Sustainable Utilization of Construction and Demolition Waste as a Subgrade Material Using the Process of Geopolymerization

Sustainable Utilization of Construction and Demolition Waste as a Subgrade Material Using the Process of Geopolymerization | 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 Sustainable Utilization of Construction and Demolition Waste as a Subgrade Material Using the Process of Geopolymerization Alok Bijalwan, Anil Kumar Mishra This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8284796/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract The present study examines the potential use of recycled fine aggregates (RFA) generated from construction and demolition waste as a principal component in geopolymer binder systems as a subgrade material, when paired with fly ash (FA) and ground granulated blast furnace slag (GGBS). Various samples were prepared to assess and identify the ideal binder composition that meets the necessary mechanical and durability specifications for subgrade applications. Geopolymer samples activated only with NaOH demonstrated a higher unconfined compressive strength (UCS) compared to those activated with a sodium silicate and a mixture of sodium hydroxide and sodium silicate in the ratio of 1. The UCS values of the RFA-FA-GGBS geopolymers cured at 60 \(\:^\circ\:\) C show a slight increase compared to ambient cured samples. The result showed that all geopolymer samples met the minimum strength criteria for application as a subgrade, sub-base, and base layers. Similarly, the soaked CBR values of the geopolymer-treated recycled fine aggregates met the minimum criteria for cement-stabilised subgrade or subbase material as stipulated by the Indian standard. The toxicity characteristic leaching procedure (TCLP) test results demonstrated that the concentration of the heavy metals in the leachate generated from the samples was within the limits set by the US Environmental Protection Agency. Construction and demolition waste valorization geopolymerisation pavement UCS 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 1. Introduction The construction sector is essential for the growth and sustainability of contemporary infrastructure; however, it remains one of the leading causes of construction and demolition (C&D) waste generation. Concrete, bricks, metals, timber, glass, and plastics are among the materials that are considered C&D waste. The C&D waste is generated by various activities, including the construction, renovation, and demolition of structures (Wu et al., 2016 ). Conventional methods of waste management, which frequently involve incineration and landfilling, present significant environmental hazards, such as greenhouse gas emissions, pollution, and land degradation. As the global population expands and urban areas evolve, the increase in new construction initiatives, infrastructure enhancement, building refurbishments, and demolition of obsolete structures has exacerbated the issue of C&D waste. When this issue is examined in terms of numbers, its size becomes even clearer. The annual generation of the global C&D waste is more than 10 billion tonnes, and constitutes more than 35% of the world's disposal sites, with a substantial fraction of this waste ultimately deposited in landfills. India is a major contributor to global C&D waste, ranking third behind China and the US (Wu et al., 2019 ). The US generates more than 600 million tonnes of C&D waste annually, a significant increase from the approximately 120 million tonnes produced in the 1990s. China is believed to be the largest producer in the world, with an estimated 1.13 billion tonnes of C&D waste produced in 2014. Worldwide, this waste constitutes a significant fraction of the solid waste stream, sometimes estimated at 30–40% of total solid waste. This corresponds to several billion tonnes of C&D waste produced annually, a quantity anticipated to increase; worldwide waste generation in 2050 is forecast to be around twice that of 2016 (Petrović and Thomas, 2024 ). This substantial quantity of waste highlights a critical global issue: the necessity of sustainably managing and valorising construction and demolition waste, instead of depending on conventional disposal methods. The handling of C&D waste remains predominantly unsustainable, with a significant portion of debris ultimately deposited in landfills or illegally dumped. These kinds of activities use up extremely valuable land and put the natural environment in serious jeopardy. The emission of greenhouse gases (CO₂, CH₄) can be exacerbated by the decomposition of organic components or specific reactions in buried debris, which further exacerbates pollution. Disposal of C&D debris in landfills has resulted in detrimental environmental effects, including soil, water and air pollution, emission of greenhouse gases, and significant health issues (Yazdani et al., 2021 ). In addition, the building sector is irresponsibly depleting energy and natural resources. The construction sector is accountable for 30% of the global anthropogenic CO 2 emissions (Silva et al., 2020 ). Motivated by eco-friendly practices like the circular economy and sustainable development, the building sector actively seeks ways to reduce resource usage and carbon emissions. In recent years, researchers have been increasingly focused on sustainable waste management practices to address these environmental concerns. One promising approach is the utilization of C&D waste through geopolymerization. Geopolymers are inorganic polymers synthesized using alkaline solutions by the chemical activation of aluminosilicate materials, such as fly ash (FA) or slag (Provis and Bernal, 2013 ). Geopolymers exhibit environmentally sustainable features, including enhanced mechanical properties, outstanding durability (Neupane et al., 2018 ) and resistance to acids, sulphates (Kwasny et al., 2018 ) and elevated temperatures (Xiao et al., 2020 ) in comparison to Portland cement-based systems. The amount of amorphous material present in the raw materials is a critical factor governing their reactivity during alkali activation (Diaz et al., 2010 ). This process offers a sustainable substitute to conventional ordinary Portland cement (OPC), known for its large carbon footprint. It is used in concrete and is one of the high-carbon, resource-intensive materials used extensively in conventional buildings. It is commonly recognised that the manufacturing of OPC contributes significantly to greenhouse gas emissions, making up approximately 7–8% of world CO₂ emissions. The calcination of limestone and the substantial energy use in cement kilns emit around 1.6 billion tonnes of CO₂ annually. In addition to cement, manufacturing other prevalent construction products and extracting raw aggregates carry further environmental burdens. The extraction of limestone, sand, and gravel for construction damages natural landscapes and may disturb local ecosystems. The mining and processing of raw materials generate numerous emissions and pollutants, leading to air quality deterioration, biodiversity decline, and other environmental strains. The construction industry's whole range of activities, from making materials to building things, is thought to be accountable for a substantial portion of the global greenhouse gas emission and resource use. According to earlier research, 30% adherent mortar is present around the aggregates (Cartuxo et al., 2015 ; Ghorbel et al., 2020 ). Along with many pores and microcracks, the adhering mortar gives the aggregates a rough surface texture, increasing their porosity and capacity to absorb water (Ghorbel et al., 2020 ). Additionally, the hydration in the concrete is hampered by the greater water absorption tendency of the recycled aggregates in comparison to normal aggregate. The concrete requires an increased quantity of water to maintain a sufficient amount of workability, as C&D waste aggregates have a higher water absorption rate (Bektas et al., 2009 ; Chandru et al., 2023 ; Ghani et al., 2020 ). Geopolymers generally use less water, which lessens the detrimental effect of high-water-absorbing recycled aggregates on workability. Their distinct hydration mechanism further reduces the concrete's susceptibility to water absorption properties of the recycled particles. The rapid industrialization and urbanization have led to a growth in the generation of waste materials. Simultaneously, the construction industry faces the challenge of sourcing sustainable materials that decrease the environmental impact and address the growing concern for resource depletion. In this context, investigating various waste materials as a sustainable geopolymer binder for Civil engineering applications offers an innovative and eco-friendly approach to tackling these challenges. Geopolymer technology has emerged as a promising alternative to conventional cementitious binders, offering numerous benefits such as reduced CO 2 emissions, enhanced durability, and the capability to utilize a large range of waste materials as raw materials. Geopolymers are inorganic, amorphous aluminosilicate materials formed through the chemical reaction of an alumina-silicate-rich source material and an alkaline activator. Essentially, an aluminosilicate precursor and an alkaline reagent undergo a chemical reaction (commonly referred to as alkali activation) to generate a geopolymer, which results in a hardened matrix with a 3-D structure of Si–O–Al links. The activator's high pH dissolves Si and Al from the solid precursor, which subsequently reorganise and polymerise to form a solid gel, commonly known as sodium-alumino-silicate-hydrate (NASH) gel, that binds together aggregates or filler particles (Castillo et al., 2022 ). Geopolymers are receiving more attention as eco-friendly options to cement for several reasons. First, they can use waste materials from industries or natural clays as feedstock instead of new limestone. Fly ash (FA) generated from thermal power plants (Suraneni et al., 2021 ) and ground granulated blast-furnace slag (GGBS) from steel-manufacturing plants are classic examples of reactive aluminosilicate components necessary for geopolymerization. Multiple studies have assessed the feasibility of utilising Construction and Demolition Waste (CDW) as a raw material for geopolymer synthesis (Alhawat et al., 2022 ; Dadsetan et al., 2019 ; Ye et al., 2022 ). Research indicates that many components of Construction and Demolition waste (CDW) including waste concrete, (Robayo-Salazar et al., 2017 ; Tefa et al., 2021 ; Zaharaki et al., 2016 ) glass,(Lu and Poon, 2018 ; Zhang et al., 2017 ) and ceramic tiles (Mahmoodi et al., 2020 ) can supply the requisite reactive components in an alkaline solution. This initiates the development of geopolymer gels, enabling CDW-based geopolymers to attain characteristics similar to those derived from conventional materials. Studies on materials derived from masonry waste indicate that mixed fractions can be readily utilised in the geopolymerization process (Tan et al., 2022 ; Yıldırım et al., 2021 ). Numerous recent studies have investigated the application of fly ash (FA) and ground granulated blast-furnace slag (GGBS) in road subgrade, sub-base, and base construction (Murmu et al., 2020 ; Sukprasert et al., 2021 ). In contrast, the potential use of the recycled fine fraction of construction and demolition waste in various road pavement layers remains significantly underexplored. Typically, a mixed C&D waste contains substantial mineral debris, particularly concrete rubble (from demolished concrete and masonry) and ceramic materials such as bricks, tiles, and plaster. These wastes consist primarily of silica, alumina, calcium, and other oxides often found in conventional binders. The fine powder produced from crushed concrete, which contains remains of hydrated cement and fine aggregates and pulverised brick or masonry debris, is abundant in SiO₂, Al₂O₃, and CaO. This composition facilitates geopolymerization: silica and alumina serve as network-forming species for the NASH gel, while calcium (notably from concrete waste) can contribute to forming CASH-type phases or enhance early strength. C&D waste can serve as a precursor by undergoing initial processing, such as crushing and milling, to achieve a fine particle size, improving its reactivity. Research has indicated that the powder obtained from building debris, comprising a combination of hydrated cement paste, unreacted cement particles, and fine sand or brick fragments, can fulfil the chemical criteria for geopolymer binders (Alhawat et al., 2022 ). This technology allows the recycling of various industrial byproducts, such as FA, slag, rice husk ash, waste materials like water treatment sludge, C&D waste, and petroleum sludge, into valuable construction materials. According to the Building Material Promotion Council (BMTPC), India produces roughly 155 million tonnes of C&D waste annually, and just 1% of this waste is recycled. This brings the importance of investigating C&D waste performance for various civil engineering applications. Recycled concrete aggregates are generated from construction and demolition debris by grinding and sieving the material in recycling facilities, classified as fine and coarse particles based on particle size. Over several decades, numerous prior researchers examined the efficacy of recycled coarse aggregates (RCA) in concrete as a substitute for natural coarse aggregates. These studies suggested that the strength and durability of concrete that contained RCA were marginally inferior to those of control concrete at varying substitution levels. In contrast, limited research has been conducted on the use of recycled fine aggregates (RFA) made from C&D waste as a substitute for natural fine aggregates (NFA) in comparison to recycled coarse aggregates. Recycled aggregates, derived from crushing C&D waste, have reduced mechanical strength compared to normal aggregates (Bogas et al., 2016 ; Mardani-Aghabaglou et al., 2015 ). 2. Material characterization 2.1 Materials In this study, the C&D waste was collected from the IIT Guwahati campus, Assam. The FA was sourced from a thermal power plant located in the Punjab state in India, while GGBS was procured from Jindal Saw Ltd. in Gujarat, India. The primary composition of the collected C&D waste was recycled concrete and mortar. After C&D waste collection, the impurities such as wood, plastic, and metals were separated from the C&D waste. After the separation process, it was crushed into finer particles. After the crushing, it was sieved through a 4.75 mm sieve, and particles that passed through this sieve were used as fine aggregate, and the retained portion of the waste was used as coarse aggregate. The RFA was primarily composed of sand at 85.4% (4.75 − 0.075 mm). The grain size distribution was assessed by doing sieve analysis per ASTM 2007 (ASTM, 2007 ), and it was observed that the RFA was primarily composed of sand at 85.4% (4.75 − 0.075 mm), with the remaining fine particles being 14.2% (< 0.075 mm). The compaction characteristic of the RFA was obtained by conducting a Proctor compaction test as per the ASTM D698. ASTM D854 (ASTM, 2000 ) was used to determine the specific gravity of the RFA. Table 1 summarises the characteristics of RFA. Table 1 Physical properties of RFA from Construction and Demolition waste Serial No. Properties Confirming to code Result 1 Optimum moisture content (OMC) ASTM D698 19.17% 2 Maximum Dry density (MDD) ASTM D698 1.53 gm/cc 3 Specific Gravity ASTM D854 2.56 4 Unconfined Compressive Strength (UCS) ASTMD2166 ND 5 Soaked CBR values IS 2720: Part 16: 1987 13.14% Figure 1 shows the RFA, FA, and GGBS used in the current study. The shape of RFA from C&D waste was observed to be angular, since these are typically produced through mechanical crushing, which creates sharp edges and irregular surfaces due to brittle fracture. The SEM images of GGBS and FA in Fig. 2 show them as angular and spherical with a few irregular shapes, respectively. The round shape of FA particles makes the mix easier to deal with because round particles make the mix easier to work with. The data in Table 2 present the chemical compositions of the FA and GGBS obtained from the XRF study. The precursor binding material, consisting of FA and GGBS, is employed in the production of geopolymer along with recycled fines aggregates sourced from C&D activities. The FA used for this study is a Class F type as per ASTM C 618 (ASTM, 1999 ), as indicated by the XRF analysis. The sum total of SiO 2 , Al 2 O 3 , and Fe 2 O 3 exceeds 70%, as presented in Table 2 . The primary oxides present in GGBS include CaO at 35.56%, SiO 2 at 33.15%, Al 2 O 3 at 17.67%, and MgO at 5.52%. The presence of a significant amount of CaO in GGBS, when activated by an alkaline solution, can lead to the development of a CSH gel in conjunction with the geopolymer gel. The CSH gel exhibits superior binding characteristics. The XRD pattern of RFA revealed an abundance of minerals, including Quartz and Calcite. The primary components of Class-F fly ash are quartz and mullite, as verified by XRD investigation; whereas, GGBS contains calcite and quartz minerals, as illustrated in Fig. 3 . The Energy-Dispersive X-ray Spectroscopy (EDS) of the recycled fine aggregates (RFA) from construction and demolition waste, shown in Fig. 4 , reveals that the elevated levels of Calcium (Ca) and Oxygen (O) are significant indications of the presence of hydrated cement paste. Cement in concrete reacts with water to produce binding agents, primarily calcium silicate hydrates (C-S-H) and calcium hydroxide (Ca(OH)₂). Calcium hydroxide can react with atmospheric carbon dioxide over time to produce calcium carbonate (CaCO₃). These calcium-rich compounds are essential components of the mortar and paste that bond to the initial aggregates in the concrete. Table 2 XRF showing the Chemical composition of FA, GGBS Chemical Composition (%) Fly ash (FA) Ground granulated blast furnace slag (GGBS) SiO 2 55.49 33.15 Al 2 O 3 29.27 17.67 Fe 2 O 3 (T) 4.62 1.43 MnO 0.040 0.319 MgO 0.62 5.52 CaO 0.87 35.56 Na 2 O 0.00 0.34 K 2 O 1.48 0.62 TiO 2 2.17 0.66 P 2 O 5 0.49 0.01 SO 3 0.05 1.25 LOI 4.90 3.47 2.2 Alkaline Activators Alkaline activators are essential components in a geopolymerization process, as they facilitate the dissolution of precursor materials and promote the formation and hardening of the geopolymer matrix. The activation was carried out using solutions of sodium silicate (Na 2 SiO 3 , abbreviated as SS) and sodium hydroxide (NaOH, abbreviated as SH). The NaOH was initially in pellet form, which was manufactured by Merck Pvt Ltd; whereas, Na 2 SiO 3, which was in liquid form, consisting of Na 2 O = 8.0% and SiO 2 = 27% and was produced by Loba Chemie Pvt. Ltd. The researchers proposed an appropriate concentration range for NaOH of 4.5 to 18 molars (Yaghoubi et al., 2018 ) (Nematollahi and Sanjayan, 2014 ). Considering both economic and safety perspectives, low-concentration solutions of NaOH (i.e., 6, 8, and 10M) were used for this investigation. The solution was prepared primarily one day prior to its casting. Initially, NaOH is used alone for the activation of the geopolymer matrix. The proportion of Na 2 SiO 3 to NaOH (i.e. SS/SH) was set to 1 to investigate the impact of the activator on construction and demolition waste amended with industrial byproducts, specifically FA and GGBS. The Na 2 SiO 3 liquid solution was combined to facilitate the gelation and precipitation of silicates during geopolymerization (Khale and Chaudhary, 2007 ). Numerous investigations indicate that alkaline silicate promotes the formation of soluble SiO 2 monomers, resulting in improved microstructure and enhanced mechanical performance (Vidal et al., 2018 ). 3 Experimental Methodology 3.1 Sample Preparation This research examines geopolymers derived from RFA from C&D waste, employing FA and GGBS in an equal ratio as binding agents. This study examines the correlation between binder content and strength development by casting geopolymer samples with varying substitution levels, specifically replacing C&D waste with 30, 40, and 50% binder. Two alkline activators are used. In one sample batch, only NaOH is used. The second batch employed an alkaline activator consisting of NaOH and Na 2 SiO 3 . This combination was chosen based on existing literature indicating that supplemental silica from Na 2 SiO 3 enhances polymerisation, leading to a microstructure with improved mechanical strength (Hoy et al., 2018 ; Yaghoubi et al., 2018 ). The strength enhancement of C&D-based geopolymers samples was examined in relation to the activator concentration using three molarities of NaOH, i.e. 6, 8, and 10 M. The activator solution was prepared 24 hours before the sample preparation by dissolving the appropriate quantity of NaOH pellets in DI-water. The selection of this concentration range was influenced by economic and safety factors. Furthermore, a 1:1 volumetric ratio was used to examine the influence of the Na 2 SiO 3 to NaOH proportion on geopolymer strength. The strength of the polymerised composites was assessed by assessing their unconfined compressive strength (UCS) and California bearing ratio (CBR), by taking into account different curing durations and conditions. In this study, the prepared UCS samples are tested under two distinct curing conditions, which include ambient exposure at room temperature, specifically air drying at room temperature, and heat curing at 60°C for different curing periods. A curing duration of 3, 7, and 28 days is considered for ambient curing conditions as per ASTM D2166 and 3 days for heat-cured samples. Prior to testing for the CBR, the specimens were cured in DI water at ambient temperature for 3 days, followed by soaking them for an additional 4 days. The durability of the C&D-based geopolymers was examined by exposing the 7-day cured samples to a number of wetting-drying cycles as instructed in IS 4332-4 (1968), and then the performance of the specimens was assessed in terms of percentage mass loss. Also, the geopolymer samples' microstructural changes are studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM) tests. Details of different C&D mix proportions, NaOH molarity and Na 2 SiO 3 /NaOH (SS/SH) proportions, curing condition & duration employed in this investigation can be found in Table 3 . Table 3 Mix Proportions of samples Molarity Mix Proportion Ambient Curing Heat Curing Alkaline Activators 6M 70% RFA + 15% FA + 15% GGBS 3, 7, & 28 days 3 days NaOH (SH) 60% RFA + 20% FA + 20% GGBS 50% RFA + 25% FA + 25% GGBS 8M 70% RFA + 15% FA + 15% GGBS 3, 7, & 28 days 3 days 60% RFA + 20% FA + 20% GGBS 50% RFA + 25% FA + 25% GGBS 10M 70% RFA + 15% FA + 15% GGBS 3, 7, & 28 days 3 days 60% RFA + 20% FA + 20% GGBS 50% RFA + 25% FA + 25% GGBS 6M 70% RFA + 15% FA + 15% GGBS 3, 7, & 28 days 3 days SS:SH = 1 60% RFA + 20% FA + 20% GGBS 50% RFA + 25% FA + 25% GGBS 8M 70% RFA + 15% FA + 15% GGBS 3, 7, & 28 days 3 days 60% RFA + 20% FA + 20% GGBS 50% RFA + 25% FA + 25% GGBS 10M 70% RFA + 15% FA + 15% GGBS 3, 7, & 28 days 3 days 60% RFA + 20% FA + 20% GGBS 50% RFA + 25% FA + 25% GGBS RFA- Recycled Fine aggregates, FA- Fly Ash, GGBS- Ground Granulated Blast Slag, SH- Sodium Hydroxide, SS- Sodium Silicate, M- Molarity of Sodium Hydroxide 30%B = 70% RF + 15% FA + 15% GGBS, B= (FA + GGBS), R1 = SS/SH ratio 1. 3.2 Unconfined Compression test After compacting the samples to their maximum dry density (MDD) and optimum moisture content (OMC) conditions, the UCS was determined following ASTM D2166/D2166M-22 standards. For each mix design, three specimens were made and loaded at a constant strain rate of 1.25 mm/min until failure occurred. The final UCS for each composition was reported as the average of the three peak strength values obtained. The final UCS for each composition was documented as the mean of the three peak strength values acquired. 3.3 California bearing ratio tests The CBR of the specimens was determined as per IS 2720 (Part 16): 1987. Specimen preparation, guided by IRC-37, involved static compaction within a 150 mm diameter, 175 mm high mould to achieve 97% of the maximum dry density. All tests were performed under soaked conditions, which involved immersing the specimens in water for a four-day period prior to testing. A 5 kg surcharge was applied to the specimen after the soaking period to prevent disturbance during testing. A 50 mm diameter plunger was then advanced into the specimen at a fixed strain rate of 1.25 mm/min, and the corresponding load versus penetration data was recorded. The CBR values were computed from this curve at 2.5 mm and 5 mm penetration depths. When the CBR value corresponding to a penetration depth of 2.5 mm exceeds that at 5 mm, the former is reported to be the CBR value of the specimen. The test is repeated if the CBR for a penetration depth of 5 mm is higher than that of 2.5 mm, and if the findings are identical, the former is recorded as the CBR value of the specimen. 3.4 Durability tests The durability of different specimens was examined by exposing the specimens to a number of wetting-drying cycles as per the guidelines provided by IS 4332-4 (1968). The standard moulded samples of different mixes, after a curing period of 7 days, were submerged in DI-water for 5 hours to start the wetting-drying cycles. The initial phase of each cycle involved drying samples at 70°C for 42 hours, followed by a one-hour cooling period at room temperature. After cooling, each dried specimen was brushed using a wire brush for 17–20 vertical strokes, and then its weight was measured to determine the material loss, and then subjected to the next wetting phase. This entire procedure constituted one 48-hour cycle, which was repeated for a total of 12 cycles. The mass loss percentage of different mixes was assessed after undergoing 12 wetting-drying cycles. 3.5 Toxicity characteristics leaching procedure (TCLP) test The TCLP test for the stabilised geopolymer samples was performed as per USEPA 1311 to assess their leaching characteristics(USEPA, 1999 ). For each test, a 5 g sample, passing through a 2 mm sieve, was carefully prepared. The extraction fluid was composed of acetic acid and DI water, with the pH cautiously adjusted to 4.93 ± 0.05 using a 1 N NaOH solution. The sample was added to 100 g of the extraction fluid, maintaining a 1:20 solid-to-liquid ratio, and shaken in a shaker for 18 hours at a speed of 30 ± 2 rpm. Following the shaking, the slurry was filtered through a glass fiber filter. The elemental concentration in the resulting leachate was then subsequently analysed using Inductively Coupled Plasma Mass Spectrometry (ICP-MS). The test was conducted thrice for each sample, and the final value reported is the arithmetic mean of these three trials. 3.6 XRD tests In the XRD test, the sample is subjected to a filtered X-ray beam. As the beam enters the material, it causes the electrons in the mineral atoms to vibrate and thus reflect the beam across consecutive planes. The intensity of the diffracted X-ray is constantly monitored with increasing incidence angle until the diffracted intensity reaches a maximum value, and thus an XRD pattern is obtained. Once the test is completed, the samples are pulverised into a very fine powder and then dried in an oven before being used for the XRD analysis. The XRD pattern of different specimens was obtained by scanning in a range of 5 \(\:^\circ\:\) to 80 \(\:^\circ\:\) (2 \(\:{\theta\:}\) ). Identification of mineral phases was conducted utilising PANalytical's X'Pert HighScore Plus software. The analysis consisted of correlating experimental diffraction patterns with the Powder Diffraction File (PDF-2) database, which is provided by the International Centre for Diffraction Data (ICDD). 3.7 SEM analysis The morphology of different C&D waste, FA and GGBS mixes was analysed using the Gemini field emission scanning electron microscope. The samples were pulverised to fine powders after the UCS tests and oven-dried before the SEM analysis. A carbon tape is adhered to a stub, and the powdered specimen is placed above it. Prior to imaging, the powdered sample was sputter-coated with a thin layer of gold to ensure electrical conductivity. The SEM analysis was then conducted to capture micrographs at the desired levels of magnification. 3.8 Energy-Dispersive X-ray Spectroscopy (EDS) The EDS, also sometimes called EDX, EDXS, or XEDS, is a method used to identify and quantify the elemental composition of a sample. EDS is dependent on the distinct atomic arrangement of every element. Each element possesses a distinct configuration of electrons surrounding its nucleus. When a sample is exposed to an X-ray source or, more frequently in EDS, an electron beam (such as in a SEM), these electrons may interact with the electrons in the sample's atoms. This interaction can pull away one electron from its orbital position within an atom of the sample. To compensate for the vacancy, an electron from a higher energy level will transition to a lower energy level, resulting in energy emission in the form of an X-ray. EDS can identify and measure the elements in a sample by looking at the energies and levels of the reflected X-rays. Before EDS analysis, the sample was prepared by adding a conductive carbon coating to enable elemental mapping and analysis. 4 Results and Discussions 4.1 Effect of binder content, NaOH molarity, SS/SH ratio and curing period on UCS In this study, the test specimens for unconfined compressive strength have been cast by blending different proportions of binder (FA and GGBS) with recycled fine aggregate for a curing duration of 3, 7, and 28 days under ambient conditions, i.e., air dried at room temperature. The binder consists of FA and GGBS, in which the FA/GGBS ratio is kept at 1. Samples were prepared by replacing construction and demolition waste with 30%, 40%, and 50% binder, for different concentrations of sodium hydroxide (6, 8, and 10M). Two variations in the alkaline activators are considered in the first one; only sodium hydroxide (NaOH or SH) is considered as an activator, while the other ratio of NaOH to sodium silicate (Na 2 SO 3 or SS) in a ratio of 1 was considered in this study. Figure 5 depicts the variation of the strength of RFA-FA-GGBS-based geopolymer with various binder content, curing period and NaOH molarity. 4.2 Effect of binder content, NaOH molarity, SS/SH ratio and curing period on UCS Curing duration plays a significant role in how geopolymer materials develop their strength. Figure 5 presents the UCS results for samples cured at ambient conditions for 3, 7, and 28 days with various activator concentrations, binder contents and SS/SH ratio 1. It is clear that, irrespective of the alkaline activator concentration, binder content, or SS/SH ratio, the UCS values consistently rise as the curing duration extends from 3 to 28 days. In the initial three days, the alumina and silica from the precursor materials get released upon alkali activation, which results in the formation of geopolymeric gels. Progressively, the gels toughen, thus leading to strength development in due course of time. Therefore, the strength of the 3-day-cured specimens is relatively less compared to 28-day-cured samples, irrespective of the concentration of NaOH, binder content and SS/SH ratio. With the prolongation of the curing time from 3 to 7 days, a sharp rise in strength could be seen in Fig. 5 . After 7 days of curing, the geopolymeric gels formed from the alkali activation of RFA, FA, and GGBS undergo additional polymerisation and cross-linking, resulting in a compact and an increase in the interconnected geopolymer network, producing additional strength. A further increase in the curing time up to 28 days, the strength of the RFA-FA-GGBS geopolymer samples further increases; however, the rate of increment was not significant. Samantasinghar and Singh ( 2021 ) reported similar observations for soil treated with FA-GGBS geopolymer, where a considerable strength improvement is shown up to 7 days of curing; beyond that, the rate of increase becomes marginal. Shi et al. ( 2022 ) also observed that the growth rate of the strength of clay modified with metakaolin-based geopolymer is very significant in the first 7 days, beyond which the rate gradually slows down. This behaviour is mainly owing to the fast condensation of the geopolymer in the beginning 7 days, a period during which the majority of the available aluminosilicate sources from various precursors are utilised. The rate of strength gain consequently slows down after this period. After 28 days, the condensation process is almost finished, forming a more stable geopolymer matrix that contributes to increased strength relative to earlier stages. The 28-day strength serves as a standard for assessing the performance of cementitious materials, such as geopolymers. 4.3 Influence of NaOH concentration in alkaline solution on the UCS of RFA-FA-GGBS geopolymer The concentration of the alkaline solution plays a significant role in the development of strength in geopolymer samples. The plot in Fig. 6 presents the change in the UCS of RFA-FA-GGBS geopolymers resulting from variations in the NaOH concentration in the alkaline solution for different binder contents and curing periods. Similarly, the plot in Fig. 7 presents the change in the UCS of RFA-FA-GGBS geopolymers due to variations in the NaOH concentration in the alkaline solution, for different binder contents and curing periods, and an SS/SH ratio of 1. It has been observed that for any binder content, curing period and SS/SH ratio, the strength of RFA-FA-GGBS geopolymer samples significantly increases with the rise in the concentration of NaOH. For example, the UCS for 28-day cured samples with 30% binder significantly enhanced from 9.93 to 13.12 MPa upon increasing the concentration of NaOH from 6 to 10M. With the increase in NaOH concentration, the pH of the material rises, facilitating the faster dissolution of alumina and silica from the precursor material. This leads to extensive geopolymeric gel formation, which binds the particles of the raw materials and results in increased strength. The solubility of the aluminosilicate source materials increases with the rise in the concentration of NaOH, resulting in a rapid dissolution of free [SiO 4 ] − and [AlO 4 ] − tetrahedral, which undergo polymerisation to create a negatively charged Si-O-Al-O bond. Therefore, a higher concentration of NaOH can generate a large amount of Na + cations to cater to a charge imbalance, which is essential for the strength and stability of the resulting geopolymer materials. In geopolymerization, sodium hydroxide is the main dissolving agent. It makes the surroundings alkaline, which breaks down the amorphous aluminosilicate phases that are in the precursor materials. The hydroxide ions break the Si-O and Al-O bonds in the glassy forms of materials like GGBS and fly ash, letting silicate and aluminate species dissolve. This process, called depolymerisation, is very important for getting the reactive species ready for the polycondensation processes that build the three-dimensional geopolymer network. The high pH environment that NaOH creates, usually between 12 and 14, gives these dissolution processes the push they need to happen at room temperature or slightly higher. The efficiency of NaOH as an activator is determined by various factors, including concentration, temperature, and the composition of the precursor materials. Higher concentrations often promote dissolving, but they may also cause rapid setting and potential strength loss due to incomplete reactions or the creation of competing phases. Sodium silicate generally serves two major functions in the geopolymerization process. Firstly, it increases the pH of the medium, and secondly, it introduces reactive silica into the system. These silicate species, coupled with the dissolved aluminates, undergo a polycondensation process to produce the three-dimensional aluminosilicate network that forms the geopolymer gel. Zhang et al. ( 2011 ) also reported the increase of UCS of mine tailings and FA-based geopolymer with the rise in the concentration of NaOH from 5 to 15M. Numerous studies have further shown that the relationship between NaOH concentration and strength is not linear. An optimal concentration is typically observed, beyond which strength development either plateaus or begins to decline (Hamid and Alnuaim, 2023 ; Manjarrez and Zhang, 2018 ; Noolu et al., 2021 ; Tajaddini et al., 2023 ). The loss of strength at elevated molarities is likely due to an inhibition of the geopolymerization reaction. An overabundance of hydroxide ions (OH – ) is thought to cause aluminate and silicate ions to precipitate prematurely, which obstructs the formation of a continuous and well-ordered polymer structure. Furthermore, the corresponding excess of sodium cations (Na + ) may be detrimental, as it can disturb the charge imbalance. While sodium silicate is necessary for geopolymerization, an excess of it can reduce the geopolymer's compressive strength. An excess of silicate can disrupt the balance of the geopolymerization reaction, causing the development of a less robust network. Specifically, an overabundance of silicon can result in a reduced number of strong Si-O-Al bonds, which are crucial for the material's strength 4.4 Influence of heat curing on the UCS of RFA-FA-GGBS geopolymer The temperature and curing conditions of a geopolymer material can have considerable effects on how it develops strength. The influence of heat curing on UCS of RF-FA-GGBS geopolymers, for various binder content (i.e. 30, 40, and 50%), curing period & NaOH concentration (6, 8, & 10M), for a SS/SH ratio of 1, was investigated. The prepared samples were permitted to set at room temperature for a period of 1 day in the beginning, then cured inside an oven at 60 \(\:^\circ\:\) C for a duration of 3 days. Since heating the freshly prepared samples at a higher temperature results in a rapid loss in moisture, which might result in strength reduction owing to shrinking and cracking of the samples. From Fig. 8 , it was observed that there is not much gain in the strength of the RFA-FA-GGBS geopolymers. This may be due to the high amount of calcium present in the recycled fine aggregates and GGBS, as the GGBS can influence the temperature dependence of geopolymer curing. While it can enhance early strength, a high GGBS content might reduce the need for high-temperature curing for further strength improvement. 4.5 CBR of RFA-FA-GGBS geopolymers The suitability of the recycled fine aggregate from C&D waste for road construction was evaluated using the California Bearing Ratio (CBR) test, which measures bearing resistance. The material achieved a soaked CBR value of 13.14%, thus satisfying the minimum criteria for road application. According to the guidelines set up by IRC:37-2012 (IRC-37, 2012 ) materials used in subgrade construction must have a minimum CBR value of 8%. Samples were allowed to cure at room temperature for three days before being immersed in water for four days under a 5kg surcharge load. Figure 9 displays the soaked CBR values of RFA-FA-GGBS geopolymer samples that were subjected to different sodium hydroxide concentrations, SS/SH ratios, and binder contents. Higher NaOH concentrations accelerate the dissolution of alumina and silica from source materials, promoting the formation of a geopolymer gel. This gel binds the particles together, leading to increased strength, bearing resistance, and higher CBR values, which are further enhanced by a greater binder content. The CBR values of the samples having only sodium hydroxide as alkaline activator show greater CBR values than the SS/SH ratio 1. This may be due to some possible reasons. The sodium silicate solution is much thicker (more viscous) than the sodium hydroxide solution. Because of its high viscosity, the mix might be sticky and hard to compact well. The less viscous NaOH-only mix probably made it easier to deal with, which led to a more even mixture and a higher density when it was compacted. A material that is denser and more compacted will almost always have a higher CBR value. Another possible reason for this may be due to the presence of a sufficient amount of reactive silica and alumina in the precursor materials, like recycled fine aggregates, fly ash, and GGBS. Some studies indicated that CBR values declined as Na 2 SO 3 concentrations increased in alkaline solutions (Arulrajah et al., 2016 ; Chandra et al., 2021 ). According to the IRC: SP:89 [52], the least CBR value for a cement-stabilized blend used as subgrade material must be 15%. Also, the IRC: 51-1992 [53] says that a lime-stabilized subbase must have a CBR value of at least 15% for rural roads. As demonstrated in Fig. 9 , all RFA-FA-GGBS geopolymer samples are suitable for use as subgrade, subbase or base material, as their soaked CBR values exceed the minimum requirements regardless of the binder content and NaOH concentration. 4.6 Evaluation of the durability of RFA-FA-GGBS geopolymers The present study is focused on the improvement of the strength of RFA-FA-GGBS geopolymers and their feasibility to be used as a subgrade, subbase, or base material for road construction. Although the UCS is one of the major parameters for evaluating the strength performance of geopolymer or any other stabilized materials, it also has to be assessed in terms of its durability. The most widely used durability tests are freeze-thaw and wetting-drying tests. Freeze-thaw durability test is best suited for cold regions. In tropical countries like India, the subgrade, subbase or base material of roads often comes across seasonal changes during summer and rainy seasons, which might affect the strength performance of the construction materials. Thus, evaluation of the performance of RFA-FA-GGBS geopolymers against wetting-drying cycle becomes very important. The plot in Fig. 10 , presents the variation of weight reduction of RFA-FA-GGBS geopolymers with various molarities of NaOH, for different binder contents after 12 wetting-drying cycles. It can be seen that the amount of weight reduction reduces with a rise in the concentration of NaOH and binder content. For example, in Fig. 10 , when only NaOH is used and a binder content of 30%, there is a reduction in mass loss from 4.28 to 3.81% with the increase in NaOH concentration from 6 to 10 M. Also, the percentage of weight reduction reduced from 5.74 to 3.71% with the rise in binder content from 30 to 50% for a 6 M NaOH concentration and SS/SH of proportion 1. The dissolution rate of alumina and silica from the precursor materials increases with the NaOH concentration, which leads to the formation of a large amount of geopolymer gels, thereby promoting the generation of a more interconnected and closely packed geopolymer matrix. This decreases the porosity and water absorption capacity, subsequently decreasing the weight loss of the geopolymer composite during the wetting-drying cycle. Besides, the increment of binder content ensured sufficient alumina and silica to promote better geopolymerisation reaction, resulting in a denser interconnected structure, which subsequently reduces the percentage of mass loss during the wetting-drying cycle. Furthermore, it can be observed in Fig. 10 that the weight loss of the geopolymer specimens with only NaOH as alkaline activator was relatively lower than that at a SS/SH ratio of 1. For example, with the 10M solution of NaOH and 50% binder content, the weight loss was 1.84%; whereas, for an SS/SH ratio of 1, it was increased to 2.53%. The highest amount of weight loss rose up to 5.74% for a binder content of 30%, NaOH of 6 M concentration, and an SS/SH ratio of 1. 4.7 Microstructural and Morphological Analysis The microstructure and morphology of RFA-FA-GGBS geopolymer specimens were studied using SEM and XRD tests. The 28-day ambient-cured samples after UCS tests were pulverised to fine powder, oven dried and then used for the microstructural investigations. At 6 M solutions of NaOH, some non-reacted or partially reacted FA and GGBS particles could be seen with very few reaction products, as evident in Fig. 11 . At a higher concentration, i.e. 10 M of NaOH, this was not the case, though. The observed increase in compressive strength when increasing the molarity from 6M to 10M results directly from microstructural densification. An increased concentration of alkaline solution facilitates a more thorough dissolution of the FA and GGBS, resulting in a greater volume of the binding phases (CASH, NASH). This abundance of gel creates a more tightly packed and homogeneous internal structure, which is inherently stronger and better at resisting compressive loads. With the increase in molarity from 6 to 8M and from 8 to 10M, the FA and GGBS particles get dissolved with the subsequent formation of a large amount of CASH, NASH, CSH, etc., which leads to a denser structure, thereby increasing the compressive strength of the specimen. The XRD pattern of different specimens shows the presence of Quartz peak at 26.8 \(\:^\circ\:\) in all the plots, indicating its highly unreactive nature as shown in Fig. 12 . The calcium–aluminosilicate–hydrate (CASH) gel was formed from the calcium present in GGBS upon alkali activation (Abdila et al., 2021 ; Hoy et al., 2018 ; Lekshmi and Sudhakumar, 2022 ; Miraki et al., 2022 ). The calcium present in GGBS gets dissolved to form calcium cations upon alkali activation. Simultaneously, the activator also dissolves the aluminosilicates to free [SiO 4 ] − and [AlO 4 ] – tetrahedral units, which undergo polymerisation to form silica and alumina monomers. Free Ca²⁺ ions neutralise the negatively charged alumina and silica monomers, facilitating the formation of (C–A–S–H) gel, which improves the strength of the geopolymer composite. Consequently, the increased peak intensities of geopolymer reaction products, such as CASH, CSH, NASH, and NAS, and the emergence of new peaks indicate a greater quantity of reaction products at higher NaOH (SH) concentrations, thereby contributing to improved strength relative to that observed at lower SH concentrations. 4.8 Leaching potential of the RFA-FA-GGBS-based geopolymer specimens The results of the TCLP studies for the heavy metal concentrations in the leachate are summarised in Table 4 . The data in Table 4 highlights that the leachate's contents of heavy metals (Ba, Cd, Cr, Pd, Zn, etc.) are far lower than the regulatory limitations set by the US Environmental Protection Agency. According to these results, adding more alkali activators to geopolymer samples improves their capacity to trap heavy metals. Various microscopic and big structures of aluminate and silicate compounds are formed when aluminosilicate materials undergo geopolymerization in extremely alkaline settings. By physically attaching various heavy metals, these structures efficiently capture and encapsulate them, allowing polycondensation reactions to go indefinitely (Taki et al., 2020 ). Many variables, including the nature of the metal, the properties of the raw material, the kind of activator, and the pore structure, influence the degree to which geopolymers can immobilise heavy metals (Vu and Gowripalan, 2018 ). Thus, it is evident that the use of RF-FA-GGBS-based geopolymers in road preparation applications does not pose any environmental issues related to the possible leaching of heavy metal contaminants that could potentially lead to groundwater contamination. By increasing their strength and endurance while decreasing their susceptibility to harm, geopolymers composed of RF-FA-GGBS guarantee their safe disposal. Table 4 Toxicity characteristics of the geopolymerized sample with 30% Binder (FA + GGBS) and 50% Binder and SH concentration 6M and 10M Metals 6M, 30% B (g/ml) 6M, 50% B (g/ml) 10M, 50% B (g/ml) USEPA limits for hazardous waste (g/ml) Cd 0.00 0.001 0.00 1.0 Zn 0.017 0.003 0.001 25.0 Pb 0.00 0.00 0.00 5.0 Cu 0.00 0.04 0.09 25.0 Cr 0.006 0.017 0.02 5.0 Ni 0.022 0.03 0.03 25.0 Mn 0.442 0.002 0.00 10.0 Ba 0.078 0.014 0.006 100.0 Se 0.002 0.001 0.02 1.0 5 Conclusions Based on the experimental data and subsequent analysis, the following conclusions were reached: With the increase in binder content (FA + GGBS) from 30% to 50%, the UCS values of the geopolymers significantly increased regardless of any SH concentration, SS/SH ratio, and curing period. On increasing the molarity of SH from 6M to 10M in RFA-FA-GGBS geopolymer, the strength increases regardless of activator and curing conditions. While when we keep the SS/SH = 1, the strength decreases, as some silica is necessary for geopolymerization, an excessive amount can have a negative impact. Too much silica can disrupt the Si/Al ratio, a critical factor for forming strong geopolymer bonds. An imbalance can lead to a less dense and weaker structure. The UCS values of the RFA-FA-GGBS geopolymers cured at 60 \(\:^\circ\:\) C show a slight increase compared to ambient cured samples. The soaked CBR values of the geopolymerized treated recycled fine aggregates satisfy the minimum CBR values recommended for cement-stabilised subgrade or subbase material as per IRC: SP:89-2010. The percentage mass loss in all the geopolymer samples is less than 5.74% after 12 alternate drying and wetting cycles, which confirms the durability of the samples. Enhanced durability: When we keep the alkaline activator NaOH, only the durability of the samples is higher compared with a 1 ratio, leading to the formation of a dense matrix. All the RFA-FA-GGBS geopolymer specimens satisfy the limiting strength norms for cement stabilised subgrade (> 1.2 MPa) and subbase (> 1.7 MPa) as per IRC (2014). XRD test showed the presence of CASH gel as the primary reaction product, which contributed towards the strength enhancement of the RFA-FA-GGBS geopolymer specimens. Scanning electron microscopy (SEM) confirmed that higher concentrations of SH led to the enhanced dissolution of the raw materials, resulting in a significant aluminosilicate gel development, which subsequently contributed to higher strength. The TCLP results demonstrate that the geopolymer samples' leachate had heavy metal levels which fall within the limits set by the USEPA. Declarations Funding statement No funding is received to carry out this research work. 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Constr Build Mater 25(9):3773–3781 Zhang S, Keulen A, Arbi K, Ye G (2017) Waste glass as partial mineral precursor in alkali-activated slag/fly ash system. Cem Concr Res 102:29–40 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted 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. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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1","display":"","copyAsset":false,"role":"figure","size":2451545,"visible":true,"origin":"","legend":"\u003cp\u003eImages of (a)RFA, (b)FA, (c)GGBS\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-8284796/v1/8a040676e5b91c03c44dc7d1.png"},{"id":99312189,"identity":"80eff579-0dc8-49d7-bd45-c18b742160a2","added_by":"auto","created_at":"2025-12-31 16:18:15","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":3717358,"visible":true,"origin":"","legend":"\u003cp\u003eSEM images of the (a)RFA, (b)FA, (c)GGBS\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-8284796/v1/059925fd7a30ff66238955a3.png"},{"id":98991241,"identity":"f084ed8c-7bd0-489f-929e-67be51ee7ae6","added_by":"auto","created_at":"2025-12-25 10:28:28","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":658019,"visible":true,"origin":"","legend":"\u003cp\u003eXRD of the (a)RFA (b)FA (c)GGBS\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-8284796/v1/30dbe343115f97e31b390ea8.png"},{"id":99312639,"identity":"91f79452-0e31-49fb-9bda-24ba38dd8806","added_by":"auto","created_at":"2025-12-31 16:19:15","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":45567,"visible":true,"origin":"","legend":"\u003cp\u003eEDS image of the recycled fine aggregates (RCA)\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-8284796/v1/4413b424ea4d6fa94675bd48.png"},{"id":99313043,"identity":"c648bc06-ee19-4851-b578-9c228ffac2e9","added_by":"auto","created_at":"2025-12-31 16:19:43","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":124824,"visible":true,"origin":"","legend":"\u003cp\u003eUCS of RFA-FA-GGBS geopolymers cured at ambient conditions for 3,7, and 28 days, with (a) Only 6M,8M, and 10M NaOH, (b) 6M,8M, and 10M NaOH and SS/SH ratio =1\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-8284796/v1/f3971733a3d666f2c5dae627.png"},{"id":98991254,"identity":"86e485cb-f8da-4a43-8461-52a01ec894f9","added_by":"auto","created_at":"2025-12-25 10:28:28","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":159999,"visible":true,"origin":"","legend":"\u003cp\u003eVariation of UCS values of RFA-FA-GGBS geopolymer with different curing periods and different molarity of NaOH for 30%, 40%, and 50% Binder.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-8284796/v1/b722ae6f011a9fa8703e63bc.png"},{"id":98991251,"identity":"bb009841-fce4-42a8-9206-7fdcfb11b693","added_by":"auto","created_at":"2025-12-25 10:28:28","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":175460,"visible":true,"origin":"","legend":"\u003cp\u003eVariation of UCS values of RFA-FA-GGBS geopolymer with different curing period and different molarity of NaOH for 30%, 40% and 50% Binder and SS/SH=1.\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-8284796/v1/722c0d317b3b8abd455fe99a.png"},{"id":99313093,"identity":"4fa3c772-6426-4b84-92d1-741d630e533f","added_by":"auto","created_at":"2025-12-31 16:19:47","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":284910,"visible":true,"origin":"","legend":"\u003cp\u003eUCS of heat-cured RFA-FA-GGBS geopolymers for a curing period of 3days at a temperature of 60°C, (a) Only 8M NaOH (b) 8M NaOH and SS/SH ratio =1\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-8284796/v1/a092eefbdbe8adcade53d78d.png"},{"id":98991249,"identity":"0d249aed-8d79-4aae-929b-0fb772d2259a","added_by":"auto","created_at":"2025-12-25 10:28:28","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":59510,"visible":true,"origin":"","legend":"\u003cp\u003eSoaked CBR values of RFA-FA-GGBS geopolymers at different molarities of SH, binder content (a) Only NaOH (b) NaOH and SS/SH ratio =1\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-8284796/v1/4f316d9ae319499a75e194d4.png"},{"id":98991259,"identity":"4a6d39f4-4390-40a3-8aac-49cf6123a139","added_by":"auto","created_at":"2025-12-25 10:28:28","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":26146,"visible":true,"origin":"","legend":"\u003cp\u003eMass loss of RFA-FA-GGBS geopolymers after 12 wetting-drying cycles at different molarities of SH, binder content (a) Only NaOH (b) NaOH and SS/SH ratio =1\u003c/p\u003e","description":"","filename":"10.png","url":"https://assets-eu.researchsquare.com/files/rs-8284796/v1/55809a77cb9b44cf50973cc9.png"},{"id":98991274,"identity":"3d636bcf-d812-4267-9ca5-5ee4d4a5eca8","added_by":"auto","created_at":"2025-12-25 10:28:29","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":8071487,"visible":true,"origin":"","legend":"\u003cp\u003eSEM image of RFA-FA-GGBS geopolymers at 10KX magnification with (a) 6M 50%B (b) 8M 50%B, (c) 10M 50%B\u003c/p\u003e","description":"","filename":"11.png","url":"https://assets-eu.researchsquare.com/files/rs-8284796/v1/786cbfd1e72106c90f7a6f49.png"},{"id":98991277,"identity":"a7d21b5f-9e95-4319-a7d9-ec95b66ac8ea","added_by":"auto","created_at":"2025-12-25 10:28:29","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":28056,"visible":true,"origin":"","legend":"\u003cp\u003eXRD pattern of 28 days ambient cured RFA-FA-GGBS geopolymers with 50% binder, (a) 10M 50%B, (b) 6M 50%B.\u003c/p\u003e","description":"","filename":"12.png","url":"https://assets-eu.researchsquare.com/files/rs-8284796/v1/72f76b50c131c9344db5c5da.png"},{"id":99788078,"identity":"22967f3d-8aa7-472e-a5aa-c588317e65a8","added_by":"auto","created_at":"2026-01-08 12:44:24","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":18888022,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8284796/v1/a64efe75-a56f-4636-b3ca-a4c03434cf43.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"\u003cp\u003eSustainable Utilization of Construction and Demolition Waste as a Subgrade Material Using the Process of Geopolymerization\u003c/p\u003e","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eThe construction sector is essential for the growth and sustainability of contemporary infrastructure; however, it remains one of the leading causes of construction and demolition (C\u0026amp;D) waste generation. Concrete, bricks, metals, timber, glass, and plastics are among the materials that are considered C\u0026amp;D waste. The C\u0026amp;D waste is generated by various activities, including the construction, renovation, and demolition of structures (Wu et al., \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). Conventional methods of waste management, which frequently involve incineration and landfilling, present significant environmental hazards, such as greenhouse gas emissions, pollution, and land degradation.\u003c/p\u003e \u003cp\u003eAs the global population expands and urban areas evolve, the increase in new construction initiatives, infrastructure enhancement, building refurbishments, and demolition of obsolete structures has exacerbated the issue of C\u0026amp;D waste. When this issue is examined in terms of numbers, its size becomes even clearer. The annual generation of the global C\u0026amp;D waste is more than 10\u0026nbsp;billion tonnes, and constitutes more than 35% of the world's disposal sites, with a substantial fraction of this waste ultimately deposited in landfills. India is a major contributor to global C\u0026amp;D waste, ranking third behind China and the US (Wu et al., \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). The US generates more than 600\u0026nbsp;million tonnes of C\u0026amp;D waste annually, a significant increase from the approximately 120\u0026nbsp;million tonnes produced in the 1990s. China is believed to be the largest producer in the world, with an estimated 1.13\u0026nbsp;billion tonnes of C\u0026amp;D waste produced in 2014. Worldwide, this waste constitutes a significant fraction of the solid waste stream, sometimes estimated at 30\u0026ndash;40% of total solid waste. This corresponds to several billion tonnes of C\u0026amp;D waste produced annually, a quantity anticipated to increase; worldwide waste generation in 2050 is forecast to be around twice that of 2016 (Petrović and Thomas, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). This substantial quantity of waste highlights a critical global issue: the necessity of sustainably managing and valorising construction and demolition waste, instead of depending on conventional disposal methods.\u003c/p\u003e \u003cp\u003eThe handling of C\u0026amp;D waste remains predominantly unsustainable, with a significant portion of debris ultimately deposited in landfills or illegally dumped. These kinds of activities use up extremely valuable land and put the natural environment in serious jeopardy. The emission of greenhouse gases (CO₂, CH₄) can be exacerbated by the decomposition of organic components or specific reactions in buried debris, which further exacerbates pollution.\u003c/p\u003e \u003cp\u003eDisposal of C\u0026amp;D debris in landfills has resulted in detrimental environmental effects, including soil, water and air pollution, emission of greenhouse gases, and significant health issues (Yazdani et al., \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). In addition, the building sector is irresponsibly depleting energy and natural resources. The construction sector is accountable for 30% of the global anthropogenic CO\u003csub\u003e2\u003c/sub\u003e emissions (Silva et al., \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Motivated by eco-friendly practices like the circular economy and sustainable development, the building sector actively seeks ways to reduce resource usage and carbon emissions.\u003c/p\u003e \u003cp\u003eIn recent years, researchers have been increasingly focused on sustainable waste management practices to address these environmental concerns. One promising approach is the utilization of C\u0026amp;D waste through geopolymerization. Geopolymers are inorganic polymers synthesized using alkaline solutions by the chemical activation of aluminosilicate materials, such as fly ash (FA) or slag (Provis and Bernal, \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). Geopolymers exhibit environmentally sustainable features, including enhanced mechanical properties, outstanding durability (Neupane et al., \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2018\u003c/span\u003e) and resistance to acids, sulphates (Kwasny et al., \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2018\u003c/span\u003e) and elevated temperatures (Xiao et al., \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2020\u003c/span\u003e) in comparison to Portland cement-based systems. The amount of amorphous material present in the raw materials is a critical factor governing their reactivity during alkali activation (Diaz et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2010\u003c/span\u003e). This process offers a sustainable substitute to conventional ordinary Portland cement (OPC), known for its large carbon footprint. It is used in concrete and is one of the high-carbon, resource-intensive materials used extensively in conventional buildings. It is commonly recognised that the manufacturing of OPC contributes significantly to greenhouse gas emissions, making up approximately 7\u0026ndash;8% of world CO₂ emissions. The calcination of limestone and the substantial energy use in cement kilns emit around 1.6\u0026nbsp;billion tonnes of CO₂ annually. In addition to cement, manufacturing other prevalent construction products and extracting raw aggregates carry further environmental burdens. The extraction of limestone, sand, and gravel for construction damages natural landscapes and may disturb local ecosystems. The mining and processing of raw materials generate numerous emissions and pollutants, leading to air quality deterioration, biodiversity decline, and other environmental strains. The construction industry's whole range of activities, from making materials to building things, is thought to be accountable for a substantial portion of the global greenhouse gas emission and resource use.\u003c/p\u003e \u003cp\u003eAccording to earlier research, 30% adherent mortar is present around the aggregates (Cartuxo et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Ghorbel et al., \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Along with many pores and microcracks, the adhering mortar gives the aggregates a rough surface texture, increasing their porosity and capacity to absorb water (Ghorbel et al., \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Additionally, the hydration in the concrete is hampered by the greater water absorption tendency of the recycled aggregates in comparison to normal aggregate. The concrete requires an increased quantity of water to maintain a sufficient amount of workability, as C\u0026amp;D waste aggregates have a higher water absorption rate (Bektas et al., \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Chandru et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Ghani et al., \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Geopolymers generally use less water, which lessens the detrimental effect of high-water-absorbing recycled aggregates on workability. Their distinct hydration mechanism further reduces the concrete's susceptibility to water absorption properties of the recycled particles.\u003c/p\u003e \u003cp\u003eThe rapid industrialization and urbanization have led to a growth in the generation of waste materials. Simultaneously, the construction industry faces the challenge of sourcing sustainable materials that decrease the environmental impact and address the growing concern for resource depletion. In this context, investigating various waste materials as a sustainable geopolymer binder for Civil engineering applications offers an innovative and eco-friendly approach to tackling these challenges. Geopolymer technology has emerged as a promising alternative to conventional cementitious binders, offering numerous benefits such as reduced CO\u003csub\u003e2\u003c/sub\u003e emissions, enhanced durability, and the capability to utilize a large range of waste materials as raw materials. Geopolymers are inorganic, amorphous aluminosilicate materials formed through the chemical reaction of an alumina-silicate-rich source material and an alkaline activator. Essentially, an aluminosilicate precursor and an alkaline reagent undergo a chemical reaction (commonly referred to as alkali activation) to generate a geopolymer, which results in a hardened matrix with a 3-D structure of Si\u0026ndash;O\u0026ndash;Al links. The activator's high pH dissolves Si and Al from the solid precursor, which subsequently reorganise and polymerise to form a solid gel, commonly known as sodium-alumino-silicate-hydrate (NASH) gel, that binds together aggregates or filler particles (Castillo et al., \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Geopolymers are receiving more attention as eco-friendly options to cement for several reasons. First, they can use waste materials from industries or natural clays as feedstock instead of new limestone. Fly ash (FA) generated from thermal power plants (Suraneni et al., \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2021\u003c/span\u003e) and ground granulated blast-furnace slag (GGBS) from steel-manufacturing plants are classic examples of reactive aluminosilicate components necessary for geopolymerization. Multiple studies have assessed the feasibility of utilising Construction and Demolition Waste (CDW) as a raw material for geopolymer synthesis (Alhawat et al., \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Dadsetan et al., \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Ye et al., \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Research indicates that many components of Construction and Demolition waste (CDW) including waste concrete, (Robayo-Salazar et al., \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Tefa et al., \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Zaharaki et al., \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e2016\u003c/span\u003e) glass,(Lu and Poon, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Zhang et al., \u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e2017\u003c/span\u003e) and ceramic tiles (Mahmoodi et al., \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2020\u003c/span\u003e) can supply the requisite reactive components in an alkaline solution. This initiates the development of geopolymer gels, enabling CDW-based geopolymers to attain characteristics similar to those derived from conventional materials. Studies on materials derived from masonry waste indicate that mixed fractions can be readily utilised in the geopolymerization process (Tan et al., \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Yıldırım et al., \u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Numerous recent studies have investigated the application of fly ash (FA) and ground granulated blast-furnace slag (GGBS) in road subgrade, sub-base, and base construction (Murmu et al., \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Sukprasert et al., \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). In contrast, the potential use of the recycled fine fraction of construction and demolition waste in various road pavement layers remains significantly underexplored.\u003c/p\u003e \u003cp\u003eTypically, a mixed C\u0026amp;D waste contains substantial mineral debris, particularly concrete rubble (from demolished concrete and masonry) and ceramic materials such as bricks, tiles, and plaster. These wastes consist primarily of silica, alumina, calcium, and other oxides often found in conventional binders. The fine powder produced from crushed concrete, which contains remains of hydrated cement and fine aggregates and pulverised brick or masonry debris, is abundant in SiO₂, Al₂O₃, and CaO. This composition facilitates geopolymerization: silica and alumina serve as network-forming species for the NASH gel, while calcium (notably from concrete waste) can contribute to forming CASH-type phases or enhance early strength. C\u0026amp;D waste can serve as a precursor by undergoing initial processing, such as crushing and milling, to achieve a fine particle size, improving its reactivity. Research has indicated that the powder obtained from building debris, comprising a combination of hydrated cement paste, unreacted cement particles, and fine sand or brick fragments, can fulfil the chemical criteria for geopolymer binders (Alhawat et al., \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). This technology allows the recycling of various industrial byproducts, such as FA, slag, rice husk ash, waste materials like water treatment sludge, C\u0026amp;D waste, and petroleum sludge, into valuable construction materials.\u003c/p\u003e \u003cp\u003eAccording to the Building Material Promotion Council (BMTPC), India produces roughly 155\u0026nbsp;million tonnes of C\u0026amp;D waste annually, and just 1% of this waste is recycled. This brings the importance of investigating C\u0026amp;D waste performance for various civil engineering applications. Recycled concrete aggregates are generated from construction and demolition debris by grinding and sieving the material in recycling facilities, classified as fine and coarse particles based on particle size. Over several decades, numerous prior researchers examined the efficacy of recycled coarse aggregates (RCA) in concrete as a substitute for natural coarse aggregates. These studies suggested that the strength and durability of concrete that contained RCA were marginally inferior to those of control concrete at varying substitution levels. In contrast, limited research has been conducted on the use of recycled fine aggregates (RFA) made from C\u0026amp;D waste as a substitute for natural fine aggregates (NFA) in comparison to recycled coarse aggregates. Recycled aggregates, derived from crushing C\u0026amp;D waste, have reduced mechanical strength compared to normal aggregates (Bogas et al., \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Mardani-Aghabaglou et al., \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2015\u003c/span\u003e).\u003c/p\u003e"},{"header":"2. Material characterization","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Materials\u003c/h2\u003e \u003cp\u003eIn this study, the C\u0026amp;D waste was collected from the IIT Guwahati campus, Assam. The FA was sourced from a thermal power plant located in the Punjab state in India, while GGBS was procured from Jindal Saw Ltd. in Gujarat, India. The primary composition of the collected C\u0026amp;D waste was recycled concrete and mortar. After C\u0026amp;D waste collection, the impurities such as wood, plastic, and metals were separated from the C\u0026amp;D waste. After the separation process, it was crushed into finer particles. After the crushing, it was sieved through a 4.75 mm sieve, and particles that passed through this sieve were used as fine aggregate, and the retained portion of the waste was used as coarse aggregate. The RFA was primarily composed of sand at 85.4% (4.75\u0026thinsp;\u0026minus;\u0026thinsp;0.075 mm). The grain size distribution was assessed by doing sieve analysis per ASTM \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2007\u003c/span\u003e (ASTM, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2007\u003c/span\u003e), and it was observed that the RFA was primarily composed of sand at 85.4% (4.75\u0026thinsp;\u0026minus;\u0026thinsp;0.075 mm), with the remaining fine particles being 14.2% (\u0026lt;\u0026thinsp;0.075 mm). The compaction characteristic of the RFA was obtained by conducting a Proctor compaction test as per the ASTM D698. ASTM D854 (ASTM, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2000\u003c/span\u003e) was used to determine the specific gravity of the RFA. Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e summarises the characteristics of RFA.\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\u003ePhysical properties of RFA from Construction and Demolition waste\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\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=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSerial No.\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eProperties\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eConfirming to code\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eResult\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOptimum moisture content (OMC)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eASTM D698\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e19.17%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMaximum Dry density (MDD)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eASTM D698\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.53 gm/cc\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSpecific Gravity\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eASTM D854\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2.56\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eUnconfined Compressive Strength (UCS)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eASTMD2166\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eND\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSoaked CBR values\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eIS 2720: Part 16: 1987\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e13.14%\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\u003eFigure \u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e shows the RFA, FA, and GGBS used in the current study. The shape of RFA from C\u0026amp;D waste was observed to be angular, since these are typically produced through mechanical crushing, which creates sharp edges and irregular surfaces due to brittle fracture. The SEM images of GGBS and FA in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e show them as angular and spherical with a few irregular shapes, respectively. The round shape of FA particles makes the mix easier to deal with because round particles make the mix easier to work with. The data in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e present the chemical compositions of the FA and GGBS obtained from the XRF study. The precursor binding material, consisting of FA and GGBS, is employed in the production of geopolymer along with recycled fines aggregates sourced from C\u0026amp;D activities. The FA used for this study is a Class F type as per ASTM C 618 (ASTM, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e1999\u003c/span\u003e), as indicated by the XRF analysis. The sum total of SiO\u003csub\u003e2\u003c/sub\u003e, Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, and Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e exceeds 70%, as presented in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. The primary oxides present in GGBS include CaO at 35.56%, SiO\u003csub\u003e2\u003c/sub\u003e at 33.15%, Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e at 17.67%, and MgO at 5.52%. The presence of a significant amount of CaO in GGBS, when activated by an alkaline solution, can lead to the development of a CSH gel in conjunction with the geopolymer gel. The CSH gel exhibits superior binding characteristics. The XRD pattern of RFA revealed an abundance of minerals, including Quartz and Calcite. The primary components of Class-F fly ash are quartz and mullite, as verified by XRD investigation; whereas, GGBS contains calcite and quartz minerals, as illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. The Energy-Dispersive X-ray Spectroscopy (EDS) of the recycled fine aggregates (RFA) from construction and demolition waste, shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, reveals that the elevated levels of Calcium (Ca) and Oxygen (O) are significant indications of the presence of hydrated cement paste. Cement in concrete reacts with water to produce binding agents, primarily calcium silicate hydrates (C-S-H) and calcium hydroxide (Ca(OH)₂). Calcium hydroxide can react with atmospheric carbon dioxide over time to produce calcium carbonate (CaCO₃). These calcium-rich compounds are essential components of the mortar and paste that bond to the initial aggregates in the concrete.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\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\u003eXRF showing the Chemical composition of FA, GGBS\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\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 \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eChemical Composition (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eFly ash (FA)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eGround granulated blast furnace slag (GGBS)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSiO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e55.49\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e33.15\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e29.27\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e17.67\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e (T)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4.62\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.43\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMnO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.040\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.319\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\u003e0.62\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e5.52\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\u003e0.87\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e35.56\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNa\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.34\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eK\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.48\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.62\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTiO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e2.17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.66\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eP\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.49\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.01\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.25\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLOI\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4.90\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e3.47\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\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Alkaline Activators\u003c/h2\u003e \u003cp\u003eAlkaline activators are essential components in a geopolymerization process, as they facilitate the dissolution of precursor materials and promote the formation and hardening of the geopolymer matrix. The activation was carried out using solutions of sodium silicate (Na\u003csub\u003e2\u003c/sub\u003eSiO\u003csub\u003e3\u003c/sub\u003e, abbreviated as SS) and sodium hydroxide (NaOH, abbreviated as SH). The NaOH was initially in pellet form, which was manufactured by Merck Pvt Ltd; whereas, Na\u003csub\u003e2\u003c/sub\u003eSiO\u003csub\u003e3,\u003c/sub\u003e which was in liquid form, consisting of Na\u003csub\u003e2\u003c/sub\u003eO\u0026thinsp;=\u0026thinsp;8.0% and SiO\u003csub\u003e2\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;27% and was produced by Loba Chemie Pvt. Ltd. The researchers proposed an appropriate concentration range for NaOH of 4.5 to 18 molars (Yaghoubi et al., \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2018\u003c/span\u003e) (Nematollahi and Sanjayan, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Considering both economic and safety perspectives, low-concentration solutions of NaOH (i.e., 6, 8, and 10M) were used for this investigation. The solution was prepared primarily one day prior to its casting. Initially, NaOH is used alone for the activation of the geopolymer matrix. The proportion of Na\u003csub\u003e2\u003c/sub\u003eSiO\u003csub\u003e3\u003c/sub\u003e to NaOH (i.e. SS/SH) was set to 1 to investigate the impact of the activator on construction and demolition waste amended with industrial byproducts, specifically FA and GGBS. The Na\u003csub\u003e2\u003c/sub\u003eSiO\u003csub\u003e3\u003c/sub\u003e liquid solution was combined to facilitate the gelation and precipitation of silicates during geopolymerization (Khale and Chaudhary, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). Numerous investigations indicate that alkaline silicate promotes the formation of soluble SiO\u003csub\u003e2\u003c/sub\u003e monomers, resulting in improved microstructure and enhanced mechanical performance (Vidal et al., \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2018\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e"},{"header":"3 Experimental Methodology","content":"\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Sample Preparation\u003c/h2\u003e \u003cp\u003eThis research examines geopolymers derived from RFA from C\u0026amp;D waste, employing FA and GGBS in an equal ratio as binding agents. This study examines the correlation between binder content and strength development by casting geopolymer samples with varying substitution levels, specifically replacing C\u0026amp;D waste with 30, 40, and 50% binder. Two alkline activators are used. In one sample batch, only NaOH is used. The second batch employed an alkaline activator consisting of NaOH and Na\u003csub\u003e2\u003c/sub\u003eSiO\u003csub\u003e3\u003c/sub\u003e. This combination was chosen based on existing literature indicating that supplemental silica from Na\u003csub\u003e2\u003c/sub\u003eSiO\u003csub\u003e3\u003c/sub\u003e enhances polymerisation, leading to a microstructure with improved mechanical strength (Hoy et al., \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Yaghoubi et al., \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). The strength enhancement of C\u0026amp;D-based geopolymers samples was examined in relation to the activator concentration using three molarities of NaOH, i.e. 6, 8, and 10 M. The activator solution was prepared 24 hours before the sample preparation by dissolving the appropriate quantity of NaOH pellets in DI-water. The selection of this concentration range was influenced by economic and safety factors. Furthermore, a 1:1 volumetric ratio was used to examine the influence of the Na\u003csub\u003e2\u003c/sub\u003eSiO\u003csub\u003e3\u003c/sub\u003e to NaOH proportion on geopolymer strength.\u003c/p\u003e \u003cp\u003eThe strength of the polymerised composites was assessed by assessing their unconfined compressive strength (UCS) and California bearing ratio (CBR), by taking into account different curing durations and conditions. In this study, the prepared UCS samples are tested under two distinct curing conditions, which include ambient exposure at room temperature, specifically air drying at room temperature, and heat curing at 60\u0026deg;C for different curing periods. A curing duration of 3, 7, and 28 days is considered for ambient curing conditions as per ASTM D2166 and 3 days for heat-cured samples. Prior to testing for the CBR, the specimens were cured in DI water at ambient temperature for 3 days, followed by soaking them for an additional 4 days. The durability of the C\u0026amp;D-based geopolymers was examined by exposing the 7-day cured samples to a number of wetting-drying cycles as instructed in IS 4332-4 (1968), and then the performance of the specimens was assessed in terms of percentage mass loss. Also, the geopolymer samples' microstructural changes are studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM) tests. Details of different C\u0026amp;D mix proportions, NaOH molarity and Na\u003csub\u003e2\u003c/sub\u003eSiO\u003csub\u003e3\u003c/sub\u003e/NaOH (SS/SH) proportions, curing condition \u0026amp; duration employed in this investigation can be found in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\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\u003eMix Proportions of samples\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\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=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMolarity\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMix Proportion\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eAmbient Curing\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eHeat Curing\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eAlkaline Activators\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e6M\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e70% RFA\u0026thinsp;+\u0026thinsp;15% FA\u0026thinsp;+\u0026thinsp;15% GGBS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e3, 7, \u0026amp; 28 days\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e3 days\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\" morerows=\"8\" rowspan=\"9\"\u003e \u003cp\u003e\u003cb\u003eNaOH (SH)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e60% RFA\u0026thinsp;+\u0026thinsp;20% FA\u0026thinsp;+\u0026thinsp;20% GGBS\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e50% RFA\u0026thinsp;+\u0026thinsp;25% FA\u0026thinsp;+\u0026thinsp;25% GGBS\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e8M\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e70% RFA\u0026thinsp;+\u0026thinsp;15% FA\u0026thinsp;+\u0026thinsp;15% GGBS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e3, 7, \u0026amp; 28 days\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e3 days\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e60% RFA\u0026thinsp;+\u0026thinsp;20% FA\u0026thinsp;+\u0026thinsp;20% GGBS\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e50% RFA\u0026thinsp;+\u0026thinsp;25% FA\u0026thinsp;+\u0026thinsp;25% GGBS\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e10M\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e70% RFA\u0026thinsp;+\u0026thinsp;15% FA\u0026thinsp;+\u0026thinsp;15% GGBS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e3, 7, \u0026amp; 28 days\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e3 days\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e60% RFA\u0026thinsp;+\u0026thinsp;20% FA\u0026thinsp;+\u0026thinsp;20% GGBS\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e50% RFA\u0026thinsp;+\u0026thinsp;25% FA\u0026thinsp;+\u0026thinsp;25% GGBS\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e6M\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e70% RFA\u0026thinsp;+\u0026thinsp;15% FA\u0026thinsp;+\u0026thinsp;15% GGBS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e3, 7, \u0026amp; 28 days\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e3 days\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\" morerows=\"8\" rowspan=\"9\"\u003e \u003cp\u003e\u003cb\u003eSS:SH\u003c/b\u003e\u0026thinsp;=\u0026thinsp;1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e60% RFA\u0026thinsp;+\u0026thinsp;20% FA\u0026thinsp;+\u0026thinsp;20% GGBS\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e50% RFA\u0026thinsp;+\u0026thinsp;25% FA\u0026thinsp;+\u0026thinsp;25% GGBS\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e8M\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e70% RFA\u0026thinsp;+\u0026thinsp;15% FA\u0026thinsp;+\u0026thinsp;15% GGBS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e3, 7, \u0026amp; 28 days\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e3 days\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e60% RFA\u0026thinsp;+\u0026thinsp;20% FA\u0026thinsp;+\u0026thinsp;20% GGBS\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e50% RFA\u0026thinsp;+\u0026thinsp;25% FA\u0026thinsp;+\u0026thinsp;25% GGBS\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e10M\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e70% RFA\u0026thinsp;+\u0026thinsp;15% FA\u0026thinsp;+\u0026thinsp;15% GGBS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e3, 7, \u0026amp; 28 days\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e3 days\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e60% RFA\u0026thinsp;+\u0026thinsp;20% FA\u0026thinsp;+\u0026thinsp;20% GGBS\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e50% RFA\u0026thinsp;+\u0026thinsp;25% FA\u0026thinsp;+\u0026thinsp;25% GGBS\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"5\"\u003e\u003cb\u003eRFA-\u003c/b\u003eRecycled Fine aggregates, \u003cb\u003eFA-\u003c/b\u003eFly Ash, \u003cb\u003eGGBS-\u003c/b\u003e Ground Granulated Blast Slag,\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"5\"\u003e\u003cb\u003eSH-\u003c/b\u003eSodium Hydroxide, \u003cb\u003eSS-\u003c/b\u003e Sodium Silicate, \u003cb\u003eM-\u003c/b\u003eMolarity of Sodium Hydroxide\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"5\"\u003e\u003cb\u003e30%B\u003c/b\u003e\u0026thinsp;=\u0026thinsp;70% RF\u0026thinsp;+\u0026thinsp;15% FA\u0026thinsp;+\u0026thinsp;15% GGBS, \u003cb\u003eB=\u003c/b\u003e(FA\u0026thinsp;+\u0026thinsp;GGBS), \u003cb\u003eR1\u0026thinsp;=\u003c/b\u003e\u0026thinsp;SS/SH ratio 1.\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Unconfined Compression test\u003c/h2\u003e \u003cp\u003eAfter compacting the samples to their maximum dry density (MDD) and optimum moisture content (OMC) conditions, the UCS was determined following ASTM D2166/D2166M-22 standards. For each mix design, three specimens were made and loaded at a constant strain rate of 1.25 mm/min until failure occurred. The final UCS for each composition was reported as the average of the three peak strength values obtained. The final UCS for each composition was documented as the mean of the three peak strength values acquired.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e3.3 California bearing ratio tests\u003c/h2\u003e \u003cp\u003eThe CBR of the specimens was determined as per IS 2720 (Part 16): 1987. Specimen preparation, guided by IRC-37, involved static compaction within a 150 mm diameter, 175 mm high mould to achieve 97% of the maximum dry density. All tests were performed under soaked conditions, which involved immersing the specimens in water for a four-day period prior to testing. A 5 kg surcharge was applied to the specimen after the soaking period to prevent disturbance during testing. A 50 mm diameter plunger was then advanced into the specimen at a fixed strain rate of 1.25 mm/min, and the corresponding load versus penetration data was recorded. The CBR values were computed from this curve at 2.5 mm and 5 mm penetration depths. When the CBR value corresponding to a penetration depth of 2.5 mm exceeds that at 5 mm, the former is reported to be the CBR value of the specimen. The test is repeated if the CBR for a penetration depth of 5 mm is higher than that of 2.5 mm, and if the findings are identical, the former is recorded as the CBR value of the specimen.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e3.4 Durability tests\u003c/h2\u003e \u003cp\u003eThe durability of different specimens was examined by exposing the specimens to a number of wetting-drying cycles as per the guidelines provided by IS 4332-4 (1968). The standard moulded samples of different mixes, after a curing period of 7 days, were submerged in DI-water for 5 hours to start the wetting-drying cycles. The initial phase of each cycle involved drying samples at 70\u0026deg;C for 42 hours, followed by a one-hour cooling period at room temperature. After cooling, each dried specimen was brushed using a wire brush for 17\u0026ndash;20 vertical strokes, and then its weight was measured to determine the material loss, and then subjected to the next wetting phase. This entire procedure constituted one 48-hour cycle, which was repeated for a total of 12 cycles. The mass loss percentage of different mixes was assessed after undergoing 12 wetting-drying cycles.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.5 Toxicity characteristics leaching procedure (TCLP) test\u003c/h2\u003e \u003cp\u003eThe TCLP test for the stabilised geopolymer samples was performed as per USEPA 1311 to assess their leaching characteristics(USEPA, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e1999\u003c/span\u003e). For each test, a 5 g sample, passing through a 2 mm sieve, was carefully prepared. The extraction fluid was composed of acetic acid and DI water, with the pH cautiously adjusted to 4.93\u0026thinsp;\u0026plusmn;\u0026thinsp;0.05 using a 1 N NaOH solution. The sample was added to 100 g of the extraction fluid, maintaining a 1:20 solid-to-liquid ratio, and shaken in a shaker for 18 hours at a speed of 30\u0026thinsp;\u0026plusmn;\u0026thinsp;2 rpm. Following the shaking, the slurry was filtered through a glass fiber filter. The elemental concentration in the resulting leachate was then subsequently analysed using Inductively Coupled Plasma Mass Spectrometry (ICP-MS). The test was conducted thrice for each sample, and the final value reported is the arithmetic mean of these three trials.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e3.6 XRD tests\u003c/h2\u003e \u003cp\u003eIn the XRD test, the sample is subjected to a filtered X-ray beam. As the beam enters the material, it causes the electrons in the mineral atoms to vibrate and thus reflect the beam across consecutive planes. The intensity of the diffracted X-ray is constantly monitored with increasing incidence angle until the diffracted intensity reaches a maximum value, and thus an XRD pattern is obtained. Once the test is completed, the samples are pulverised into a very fine powder and then dried in an oven before being used for the XRD analysis. The XRD pattern of different specimens was obtained by scanning in a range of 5\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:^\\circ\\:\\)\u003c/span\u003e\u003c/span\u003e to 80\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:^\\circ\\:\\)\u003c/span\u003e\u003c/span\u003e (2\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\theta\\:}\\)\u003c/span\u003e\u003c/span\u003e). Identification of mineral phases was conducted utilising PANalytical's X'Pert HighScore Plus software. The analysis consisted of correlating experimental diffraction patterns with the Powder Diffraction File (PDF-2) database, which is provided by the International Centre for Diffraction Data (ICDD).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e3.7 SEM analysis\u003c/h2\u003e \u003cp\u003eThe morphology of different C\u0026amp;D waste, FA and GGBS mixes was analysed using the Gemini field emission scanning electron microscope. The samples were pulverised to fine powders after the UCS tests and oven-dried before the SEM analysis. A carbon tape is adhered to a stub, and the powdered specimen is placed above it. Prior to imaging, the powdered sample was sputter-coated with a thin layer of gold to ensure electrical conductivity. The SEM analysis was then conducted to capture micrographs at the desired levels of magnification.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003e3.8 Energy-Dispersive X-ray Spectroscopy (EDS)\u003c/h2\u003e \u003cp\u003eThe EDS, also sometimes called EDX, EDXS, or XEDS, is a method used to identify and quantify the elemental composition of a sample. EDS is dependent on the distinct atomic arrangement of every element. Each element possesses a distinct configuration of electrons surrounding its nucleus. When a sample is exposed to an X-ray source or, more frequently in EDS, an electron beam (such as in a SEM), these electrons may interact with the electrons in the sample's atoms. This interaction can pull away one electron from its orbital position within an atom of the sample. To compensate for the vacancy, an electron from a higher energy level will transition to a lower energy level, resulting in energy emission in the form of an X-ray. EDS can identify and measure the elements in a sample by looking at the energies and levels of the reflected X-rays. Before EDS analysis, the sample was prepared by adding a conductive carbon coating to enable elemental mapping and analysis.\u003c/p\u003e \u003c/div\u003e"},{"header":"4 Results and Discussions","content":"\u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003e4.1 Effect of binder content, NaOH molarity, SS/SH ratio and curing period on UCS\u003c/h2\u003e \u003cp\u003eIn this study, the test specimens for unconfined compressive strength have been cast by blending different proportions of binder (FA and GGBS) with recycled fine aggregate for a curing duration of 3, 7, and 28 days under ambient conditions, i.e., air dried at room temperature. The binder consists of FA and GGBS, in which the FA/GGBS ratio is kept at 1. Samples were prepared by replacing construction and demolition waste with 30%, 40%, and 50% binder, for different concentrations of sodium hydroxide (6, 8, and 10M). Two variations in the alkaline activators are considered in the first one; only sodium hydroxide (NaOH or SH) is considered as an activator, while the other ratio of NaOH to sodium silicate (Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e3\u003c/sub\u003e or SS) in a ratio of 1 was considered in this study. Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e depicts the variation of the strength of RFA-FA-GGBS-based geopolymer with various binder content, curing period and NaOH molarity.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003e4.2 Effect of binder content, NaOH molarity, SS/SH ratio and curing period on UCS\u003c/h2\u003e \u003cp\u003eCuring duration plays a significant role in how geopolymer materials develop their strength. Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e presents the UCS results for samples cured at ambient conditions for 3, 7, and 28 days with various activator concentrations, binder contents and SS/SH ratio 1. It is clear that, irrespective of the alkaline activator concentration, binder content, or SS/SH ratio, the UCS values consistently rise as the curing duration extends from 3 to 28 days. In the initial three days, the alumina and silica from the precursor materials get released upon alkali activation, which results in the formation of geopolymeric gels. Progressively, the gels toughen, thus leading to strength development in due course of time. Therefore, the strength of the 3-day-cured specimens is relatively less compared to 28-day-cured samples, irrespective of the concentration of NaOH, binder content and SS/SH ratio. With the prolongation of the curing time from 3 to 7 days, a sharp rise in strength could be seen in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e. After 7 days of curing, the geopolymeric gels formed from the alkali activation of RFA, FA, and GGBS undergo additional polymerisation and cross-linking, resulting in a compact and an increase in the interconnected geopolymer network, producing additional strength. A further increase in the curing time up to 28 days, the strength of the RFA-FA-GGBS geopolymer samples further increases; however, the rate of increment was not significant. Samantasinghar and Singh (\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2021\u003c/span\u003e) reported similar observations for soil treated with FA-GGBS geopolymer, where a considerable strength improvement is shown up to 7 days of curing; beyond that, the rate of increase becomes marginal. Shi et al. (\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2022\u003c/span\u003e) also observed that the growth rate of the strength of clay modified with metakaolin-based geopolymer is very significant in the first 7 days, beyond which the rate gradually slows down. This behaviour is mainly owing to the fast condensation of the geopolymer in the beginning 7 days, a period during which the majority of the available aluminosilicate sources from various precursors are utilised. The rate of strength gain consequently slows down after this period. After 28 days, the condensation process is almost finished, forming a more stable geopolymer matrix that contributes to increased strength relative to earlier stages. The 28-day strength serves as a standard for assessing the performance of cementitious materials, such as geopolymers.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003e4.3 Influence of NaOH concentration in alkaline solution on the UCS of RFA-FA-GGBS geopolymer\u003c/h2\u003e \u003cp\u003eThe concentration of the alkaline solution plays a significant role in the development of strength in geopolymer samples. The plot in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e presents the change in the UCS of RFA-FA-GGBS geopolymers resulting from variations in the NaOH concentration in the alkaline solution for different binder contents and curing periods. Similarly, the plot in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e presents the change in the UCS of RFA-FA-GGBS geopolymers due to variations in the NaOH concentration in the alkaline solution, for different binder contents and curing periods, and an SS/SH ratio of 1. It has been observed that for any binder content, curing period and SS/SH ratio, the strength of RFA-FA-GGBS geopolymer samples significantly increases with the rise in the concentration of NaOH. For example, the UCS for 28-day cured samples with 30% binder significantly enhanced from 9.93 to 13.12 MPa upon increasing the concentration of NaOH from 6 to 10M. With the increase in NaOH concentration, the pH of the material rises, facilitating the faster dissolution of alumina and silica from the precursor material. This leads to extensive geopolymeric gel formation, which binds the particles of the raw materials and results in increased strength.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe solubility of the aluminosilicate source materials increases with the rise in the concentration of NaOH, resulting in a rapid dissolution of free [SiO\u003csub\u003e4\u003c/sub\u003e] \u003csup\u003e\u0026minus;\u003c/sup\u003e and [AlO\u003csub\u003e4\u003c/sub\u003e] \u003csup\u003e\u0026minus;\u003c/sup\u003e tetrahedral, which undergo polymerisation to create a negatively charged Si-O-Al-O bond. Therefore, a higher concentration of NaOH can generate a large amount of Na\u003csup\u003e+\u003c/sup\u003e cations to cater to a charge imbalance, which is essential for the strength and stability of the resulting geopolymer materials. In geopolymerization, sodium hydroxide is the main dissolving agent. It makes the surroundings alkaline, which breaks down the amorphous aluminosilicate phases that are in the precursor materials. The hydroxide ions break the Si-O and Al-O bonds in the glassy forms of materials like GGBS and fly ash, letting silicate and aluminate species dissolve. This process, called depolymerisation, is very important for getting the reactive species ready for the polycondensation processes that build the three-dimensional geopolymer network. The high pH environment that NaOH creates, usually between 12 and 14, gives these dissolution processes the push they need to happen at room temperature or slightly higher. The efficiency of NaOH as an activator is determined by various factors, including concentration, temperature, and the composition of the precursor materials. Higher concentrations often promote dissolving, but they may also cause rapid setting and potential strength loss due to incomplete reactions or the creation of competing phases. Sodium silicate generally serves two major functions in the geopolymerization process. Firstly, it increases the pH of the medium, and secondly, it introduces reactive silica into the system. These silicate species, coupled with the dissolved aluminates, undergo a polycondensation process to produce the three-dimensional aluminosilicate network that forms the geopolymer gel. Zhang et al. (\u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e2011\u003c/span\u003e) also reported the increase of UCS of mine tailings and FA-based geopolymer with the rise in the concentration of NaOH from 5 to 15M. Numerous studies have further shown that the relationship between NaOH concentration and strength is not linear. An optimal concentration is typically observed, beyond which strength development either plateaus or begins to decline (Hamid and Alnuaim, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Manjarrez and Zhang, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Noolu et al., \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Tajaddini et al., \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). The loss of strength at elevated molarities is likely due to an inhibition of the geopolymerization reaction. An overabundance of hydroxide ions (OH\u003csup\u003e\u0026ndash;\u003c/sup\u003e) is thought to cause aluminate and silicate ions to precipitate prematurely, which obstructs the formation of a continuous and well-ordered polymer structure. Furthermore, the corresponding excess of sodium cations (Na\u003csup\u003e+\u003c/sup\u003e) may be detrimental, as it can disturb the charge imbalance.\u003c/p\u003e \u003cp\u003eWhile sodium silicate is necessary for geopolymerization, an excess of it can reduce the geopolymer's compressive strength. An excess of silicate can disrupt the balance of the geopolymerization reaction, causing the development of a less robust network. Specifically, an overabundance of silicon can result in a reduced number of strong Si-O-Al bonds, which are crucial for the material's strength\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003e4.4 Influence of heat curing on the UCS of RFA-FA-GGBS geopolymer\u003c/h2\u003e \u003cp\u003eThe temperature and curing conditions of a geopolymer material can have considerable effects on how it develops strength. The influence of heat curing on UCS of RF-FA-GGBS geopolymers, for various binder content (i.e. 30, 40, and 50%), curing period \u0026amp; NaOH concentration (6, 8, \u0026amp; 10M), for a SS/SH ratio of 1, was investigated. The prepared samples were permitted to set at room temperature for a period of 1 day in the beginning, then cured inside an oven at 60\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:^\\circ\\:\\)\u003c/span\u003e\u003c/span\u003eC for a duration of 3 days. Since heating the freshly prepared samples at a higher temperature results in a rapid loss in moisture, which might result in strength reduction owing to shrinking and cracking of the samples. From Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e, it was observed that there is not much gain in the strength of the RFA-FA-GGBS geopolymers. This may be due to the high amount of calcium present in the recycled fine aggregates and GGBS, as the GGBS can influence the temperature dependence of geopolymer curing. While it can enhance early strength, a high GGBS content might reduce the need for high-temperature curing for further strength improvement.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec19\" class=\"Section2\"\u003e \u003ch2\u003e4.5 CBR of RFA-FA-GGBS geopolymers\u003c/h2\u003e \u003cp\u003eThe suitability of the recycled fine aggregate from C\u0026amp;D waste for road construction was evaluated using the California Bearing Ratio (CBR) test, which measures bearing resistance. The material achieved a soaked CBR value of 13.14%, thus satisfying the minimum criteria for road application. According to the guidelines set up by IRC:37-2012 (IRC-37, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2012\u003c/span\u003e) materials used in subgrade construction must have a minimum CBR value of 8%. Samples were allowed to cure at room temperature for three days before being immersed in water for four days under a 5kg surcharge load. Figure\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e displays the soaked CBR values of RFA-FA-GGBS geopolymer samples that were subjected to different sodium hydroxide concentrations, SS/SH ratios, and binder contents. Higher NaOH concentrations accelerate the dissolution of alumina and silica from source materials, promoting the formation of a geopolymer gel. This gel binds the particles together, leading to increased strength, bearing resistance, and higher CBR values, which are further enhanced by a greater binder content. The CBR values of the samples having only sodium hydroxide as alkaline activator show greater CBR values than the SS/SH ratio 1. This may be due to some possible reasons. The sodium silicate solution is much thicker (more viscous) than the sodium hydroxide solution. Because of its high viscosity, the mix might be sticky and hard to compact well. The less viscous NaOH-only mix probably made it easier to deal with, which led to a more even mixture and a higher density when it was compacted. A material that is denser and more compacted will almost always have a higher CBR value. Another possible reason for this may be due to the presence of a sufficient amount of reactive silica and alumina in the precursor materials, like recycled fine aggregates, fly ash, and GGBS. Some studies indicated that CBR values declined as Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e3\u003c/sub\u003e concentrations increased in alkaline solutions (Arulrajah et al., \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Chandra et al., \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAccording to the IRC: SP:89 [52], the least CBR value for a cement-stabilized blend used as subgrade material must be 15%. Also, the IRC: 51-1992 [53] says that a lime-stabilized subbase must have a CBR value of at least 15% for rural roads. As demonstrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e, all RFA-FA-GGBS geopolymer samples are suitable for use as subgrade, subbase or base material, as their soaked CBR values exceed the minimum requirements regardless of the binder content and NaOH concentration.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec20\" class=\"Section2\"\u003e \u003ch2\u003e4.6 Evaluation of the durability of RFA-FA-GGBS geopolymers\u003c/h2\u003e \u003cp\u003eThe present study is focused on the improvement of the strength of RFA-FA-GGBS geopolymers and their feasibility to be used as a subgrade, subbase, or base material for road construction. Although the UCS is one of the major parameters for evaluating the strength performance of geopolymer or any other stabilized materials, it also has to be assessed in terms of its durability. The most widely used durability tests are freeze-thaw and wetting-drying tests. Freeze-thaw durability test is best suited for cold regions. In tropical countries like India, the subgrade, subbase or base material of roads often comes across seasonal changes during summer and rainy seasons, which might affect the strength performance of the construction materials. Thus, evaluation of the performance of RFA-FA-GGBS geopolymers against wetting-drying cycle becomes very important.\u003c/p\u003e \u003cp\u003eThe plot in Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e, presents the variation of weight reduction of RFA-FA-GGBS geopolymers with various molarities of NaOH, for different binder contents after 12 wetting-drying cycles. It can be seen that the amount of weight reduction reduces with a rise in the concentration of NaOH and binder content. For example, in Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e, when only NaOH is used and a binder content of 30%, there is a reduction in mass loss from 4.28 to 3.81% with the increase in NaOH concentration from 6 to 10 M. Also, the percentage of weight reduction reduced from 5.74 to 3.71% with the rise in binder content from 30 to 50% for a 6 M NaOH concentration and SS/SH of proportion 1.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe dissolution rate of alumina and silica from the precursor materials increases with the NaOH concentration, which leads to the formation of a large amount of geopolymer gels, thereby promoting the generation of a more interconnected and closely packed geopolymer matrix. This decreases the porosity and water absorption capacity, subsequently decreasing the weight loss of the geopolymer composite during the wetting-drying cycle. Besides, the increment of binder content ensured sufficient alumina and silica to promote better geopolymerisation reaction, resulting in a denser interconnected structure, which subsequently reduces the percentage of mass loss during the wetting-drying cycle.\u003c/p\u003e \u003cp\u003eFurthermore, it can be observed in Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e that the weight loss of the geopolymer specimens with only NaOH as alkaline activator was relatively lower than that at a SS/SH ratio of 1. For example, with the 10M solution of NaOH and 50% binder content, the weight loss was 1.84%; whereas, for an SS/SH ratio of 1, it was increased to 2.53%. The highest amount of weight loss rose up to 5.74% for a binder content of 30%, NaOH of 6 M concentration, and an SS/SH ratio of 1.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec21\" class=\"Section2\"\u003e \u003ch2\u003e4.7 Microstructural and Morphological Analysis\u003c/h2\u003e \u003cp\u003eThe microstructure and morphology of RFA-FA-GGBS geopolymer specimens were studied using SEM and XRD tests. The 28-day ambient-cured samples after UCS tests were pulverised to fine powder, oven dried and then used for the microstructural investigations.\u003c/p\u003e \u003cp\u003eAt 6 M solutions of NaOH, some non-reacted or partially reacted FA and GGBS particles could be seen with very few reaction products, as evident in Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e. At a higher concentration, i.e. 10 M of NaOH, this was not the case, though. The observed increase in compressive strength when increasing the molarity from 6M to 10M results directly from microstructural densification. An increased concentration of alkaline solution facilitates a more thorough dissolution of the FA and GGBS, resulting in a greater volume of the binding phases (CASH, NASH). This abundance of gel creates a more tightly packed and homogeneous internal structure, which is inherently stronger and better at resisting compressive loads.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eWith the increase in molarity from 6 to 8M and from 8 to 10M, the FA and GGBS particles get dissolved with the subsequent formation of a large amount of CASH, NASH, CSH, etc., which leads to a denser structure, thereby increasing the compressive strength of the specimen.\u003c/p\u003e \u003cp\u003eThe XRD pattern of different specimens shows the presence of Quartz peak at 26.8\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:^\\circ\\:\\)\u003c/span\u003e\u003c/span\u003e in all the plots, indicating its highly unreactive nature as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e. The calcium\u0026ndash;aluminosilicate\u0026ndash;hydrate (CASH) gel was formed from the calcium present in GGBS upon alkali activation (Abdila et al., \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Hoy et al., \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Lekshmi and Sudhakumar, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Miraki et al., \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). The calcium present in GGBS gets dissolved to form calcium cations upon alkali activation. Simultaneously, the activator also dissolves the aluminosilicates to free [SiO\u003csub\u003e4\u003c/sub\u003e] \u003csup\u003e\u0026minus;\u003c/sup\u003e and [AlO\u003csub\u003e4\u003c/sub\u003e] \u003csup\u003e\u0026ndash;\u003c/sup\u003e tetrahedral units, which undergo polymerisation to form silica and alumina monomers. Free Ca\u0026sup2;⁺ ions neutralise the negatively charged alumina and silica monomers, facilitating the formation of (C\u0026ndash;A\u0026ndash;S\u0026ndash;H) gel, which improves the strength of the geopolymer composite. Consequently, the increased peak intensities of geopolymer reaction products, such as CASH, CSH, NASH, and NAS, and the emergence of new peaks indicate a greater quantity of reaction products at higher NaOH (SH) concentrations, thereby contributing to improved strength relative to that observed at lower SH concentrations.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec22\" class=\"Section2\"\u003e \u003ch2\u003e4.8 Leaching potential of the RFA-FA-GGBS-based geopolymer specimens\u003c/h2\u003e \u003cp\u003eThe results of the TCLP studies for the heavy metal concentrations in the leachate are summarised in Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. The data in Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e highlights that the leachate's contents of heavy metals (Ba, Cd, Cr, Pd, Zn, etc.) are far lower than the regulatory limitations set by the US Environmental Protection Agency. According to these results, adding more alkali activators to geopolymer samples improves their capacity to trap heavy metals. Various microscopic and big structures of aluminate and silicate compounds are formed when aluminosilicate materials undergo geopolymerization in extremely alkaline settings. By physically attaching various heavy metals, these structures efficiently capture and encapsulate them, allowing polycondensation reactions to go indefinitely (Taki et al., \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Many variables, including the nature of the metal, the properties of the raw material, the kind of activator, and the pore structure, influence the degree to which geopolymers can immobilise heavy metals (Vu and Gowripalan, \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Thus, it is evident that the use of RF-FA-GGBS-based geopolymers in road preparation applications does not pose any environmental issues related to the possible leaching of heavy metal contaminants that could potentially lead to groundwater contamination. By increasing their strength and endurance while decreasing their susceptibility to harm, geopolymers composed of RF-FA-GGBS guarantee their safe disposal.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eToxicity characteristics of the geopolymerized sample with 30% Binder (FA\u0026thinsp;+\u0026thinsp;GGBS) and 50% Binder and SH concentration 6M and 10M\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\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 \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMetals\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e6M, 30% B (g/ml)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e6M, 50% B (g/ml)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e10M, 50% B (g/ml)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eUSEPA limits for hazardous waste (g/ml)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eCd\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.001\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e1.0\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eZn\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.017\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.003\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.001\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e25.0\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003ePb\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e5.0\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eCu\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.04\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.09\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e25.0\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eCr\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.006\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.017\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.02\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e5.0\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eNi\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.022\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.03\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.03\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e25.0\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eMn\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.442\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.002\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e10.0\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eBa\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.078\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.014\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.006\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e100.0\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eSe\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0.002\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.001\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.02\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e1.0\u003c/b\u003e\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"},{"header":"5 Conclusions","content":"\u003cp\u003eBased on the experimental data and subsequent analysis, the following conclusions were reached:\u003c/p\u003e \u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003eWith the increase in binder content (FA\u0026thinsp;+\u0026thinsp;GGBS) from 30% to 50%, the UCS values of the geopolymers significantly increased regardless of any SH concentration, SS/SH ratio, and curing period.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eOn increasing the molarity of SH from 6M to 10M in RFA-FA-GGBS geopolymer, the strength increases regardless of activator and curing conditions.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eWhile when we keep the SS/SH\u0026thinsp;=\u0026thinsp;1, the strength decreases, as some silica is necessary for geopolymerization, an excessive amount can have a negative impact. Too much silica can disrupt the Si/Al ratio, a critical factor for forming strong geopolymer bonds. An imbalance can lead to a less dense and weaker structure.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eThe UCS values of the RFA-FA-GGBS geopolymers cured at 60\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:^\\circ\\:\\)\u003c/span\u003e\u003c/span\u003eC show a slight increase compared to ambient cured samples.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eThe soaked CBR values of the geopolymerized treated recycled fine aggregates satisfy the minimum CBR values recommended for cement-stabilised subgrade or subbase material as per IRC: SP:89-2010.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eThe percentage mass loss in all the geopolymer samples is less than 5.74% after 12 alternate drying and wetting cycles, which confirms the durability of the samples.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eEnhanced durability: When we keep the alkaline activator NaOH, only the durability of the samples is higher compared with a 1 ratio, leading to the formation of a dense matrix.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eAll the RFA-FA-GGBS geopolymer specimens satisfy the limiting strength norms for cement stabilised subgrade (\u0026gt;\u0026thinsp;1.2 MPa) and subbase (\u0026gt;\u0026thinsp;1.7 MPa) as per IRC (2014).\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eXRD test showed the presence of CASH gel as the primary reaction product, which contributed towards the strength enhancement of the RFA-FA-GGBS geopolymer specimens.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eScanning electron microscopy (SEM) confirmed that higher concentrations of SH led to the enhanced dissolution of the raw materials, resulting in a significant aluminosilicate gel development, which subsequently contributed to higher strength.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eThe TCLP results demonstrate that the geopolymer samples' leachate had heavy metal levels which fall within the limits set by the USEPA.\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eFunding statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNo funding is received to carry out this research work.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDisclosure statement\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no potential conflict of interest.\u0026nbsp;\u003c/p\u003e\u003cp\u003eCompeting Interests\u0026nbsp;The authors declare no competing interests.\u003c/p\u003e\n\u003cp\u003eThe authors declare that no funds, grants, or other support were received during the preparation of this manuscript.\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eAlok Bijalwan: Conceptualization, Methodology, Investigation, Data Formal analysis, Writing \u0026ndash; Original draft preparation.Anil Kumar Mishra: Conceptualization, Supervision, Data Formal analysis, Writing- Reviewing and Editing.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAbdila SR, Abdullah MMAB, Ahmad R, Rahim SZA, Rychta M, Wnuk I, Nabiałek M, Muskalski K, Tahir MFM, Syafwandi, Isradi M, Gucwa M (2021) Evaluation on the Mechanical Properties of Ground Granulated Blast Slag (GGBS) and Fly Ash Stabilized Soil via Geopolymer Process. 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Constr Build Mater 330:127232\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYıldırım G, Kul A, \u0026Ouml;z\u0026ccedil;elikci E, Şahmaran M, Aldemir A, Figueira D, Ashour A (2021) Development of alkali-activated binders from recycled mixed masonry-originated waste. J Building Eng 33:101690\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZaharaki D, Galetakis M, Komnitsas K (2016) Valorization of construction and demolition (C\u0026amp;D) and industrial wastes through alkali activation. Constr Build Mater 121:686\u0026ndash;693\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhang L, Ahmari S, Zhang J (2011) Synthesis and characterization of fly ash modified mine tailings-based geopolymers. Constr Build Mater 25(9):3773\u0026ndash;3781\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhang S, Keulen A, Arbi K, Ye G (2017) Waste glass as partial mineral precursor in alkali-activated slag/fly ash system. Cem Concr Res 102:29\u0026ndash;40\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Construction and demolition waste, valorization, geopolymerisation, pavement, UCS","lastPublishedDoi":"10.21203/rs.3.rs-8284796/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8284796/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe present study examines the potential use of recycled fine aggregates (RFA) generated from construction and demolition waste as a principal component in geopolymer binder systems as a subgrade material, when paired with fly ash (FA) and ground granulated blast furnace slag (GGBS). Various samples were prepared to assess and identify the ideal binder composition that meets the necessary mechanical and durability specifications for subgrade applications. Geopolymer samples activated only with NaOH demonstrated a higher unconfined compressive strength (UCS) compared to those activated with a sodium silicate and a mixture of sodium hydroxide and sodium silicate in the ratio of 1. The UCS values of the RFA-FA-GGBS geopolymers cured at 60\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:^\\circ\\:\\)\u003c/span\u003e\u003c/span\u003eC show a slight increase compared to ambient cured samples. The result showed that all geopolymer samples met the minimum strength criteria for application as a subgrade, sub-base, and base layers. Similarly, the soaked CBR values of the geopolymer-treated recycled fine aggregates met the minimum criteria for cement-stabilised subgrade or subbase material as stipulated by the Indian standard. The toxicity characteristic leaching procedure (TCLP) test results demonstrated that the concentration of the heavy metals in the leachate generated from the samples was within the limits set by the US Environmental Protection Agency.\u003c/p\u003e","manuscriptTitle":"Sustainable Utilization of Construction and Demolition Waste as a Subgrade Material Using the Process of Geopolymerization","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-12-25 10:28:23","doi":"10.21203/rs.3.rs-8284796/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"8b1a7310-2748-4cae-931f-f251af746941","owner":[],"postedDate":"December 25th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-05-04T04:38:44+00:00","versionOfRecord":[],"versionCreatedAt":"2025-12-25 10:28:23","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8284796","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8284796","identity":"rs-8284796","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}