moisture, the microstructure becomes denser and less porous, resulting in increased compressive strength. Most of the samples performed better than their counterparts at 24°C, indicating enhanced hydration kinetics and matrix development under high temperature conditions [ 53 ]. However, the decrease in strength at 24°C for certain compositions (5% RHA and 8% cement and only 10% RHA without any cement) indicates insufficient binder activation or incomplete pozzolanic reactions, which is consistent with the thermal sensitivity of waste-derived binders [ 58 ]. This temperature-dependent strength behaviour underscores the importance of optimal curing environments, particularly in low-binder, high-RHA compositions. Additionally, this study emphasizes the role of the cement dosage in strength control. In a 10% RHA blend, increasing the cement content from 8–10% at 30°C improved the strength from 1.65 to 2.00 MPa, demonstrating the compensatory effect of the cement. However, beyond a critical limit, additional cement may not yield linear gains because of potential shrinkage-induced microcracking [ 46 ]. Therefore, balancing the binder-to-aggregate ratio and curing parameters is essential to achieve structural-grade unfired bricks. From a microstructural perspective, the interaction between the amorphous silica of RHA and the cement hydration product leads to the secondary formation of C–S–H, improving the interfacial bonds and load-bearing capacity. However, excessive RHA or insufficient cement can lead to weak particle bonding and high porosity, which ultimately reduces strength [ 59 ]. This study supports the integration of agro-industrial waste into low-carbon masonry through optimized material design. The 5% RHA and 12% cement, and the 5% RHA and 10% cement compositions demonstrated particularly promising compressive strengths, which are consistent with the sustainable construction goals of reducing cement usage [ 60 ]. These results confirm that judicious mixing of RHA and cement under controlled curing can produce high-performance nonburnt bricks, which support climate-resilient infrastructure and SDG 11 and SDG 12. SEM analysis In this study, SEM images were taken at a magnification of x500, where the high-vacuum mode and SED were set to 20.0 kV, and the electron beam current or standard probe current (Std-PC) was set to 30 kV. After that, the morphology of the control sample at 30°C exhibited multiple cracks and small micropores, as shown in Fig. 15 . On the other hand, the control sample cured at 24°C also exhibits a similar structure, as shown in Fig. 16 . which is consistent with recent studies [ 13 ].. Both control samples without cement and RHA, a small amount of CaO, and a significant amount of SiO2 were present, which resulted in this incomplete pozzolanic reaction. As a result, the flocculated hydration products exhibited, but the control sample at 24°C had larger flocculated hydration products due to the relatively low temperature and humidity. Meanwhile, the SEM micrograph of the brick made by adding 5% RHA and 12% cement (5RHA12C) to the soil and curing at 30°C showed a fibrous and honeycomb compact matrix, and the flocculated hydration products were reduced, forming a multi-layered hydration product by intermixing with each other, as shown in Fig. 17 . This dense matrix is formed due to the aggregation of different silicate phases, which provides strength to the porous brick, which is consistent with recent studies [ 61 , 62 ]. The same structure was observed in the SEM image of a brick sample made of the same type of material (5% RHA and 12% cement), but cured at 24°C with moisture, as shown in Fig. 18 . In particular, in Greencrete block, the pozzolanic activity of RHA and cement increases the particle bonding, where reactive silica interacts with calcium hydroxide to form secondary calcium silicate hydrate (C-S-H), improving the matrix structure, strength development, and long-term durability. Although the curing conditions were different, Ca(OH)₂ crystals were observed in both 5RHA12C block samples, which were formed as a result of the initial hydration of the cement, which then reacted with the high SiO2 content of RHA to form calcium silicate hydrate (C–S–H) gel [ 39 , 63 ]. Recent studies have shown that with the increase in C–S–H formation, the amount of CH plates decreases, which makes the clay matrix more interconnected and contributes to the improved performance of the brick As a result, the maximum compressive strength values of the two 5RHA 12C samples cured at 30°C and 24°C with humidity were 3.53 MPa and 2.51 MPa, respectively, which are consistent with recent studies [ 60 ]. Table 3 The Energy Dispersive X-ray spectroscopy (EDS) results Formula Weight % Mol% Cations Control 5RHA12C Control 5RHA12C Control 5RHA12C 30°C 24°C 30°C 24°C 30°C 24°C 30°C 24°C 30°C 24°C 30°C 24°C C 4.43 3.30 21.09 15.90 0.00 0.00 0.21 Na2O 0.44 0.14 0.76 0.41 0.13 0.80 0.13 0.04 0.56 MgO 2.07 1.61 0.69 2.61 3.70 2.29 1.00 4.22 0.48 0.37 0.15 3.45 Al2O3 28.75 22.69 19.97 20.27 20.36 12.72 11.33 12.95 5.29 4.08 3.45 7.22 SiO2 36.52 47.74 52.64 49.96 43.89 45.44 50.67 54.16 5.71 7.28 7.72 0.45 K2O 4.09 3.18 2.76 2.46 3.14 1.93 1.69 1.70 0.82 0.62 0.52 2.72 CaO 0.67 1.25 12.31 17.55 0.87 1.27 12.70 20.38 0.11 0.20 1.94 0.77 FeO 27.89 18.66 8.18 6.38 28.04 14.85 6.59 5.78 3.64 2.38 1.00 0.21 EDS analysis Energy Dispersive X-ray Spectroscopy (EDS) is a special technique for analysis of the elemental composition of Greencrete bricks by the help of this method the amount of SiO₂, alumina, calcium oxide, and other elements in the mixes is identified. In this research, EDS reveals that the uncured brick sample made only of clay and cured at 30°C is rich in high levels of silica (SiO₂), as shown in Fig. 19 . According to the data in Table 3 , this sample contains 36.52 wt%, 43.89 mol% SiO₂, 28.75 wt%, 20.36 mol% Al₂O₃, and 0.67 wt%, 0.87 mol% CaO. A similar pattern was observed for the brick cured at 24°C (shown in Fig. 20 ). According to Table 3 , this sample contains 47.74 wt%, 45.44 mol% SiO₂, 22.96 wt%, 12.72 mol% Al₂O₃, and 1.25 wt%, 1.27 mol% CaO. In these two samples, SiO₂ reacts with CaO to form CaO-SiO₂-H₂O gel (C-S-H), which is formed by the hydration of calcium silicate and is characterized by its complex and variable structure [ 66 ]. . Due to the absence of RHA and cement, flocculated hydration products, although formed in small amounts, are not sufficient to create a compact matrix, resulting in multiple cracks and micropore development. However, due to the relatively low temperature and humidity during curing, and the relatively higher presence of CaO, more flocculated hydration products were formed in the control sample at 24°C. According to Table 3 , both samples of 5RHA12C contained 12.31 wt%, 12.70 mol% and 17.55 wt%, 20.38 mol% CaO, respectively. These two samples had relatively higher SiO₂ and CaO contents compared to the bricks, as shown in Figs. 20 and 21 . SiO₂, or amorphous silica, came from RHA, which exhibits high pozzolanic reactivity (amorphous silica gel) and contributes to the acceleration of geopolymerization reactions in the brick matrix. CaO came from cement, which plays a primary role in the formation of calcium silicate hydrate (C–S–H) gel, the main hydration product of cement [ 65 , 66 ]. Previous research mentions that the formation of C–S–H gel and amorphous silica gel is due to the following process: xC + yS + tH→xC-S-H + other products (4) where C = CaO, H = H₂O, S = SiO₂, A = Al₂O₃, and C = CO₂; x, y, and t are molecular quantities [ 64 ]. Fig. _ 22 EDS image of the 5RHA10C sample cured at 30°C. From Eq. (4), the change in molar volume during carbonation of C–S–H depends on the C/S ratio, the amount of water in C–S–H, and the water in the silica gel. Unlike the carbonation reaction between CH and CO₂, the volume change during carbonation of C–S–H varies with the C–S–H phase with different C/S ratios, which leads to the investigation of CCUS concrete [ 65 ]. In the presence of Ca²⁺, the system releases more silica and existing alumina species (Al₂O₃), which are able to form C–A–H and C–(A)–S–H phases, ensuring better cohesion between the different components of the matrix [ 39 , 66 , 67 ]. However, the additional hydration in the bricks cured with moisture at 24°C resulted in a weaker matrix compared to the bricks cured at 30°C, leading to reduced overall mechanical strength and durability, despite the bonding of the C–A–H gel—consistent with previous studies [ 68 , 69 , 70 ]. Conclusion This study systematically evaluated the performance of soil-based RHA-cement Greencrete blocks under two curing conditions: 24°C with moisture and 30°C without moisture. The results confirm the important interrelationship between mix composition and the curing environment in determining the physical, mechanical, and microstructural properties of sustainable, waste-based masonry materials. The key conclusions are as follows: Microstructural insights : SEM-EDS analysis confirmed that 5% RHA and 12% cement performance (5RHA12C, both 30°C and 24°C) is the best combination, which produces a homogeneous and dense binder phase with minimal microcracking and pore connectivity. At the same time, both samples presented a highly compact composite structure with the highest physical and mechanical performance. This combination exhibited compressive strengths of 3.67 MPa and 2.83 MPa at curing temperatures of 30°C and 24°C, respectively, which are the highest in this study. The compressive strength of the brick is equivalent to the C grade of conventional burnt clay brick as per the Indian standard (IS 1077:1992) and falls within the EB-2 grade of earth brick as per the German standard DIN 18945 (2013–08). These bricks are ideal for low-rise constructions where stresses are lower, such as sheds, and can also be used in insulating constructions and the construction of partitions. The negative effects of excess RHA are as follows: an RHA content of more than 10% without adequate cement leads to a high absorption rate and reduced strength due to increased voids and weak particle bonding. This emphasizes the need to maintain a balanced binder ratio to realize the benefits of agro-industrial waste utilization. Optimized RHA incorporation A moderate RHA content (5% by weight) combined with 8–12% OPC synergistically increases the compressive strength and durability. The pozzolanic reaction between the amorphous silica in RHA and the cement hydration products creates a dense C–S–H gel matrix, which significantly improves structural integrity. Significance of moisture curing Slow curing at 24°C results in a denser, stronger, and more durable brick microstructure, as the C–S–H gel condenses and reduces microporosity. In contrast, 30°C causes very rapid curing, resulting in shrinkage-induced cracking, incomplete hydration, and low-strength structures. For example, the compressive strength of the 15R12C sample at 30°C was only 0.94 MPa, but at 24°C, it increased to 2.61 MPa—a direct result of water retention and slower reaction kinetics. During the slow curing process, the C–S–H gels are more tightly packed, and the porosity decreases, resulting in increased density. For example, the bulk density of most samples increased with 24°C curing, whereas at 30°C, rapid evaporation of water vapour caused internal shrinkage and increased the possibility of microcracks. The density of the 0RHA12C sample was 1322.67 kg/m³ at 30°C and 1389.92 kg/m³ at 24°C, indicating a more compact microstructure. RHA is a highly porous and hygroscopic material that absorbs excess water. The curing environment controls this absorption. The porosity decreases with 24°C curing, which reduces water absorption. At 30°C, rapid evaporation can lead to the formation of small pores, increasing the absorption capacity. For example, the absorption of 5RHA12C was 32% at 30°C, but decreased to 30.65% at 24°C. As the temperature increases, the hydration kinetics accelerate. However, too fast a reaction that is too fast can cause incomplete bonding and internal stresses within the cement and RHA. For example, the compressive strengths of the 10RHA and 15RHA samples cured at 30°C were relatively low. The 10RHA12C sample exhibited a compressive strength of 1.59 MPa at 30°C and 1.66 MPa at 24°C. The strength difference in the S15R12C sample was significant, 0.9459 and 2.61 MPa, clearly demonstrating the negative effects of increased temperature. Overall, this work provides strong empirical evidence supporting the emergence of RHA-based Greencrete systems under optimized curing conditions. The results offer valuable insights for developing climate-resilient, low-carbon construction materials that align with emerging global sustainability goals, including SDG 11 and SDG 12. Future studies are recommended to explore long-term sustainability, carbonation processes, and life cycle environmental assessments under field conditions to further validate large-scale adoption pathways. Abbreviations sign Description RHA Rice husk ash C Cement OPC Ordinary portland cement SEM Scanning electron microscopy EDS Energy dispersive X-ray spectroscopy RH Relative humidity, CCUS Carbon capture, utilization, and storage CEB Compressed earth bricks JIS Japan industrial standards ISO International Organization for Standardization, ASTM American Society for Testing and Materials AASHTO American association of state highway and transportation officials IS Indian standard DIN German Institute for Standardization Declarations Funding This research was conducted under the Japan Science and Technology Agency (JST), Support for Pioneering Research Initiated by the Next Generation (SPRING) program, Grant Number JPMJSP2137. Acknowledgments The authors gratefully acknowledge the support of Make Integrated Technology Limited for providing experimental materials essential to this research. Author Contributions MAFS: Conceptualization, Methodology, Data Curation, Data Analysis, Writing—Original Draft. ZH: Supervision, Reviewing. MYI: Reviewing, Formatting. Competing Interests The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Ethics Approval and Consent to Participate Not applicable. Consent for Publication Not applicable. Clinical Trial Registration Not applicable. Data Availability The data supporting the findings of this study are available from the corresponding author upon reasonable request. Code Availability Not applicable. References United Nations. World Population Prospects 2024: Summary of Results. Volume 9. New York: United Nations; 2024. UN DESA/POP/2024/TR/NO. 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Cem Concr Res. 2022;159:106858. https://doi.org/10.1016/j.cemconres.2022.106858 . Additional Declarations No competing interests reported. Supplementary Files Graphicalabstract.docx Cite Share Download PDF Status: Published Journal Publication published 05 Apr, 2026 Read the published version in Discover Sustainability → Version 1 posted Editorial decision: Revision requested 06 Nov, 2025 Reviews received at journal 23 Oct, 2025 Reviews received at journal 20 Oct, 2025 Reviewers agreed at journal 16 Oct, 2025 Reviewers agreed at journal 14 Oct, 2025 Reviewers agreed at journal 14 Oct, 2025 Reviews received at journal 20 Sep, 2025 Reviewers agreed at journal 08 Sep, 2025 Reviewers invited by journal 08 Sep, 2025 Editor assigned by journal 20 Aug, 2025 Submission checks completed at journal 20 Aug, 2025 First submitted to journal 15 Aug, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7381327","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":512969014,"identity":"c2ea1953-3e9b-42aa-a76a-6dcf805cea33","order_by":0,"name":"Muhammad Ali Fardoush Siddquy","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA9UlEQVRIiWNgGAWjYBAC+/aGBIkPDDVyIM4BmKgBPi0GPAceSM5gOGZMghaJxAfSPAzMiQ1EO8ycITnxBs8ftvS1DdyJBz4wHGbgbz/AUFyAR4tlw7FkC8k2mdxtB3g3HJwB1CJxJoHBeAY+aw72pEkYNrCBtRzm/XeYgeEGA4MxDz4th/m/SST8YU43A2n5A7RFnpAWg2MMaRIH2JgTwFqAJjAYENIi2cOQbNnYdsxw22GgX3oY0nkMzyQ24PULv/yDxNt//tTImx3v3fzhB4O1nNzxw8eM8YUYAjBDKKCTGNuMidKBovsxyVpGwSgYBaNgOAMA/4pPYb5431IAAAAASUVORK5CYII=","orcid":"","institution":"Mie University","correspondingAuthor":true,"prefix":"","firstName":"Muhammad","middleName":"Ali Fardoush","lastName":"Siddquy","suffix":""},{"id":512969015,"identity":"fb37af74-7e05-48b9-8750-3a056fbea6ce","order_by":1,"name":"Zakaria Hossain","email":"","orcid":"","institution":"Mie University","correspondingAuthor":false,"prefix":"","firstName":"Zakaria","middleName":"","lastName":"Hossain","suffix":""},{"id":512969017,"identity":"ab4604d0-1c40-4adc-8921-40ad4d6b6853","order_by":2,"name":"Md Yachin Islam","email":"","orcid":"","institution":"Mie University","correspondingAuthor":false,"prefix":"","firstName":"Md","middleName":"Yachin","lastName":"Islam","suffix":""}],"badges":[],"createdAt":"2025-08-15 12:23:34","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7381327/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7381327/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s43621-026-03138-4","type":"published","date":"2026-04-05T15:58:24+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":91389527,"identity":"5213a7af-44f8-4e56-b435-da38eb7a8e4f","added_by":"auto","created_at":"2025-09-16 03:27:58","extension":"jpeg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":178592,"visible":true,"origin":"","legend":"\u003cp\u003eTopsoil is being cut at a brick kiln. This is a picture of Godagari Upazila, Rajshahi, Bangladesh. Photo by the author\u003c/p\u003e","description":"","filename":"image1.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7381327/v1/58ecd90dcfca5a67b228df20.jpeg"},{"id":91389751,"identity":"91ed939e-cc2c-4b1e-8384-6456f8c3bb74","added_by":"auto","created_at":"2025-09-16 03:35:58","extension":"jpeg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":144441,"visible":true,"origin":"","legend":"\u003cp\u003eBrick kilns built on cropland are severely polluting the environment. The photo was taken from Natore, Rajshahi division, Bangladesh. Photo by the author\u003c/p\u003e","description":"","filename":"image2.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7381327/v1/6d7d3363d1c56ff3d86bfc8e.jpeg"},{"id":91389736,"identity":"fad9123f-9af7-42fb-96b2-c8db83dccdce","added_by":"auto","created_at":"2025-09-16 03:35:56","extension":"jpeg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":147430,"visible":true,"origin":"","legend":"\u003cp\u003eSoil (a), SEM image of soil (b), RHA (c), SEM image of RHA (d), cement (e), and SEM image of cement (f).\u003c/p\u003e","description":"","filename":"image3.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7381327/v1/e1ff2e52c3d9b44b8f0f7ddf.jpeg"},{"id":91389495,"identity":"67deaede-2ee9-4ae3-b5a9-8998d37b4f32","added_by":"auto","created_at":"2025-09-16 03:27:56","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":79253,"visible":true,"origin":"","legend":"\u003cp\u003eDistribution curves of the particle sizes for the cement, RHA, and soil [35, 36].\u003c/p\u003e","description":"","filename":"image4.png","url":"https://assets-eu.researchsquare.com/files/rs-7381327/v1/93ae1f57e992c4d56ad89bdf.png"},{"id":91390362,"identity":"00efeca4-b17b-4a34-b0a4-4539ab8f2d29","added_by":"auto","created_at":"2025-09-16 03:43:58","extension":"jpeg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":193957,"visible":true,"origin":"","legend":"\u003cp\u003eRaw material (a), raw material mixing (b), clay (c), and moulding (d).\u003c/p\u003e","description":"","filename":"image5.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7381327/v1/08b2cd8158d0265220903214.jpeg"},{"id":91389561,"identity":"ba9ba1cc-5c0f-4815-ae88-14736ea7afa2","added_by":"auto","created_at":"2025-09-16 03:27:59","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":45243,"visible":true,"origin":"","legend":"\u003cp\u003eThe mold used to make the sample brick (a), the shape of the sample brick (b)\u003c/p\u003e","description":"","filename":"image6.png","url":"https://assets-eu.researchsquare.com/files/rs-7381327/v1/574323fe9e47805ad854090f.png"},{"id":91389741,"identity":"30c25aec-33e4-4767-a02e-8a3b4f287185","added_by":"auto","created_at":"2025-09-16 03:35:57","extension":"jpeg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":101807,"visible":true,"origin":"","legend":"\u003cp\u003eCuring at 30°C in a room (a), and curing in a humid chamber at 24 ± 2°C (b)\u003c/p\u003e","description":"","filename":"image7.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7381327/v1/ff66501ae93d7eec856b8a6e.jpeg"},{"id":91389514,"identity":"7601423b-7b30-4034-a8b7-35aa1c5270da","added_by":"auto","created_at":"2025-09-16 03:27:57","extension":"jpeg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":161528,"visible":true,"origin":"","legend":"\u003cp\u003eBlocks cured at \u0026nbsp;30°C in a room (a), and cured in a humid chamber at 24 ± 2°C (b).\u003c/p\u003e","description":"","filename":"image8.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7381327/v1/3829f15852dcbcee76603e92.jpeg"},{"id":91389505,"identity":"ca25b5d6-2a12-4af2-bd81-5b5a2f1dc32b","added_by":"auto","created_at":"2025-09-16 03:27:57","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":16363,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic diagram of the water absorption test of the block samples\u003c/p\u003e","description":"","filename":"image9.png","url":"https://assets-eu.researchsquare.com/files/rs-7381327/v1/f143db20cbd9094918959413.png"},{"id":91389502,"identity":"17f93fa1-e04f-49c3-b333-fffbe187fd36","added_by":"auto","created_at":"2025-09-16 03:27:57","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":33323,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic diagram of the universal testing machine\u003c/p\u003e","description":"","filename":"image10.png","url":"https://assets-eu.researchsquare.com/files/rs-7381327/v1/c953cbb8014641605a34c68c.png"},{"id":91389743,"identity":"3742d872-e592-48eb-a062-01f490b0de8f","added_by":"auto","created_at":"2025-09-16 03:35:57","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":87783,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic diagram of the scanning electron microscope\u003c/p\u003e","description":"","filename":"image11.png","url":"https://assets-eu.researchsquare.com/files/rs-7381327/v1/6b829a0f9db4e98c3ddbc197.png"},{"id":91389525,"identity":"e2234a42-8611-498a-a508-ce0fe4d6e6cc","added_by":"auto","created_at":"2025-09-16 03:27:58","extension":"jpeg","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":138875,"visible":true,"origin":"","legend":"\u003cp\u003eVariation in the bulk density of Greencrete blocks with different RHA and cement compositions under two curing conditions\u003c/p\u003e","description":"","filename":"image12.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7381327/v1/9f28fe4a64ec017c98c392b5.jpeg"},{"id":91389789,"identity":"2733ba7d-882e-4173-a3c8-2486e482d91a","added_by":"auto","created_at":"2025-09-16 03:36:00","extension":"jpeg","order_by":13,"title":"Figure 13","display":"","copyAsset":false,"role":"figure","size":124805,"visible":true,"origin":"","legend":"\u003cp\u003eWater absorption (%) of Greencrete blocks with different RHA and cement compositions under two curing conditions\u003c/p\u003e","description":"","filename":"image13.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7381327/v1/f98357cc103db22a8334ed1a.jpeg"},{"id":91389549,"identity":"c7c5a00c-ab2a-47b1-92d0-014932b7b7a4","added_by":"auto","created_at":"2025-09-16 03:27:58","extension":"jpeg","order_by":14,"title":"Figure 14","display":"","copyAsset":false,"role":"figure","size":163851,"visible":true,"origin":"","legend":"\u003cp\u003eCompressive strength (MPa) of Greencrete blocks with different RHA and cement compositions under two curing conditions\u003c/p\u003e","description":"","filename":"image14.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7381327/v1/1bd6a95cf55b4a5cd1ce7e25.jpeg"},{"id":91389737,"identity":"d685e545-a2b7-4fd4-9864-73e5f983645a","added_by":"auto","created_at":"2025-09-16 03:35:57","extension":"jpeg","order_by":15,"title":"Figure 15","display":"","copyAsset":false,"role":"figure","size":146881,"visible":true,"origin":"","legend":"\u003cp\u003eSEM image at ×500 magnification of the control sample cured at 30 °C\u003c/p\u003e","description":"","filename":"image15.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7381327/v1/8413887b1cdbc5b20ed12ea2.jpeg"},{"id":91389531,"identity":"57aacf35-4365-4e0c-8408-7cc7d1e88339","added_by":"auto","created_at":"2025-09-16 03:27:58","extension":"jpeg","order_by":16,"title":"Figure 16","display":"","copyAsset":false,"role":"figure","size":154300,"visible":true,"origin":"","legend":"\u003cp\u003eSEM image at ×500 magnification of the control sample cured at 24 °C..\u003c/p\u003e","description":"","filename":"image16.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7381327/v1/ce93601f3a514bb8114d7c04.jpeg"},{"id":91390363,"identity":"1799a04e-a9f8-42ee-8da8-3d3d75a9f157","added_by":"auto","created_at":"2025-09-16 03:43:58","extension":"jpeg","order_by":17,"title":"Figure 17","display":"","copyAsset":false,"role":"figure","size":138090,"visible":true,"origin":"","legend":"\u003cp\u003eSEM image at ×500 magnification of the 5RHA12C sample cured at 30 °C.\u003c/p\u003e","description":"","filename":"image17.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7381327/v1/7746a2ec6ada5d01bb0eefdc.jpeg"},{"id":91389498,"identity":"e9b6358d-dcf3-45e3-9db3-376c28aadaba","added_by":"auto","created_at":"2025-09-16 03:27:57","extension":"jpeg","order_by":18,"title":"Figure 18","display":"","copyAsset":false,"role":"figure","size":164214,"visible":true,"origin":"","legend":"\u003cp\u003eSEM image at ×500 magnification of the 5RHA12C sample cured at 24 °C.\u003c/p\u003e","description":"","filename":"image18.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-7381327/v1/53b92836a2d011ae9eba8990.jpeg"},{"id":91389522,"identity":"acd8bb8c-0beb-451f-b300-70e2b2ff1b8c","added_by":"auto","created_at":"2025-09-16 03:27:57","extension":"png","order_by":19,"title":"Figure 19","display":"","copyAsset":false,"role":"figure","size":61143,"visible":true,"origin":"","legend":"\u003cp\u003eEDS image of the Control sample cured at 30 °C.\u003c/p\u003e","description":"","filename":"image19.png","url":"https://assets-eu.researchsquare.com/files/rs-7381327/v1/17782a20c64c251cf6f6f4f8.png"},{"id":91390353,"identity":"7e74e400-e388-4c45-9f02-962e05af5005","added_by":"auto","created_at":"2025-09-16 03:43:57","extension":"png","order_by":20,"title":"Figure 20","display":"","copyAsset":false,"role":"figure","size":66005,"visible":true,"origin":"","legend":"\u003cp\u003eEDS image of the Control sample cured at 24 °C.\u003c/p\u003e","description":"","filename":"image20.png","url":"https://assets-eu.researchsquare.com/files/rs-7381327/v1/65229cd82101dc568974f05c.png"},{"id":91389523,"identity":"f2bce9db-7528-4dfd-a21b-8941cc84e85e","added_by":"auto","created_at":"2025-09-16 03:27:57","extension":"png","order_by":21,"title":"Figure 21","display":"","copyAsset":false,"role":"figure","size":58372,"visible":true,"origin":"","legend":"\u003cp\u003eEDS image of the 5RHA10C sample cured at 30 °C.\u003c/p\u003e","description":"","filename":"image21.png","url":"https://assets-eu.researchsquare.com/files/rs-7381327/v1/60a323e7596a426838381b7b.png"},{"id":91389747,"identity":"76591f8b-3d63-4a4f-acb9-9c17c9cf8054","added_by":"auto","created_at":"2025-09-16 03:35:57","extension":"png","order_by":22,"title":"Figure 22","display":"","copyAsset":false,"role":"figure","size":72982,"visible":true,"origin":"","legend":"\u003cp\u003eEDS image of the 5RHA10C sample cured at 30 °C.\u003c/p\u003e","description":"","filename":"image22.png","url":"https://assets-eu.researchsquare.com/files/rs-7381327/v1/82177832b5dbd24a24c659ac.png"},{"id":106343800,"identity":"a893ac27-fe80-485a-a06c-28a3d0a4d2a9","added_by":"auto","created_at":"2026-04-07 16:09:38","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3572905,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7381327/v1/dd104c97-1b52-459f-a8e1-3da1f30d0ad3.pdf"},{"id":91390351,"identity":"96648969-a602-404f-aa75-bd591cfada53","added_by":"auto","created_at":"2025-09-16 03:43:57","extension":"docx","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":526541,"visible":true,"origin":"","legend":"","description":"","filename":"Graphicalabstract.docx","url":"https://assets-eu.researchsquare.com/files/rs-7381327/v1/0c588e937fe9e6870b9885b5.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Thermo-responsive engineering of Greencrete blocks: a foundational study toward waste-based next-generation concrete","fulltext":[{"header":"Introduction","content":"\u003cp\u003eThe global population is projected to reach 8.2\u0026nbsp;billion in 2024 and is expected to continue growing for the next 50 to 60 years. The United Nations estimates that the world population will peak at 10.3\u0026nbsp;billion by the middle of the 2080s [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. In 1950, only 30% of the global population lived in urban areas. However, due to increasing industrialization, infrastructure development, and economic opportunities, the urban population rose to 55% by 2018. If this trend continues, approximately 68% of the world\u0026rsquo;s population will reside in cities by 2050 [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. In addition to population growth, urbanization, defined by the expansion of built-up areas, has accelerated significantly [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Numerous studies have established that urbanization has a broad range of environmental and socioeconomic impacts, including the depletion of local resources, the degradation of landscapes and ecosystems, and increased greenhouse gas emissions that contribute to climate change. [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Bricks have long been an essential material associated with urbanization, and archaeological evidence suggests that burnt bricks were foundational to early urban centers and that the demand for burnt clay bricks remains strong due to their durability, affordability, and widespread availability [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eGlobally, approximately 1,500\u0026nbsp;billion burnt clay bricks are produced annually, with approximately 87% of production, approximately 1,300\u0026nbsp;billion bricks concentrated in Asia. This industry consumes more than 3.13\u0026nbsp;billion cubic meters of clay each year, contributing to severe land degradation [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. Furthermore, brick kilns in Asia alone consume approximately 110\u0026nbsp;million tonnes of coal annually, with each brick emitting approximately 0.41 kg of CO₂, resulting in the brick industry accounting for approximately 2.7% of global carbon emissions [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. In response, the construction industry is transitioning toward more sustainable building materials. A significant innovation in this transition is the development of unfired or compressed earth bricks (CEBs), also known as Greencrete blocks. Greencrete, a modified term for green concrete, has developed over decades through efforts to incorporate industrial and agricultural waste into concrete production, aiming to enhance performance, reduce environmental impact, and lower costs. Defined as any material with a lower carbon footprint and specific energy content than conventional OPC concrete, Greencrete is vital for meeting future construction needs while conserving natural resources [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eThese blocks utilize locally sourced soil, stabilized with minimal cement and pozzolanic agro-industrial by-products such as rice husk ash (RHA). The performance of stabilized CEBs depends on several parameters, including the soil gradation, water content, compressive strength, and the type and proportion of stabilizers used [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. The high silica content in RHA reacts with calcium hydroxide during cement hydration, forming calcium silicate hydrate (C-S-H) compounds. These compounds enhance the structural integrity of the bricks, making them stronger and more durable. Consequently, RHA is an environmentally friendly and cost-effective soil stabilizer [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e], with the potential to reduce carbon emissions by up to 80% compared with conventional fired bricks [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e].\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eIn 2024/25, global rice production reached 535.8\u0026nbsp;million tonnes, representing an increase of 13.7\u0026nbsp;million tonnes from the previous year [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. Japan alone produces approximately 7.3\u0026nbsp;million tonnes of rice annually, generating approximately 2\u0026nbsp;million tonnes of rice husks\u0026mdash;most of which remain underutilized and present significant waste management challenges [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. Rice husks constitute 20 to 22% of the rice's total weight of rice, with approximately 25% of the husks converted to ash upon incineration [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. Due to its high silica and pozzolanic content, RHA has been extensively studied as a next-generation material in sustainable construction [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. Moreover, recent advancements have incorporated carbon capture, utilization, and storage (CCUS) technologies into cementitious systems. Through O₂-curing and mineral carbonation, captured CO₂ reacts with calcium hydroxide to form stable calcium carbonate (CaCO₃), which not only improves the performance of the material but also enhances long-term carbon sequestration [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. This shift, from traditional burnt bricks to CCUS-enabled Greencrete, embodies the circular economy approach and the evolution of low-carbon construction technologies aligned with net-zero emission goals [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eTraditional burnt bricks exhibit compressive strengths ranging from 10.27 MPa to 19.71 MPa, densities between 1549 kg/m\u0026sup3; and 1989 kg/m\u0026sup3;, and water absorption rates ranging from 10\u0026ndash;18% [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. In one study, bricks containing 2.5% RHA achieved a compressive strength of 16.21 MPa, with a density of 1549 kg/m\u0026sup3; and 14.5% water absorption [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. These results indicate the potential of RHA for developing lightweight and sustainable bricks with acceptable performance characteristics. Several investigations have confirmed that 5 to 15% RHA substitution improves the compressive strength, with 10% RHA frequently yielding optimal results. Additionally, RHA reduces water absorption and enhances long-term durability [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. Nevertheless, in addition to composition, the curing environment, particularly temperature and humidity, plays a decisive role in influencing brick quality. Studies have demonstrated that controlled curing at 24\u0026deg;C with a relative humidity\u0026thinsp;\u0026ge;\u0026thinsp;90% accelerates the hydration process of RHA-cement-soil blocks, increasing density and compressive strength while minimizing porosity [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]. In contrast, ambient curing at room temperature (approximately 30\u0026deg;C) slows hydration, resulting in increased porosity, reduced durability, and decreased mechanical performance [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. Controlled curing at 24\u0026deg;C (RH\u0026thinsp;\u0026gt;\u0026thinsp;90%) ensures sufficient internal moisture, promotes complete hydration and reduces microcracks, which leads to strength that is 30% greater than that of ambient-cured samples after 7 days. Water absorption rates typically remain between 16% and 18%, and overall durability improves by 25\u0026ndash;30%. Autoclave curing, involving elevated temperature and pressure, has also been shown to increase the compressive strength by 65\u0026ndash;85% while reducing water absorption from 18\u0026ndash;8% [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e].\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eRecent research has demonstrated that the curing environment, particularly temperature and humidity, substantially influences the physical, mechanical, and environmental performance of unfired bricks manufactured with soil, rice husk ash (RHA), and cement. Accordingly, a comparative investigation of controlled curing conditions (24\u0026deg;C, relative humidity\u0026thinsp;\u0026ge;\u0026thinsp;90%) versus ambient room temperature curing (30\u0026deg;C, natural humidity) is both pertinent and essential. This study seeks to address existing knowledge deficiencies by empirically evaluating the performance of Greencrete blocks under these two distinct curing regimes. Despite evident environmental and performance advantages associated with Greencrete and CCUS concrete-enabled materials, their large-scale implementation remains constrained due to gaps in scientific understanding and the absence of standardized methodologies. Most extant studies predominantly focus on material-level properties without thoroughly examining curing dynamics, carbon sequestration potential, and lifecycle performance. Furthermore, the thermal responsiveness of waste-derived Greencrete materials remains largely unexplored. To bridge these gaps, this research conducts a comprehensive experimental analysis of the thermal responsiveness of Greencrete blocks composed of soil, RHA, and cement. A comparative assessment evaluates key performance indicators\u0026mdash;including compressive strength, water absorption, and bulk density\u0026mdash;under controlled (24\u0026deg;C, RH\u0026thinsp;\u0026ge;\u0026thinsp;90%) and ambient (30\u0026deg;C) curing environments at 28 days. The findings aim to elucidate the influence of curing parameters on hydration kinetics, thereby supporting the development of climate-responsive, low-carbon construction materials in alignment with global sustainability objectives.\u003c/p\u003e"},{"header":"Materials and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003eMaterials\u003c/h2\u003e\u003cdiv id=\"Sec4\" class=\"Section3\"\u003e\u003ch2\u003eSoil\u003c/h2\u003e\u003cp\u003eIn this study, the expansive soil used for Greencrete block-making was collected from the Handa area of Tsu city, Mie Prefecture, Japan, approximately 22 km from Mie University. This location was chosen because of the naturally weak, expansive, and poorly consolidated nature of the soil, which presents geotechnical challenges. The representative samples were collected via a systematic soil sampling method, following standard geotechnical procedures. The soil under investigation is classified as A-7\u0026ndash;5(5) according to the American Association of State Highway and Transportation Officials (AASHTO) classification system, which typically represents a highly plastic clayey soil with poor drainage characteristics [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e].\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe samples for testing were prepared via the air-drying method according to the JIS A 1201:2020 standard. In this method, the soil is dried in a shaded area under normal ambient conditions until it reaches a constant mass, ensuring that the physical properties of the soil remain unchanged. The grain size distribution of the soil was subsequently determined via sieve and hydrometer analyses as per JIS A 1204:2020. Notably, this standard aligns with the internationally recognized International Organization for Standardization, ISO 17892-4:2016 standard. The test results revealed that the soil particle sizes ranged from 0.001 mm to 2.0 mm, indicating a predominantly fine-grained soil. The analysis is presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. On the other hand, tests according to JIS A 1205:2020 determined the soil's liquid limit (58.21%), plastic limit (31.05%), sand content (6.2%), silt content (52.56%), and clay content (41.24%), as shown in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. Additionally, energy dispersive X-ray spectroscopy (EDS) analysis revealed that the soil contained 91.10% silica, 4.35% carbon dioxide (CO₂), 2.40% potassium oxide (K₂O), and 0.57% calcium oxide (CaO). On scientific grounds, this soil is considered suitable for stabilization [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e].\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\n\u003ch3\u003eRice husk ash\u003c/h3\u003e\n\u003cp\u003eIn this study, rice husk ash (RHA) with a high silica content of 93.30% was obtained from Make Integrated Technology Co., Ltd., Osaka, Japan. The supplier also provided the material's composition. A high silica level was achieved by burning the rice husk in a computer-controlled incinerator at 650\u0026ndash;700\u0026deg;C for 27 hours. The particle size of this RHA ranged from 0.07 to 0.3 mm (as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e), with a specific gravity of 1.47 and a loss on ignition of 4.00\u0026ndash;6.00% [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. Among the chemical components, this RHA contains 93.30% silica (SiO₂), 4.49% potassium oxide (K₂O), 0.82% calcium oxide (CaO), 0.43% phosphorus pentoxide (P₂O₅), 0.06% iron oxide (Fe₂O₃), 0.04% alumina (Al₂O₃), and 0.86% other compounds. According to research, RHA is 100% effective for making hollow blocks and is widely acclaimed as an eco-friendly construction material owing to its physio-chemical properties and specific gravity [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e].\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\n\u003ch3\u003ePortland cement\u003c/h3\u003e\n\u003cp\u003eOrdinary Portland cement (OPC) was used in minimal amounts in this study, primarily to activate the pozzolanic reaction by providing calcium oxide ions, which help bind the materials together. As shown in Table\u0026nbsp;4, the physical and chemical properties of OPC enable it to act effectively as an activator and binder. The cement itself contains alite (Ca₃SiO₅), which is the main phase responsible for the early and high strength of Portland cement. The decision to use the minimum required dosage of OPC in this study was driven by the aim of reducing cement consumption, increasing durability, and taking advantage of the ready market availability of OPC and its effectiveness as an amorphous SiO₂ activator in pozzolanic systems [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e, \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e].\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eMajor properties of OPC [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e].\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"2\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eProperty\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eValue\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSpecific Gravity, g/cm\u003csup\u003e3\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e3.15\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSpecific surface area, m\u003csup\u003e2\u003c/sup\u003e/kg\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e340\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eLoss of Ignition, %\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u0026lt;\u0026thinsp;4\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eInitial setting time, minutes\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e170\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eFinal setting time, minutes\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e255\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e28-day compressive strength, MPa\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e33\u0026ndash;53\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCalcium Oxide (CaO), %\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e63.40\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSilica (SiO\u003csub\u003e2\u003c/sub\u003e), %\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e21.60\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eIron Oxide (Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e), %\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e5.35\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAlumina (Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e), %\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e4.45\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSulfur trioxide (SO\u003csub\u003e3\u003c/sub\u003e), %\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1.92\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eMagnesium oxide (MgO), %\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1.65\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003ePotassium Oxide (K\u003csub\u003e2\u003c/sub\u003eO), %\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0.22\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSodium oxide (Na\u003csub\u003e2\u003c/sub\u003eO), %\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0.11\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eMagnesium oxide (MgO), %\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e1.65\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\n\u003ch3\u003eSample Preparation\u003c/h3\u003e\n\u003cp\u003eIn this study, 16 different mix proportions Greencrete block samples were prepared separately via an established process. For each of the three sample types, 1000 g of clay, cement, or RHA was used to make the blocks. The specific proportions used for mixing and production of the samples are given in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. Each mixture was labeled with an identifier (Control to 15RHA12C) for statistical analysis and performance evaluation. The preparation of samples followed the JIS R 5201:2015 standard, with the procedure schematically presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eParametric study of the soil, RHA, and cement.\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"6\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eMix types\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eIndex\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"4\" nameend=\"c6\" namest=\"c3\"\u003e\u003cp\u003eMaterial types (% by weight)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eSoil, %\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eRHA, %\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eCement, %\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003eWater, %\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSoil\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eControl\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e100\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e30\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSoil\u0026thinsp;+\u0026thinsp;8%\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0RHA8C\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e100\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e32\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSoil\u0026thinsp;+\u0026thinsp;10% Cement\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0RHA10C\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e100\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e32.5\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSoil\u0026thinsp;+\u0026thinsp;12% Cement\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e0RHA12C\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e100\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e12\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e33\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSoil\u0026thinsp;+\u0026thinsp;5% RHA\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e5RHA0C\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e100\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e33\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSoil\u0026thinsp;+\u0026thinsp;5% RHA\u0026thinsp;+\u0026thinsp;8% Cement\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e5RHA8C\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e100\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e34\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSoil\u0026thinsp;+\u0026thinsp;5% RHA\u0026thinsp;+\u0026thinsp;10% Cement\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e5RHA10C\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e100\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e35\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSoil\u0026thinsp;+\u0026thinsp;5% RHA\u0026thinsp;+\u0026thinsp;12% Cement\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e5RHA12C\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e100\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e5\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e12\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e36\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSoil\u0026thinsp;+\u0026thinsp;10% RHA\u0026thinsp;+\u0026thinsp;0% Cement\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e10RHA0C\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e100\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e36\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSoil\u0026thinsp;+\u0026thinsp;10% RHA\u0026thinsp;+\u0026thinsp;8% Cement\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e10RHA8C\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e100\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e35\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSoil\u0026thinsp;+\u0026thinsp;10% RHA\u0026thinsp;+\u0026thinsp;10% Cement\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e10RHA10C\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e100\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e36\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSoil\u0026thinsp;+\u0026thinsp;10% RHA\u0026thinsp;+\u0026thinsp;12% Cement\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e10RHA12C\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e100\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e12\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e37\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSoil\u0026thinsp;+\u0026thinsp;15% RHA\u0026thinsp;+\u0026thinsp;0% Cement\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e15RHA0C\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e100\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e15\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e39\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSoil\u0026thinsp;+\u0026thinsp;15% RHA\u0026thinsp;+\u0026thinsp;8% Cement\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e15RHA8C\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e100\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e15\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e38\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSoil\u0026thinsp;+\u0026thinsp;15% RHA\u0026thinsp;+\u0026thinsp;10% Cement\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e15RHA10C\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e100\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e15\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e10\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e39\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSoil\u0026thinsp;+\u0026thinsp;15% RHA\u0026thinsp;+\u0026thinsp;12% Cement\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e15RHA12C\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e100\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e15\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e12\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e40\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eFirst, the raw materials were thoroughly mixed manually in a container until a homogeneous mixture was obtained. To ensure adequate plasticity and adhesion, 30 to 40% of the total dry weight of the ingredients was mixed with water to prepare the clay paste so that the paste could be easily placed and shaped in the mold by hand. This method resembles the traditional clay paste preparation for making common burnt clay building bricks in the Indian subcontinent. As per Indian Standard IS 1077 (1992), 20\u0026ndash;30% water by weight is recommended for the preparation of common burnt clay building bricks [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]. In this study, the use of RHA required slightly more water to produce a similar type of mortar.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eIn this study, 100% clay was used to make the control samples. Additionally, in the preparation of the other samples, higher doses of RHA, 5%, 10%, and 15%, were selected than those reported in previous studies [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]. This is consistent with the use of RHA in existing studies [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e]. In this study, 8%, 10%, and 12% cement was also mixed with RHA, so that the combined pozzolanic reaction of these two components would ensure an optimal ratio of Ca⁺ ions. Moreover, the use of a minimal amount of cement in construction materials and the incorporation of RHA as a replacement enhance both environmental protection and material efficiency.\u003c/p\u003e\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\u003ch2\u003eCuring\u003c/h2\u003e\u003cp\u003eAfter removal from the mold, the Greencrete blocks were cured for 28 days in two different ways. Among them, one set was cured in a room at 30\u0026deg;C without any humidity to represent natural conditions, allowing sufficient strength and durability to be achieved quickly, which is consistent with existing research [\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e]. The curing process shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e (a) was carried out following the basic requirements of the Japanese Industrial Standard A 1132:2020, which meets the international standard ISO 1920-3:2004. Another batch of sample bricks was cured at 24\u0026thinsp;\u0026plusmn;\u0026thinsp;2\u0026deg;C and 50\u0026ndash;90% humidity in a chamber for 28 days, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e(b), where the basic requirements of JIS A 1132:2020 were also followed. A similar method has been followed for sample curing in other studies [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]. This integrated and consistent sample preparation process ensures that all samples provide comparable quality, repeatability, and reliable test results.\u003c/p\u003e\u003c/div\u003e\n\u003ch3\u003eTesting method\u003c/h3\u003e\n\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\u003ch2\u003eBulk density\u003c/h2\u003e\u003cp\u003eThe density of the Greencrete block samples, which are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e8\u003c/span\u003e(a) and (b), was evaluated following the procedures outlined in American Society for Testing and Materials (ASTM) C67/C67M [\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e] or an equivalent standardized methodology. The bulk density was subsequently calculated via Eq.\u0026nbsp;(1), ensuring consistency with established analytical frameworks for masonry materials.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eρ\u0026thinsp;=\u0026thinsp;mv (1)\u003c/p\u003e\u003cp\u003ewhere\u003c/p\u003e\u003cp\u003eρ\u0026thinsp;=\u0026thinsp;bulk density\u003c/p\u003e\u003cp\u003em\u0026thinsp;=\u0026thinsp;mass\u003c/p\u003e\u003cp\u003e\u003cem\u003ev\u003c/em\u003e\u0026thinsp;=\u0026thinsp;volume\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\u003ch2\u003eWater Absorption Test\u003c/h2\u003e\u003cp\u003eThe evaluation of the water absorption properties of the Greencrete block samples was conducted via the standardized methodology prescribed in JIS R 1250:2011 (ISO 10545-3\u003cb\u003e)\u003c/b\u003e, which specifies the fundamental procedure for water absorption testing, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e9\u003c/span\u003e. The oven-absorption percentage was subsequently computed via Eq.\u0026nbsp;2, ensuring methodological consistency and accuracy. The dry mass (M₁) and saturated mass (M₁A) of each sample were precisely measured, and the water\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cem\u003ea\u003c/em\u003e\u0026thinsp;=\u0026thinsp;\u003cem\u003eM\u003c/em\u003e\u003csub\u003e\u003cem\u003e1A\u003c/em\u003e\u003c/sub\u003e-\u003cem\u003eM\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e \u003cem\u003eM\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e \u003cem\u003e\u0026times;100\u003c/em\u003e (2)\u003c/p\u003e\u003cp\u003ewhere\u003c/p\u003e\u003cp\u003ea\u0026thinsp;=\u0026thinsp;water absorption (%)\u003c/p\u003e\u003cp\u003e\u003cem\u003eM\u003c/em\u003e\u003csub\u003e\u003cem\u003e1\u003c/em\u003e\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;dry weight of the bricks (g)\u003c/p\u003e\u003cp\u003e\u003cem\u003eM\u003c/em\u003e\u003csub\u003e\u003cem\u003e1A\u003c/em\u003e\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;saturated weight of the bricks (g)\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\u003ch2\u003eCompressive strength test\u003c/h2\u003e\u003cp\u003eThe compressive strength assessment of the brick samples was performed via a universal testing machine, the schematic diagram in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e8\u003c/span\u003e, adhering to the guidelines specified in JIS R 1250:2011, or an equivalent standardized test protocol. The peak load sustained by each sample during the test was meticulously recorded, and the corresponding compressive strength values were derived via Eq.\u0026nbsp;3, ensuring alignment with established mechanical evaluation criteria.\u003c/p\u003e\u003cp\u003eC\u0026thinsp;=\u0026thinsp;w a N/mm\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\u003cp\u003e=w a \u0026times;1000 MPa (3)\u003c/p\u003e\u003cp\u003ewhere\u003c/p\u003e\u003cp\u003ec\u0026thinsp;=\u0026thinsp;compressive strength\u003c/p\u003e\u003cp\u003ew\u0026thinsp;=\u0026thinsp;maximum load\u003c/p\u003e\u003cp\u003ea\u0026thinsp;=\u0026thinsp;initial cross-sectional surface area\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\u003ch2\u003eMicrostructural study\u003c/h2\u003e\u003cp\u003eParticle size distribution of soil is a vital physical property that directly affects soil texture classification, while the chemical composition of soil is another key characteristic to consider when understanding its physical properties. The scanning electron microscope (SEM) uses the wave properties of electrons to magnify surface details, making it a versatile tool for analyzing soil particles and solid materials, especially in dispersive soils, due to its high resolution. SEM is a highly adaptable instrument used to examine and analyze the microstructure and properties of solid objects [\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e, \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e]. Its main advantage for examining Greencrete block samples is its ability to produce high-resolution images of material microstructure. To adhesive carbon tape, ensuring that the exposed surfaces accurately represent the brick's in-situ structure. prepare for analysis, a cross-sectional segment of the brick was mounted on a stub with double-sided\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe instrument used in this study, to observe the topographical features of the samples on a micro-scale, SEM images are produced using an ultra-high-resolution JEOL JSM-IT200, is a research-grade scanning electron microscope known for its user-friendly interface, compact ergonomic design, and versatility. It offers high-resolution imaging with spatial resolution down to approximately 3 nm at 30 kV in high vacuum mode and supports accelerating voltages (SED) from 0.5 to 30 kV, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e9\u003c/span\u003e. The SEM features both high vacuum and low vacuum modes, allowing observation of non-conductive samples without the need for conductive coatings. On the other hand, SEM is equipped with secondary and backscattered electron detectors and an integrated energy dispersive X-ray spectrometer (EDS) for real-time elemental analysis, including spectral mapping, line scanning, and automatic drift compensation. This SEM-EDX method is used to detect the presence and amount of chemical elements in brick samples during microscopy inspection based on atomic number, although it cannot distinguish between ionized and free atoms.\u003c/p\u003e\u003c/div\u003e"},{"header":"Results and discussion","content":"\u003cdiv id=\"Sec15\" class=\"Section2\"\u003e\u003ch2\u003eBulk density\u003c/h2\u003e\u003cp\u003eThe structural compactness of Greencrete block is an important indicator of mechanical performance and durability, which is significantly affected by the interaction of RHA, OPC, and curing conditions. Studies have shown that RHA is rich in amorphous silica, and its addition helps reduce the density of bricks because of its low specific gravity, high internal porosity, and thinning effect on the binder matrix [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e]. This density reduction is particularly evident when the amount of RHA exceeds 10%, which leads to an increase in voids and disruption of particle packing [\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e]. Conversely, when balanced with high OPC content\u0026mdash;especially under 24\u0026deg;C curing conditions, the high silica content [SiO₂] in RHA reacts with calcium hydroxide [Ca(OH)₂], produced by OPC hydration, to form C\u0026ndash;S\u0026ndash;H (calcium silicate hydrate). This synergistic pozzolanic reaction densifies and strengthens the microstructure of bricks or concrete, thereby increasing density and compressive strength [\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e, \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e].\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eAccording to Fig.\u0026nbsp;\u003cspan refid=\"Fig14\" class=\"InternalRef\"\u003e12\u003c/span\u003e, samples made with 15% RHA and 12% cement presented a bulk density of 1298.99 kg/m\u0026sup3; when cured in a humidity-controlled chamber at 24\u0026deg;C, whereas at 30\u0026deg;C, the bulk density was only 1110.48 kg/m\u0026sup3;. This indicates that a higher curing temperature accelerated initial water evaporation and inhibited hydrolysis and silica reactions [\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e]. Silica hydrolysis and pozzolanic reactions are slowed or inhibited due to a lack of sufficient water and time, which prevents proper interaction between SiO₂ and Ca(OH)₂ [\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e]. The same trend was observed for mixtures such as 10% RHA and 12% cement and 10% RHA and 10% cement, which achieved bulk densities of 1299.44 and 1246.75 kg/m\u0026sup3;, respectively, under 24\u0026deg;C curing. These results reveal the thermal sensitivity of the hydration dynamics and particle interlocking processes.\u003c/p\u003e\u003cp\u003eNotably, at relatively high curing temperatures (30\u0026deg;C or above) and with high RHA contents, the hydration and C\u0026ndash;S\u0026ndash;H formation in bricks are disrupted, resulting in density irregularities and structural weaknesses [\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e]. Furthermore, under moist curing conditions, mixtures containing 10\u0026ndash;15% RHA and 10\u0026ndash;12% OPC result in the lowest porosity in the matrix, with densely packed particles attributable to micropore bonding and volume‒filler effects [\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e]. When combined with optimized curing protocols, RHA-cement blocks can match or exceed traditional fired clay bricks in terms of density and performance, without high energy consumption or soil surface degradation. These results align with the sustainable construction goals outlined in SDG 11 and SDG 12 and support the transition toward net-zero construction materials [\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e].\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec16\" class=\"Section2\"\u003e\u003ch2\u003eWater absorption\u003c/h2\u003e\u003cp\u003eIn this study, the water absorption behaviour of Greencrete block at two curing temperatures and humidity levels was examined, revealing important insights into pore development and binder interactions in low-carbon masonry. The results demonstrate a distinct relationship between the RHA content, cement dosage, and curing temperature in controlling capillary pores that govern water absorption. In these studies, during the water absorption test, the samples were made with only clay dissolved in water. The same properties were observed in the sample bricks made without cement and mixed with RHA in different proportions (5%, 10% and 15%). Without the addition of RHA, simply increasing the cement content from 8\u0026ndash;12% gradually increased the water absorption from 31.5\u0026ndash;34.8% at 30\u0026deg;C, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig15\" class=\"InternalRef\"\u003e13\u003c/span\u003e, suggesting the possibility of capillary voids being blocked during initial hydration [\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e]. With 5% RHA incorporation, mixed effects were observed: 5% RHA and 8% cement, and 5% RHA and 10% cement presented moderate absorption (35.5% and 34.3%, respectively), whereas 5% RHA and 12% cement significantly decreased to 32%, probably due to improved filler-packing effects and pozzolanic refinement of the pore structure, which is consistent with the results of recent studies [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eHowever, at the 10% and 15% replacement levels, the role of RHA became more evident. The 10% RHA group exhibited the highest average absorption (38 to 40%) at both temperatures, suggesting that the additional RHA may increase the matrix porosity due to its high amount of unburned carbon and irregular particle morphology [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e, \u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e]. Interestingly, the blocks made with 10% RHA and 12% cement absorbed 40.5% of the water, and the bocks made with 10% RHA and 8% cement absorbed 38.7% of the water, which was only a slight improvement compared with each other, indicating that cement addition alone could not completely reduce the increased pore volume associated with high RHA content. Notably, the water absorption values at 24\u0026deg;C in the controlled curing chamber were reflected in the relative trend compared with those at 30\u0026deg;C, but were slightly lower, confirming the effect of higher curing temperatures on increasing hydration kinetics, and confirming the relative absorption trend in some recent studies [\u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e54\u003c/span\u003e, \u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e55\u003c/span\u003e]. The 15% RHA series further highlights the complex interplay of binder dilution and hydration control. 15% RHA and 8% cement, and 15% RHA and 10% cement showed very high absorption 47.7% and 46.3%, respectively, whereas 15% RHA and 12% cement presented an abnormal value of 1298.99%, which emphasizes the need for moisture control protocols during sample conditioning.\u003c/p\u003e\u003cp\u003eIn line with the proposed pore system instability theory, such excessive absorption could also indicate uncontrolled pore coordination, caused by insufficient cementitious matrix formation. Nevertheless, even when exogenous factors are excluded, the overall data suggest that a significant balance in the cement dosage is required to stabilize the RHA microstructure above 5%. Comparative analysis across temperature bands confirms that 30\u0026deg;C curing leads to slightly greater absorption than 24\u0026deg;C curing does, a phenomenon attributed to rapid hydration and capillary channel development under thermal acceleration. Furthermore, the trend validates the dual function of RHA as both a pozzolanic additive and an internal curing agent when used within the optimal range (~\u0026thinsp;5%) [\u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e56\u003c/span\u003e]. Overall, this study highlights the importance of finely ground RHA\u0026ndash;cement blends for adjusting the water absorption properties of unfired eco-bricks. This highlights that moderate RHA inclusion (\u0026le;\u0026thinsp;5%), when adequately balanced with the cement content, synergistically improves pore packing and reduces capillary action. In contrast, excessive RHA (\u0026ge;\u0026thinsp;10%) without adequate cement fails to achieve microstructural densification. These results support broader efforts to develop green masonry materials through agro-waste evaluation, as per SDG 12.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec17\" class=\"Section2\"\u003e\u003ch2\u003eCompressive strength\u003c/h2\u003e\u003cp\u003eThe compressive strength of Greencrete block is an important parameter to ensure structural applications and durability, especially when incorporating durable materials such as RHA. This study explored the variation in the compressive strength of block made with different RHA and cement ratios at 30\u0026deg;C and 24\u0026deg;C in a humidity-controlled chamber. The results demonstrate a nonlinear relationship between binder composition and mechanical performance, which is significantly affected by both pozzolanic reactivity and curing kinetics. According to Fig.\u0026nbsp;\u003cspan refid=\"Fig16\" class=\"InternalRef\"\u003e14\u003c/span\u003e, the 5% RHA series exhibited higher compressive strengths, with the 5% RHA and 12% cement samples achieving 3.67 MPa at 30\u0026deg;C and 2.83 MPa at 24\u0026deg;C, much higher than those of the control brick (2.05 MPa). This increase in strength is attributed to the synergistic effect of the cementitious matrix from RHA and reactive silica, which increases calcium silicate hydrate (C\u0026ndash;S\u0026ndash;H) gel formation and densifies the microstructure [\u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e57\u003c/span\u003e].\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eAdding up to the optimum limit of RHA (~\u0026thinsp;5%) increases the pozzolanic activity, fills the voids, and refines the pore networks, thereby improving the compressive strength [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. However, the strength decreases significantly at higher RHA contents (10% and 15%) unless adequately compensated by cement. For example, 15% RHA and 8% cement achieved only 0.68 MPa at 30\u0026deg;C and 0.81 MPa at 24\u0026deg;C, which is consistent with the literature that excess ash increases porosity and disrupts matrix continuity [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. The samples cured at 30\u0026deg;C and 24\u0026deg;C presented compressive strengths of 0.95 MPa and 2.61 MPa, respectively. Rapid hydration at higher temperatures results in an unconventional structure with additional pores or microcracks, which reduces the compressive strength. On the other hand, at lower curing temperatures (24\u0026deg;C) with moisture, the microstructure becomes denser and less porous, resulting in increased compressive strength. Most of the samples performed better than their counterparts at 24\u0026deg;C, indicating enhanced hydration kinetics and matrix development under high temperature conditions [\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eHowever, the decrease in strength at 24\u0026deg;C for certain compositions (5% RHA and 8% cement and only 10% RHA without any cement) indicates insufficient binder activation or incomplete pozzolanic reactions, which is consistent with the thermal sensitivity of waste-derived binders [\u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e58\u003c/span\u003e]. This temperature-dependent strength behaviour underscores the importance of optimal curing environments, particularly in low-binder, high-RHA compositions. Additionally, this study emphasizes the role of the cement dosage in strength control. In a 10% RHA blend, increasing the cement content from 8\u0026ndash;10% at 30\u0026deg;C improved the strength from 1.65 to 2.00 MPa, demonstrating the compensatory effect of the cement. However, beyond a critical limit, additional cement may not yield linear gains because of potential shrinkage-induced microcracking [\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e]. Therefore, balancing the binder-to-aggregate ratio and curing parameters is essential to achieve structural-grade unfired bricks.\u003c/p\u003e\u003cp\u003eFrom a microstructural perspective, the interaction between the amorphous silica of RHA and the cement hydration product leads to the secondary formation of C\u0026ndash;S\u0026ndash;H, improving the interfacial bonds and load-bearing capacity. However, excessive RHA or insufficient cement can lead to weak particle bonding and high porosity, which ultimately reduces strength [\u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e59\u003c/span\u003e]. This study supports the integration of agro-industrial waste into low-carbon masonry through optimized material design. The 5% RHA and 12% cement, and the 5% RHA and 10% cement compositions demonstrated particularly promising compressive strengths, which are consistent with the sustainable construction goals of reducing cement usage [\u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e60\u003c/span\u003e]. These results confirm that judicious mixing of RHA and cement under controlled curing can produce high-performance nonburnt bricks, which support climate-resilient infrastructure and SDG 11 and SDG 12.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec18\" class=\"Section2\"\u003e\u003ch2\u003eSEM analysis\u003c/h2\u003e\u003cp\u003eIn this study, SEM images were taken at a magnification of x500, where the high-vacuum mode and SED were set to 20.0 kV, and the electron beam current or standard probe current (Std-PC) was set to 30 kV. After that, the morphology of the control sample at 30\u0026deg;C exhibited multiple cracks and small micropores, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig17\" class=\"InternalRef\"\u003e15\u003c/span\u003e. On the other hand, the control sample cured at 24\u0026deg;C also exhibits a similar structure, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig18\" class=\"InternalRef\"\u003e16\u003c/span\u003e. which is consistent with recent studies [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]..\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eBoth control samples without cement and RHA, a small amount of CaO, and a significant amount of SiO2 were present, which resulted in this incomplete pozzolanic reaction.\u003c/p\u003e\u003cp\u003eAs a result, the flocculated hydration products exhibited, but the control sample at 24\u0026deg;C had larger flocculated hydration products due to the relatively low temperature and humidity.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eMeanwhile, the SEM micrograph of the brick made by adding 5% RHA and 12% cement (5RHA12C) to the soil and curing at 30\u0026deg;C showed a fibrous and honeycomb compact matrix, and the flocculated hydration products were reduced, forming a multi-layered hydration product by intermixing with each other, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig19\" class=\"InternalRef\"\u003e17\u003c/span\u003e. This dense matrix is formed due to the aggregation of different silicate phases, which provides strength to the porous brick, which is consistent with recent studies [\u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e61\u003c/span\u003e, \u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e62\u003c/span\u003e]. The same structure was observed in the SEM image of a brick sample made of the same type of material (5% RHA and 12% cement), but cured at 24\u0026deg;C with moisture, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig20\" class=\"InternalRef\"\u003e18\u003c/span\u003e.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eIn particular, in Greencrete block, the pozzolanic activity of RHA and cement increases the particle bonding, where reactive silica interacts with calcium hydroxide to form secondary calcium silicate hydrate (C-S-H), improving the matrix structure, strength development, and long-term durability. Although the curing conditions were different, Ca(OH)₂ crystals were observed in both 5RHA12C block samples, which were formed as a result of the initial hydration of the cement, which then reacted with the high SiO2 content of RHA to form calcium silicate hydrate (C\u0026ndash;S\u0026ndash;H) gel [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e, \u003cspan citationid=\"CR63\" class=\"CitationRef\"\u003e63\u003c/span\u003e].\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eRecent studies have shown that with the increase in C\u0026ndash;S\u0026ndash;H formation, the amount of CH plates decreases, which makes the clay matrix more interconnected and contributes to the improved performance of the brick As a result, the maximum compressive strength values of the two 5RHA 12C samples cured at 30\u0026deg;C and 24\u0026deg;C with humidity were 3.53 MPa and 2.51 MPa, respectively, which are consistent with recent studies [\u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e60\u003c/span\u003e].\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eThe Energy Dispersive X-ray spectroscopy (EDS) results\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"13\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c11\" colnum=\"11\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c12\" colnum=\"12\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c13\" colnum=\"13\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e\u003cp\u003eFormula\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"4\" nameend=\"c5\" namest=\"c2\"\u003e\u003cp\u003eWeight %\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"4\" nameend=\"c9\" namest=\"c6\"\u003e\u003cp\u003eMol%\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"4\" nameend=\"c13\" namest=\"c10\"\u003e\u003cp\u003eCations\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003ctr\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e\u003cp\u003eControl\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e\u003cp\u003e5RHA12C\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e\u003cp\u003eControl\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e\u003cp\u003e5RHA12C\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c11\" namest=\"c10\"\u003e\u003cp\u003eControl\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c13\" namest=\"c12\"\u003e\u003cp\u003e5RHA12C\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003e30\u0026deg;C\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003e24\u0026deg;C\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003e30\u0026deg;C\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003e24\u0026deg;C\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003e30\u0026deg;C\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c7\"\u003e\u003cp\u003e24\u0026deg;C\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c8\"\u003e\u003cp\u003e30\u0026deg;C\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c9\"\u003e\u003cp\u003e24\u0026deg;C\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c10\"\u003e\u003cp\u003e30\u0026deg;C\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c11\"\u003e\u003cp\u003e24\u0026deg;C\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c12\"\u003e\u003cp\u003e30\u0026deg;C\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c13\"\u003e\u003cp\u003e24\u0026deg;C\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eC\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e4.43\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e3.30\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e21.09\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e15.90\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c11\"\u003e\u003cp\u003e0.00\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c12\"\u003e\u003cp\u003e0.00\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c13\"\u003e\u003cp\u003e0.21\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eNa2O\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.44\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.14\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e0.76\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e0.41\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e0.13\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e\u003cp\u003e0.80\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c11\"\u003e\u003cp\u003e0.13\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c12\"\u003e\u003cp\u003e0.04\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c13\"\u003e\u003cp\u003e0.56\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eMgO\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e2.07\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e1.61\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.69\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e2.61\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e3.70\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e2.29\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e1.00\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e\u003cp\u003e4.22\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e\u003cp\u003e0.48\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c11\"\u003e\u003cp\u003e0.37\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c12\"\u003e\u003cp\u003e0.15\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c13\"\u003e\u003cp\u003e3.45\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAl2O3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e28.75\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e22.69\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e19.97\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e20.27\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e20.36\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e12.72\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e11.33\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e\u003cp\u003e12.95\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e\u003cp\u003e5.29\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c11\"\u003e\u003cp\u003e4.08\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c12\"\u003e\u003cp\u003e3.45\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c13\"\u003e\u003cp\u003e7.22\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSiO2\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e36.52\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e47.74\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e52.64\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e49.96\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e43.89\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e45.44\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e50.67\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e\u003cp\u003e54.16\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e\u003cp\u003e5.71\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c11\"\u003e\u003cp\u003e7.28\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c12\"\u003e\u003cp\u003e7.72\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c13\"\u003e\u003cp\u003e0.45\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eK2O\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e4.09\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e3.18\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e2.76\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e2.46\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e3.14\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e1.93\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e1.69\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e\u003cp\u003e1.70\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e\u003cp\u003e0.82\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c11\"\u003e\u003cp\u003e0.62\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c12\"\u003e\u003cp\u003e0.52\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c13\"\u003e\u003cp\u003e2.72\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eCaO\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e0.67\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e1.25\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e12.31\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e17.55\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e0.87\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e1.27\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e12.70\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e\u003cp\u003e20.38\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e\u003cp\u003e0.11\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c11\"\u003e\u003cp\u003e0.20\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c12\"\u003e\u003cp\u003e1.94\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c13\"\u003e\u003cp\u003e0.77\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eFeO\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e27.89\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e18.66\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e8.18\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e6.38\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e28.04\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e\u003cp\u003e14.85\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e\u003cp\u003e6.59\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e\u003cp\u003e5.78\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e\u003cp\u003e3.64\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c11\"\u003e\u003cp\u003e2.38\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c12\"\u003e\u003cp\u003e1.00\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c13\"\u003e\u003cp\u003e0.21\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec19\" class=\"Section2\"\u003e\u003ch2\u003eEDS analysis\u003c/h2\u003e\u003cp\u003eEnergy Dispersive X-ray Spectroscopy (EDS) is a special technique for analysis of the elemental composition of Greencrete bricks by the help of this method the amount of SiO₂, alumina, calcium oxide, and other elements in the mixes is identified. In this research, EDS reveals that the uncured brick sample made only of clay and cured at 30\u0026deg;C is rich in high levels of silica (SiO₂), as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig21\" class=\"InternalRef\"\u003e19\u003c/span\u003e. According to the data in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, this sample contains 36.52 wt%, 43.89 mol% SiO₂, 28.75 wt%, 20.36 mol% Al₂O₃, and 0.67 wt%, 0.87 mol% CaO.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eA similar pattern was observed for the brick cured at 24\u0026deg;C (shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig22\" class=\"InternalRef\"\u003e20\u003c/span\u003e). According to Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, this sample contains 47.74 wt%, 45.44 mol% SiO₂, 22.96 wt%, 12.72 mol% Al₂O₃, and 1.25 wt%, 1.27 mol% CaO. In these two samples, SiO₂ reacts with CaO to form CaO-SiO₂-H₂O gel (C-S-H), which is formed by the hydration of calcium silicate and is characterized by its complex and variable structure [\u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e66\u003c/span\u003e]. .\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eDue to the absence of RHA and cement, flocculated hydration products, although formed in small amounts, are not sufficient to create a compact matrix, resulting in multiple cracks and micropore development. However, due to the relatively low temperature and humidity during curing, and the relatively higher presence of CaO, more flocculated hydration products were formed in the control sample at 24\u0026deg;C. According to Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, both samples of 5RHA12C contained 12.31 wt%, 12.70 mol% and 17.55 wt%, 20.38 mol% CaO, respectively. These two samples had relatively higher SiO₂ and CaO contents compared to the bricks, as shown in Figs.\u0026nbsp;\u003cspan refid=\"Fig22\" class=\"InternalRef\"\u003e20\u003c/span\u003e and \u003cspan refid=\"Fig23\" class=\"InternalRef\"\u003e21\u003c/span\u003e.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eSiO₂, or amorphous silica, came from RHA, which exhibits high pozzolanic reactivity (amorphous silica gel) and contributes to the acceleration of geopolymerization reactions in the brick matrix. CaO came from cement, which plays a primary role in the formation of calcium silicate hydrate (C\u0026ndash;S\u0026ndash;H) gel, the main hydration product of cement [\u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e65\u003c/span\u003e, \u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e66\u003c/span\u003e]. Previous research mentions that the formation of C\u0026ndash;S\u0026ndash;H gel and amorphous silica gel is due to the following process:\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec20\" class=\"Section2\"\u003e\u003ch2\u003exC\u0026thinsp;+\u0026thinsp;yS\u0026thinsp;+\u0026thinsp;tH\u0026rarr;xC-S-H\u0026thinsp;+\u0026thinsp;other products (4)\u003c/h2\u003e\u003cp\u003ewhere C\u0026thinsp;=\u0026thinsp;CaO, H\u0026thinsp;=\u0026thinsp;H₂O, S\u0026thinsp;=\u0026thinsp;SiO₂, A\u0026thinsp;=\u0026thinsp;Al₂O₃, and C\u0026thinsp;=\u0026thinsp;CO₂; x, y, and t are molecular quantities [\u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e64\u003c/span\u003e].\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eFig.\u003cem\u003e_\u003c/em\u003e22 EDS image of the 5RHA10C sample cured at 30\u0026deg;C.\u003c/p\u003e\u003cp\u003eFrom Eq.\u0026nbsp;(4), the change in molar volume during carbonation of C\u0026ndash;S\u0026ndash;H depends on the C/S ratio, the amount of water in C\u0026ndash;S\u0026ndash;H, and the water in the silica gel. Unlike the carbonation reaction between CH and CO₂, the volume change during carbonation of C\u0026ndash;S\u0026ndash;H varies with the C\u0026ndash;S\u0026ndash;H phase with different C/S ratios, which leads to the investigation of CCUS concrete [\u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e65\u003c/span\u003e]. In the presence of Ca\u0026sup2;⁺, the system releases more silica and existing alumina species (Al₂O₃), which are able to form C\u0026ndash;A\u0026ndash;H and C\u0026ndash;(A)\u0026ndash;S\u0026ndash;H phases, ensuring better cohesion between the different components of the matrix [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e, \u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e66\u003c/span\u003e, \u003cspan citationid=\"CR67\" class=\"CitationRef\"\u003e67\u003c/span\u003e]. However, the additional hydration in the bricks cured with moisture at 24\u0026deg;C resulted in a weaker matrix compared to the bricks cured at 30\u0026deg;C, leading to reduced overall mechanical strength and durability, despite the bonding of the C\u0026ndash;A\u0026ndash;H gel\u0026mdash;consistent with previous studies [\u003cspan citationid=\"CR68\" class=\"CitationRef\"\u003e68\u003c/span\u003e, \u003cspan citationid=\"CR69\" class=\"CitationRef\"\u003e69\u003c/span\u003e, \u003cspan citationid=\"CR70\" class=\"CitationRef\"\u003e70\u003c/span\u003e].\u003c/p\u003e\u003c/div\u003e"},{"header":"Conclusion","content":"\u003cp\u003eThis study systematically evaluated the performance of soil-based RHA-cement Greencrete blocks under two curing conditions: 24\u0026deg;C with moisture and 30\u0026deg;C without moisture. The results confirm the important interrelationship between mix composition and the curing environment in determining the physical, mechanical, and microstructural properties of sustainable, waste-based masonry materials. The key conclusions are as follows:\u003c/p\u003e\u003cp\u003e\u003cb\u003eMicrostructural insights\u003c/b\u003e: SEM-EDS analysis confirmed that 5% RHA and 12% cement performance (5RHA12C, both 30\u0026deg;C and 24\u0026deg;C) is the best combination, which produces a homogeneous and dense binder phase with minimal microcracking and pore connectivity. At the same time, both samples presented a highly compact composite structure with the highest physical and mechanical performance. This combination exhibited compressive strengths of 3.67 MPa and 2.83 MPa at curing temperatures of 30\u0026deg;C and 24\u0026deg;C, respectively, which are the highest in this study. The compressive strength of the brick is equivalent to the C grade of conventional burnt clay brick as per the Indian standard (IS 1077:1992) and falls within the EB-2 grade of earth brick as per the German standard DIN 18945 (2013\u0026ndash;08). These bricks are ideal for low-rise constructions where stresses are lower, such as sheds, and can also be used in insulating constructions and the construction of partitions.\u003c/p\u003e\u003cp\u003e\u003cb\u003eThe negative effects of excess RHA are as follows: an\u003c/b\u003e RHA content of more than 10% without adequate cement leads to a high absorption rate and reduced strength due to increased voids and weak particle bonding. This emphasizes the need to maintain a balanced binder ratio to realize the benefits of agro-industrial waste utilization.\u003c/p\u003e\u003cp\u003e\u003cstrong\u003eOptimized RHA incorporation\u003c/strong\u003e\u003cp\u003eA moderate RHA content (5% by weight) combined with 8\u0026ndash;12% OPC synergistically increases the compressive strength and durability. The pozzolanic reaction between the amorphous silica in RHA and the cement hydration products creates a dense C\u0026ndash;S\u0026ndash;H gel matrix, which significantly improves structural integrity.\u003c/p\u003e\u003c/p\u003e\u003cp\u003e\u003cstrong\u003eSignificance of moisture curing\u003c/strong\u003e\u003cp\u003eSlow curing at 24\u0026deg;C results in a denser, stronger, and more durable brick microstructure, as the C\u0026ndash;S\u0026ndash;H gel condenses and reduces microporosity. In contrast, 30\u0026deg;C causes very rapid curing, resulting in shrinkage-induced cracking, incomplete hydration, and low-strength structures. For example, the compressive strength of the 15R12C sample at 30\u0026deg;C was only 0.94 MPa, but at 24\u0026deg;C, it increased to 2.61 MPa\u0026mdash;a direct result of water retention and slower reaction kinetics.\u003c/p\u003e\u003c/p\u003e\u003cp\u003eDuring the slow curing process, the C\u0026ndash;S\u0026ndash;H gels are more tightly packed, and the porosity decreases, resulting in increased density. For example, the bulk density of most samples increased with 24\u0026deg;C curing, whereas at 30\u0026deg;C, rapid evaporation of water vapour caused internal shrinkage and increased the possibility of microcracks. The density of the 0RHA12C sample was 1322.67 kg/m\u0026sup3; at 30\u0026deg;C and 1389.92 kg/m\u0026sup3; at 24\u0026deg;C, indicating a more compact microstructure.\u003c/p\u003e\u003cp\u003eRHA is a highly porous and hygroscopic material that absorbs excess water. The curing environment controls this absorption. The porosity decreases with 24\u0026deg;C curing, which reduces water absorption. At 30\u0026deg;C, rapid evaporation can lead to the formation of small pores, increasing the absorption capacity. For example, the absorption of 5RHA12C was 32% at 30\u0026deg;C, but decreased to 30.65% at 24\u0026deg;C.\u003c/p\u003e\u003cp\u003eAs the temperature increases, the hydration kinetics accelerate. However, too fast a reaction that is too fast can cause incomplete bonding and internal stresses within the cement and RHA. For example, the compressive strengths of the 10RHA and 15RHA samples cured at 30\u0026deg;C were relatively low. The 10RHA12C sample exhibited a compressive strength of 1.59 MPa at 30\u0026deg;C and 1.66 MPa at 24\u0026deg;C. The strength difference in the S15R12C sample was significant, 0.9459 and 2.61 MPa, clearly demonstrating the negative effects of increased temperature.\u003c/p\u003e\u003cp\u003eOverall, this work provides strong empirical evidence supporting the emergence of RHA-based Greencrete systems under optimized curing conditions. The results offer valuable insights for developing climate-resilient, low-carbon construction materials that align with emerging global sustainability goals, including SDG 11 and SDG 12. Future studies are recommended to explore long-term sustainability, carbonation processes, and life cycle environmental assessments under field conditions to further validate large-scale adoption pathways.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 160px;\"\u003e\n \u003cp\u003e\u003cstrong\u003esign\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 406px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eDescription\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 160px;\"\u003e\n \u003cp\u003eRHA\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 406px;\"\u003e\n \u003cp\u003eRice husk ash\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 160px;\"\u003e\n \u003cp\u003eC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 406px;\"\u003e\n \u003cp\u003eCement\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 160px;\"\u003e\n \u003cp\u003eOPC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 406px;\"\u003e\n \u003cp\u003eOrdinary portland cement\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 160px;\"\u003e\n \u003cp\u003eSEM\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 406px;\"\u003e\n \u003cp\u003eScanning electron microscopy\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 160px;\"\u003e\n \u003cp\u003eEDS\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 406px;\"\u003e\n \u003cp\u003eEnergy dispersive X-ray spectroscopy\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 160px;\"\u003e\n \u003cp\u003eRH\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 406px;\"\u003e\n \u003cp\u003eRelative humidity,\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 160px;\"\u003e\n \u003cp\u003eCCUS\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 406px;\"\u003e\n \u003cp\u003eCarbon capture, utilization, and storage\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 160px;\"\u003e\n \u003cp\u003eCEB\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 406px;\"\u003e\n \u003cp\u003eCompressed earth bricks\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 160px;\"\u003e\n \u003cp\u003eJIS\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 406px;\"\u003e\n \u003cp\u003eJapan industrial standards\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 160px;\"\u003e\n \u003cp\u003eISO\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 406px;\"\u003e\n \u003cp\u003eInternational Organization for Standardization,\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 160px;\"\u003e\n \u003cp\u003eASTM\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 406px;\"\u003e\n \u003cp\u003eAmerican Society for Testing and Materials\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 160px;\"\u003e\n \u003cp\u003eAASHTO\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 406px;\"\u003e\n \u003cp\u003eAmerican association of state highway and transportation officials\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 160px;\"\u003e\n \u003cp\u003eIS\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 406px;\"\u003e\n \u003cp\u003eIndian standard\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 160px;\"\u003e\n \u003cp\u003eDIN\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 406px;\"\u003e\n \u003cp\u003eGerman Institute for Standardization\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e"},{"header":"Declarations","content":"\u003cp\u003eFunding\u003c/p\u003e\n\u003cp\u003eThis research was conducted under the Japan Science and Technology Agency (JST), Support for Pioneering Research Initiated by the Next Generation (SPRING) program, Grant Number JPMJSP2137.\u003c/p\u003e\n\u003cp\u003eAcknowledgments\u003c/p\u003e\n\u003cp\u003eThe authors gratefully acknowledge the support of Make Integrated Technology Limited for providing experimental materials essential to this research.\u003c/p\u003e\n\u003cp\u003eAuthor Contributions\u003c/p\u003e\n\u003cp\u003eMAFS: Conceptualization, Methodology, Data Curation, Data Analysis, Writing\u0026mdash;Original Draft. \u0026nbsp; ZH: Supervision, Reviewing. MYI: Reviewing, Formatting.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eCompeting Interests\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.\u003c/p\u003e\n\u003cp\u003eEthics Approval and Consent to Participate\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003eConsent for Publication\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003eClinical Trial Registration\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003eData Availability\u003c/p\u003e\n\u003cp\u003eThe data supporting the findings of this study are available from the corresponding author upon reasonable request.\u003c/p\u003e\n\u003cp\u003eCode Availability\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eUnited Nations. 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Cem Concr Res. 2022;159:106858. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.cemconres.2022.106858\u003c/span\u003e\u003cspan address=\"10.1016/j.cemconres.2022.106858\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"discover-sustainability","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"disu","sideBox":"Learn more about [Discover Sustainability](https://www.springer.com/43621)","snPcode":"","submissionUrl":"","title":"Discover Sustainability","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Discover Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Greencrete blocks, Rice husk ash (RHA), Sustainable masonry, Compressive strength, Curing conditions","lastPublishedDoi":"10.21203/rs.3.rs-7381327/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7381327/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe relentless surge in the global population and urbanization is intensifying demands on the construction sector, underscoring the urgent need for sustainable masonry solutions with reduced environmental footprints. This study systematically investigated the structural, physical, and microstructural performance of soil, rice husk ash (RHA), and ordinary Portland cement (OPC) composite Greencrete blocks, focusing on two different curing conditions: 24\u0026deg;C with humidity and 30\u0026deg;C without moisture. Sixteen compositional matrices were prepared, focusing on low- and medium-RHA systems (0%, 5%, 10%, and 15% RHA; 0%, 8%, 10%, and 12% OPC), and subjected to qualitative evaluations\u0026mdash;namely, bulk density, water absorption, compressive strength, and energy-dispersive X-ray spectroscopy (EDS) coupled with enhanced scanning electron microscopy (SEM).\u003c/p\u003e\u003cp\u003eThe results revealed that the water absorption of the 5RHA12C sample at 24\u0026deg;C was 30.65%, which increased to 32% at 30\u0026deg;C\u0026mdash;indicating a more porous structure. Additionally, the density changed significantly, from 1301.50 kg/m\u0026sup3; at 24\u0026deg;C to 1301.99 kg/m\u0026sup3; at 30\u0026deg;C. This result proves that an appropriate ratio of rice husk ash to cement and slow curing improves the durability and performance of the resulting Greencrete blocks. However, the same sample exhibited the highest compressive strength of 2.83 MPa at 24\u0026deg;C and 3.39 MPa at 30\u0026deg;C, which is in direct contrast to the other results. SEM‒EDS analysis revealed that RHA and OPC formed a dense and homogeneous calcium silicate hydrate (C\u0026ndash;S\u0026ndash;H) gel matrix under different temperature and humidity conditions, resulting in increased compressive strength and durability.\u003c/p\u003e\u003cp\u003eOverall, the study presents strong empirical support for the use of agro-industrial waste, such as RHA, in the production of low-carbon, climate-resilient masonry units. The results align with the Sustainable Development Goals (SDGs 11 and 12) and lay the foundation for next-generation concrete research, with an emphasis on long-term performance and environmental assessment under field conditions.\u003c/p\u003e","manuscriptTitle":"Thermo-responsive engineering of Greencrete blocks: a foundational study toward waste-based next-generation concrete","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-09-16 03:27:51","doi":"10.21203/rs.3.rs-7381327/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-11-06T10:14:28+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-10-23T11:12:50+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-10-20T04:05:19+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"84301501543091313909087838495717846195","date":"2025-10-16T10:58:42+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"283485147475462217408648014064142721219","date":"2025-10-14T15:25:27+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"262808161006985795000155579070584205180","date":"2025-10-14T10:49:13+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-09-20T10:00:31+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"192449800691423875385044847044305941776","date":"2025-09-08T12:10:47+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-09-08T08:43:14+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-08-20T08:19:58+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-08-20T08:18:45+00:00","index":"","fulltext":""},{"type":"submitted","content":"Discover Sustainability","date":"2025-08-15T12:11:35+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"discover-sustainability","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"disu","sideBox":"Learn more about [Discover Sustainability](https://www.springer.com/43621)","snPcode":"","submissionUrl":"","title":"Discover Sustainability","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Discover Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"ee7c0850-3a99-42d2-8265-f678d836337c","owner":[],"postedDate":"September 16th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2026-04-07T16:05:38+00:00","versionOfRecord":{"articleIdentity":"rs-7381327","link":"https://doi.org/10.1007/s43621-026-03138-4","journal":{"identity":"discover-sustainability","isVorOnly":false,"title":"Discover Sustainability"},"publishedOn":"2026-04-05 15:58:24","publishedOnDateReadable":"April 5th, 2026"},"versionCreatedAt":"2025-09-16 03:27:51","video":"","vorDoi":"10.1007/s43621-026-03138-4","vorDoiUrl":"https://doi.org/10.1007/s43621-026-03138-4","workflowStages":[]},"version":"v1","identity":"rs-7381327","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7381327","identity":"rs-7381327","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}