Effectiveness of Agro-Industrial Conjugate Fibers in Improving Mechanical Properties of Compressed Stabilized Earth Blocks

Effectiveness of Agro-Industrial Conjugate Fibers in Improving Mechanical Properties of Compressed Stabilized Earth Blocks | 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 Effectiveness of Agro-Industrial Conjugate Fibers in Improving Mechanical Properties of Compressed Stabilized Earth Blocks Fayeq Tazwar, Saidis Salekin Aninda, Mohammad Shariful Islam This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6655978/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 This study explores the creative use of a mixed reinforcement method that combines polyester and vetiver straw to overcome the constraint of limited strength and ductility of conventional Compressed Stabilized Earth Blocks (CSEB). Although the individual use of vetiver straw and polyester fiber in soil reinforcement has been previously recognized in different scholarly literatures, this research attempts to thoroughly investigate a novel aspect of study concerning the specific role in enhancing the ductility feature of CSEBs using a conjugate mix of vetiver and polyester as a reinforcing agent. The results depicted that, specimens with polyester fiber showed better results in unconfined compressive and split tensile strength tests. However, a notable finding was that specimens with vetiver-polyester mix exerted better strain behavior for the unconfined compressive strength test. Also, the diagonal strain was improved for specimens with vetiver-polyester mix, which showcases the improved ductile attribute of the vetiver-polyester conjugate specimens, aligning with this study’s research scope. Microstructural analysis unveiled a more homogenous and isotropic soil matrix with fewer voids for the specimens with vetiver-polyester mix. This indicated a stronger bond formation between the fiber-soil interfaces. The water absorption test result also showed that specimens with vetiver-polyester mix exhibited improving results for 28 days test, which suggests that the durability of the specimen with fiber mix gradually increases over time. Ultimately, this study highlights the potential of the vetiver-polyester mix as an effective reinforcing component in cement stabilized CSEBs, for producing environmentally viable and sustainable building materials. Civil Engineering Geology Environmental Engineering CSEB Vetiver Polyester Fiber Strength Ductility 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 global construction industry is a crucial interruption in achieving the three most important Sustainable Development Goals (SDGs) that are- affordable and clean energy, climate action, and sustainable cities and communities. Buildings have a significant role in CO 2 emission, accounting for 38% of global emissions [ 1 ], which is a major contributor to environmental instability, directly linked to the progression of global warming. Traditional construction materials require high energy consumption for production, which contributes to significant greenhouse gas emissions. Production of building materials and construction activities are already responsible for 10% of global energy-related greenhouse gas emissions [ 2 ]. This number of emissions will surely impact adversely on the environment; to be more specific, it will lead to the incremental impact of the greenhouse effect. Hence, a sustainable alternative to these traditional industrial materials is necessary for reducing environmental impact and promoting long-term development. For centuries, the use of earth as a building material began with plain mud and straw with low strength and durability until it grew into fired clay bricks with mass rapid production in the kiln [ 3 ]. Nowadays, raw-earth constructions are an area of growing interest as they possess lower thermal conductivity and therefore contribute to a greener environment by reducing greenhouse emissions [ 4 – 6 ]. Earth brick is a masonry unit made primarily from the soil, and its variants include adobe bricks, fired bricks, compressed earth brick (CEB), compressed stabilized earth brick (CSEB), stabilized earth brick (SEB), etc [ 7 ]. CSEBs are promising options to replace fired burnt bricks since they take less energy to produce, are less expensive, and have a reduced carbon impact [ 8 ]. Unlike typical clay blocks, which are weaker and more prone to deformation, CSEB's compressive strength is increased with the use of stabilizers like cement or lime, making them appropriate for load-bearing constructions [ 9 , 10 ]. CSEBs are made from locally available soil and require minimal energy for production, making them an affordable and sustainable alternative to conventional building materials such as burnt clay bricks and concrete. The production costs are typically 20–30% lower due to the use of local materials and simplified production techniques. CSEB also has patronizing environmental characteristics such as efficiency in energy use, recyclability, biodegradability, etc [ 9 ]. The CSEB blocks offer better thermal insulation, reducing the necessity for artificial heating and cooling, which can improve indoor air quality and reduce respiratory problems [ 11 ]. The blocks have lower carbon emissions as they require minimal energy for production and reduce the need for transportation of construction materials. It has been examined that Concrete blocks and burnt clay bricks both emit 143 and 200 kg of CO₂ per ton respectively, whereas CSEB only produces 22 kg of CO₂ per ton [ 12 ]. CSEB technology can help to mitigate the global housing shortage, particularly in low-income communities. Considering its low cost and minimal impact on the environment, CSEBs are quickly becoming a popular new method for constructing low-rise structures [ 13 ]. Though CSEB can contribute to multiple SDGs, its effectiveness in achieving specific goals may vary according to the local context, execution strategies, and complementary initiatives. In most cases, CSEB produces greater strength than other earthen construction techniques like adobe, cob, and rammed earth [ 14 ]. Other advantages include faster production and easier construction methods that generally require less skilled labor [ 15 ]. Furthermore, it has been established that, when CSEBs are properly manufactured and used, they offer good load-bearing capacity and durability [ 16 ]. Nevertheless, CSEBs have shortcomings such as low ductility, low compressive and tensile strength, and susceptibility to weather [ 17 ]. To lessen these difficulties, stabilization is essential and is usually accomplished by adding chemical stabilizers such as cement, lime, additional cementitious materials, and fiber reinforcing [ 18 ]. However, stabilizers cannot completely mitigate these issues. Hence, the need for reinforcement materials arises. Reinforcing materials to be used in CSEB depends mostly on their purpose of use. Supplementary cementitious materials (SCM) such as WCP [ 19 ], Rice husk [ 20 ], Fly ash [ 6 ], Blast furnace slag [ 21 ], Silica fume [ 22 ], Metakaolin [ 23 ], Geopolymer [ 24 ], etc are used when strengthening is required. However, these SCMs fail to provide ductility to the material. Extreme brittle behavior of the blocks leads to sudden failure during overloading. To overcome this issue fibers have been used as the most popular reinforcing member in CSEB production. Fiber reinforcement in most cases strengthens CEBs but also improves their ductility, toughness, tensile strength, and overall durability [ 25 ]. However, fiber incorporation should be in the optimal range to amplify the strength value. Beyond that optimal range, the strength value decreases with the increase in fiber percentage [ 26 ]. Shear stresses in the soil mobilize tensile resistance in the fibers, which in turn imparts greater strength to the soil [ 27 ]. Numerous research works have been carried out throughout the years for amplifying the mechanical and durability properties of CSEB with fiber incorporation. Specimens stabilized with various natural and synthetic fibers and cement provided an effervescent performance in enhancing the properties mentioned earlier. Paul et al. [ 28 ] incorporated areca fiber in the CSEB specimens and found an increment in compressive strength (107.04–436.38%), split tensile strength (208.66–358.08%), and flexural strength (16.49–82.47%), along with the improvement in durability properties too. Paul et al. [ 18 ] also studied that volumetric shrinkage and bulk density have decreased in the vetiver straw fiber-reinforced CEBs, according to their physical characteristics. Moreover, the research study illustrated that, in terms of the strength-ductility behavior, the ductility of the CEBs was significantly enhanced by the Vetiver straw fibers. However, the increase in strength was not too great, and it did not exhibit much variation over time. The results also depicted decreased water absorption and increased wear resistance. The compressive strength of the composite soil increases up to 1% of coir content and a further increase in coir quantity results in the reduction of the values. Prasanna & Kumar [ 29 ] and Anggraini et al. [ 30 ] perceived from their studies that the percentage of water absorption increases with an increase in the percentage of coir. The tensile strength of coir-reinforced soil (oven-dry samples) increases with an increase in the percentage of coir. In the unconfined compressive strength (UCS) test, Kumar et al. [ 31 ] examined extremely compressible clay using flat and crimped polyester fibers at 0%,0.5%,1.0%,1.5%, and 2.0%. The findings showed that the UCS value will rise with increasing fiber length and/or fiber content. Fiber crimping results in a small rise in UCS. These outcomes closely resemble those discovered by Tang et al. [ 32 ]. However, the axial strain of the samples due to fiber and cement incorporation was less than that of the control specimen at peak load. Hence, there was a reduction in the ductility of the specimen after implying fiber in the specimen. The variation in physical and mechanical properties of earth block specimens for incorporating synthetic fibers also have been assessed in numerous studies. Puppala and Musenda [ 33 ] confirmed that Polypropylene fiber reinforcement increased the UCS of the soil and reduced both volumetric shrinkage strains and swell pressures of the expansive clays. Consoli et al. [ 34 ] showed that adding Polyester (PET) fiber to fine sand for a particular percentage increases the material's peak and ultimate strength along with ductility. But employing natural and synthetic fiber incorporation may result in negative strength as well. Philip et. al. [ 35 ] implied hemp fiber in the earth block specimen and found positive effects on the strength and ductility. But with flax fiber, he found negative results regarding strength values. In both cases, he found improved ductility after incorporating fiber in the specimen. Houben, H. and Guillaud [ 36 ] found that, because of inadequate fiber-matrix bonding and incorrect fiber dispersion, the addition of several natural fiber types to CSEB did not considerably increase its compressive strength and, in some cases, slightly decrease it. Also, Richardson et al. [ 37 ] examined the effects of artificial fibers on concrete. The findings demonstrated that the clumping of synthetic fibers and the resulting voids in the matrix caused a loss in compressive strength when the volume of fibers was significant. Moreover, Prasad et al. [ 38 ] investigated the effects of coir and sisal natural fibers on the characteristics of mortar. The research discovered that although these fibers improved the flexural strength and toughness, they decreased the compressive strength because of voids and uneven fiber distribution. Safiuddin et al. [ 39 ] also studied the effects of carbon fiber on mortar. He found that an increased amount of carbon fiber percentage caused a drop in compressive strength, which was attributed to micro void formation and fiber-matrix instability. The result also portrayed that, the ductility of mortar increased as the incorporation of carbon fiber. While these previous studies have illustrated the benefits of fiber reinforcement in improving ductility, they have largely overlooked the potential of combining natural and synthetic fibers to improve both strength and ductility in CSEBs. This research addresses this gap by investigating the effects of vetiver-polyester conjugate fiber mix in the CSEB specimens. The above studies investigate the effectiveness of different fibers in CSEB independently but fail to address the effects if a mixture of various fibers were to be used in production. Few previous works have discussed such effects of conjugate fibers in concrete and mortars, but no such work is available for CSEB. For example, Madhavi et al. [ 40 ] observed that the compressive strength and flexural strength of concrete with a composite mix of jute and polypropylene are enhanced by about 22% and 1–2 MPa, respectively. Sen & Reddy [ 41 ] confirmed that Sisal fabric reinforced polymer composite system achieved better increment in its flexural strength and improvement in load-deflection behavior. Hence, increasing the ductility behavior. These studies highlight the need for investigating such work in CSEB production as well. To bridge this literature gap in this research endeavor, a mix of vetiver and polyester fiber was used in CSEB production. The research not only focuses on the strength and ductility behavior of reinforced CSEBs but also compares the findings with samples containing vetiver and polyester fibers independently. The reason for choosing vetiver fiber is because, among other natural fibers, vetiver grass is an intriguing option for using as a reinforcing filler in polymer composites [ 42 ]. Moreover, it exhibits some creditable attributes such as density and volumetric shrinkage are reduced in vetiver fiber reinforced CEBs which is mentioned above. Also, strength-ductility behavior is improved in vetiver straw fiber reinforced CEBs [ 18 ]. On the other hand, among synthetic fibers, polyester fiber is utilized because it enhances the sample’s peak and ultimate strength [ 43 ]. Also, polyester is readily available, and it has a low cost [ 44 ], so collecting polyester fiber is not a problem. Moreover, as polyester fiber is a synthetic fiber, it has a low water absorption capacity [ 45 ], which can be beneficial for enhancing the durability property. All the above characteristics have led to the selection of polyester fiber. For this research work, the primary focus was centered on assessing the ductility and strength properties of CSEB specimens reinforced with vetiver-polyester conjugate fiber. These were evaluated in terms of unconfined compressive and split tensile strength tests. The durability of the specimens was examined through a water absorption test. Also, microstructural analysis was performed on the specimens to get an outlook on the interaction between soil and reinforced fibers inside the specimens. 2. Materials and methods 2.1. Primary constituents of CSEB: soil and stabilizers The three main components of CSEBs are soil, stabilizer, and water. The features of a CSEB sample are determined by the kind and quantity of elements used in combination with compaction effort [ 19 ]. 2.1.1. Soil properties There are presently insufficient comprehensive criteria for selecting suitable soil to produce CSEB specimens. But there are guidelines on soil particle size for shaping CSEB specimens. The particle sizes must be 2 mm for sand and less than 5 mm for laterite soil to ensure the binding between all materials when mixed [ 14 ]. Comprehensive research has been carried out to uncover the influence of soil grading on earth block properties. According to these studies, the best results were obtained with soil fractions in the following ranges: sand and gravel 55–75%, silt 15–30%, and clay 10–30%, respectively [ 46 ]. It is advised to add sand, crushed sand, or crushed gravel to soils that are deficient in sand or have an excessive amount of silt or clay [ 47 ]. Sekhar and Nayak [ 21 ] obtained a strength that was sufficient for extremely fine-grained soil (88% clay/silt) after adding 6% cement and 20% coarse-grained, granulated blast furnace slag. Eslam et al. [ 48 ] discovered that 88% fine soil, stabilized with 40% coarse sand and 6% cement, was appropriate for compressed earth blocks. Hallal et al. [ 49 ] observed that soils stabilized with cement and containing 76% particles showed enough strength. Recently, Limami et al. [ 50 ] showed acceptable strength for clay-based bricks (less than 50 µm). The above-mentioned research made it clear that extremely fine-grained soils can also be stabilized with cement or by adding sand to create CSEBs. Since the main raw material for CSEB production is soil, the clay content in the soil greatly affects the strength and durability [ 3 ]. Aninda & Islam [ 19 ] suggested that the ideal proportions of soil should not be more than 75% sand and gravel and no more than 30% silt and clay. The soil used for this study was obtained from Dhaka and collected between two and three meters below ground level. Different laboratory tests were conducted according to the ASTM standard to characterize the soil, and its properties are listed below in Table 1 . According to Prakash and Sridharan [ 51 ], the type of the soil sample according to their mentioned modified version of the USCS classification system was SC-SMN. Also, as Bangladesh is situated within this dynamic landscape, where rivers deposit over 2.5 billion tons of silty material annually, as part of the vast Ganges-Brahmaputra-Meghna delta, while a sizeable amount of these sediments is removed for fishing and navigation, a significant portion is left unused [ 19 ]. Therefore, riverbed sand was used in this investigation to change the clay soil's gradation. Various soil to sand ratios were tested to identify the optimal mix. By thorough examination, it was discovered that a soil-sand mixture at a ratio of 1:3 could reach the highest dry density, which was consistent with the findings from earlier research. Table 1 Properties of soil Soil Property Value Specific gravity, GS 2.68 Gravel (%) 0 Sand (%) 79.3 Fines, Passing No. 200 sieve (%) 20.7 Mean particle size, \(\:{d}_{50}\) (mm) 0.026 Liquid Limit, LL of fines (%) 35 Plastic Limit, PL of fines (%) 18 Plasticity Index, PI (%) 17 Optimum moisture content (%) 14.8 Maximum dry density (kN/m 3 ) 17 2.1.2. Stabilizer properties Compressed earth blocks that are unstabilized generally display low tensile and compressive strength, decrease in ductility, and they are susceptible to unfavorable weather conditions. Different chemical stabilizers such as cement, lime, and other cementitious materials are added to the earth mixture to overcome these issues. These stabilizers are essential for improving the engineering qualities of CSEBs, which increases their durability and applicability [ 28 ]. Cement stabilized CSEBs show better strength and durability compared to lime stabilized CSEBs [ 52 ]. However, the addition of lime to cement stabilized CSEB and earthen mortar can improve compressive strength when the soil used has greater clay content [ 53 ]. In this study, ordinary portland cement (OPC) type I was utilized as cement stabilizer at two different percentages (4% and 8%) with respect to the total mass of the specimen. According to the ASTM C109 code [ 54 ], the compressive strength of the cement sample at 28 days was found to be 47.8 MPa. The cement particles had a fineness of 240 m2/kg and a specific gravity of 3.15. Table 2 summarizes the chemical composition of the cement used. Table 2 Chemical composition of OPC type 1 cement [ 20 ] Compound Percentage by Weight (%) C 3 S 57.2 C 2 S 17.6 C 3 A 9.2 C 4 AF 7.8 MgO 3.1 SO 3 2.8 Ignition Loss 1.3 Free CaO 1.0 2.2. Fiber properties Compressed earth Blocks are reinforced with vetiver, polyester, and vetiver–polyester conjugate fiber to enhance the specimens' strength and durability. Variation in the fiber length and content in the soil results in an improvement in the strength characteristics of the soil [ 55 ]. So, the length of fibers plays a significant part in the compressive strength improvement of soil. 2.2.1. Vetiver straw fiber Vetiver straw, derived from the vetiver grass (Chrysopogon zizanioides), holds a unique position in having versatile applications, including use in mulching, roof thatching, biofuel production, etc [ 56 ]. Vetiver, a hardy perennial grass, is distinguished by its robust, fibrous, and lengthy root system. [ 57 ]. Vetiver plant thrives in diverse climates and plays a pivotal role in infrastructure protection, stabilizing flood, and coastal embankments, and riverbanks, and aiding in soil and water remediation efforts [ 58 ]. Vetiver straw fiber has some important mechanical properties, which makes this fiber a sensible element for incorporating in CSEB. These properties are tensile strength and flexibility, erosion control performance, binding and stabilization, and handicrafts and weaving. These properties improve the strength, reduce shrinkage and cracking, and enhance insulation when vetiver fiber is used as a reinforcing agent. For this study, the vetiver straw fiber was directly collected from a local farm near Gabtoli, Dhaka. The fiber was cut into 25 mm and the aspect ratio of the fiber was 20, to ensure efficient distribution in the soil matrix. 2.2.2 Polyester fiber Bangladesh is standing in a paramount position of producing and exporting polyester fiber and textiles. That’s why, managing of polyester fiber is relatively straightforward and does not require significant effort. The chemical composition of polyester fiber, specifically PET, consists of repeating units of ethylene glycol and terephthalic acid [ 59 ]. Polyester fibers are known for their environmental challenges which denote their production, use, and disposal [ 60 ]. The adverse influence that wasted polyester fiber yield is continuously affecting the environment. Polyester fiber, when not effectively managed, contributes to microplastic pollution, occupying valuable landfill spaces and potentially releasing harmful chemicals during degradation [ 61 , 62 ]. Hence, it is essential to prioritize recycling and reusing the fiber, to impede the adverse influence. Polyester fiber can be assimilated in numerous ways such as, during manufacture, consumer waste, post-consumer waste, etc [ 63 ]. Polyester fibers possess several mechanical properties, including high tensile strength, good dimensional stability, and resistance to stretching and shrinking [ 64 ]. Moreover, Polyester fiber is a synthetic fiber that can be used in pavement construction to prevent micro cracking and enhance the flexural and compressive strength of the pavement along with preventing drying shrinkage as well [ 65 ]. Consoli et al. [ 66 ] demonstrated that incorporating PET fiber in fine sand improves both peak and ultimate strength which is dependent on fiber content. From this concept, incorporating this fiber in CSEB could be a supplementary way of reusing the fiber and mitigating its impact on the environment. Therefore, this very fiber was chosen in our research study for implying in the earth block specimens. Polyester fiber was collected from a local marketplace. The average length was obtained by using a vernier caliper as 30 mm and thickness obtained from scanning electron microscope (SEM) images was 70 µm respectively. The polyester fiber received from the market was soaked in cold water for one day to remove any impurities before being used in the CSEB specimens. 2.3. Methods of preparing samples A total of three fiber combinations involving 1.5% vetiver straw, 1.5% polyester fiber, and vetiver-polyester conjugate mix with 0.75% for each of the fiber were integrated into the CSEB specimen. The percentages of the fibers represent their portion relative to the total specimen weight. For each of the three fiber combinations, cement content of 4% and 8% of total specimen weight were utilized in the CSEB specimens. For preparing the cylindrical specimens, at first, the sand and clay samples were oven dried for 24 hours and then screened to trim any objectionable elements. In accordance with ASTM D698 [ 67 ], a standard proctor compaction test was performed, to measure the mixture's optimal moisture content (OMC). This approach called for the use of a conventional mold with a diameter of 4 inches (101.6 mm). Three layers of materials that passed through a No. 4 sieve were compacted, and each layer was tamped 25 times with a 5.50 lb-f (24.465 N) hammer held 12 inches (304.8 mm) above the ground. To determine the link between dry density and moisture content, this process was repeated for different molding water contents. The soil sample contained OMC of roughly 14.8% and a maximum dry density of 17 kN/m3, according to the compaction curves displayed in Fig. 1 by the standard proctor compaction test. Studies on the relationship between the fiber-bond strength and the grain size of specific soils indicate that finer sand particles have more fiber bond strength than coarse grained soils and silts have even better performance [ 68 ]. That’s why in our work, sand to clay proportion was 3:1; to keep larger sand proportion in the specimens and enhance the bond strength of the soil matrix. The clay sample was then crushed and ground to a finer powder with a hammer. Then adequate amount of sand and clay was mixed properly according to the ratio. After that, each of the three fiber combinations and required amount of cement were properly weighted and mixed homogeneously in dry condition for preparing the specimens. Then, the required amount of water attained by the OMC in the standard proctor compaction test was added to the soil-fiber mixture. After adding water to the sample, the mixture was mixed circumstantially unless a homogenous mix was prepared. Next, the inside surface of the unconfined compression mold was greased to prevent the specimens getting stuck in the mold during the time of taking out. The type of mold was cylindrical in shape (50 mm. diameter and 100 mm. height). Afterward, the soil mix was poured into the mold in three layers. During the preparation of the specimens, compaction was done by a metal rod weighing 279 g with a drop height of 25 cm, and the blow counts per layer were 25. The amount of compaction energy employed for sample preparation was calculated using the following Eq. (1) suggested by ASTM D 698–12. Compaction energy required = \(\:\frac{No.\:of\:layers\times\:No.\:of\:blows\:per\:layer\times\:weight\:of\:hammer\times\:drop\:height}{volume\:of\:the\:mold}\) (1) After the completion of compacting the top layer, the undulated surface was leveled off with a straightedge. Following that, the sample was taken out of the mold with proper caution. The samples were then kept in a plastic container to avoid moisture loss and were left in a moist room and water was sprinkled daily in reason of curing for 7 and 28 days at a mean temperature of 25 ± 1◦C with a relative humidity of at least 96%. The mixture percentage of different materials with the cement stabilizer considered in preparing the samples along with the codes of the samples are presented in Table 3 . Table 3 Mixture proportions for sample preparation Specimen ID with Fiber Cement (wt.%) Water Added (%) P 1.5% 4 14.8 V1.5% 4 14.8 V (0.75%) + P (0.75%) 4 14.8 P 1.5% 8 14.8 V1.5% 8 14.8 V (0.75%) + P (0.75%) 8 14.8 [N.B: For Sample ID, C stands for Cement content, P 1.5%/V 1.5%/V 0.75%+P 0.75% stands for Polyester/Vetiver/ Polyester-Vetiver combination with their percentages, 7D/28D Stands for 7 days/28 days test] 2.4. Unconfined compressive and split tensile strength test Strength characteristics of all specimens were assessed in terms of unconfined compressive strength (UCS) and split tensile strength (STS) test. The UCS test was performed according to ASTM D5102 [ 69 ]. After curing for 7 days and 28 days, the specimens were gathered for testing. The specimens remained for 24 hours in an oven set to 110 ± 1◦C. After that, both testing procedures were allowed to cool for four hours before they started. The bedding surface was thoroughly cleaned before the test started to guarantee uniform contact and loading. To make loading easier, there were two plates- one at the top and one at the bottom, were used. The specimens were carefully positioned with respect to the testing machine's center before testing to prevent any eccentric loading. Readings of axial force and deformation were taken for each specimen test, and the axial deformation rate of 1% per minute was maintained [ 53 ]. The STS test was performed according to ASTM C496-96 [ 70 ]. The cylindrical specimens were placed horizontally and loaded to failure with a deformation rate of 0.50 mm/min. A schematic diagram for the two tests is sequentially attached below in Fig. 2 2.5. Water absorption test The water absorption test was performed to give an insight into the durability of the specimens. The test was conducted according to ASTM C67 [ 71 ]. After curing for 7 and 28 days, the samples were oven dried for 24 hours to acquire their dry weight. The weight of the oven dried samples (W1) was traced. Then the samples were totally immersed in water, keeping the top of the sample at least 2 mm below the water surface. After that, the entire system was left like this for 24 hours and the final saturated weight of the sample (W2) was measured. The water absorption of the samples was then, calculated from Eq. (2): Wa (%) = \(\:\frac{(\text{W}2\:-\:\text{W}1)}{W1}\times\:100\%\) (2) Water absorption was quantified with respect to the samples’ oven dry weight. The test's objective was to evaluate the moisture resistance after spending a full day in the water, which will provide a notable insight into the suitability for construction in varying environmental conditions. 2.6. Microstructural analysis The scanning electron microscope (SEM) analysis was performed for microstructural examination and the test was carried out on three types of samples with 8% cement content at 28 days, containing 1.5% polyester, 1.5% vetiver straw fiber and vetiver-polyester conjugate mix of 0.75% of both fibers. The equipment to conduct SEM analysis was Zeiss Sigma 300 VP from Oberkochen, Germany. After being dried for 24 h in the oven, one prismatic piece was detached from each type of sample and positioned onto a stud. Subsequently, these samples were introduced into the chamber of the SEM machine. The working lengths were maintained within the range of 2 and 4.6 mm, with the acceleration voltage set at 2 kV. 3. Results and discussions 3.1. Strength and ductility behavior 3.1.1 Unconfined compressive strength The unconfined compressive strength test results of CSEB specimens stabilized with three fiber combinations and cement after 7 and 28 days of curing are sequentially illustrated in Fig. 3 and Fig. 4 . The figures show that specimens reinforced with polyester fiber showed the highest strength value among all the fiber combinations for both 7 and 28 days. But when the specimens containing polyester, vetiver, and vetiver-polyester mix, were compared with the control specimens for 7 days test results with 4% cement content, it was observed that specimens with polyester fiber achieved the highest compressive strength value as shown in Fig. 3 (a). However, there was a significant reduction in the strength value compared to the control specimens for the remaining results. The reason behind this outcome can be attributed to the knotting and clumping of the reinforced fibers in the soil matrix. That’s why there persisted less cohesion between the fiber and the soil and hence, the soil-fiber composite weakened. Which led to the reduction of strength value in the specimens. Guo et al. [ 72 ] also stated identical reasoning in response to compressive strength reduction for Basalt fiber reinforced concrete. Moreover, the fibers were regarded as a filler in the mortar matrix when subjected to compressive loading. However, the effect of knotting and clumping of the fibers created discontinuities and voids in the matrix and lowered the strength of the specimens as a result. Ismail & Yaacob [ 73 ] also pointed out similar reasoning for the effect in strength due to the presence of fiber. Furthermore, the presence of fiber reduced the overall cement percentage of the soil matrix. So, there existed less coating for each fiber and consequently, the bonding between the fiber and soil matrix became weak hence, leading to a reduction in compressive strength, which resembles the explanation of Thanushan et al. [ 74 ]. Inspection of the deformation characteristics was performed through stress-strain response under axial loading. A considerable improvement in strain value was observed for all the specimens with fiber reinforcement, in comparison to the control specimens. This is because, apart from the knotting and clumping of fibers inside of the specimens, fibers and the soil matrix worked together to resist the propagation of cracks in the specimen by forming bridges across cracks, which improved the strain of the specimens consequently. Danso et al. [ 75 ] also theorized a similar conception regarding this phenomenon. Moreover, it is seen from Fig. 3 and Fig. 4 that the vetiver-polyester mix performed significantly better than the control, vetiver, and polyester incorporated specimens individually in terms of greater strain for each case. Because the presence of both the fibers adhered to the soil matrix more firmly and the voids in the soil were reduced greatly due to polyester fiber, which influenced the bridging effect intensively and the strain behavior of the specimen increased. Therefore, from a ductility point of view, specimens with vetiver-polyester mix sustained more efficiently than specimens with vetiver and polyester fiber and enhanced the ability to deform under compressive stress, preventing sudden failure. The failure of fiber reinforced specimens appeared with multiple fine cracks, and the failure was gradual with the fiber combination to the cracks being formed. Figure 5 represents the failure pattern of the specimens with 3 fiber combinations which shows that specimens with polyester fiber for both cement percentages wielded bulging or lateral expansion, which corresponds to the ductility behavior of the specimens. Again, the type of cracks that appeared in the specimens with vetiver fiber corresponds to shear failure. Lastly, for specimens with polyester-vetiver mix, specimens with 4% cement content showed bulging failure and the one with 8% cement content demonstrated shear failure. The types of failure for all the specimens above demonstrated improved ductile behavior. 3.1.2 Split tensile strength The split tensile strength test results of the specimens with three fiber combinations are illustrated in Fig. 6 and Fig. 7 . The test results for the specimens are somewhat similar to the unconfined compressive strength test. Except for the fact that the ultimate tensile strength value of the specimens with the vetiver-polyester mix is in between the stress values of the specimens with the other two fiber combinations, for both 7 and 28 days tests. The maximum tensile strength was obtained for specimens containing polyester fiber because the interfacial bonding between the soil matrix and polyester fiber was stronger than vetiver fiber. A single vetiver fiber occupies more space than polyester fiber in a soil matrix. This led to a weaker bond between the soil matrix and vetiver fiber because of the presence of larger voids, resulting in less tensile strength generation. Therefore, during the implication of diagonal stress, when the fibers tended to reduce the cracks through adhesion with soil particles and resisting the splitting up of the specimen diagonally, polyester fiber having greater surface bonding with the soil matrix, did the work more profoundly than other two fiber combination types, which was seen from the SEM images during the microstructural analysis later. Here, the cracks formed vertically from top to bottom before failure for all the specimens which are represented in Fig. 8 . For the compressive strength test, specimens with vetiver-polyester mix exhibited maximum longitudinal strain value in all cases. However, for the split tensile strength test, specimens with polyester fiber were higher in terms of diagonal stress and strain value, which indicated an improvement in the ductility behavior of the specimen. This can be theorized as more polyester fiber was available in a particular soil matrix than vetiver straw fiber, the bonding between polyester fiber and soil matrix induced an extensive bridging effect during crack formation and hence, the tensile resistance was also greater than all the three specimen types. The SEM images also unveiled that polyester fiber having a slender structure, adhered to the soil particles more firmly than the remaining two fiber types and reduced the voids in the soil. The frictional resistance between polyester fiber and the hardened soil matrix accelerated due to the large number of C-S-H gels during the curing phase, reducing the formation of cracks when the load was subjected to the specimen. This phenomenon resulted in greater diagonal strain value and increased ductility for specimens with polyester fiber. So, the failure happened more gradually and resembled a ductile material. This finding is in good agreement with the findings of Danso et al. [ 76 ], Bouhichaet al. [ 77 ], and Cai et al. [ 78 ]. Also, specimens with vetiver-polyester mix showed better results in tensile strength and diagonal strain value than specimens with vetiver fiber. The presence of both fibers in the specimens with vetiver-polyester mix aided in the adhesion with the soil matrix more effectively, which resulted in better ductility for the specimens. The failure pattern from Fig. 8 depicts that for all the specimens with three fiber combinations and both the cement contents, there persists a continuous diagonal crack in the specimens which represents improved ductile behavior for the specimens with fiber reinforcement. 3.2. Durability property 3.2.1. Water absorption Table 4 illustrates the water absorption test results of all the specimens containing each of the three fiber combinations with both cement percentages. Figure 9 demonstrates the graphical illustration of the results of the water absorption test of the specimens. The graphs from Fig. 9 (a) and Fig. 9 (b) show that the increment of cement content of the specimens by 8% resulted in a reduction in water absorption than specimens with 4% cement content. This is because cement content forms C-S-H gel with soil particles, which leads to the formation of C-H plates, and these plates reduce the pores inside the cement-soil mix. Therefore, more amount of cement was present in specimens with 8% cement content, which reduced the pores in the soil matrix largely than the specimens with 4% cement content. So, the water absorption was also less for the specimens containing 8% cement content. Moreover, vetiver fiber is a natural fiber and has a higher water absorption capacity than polyester fiber. Hence, it absorbed some of the water when water permeated into the specimen. The value of water absorption results of specimens with vetiver-polyester mix prevails in between the results of specimens with polyester and vetiver fiber. This can be hypothesized as both fibers were present in the specimen, the vetiver fiber took part in soaking up the water as it is a natural fiber [ 79 ]. On the contrary, polyester fiber, being a synthetic fiber, did not participate in absorbing water as much. So, the water absorption persisted in the mid-range for this vetiver-polyester fiber combination. This leads to the outcome of better durability of the vetiver-polyester specimens than with the specimens of vetiver fiber. Table 4 Water absorption test results with different cement content Specimen ID Water Absorption (4% cement) Water Absorption (8% cement) P1.5% 7D 5.51 4.28 P1.5% 28D 4.81 2.96 V1.5% 7D 6.98 5.43 V1.5% 28D 5.63 4.07 V (0.75%) + P (0.75%) 7D 6.28 4.96 V (0.75%) + P (0.75%) 28D 5.47 3.27 3.3 Microstructural analysis Figure 10 , Fig. 11 , and Fig. 12 represent the SEM images of the three types of specimens with 8% cement content which was conducted at 28 days. Because, at 28 days, the UCS and STS tests exhibited maximum stress-strain values for all types of specimens. The images demonstrate that the distributed fibers build a three-dimensional lattice within the soil, which aids in interlocking the soil grains. This interlocking system helps in forming a cohesive matrix. The interlocking not only binds the soil particles but also evenly distributes stress throughout the matrix. This helps in resisting localized failures, which is mostly important for the unconfined compressive strength test. When these reinforced specimens were subjected to lateral stress, the fibers acted as bridges across the developing microcracks which efficiently restrained tension-induced fracture development and restricted soil-fiber matrix displacement. This bridging effect delayed the propagation of fractures, thus reducing the displacement between the fiber and soil matrix. Moreover, the bridging effect is one of the main reasons the fiber reinforced specimens exhibited better ductility than the control specimens because the fiber in the soil matrix helps the materials absorb more energy before falling. The images also depict that for all types of specimens, C-H plates are formed in the soil matrix, which is a clear indication of the composition of C-S-H gels in the soil. C-S-H is a primary product in cementitious systems, and its presence in the soil matrix suggests the improved bonding between the fiber and soil. This improved bonding directly contributes to both strength and ductility, as the matrix becomes more resistant to debonding under stress. For this reason, CSEB specimens with fiber reinforcement showed better results in ductility than the control specimens in the unconfined compressive strength test which is shown in Fig. 3 and Fig. 4 . The SEM images of V1.5%28D specimens in Fig. 10 (a) and Fig. 10 (b) show that several clay particles stick to the surface of the vetiver straw fiber. This adhesion is important for the enhancement of bonding and frictional force between the soil matrix and the fiber. Also, there persist voids in between the vetiver fiber and the soil matrix interface which reduces the ductility behavior of the specimen when they are subjected to lateral and diagonal stresses. Figure 11 shows the SEM images of the P1.5%28D specimen. When the images of Fig. 10 and Fig. 11 are compared, it is seen that as much space one vetiver straw fiber takes up, multiple polyester fiber occupies the same space. Figure 11 (b) also shows that polyester fibers are attached to the soil matrix strongly and there is no void present between the fiber-soil matrix interfaces. This has driven a greater bond formation between the polyester fiber and soil matrix and eventually increased the ductility behavior greater than specimens with vetiver straw fiber. Lastly, Fig. 12 represents the SEM images of V (0.75%) + P (0.75%) 28D specimen. As both the fibers are present in this type, polyester fiber along with vetiver fiber attaches with the soil matrix firmly and ensures more rigid bonding and frictional force with the soil matrix than the other two types of specimens which are visible in Fig. 12 (b). Also, the presence of polyester fiber assisted in filling up the pores which has made the specimen more rigid. So, when the specimen is subjected to vertical stress, due to the enhancement of the bridging effect, it induces maximum ductility among all three types. 4. Conclusions The research's scope was to examine the strength and durability properties of the specimens containing vetiver-polyester mix and the findings were compared with the results of specimens containing other two fiber combinations. In this study, fiber and cement was utilized as stabilizers in the earth block specimens. This study can be concluded with the following outcomes: Considering the strength properties, it was observed that for the UCS test, fiber incorporation did not affect the unconfined compressive strength greatly, and in some cases, it had an adverse impact, showing a decrease in compressive strength when compared to the strength of control specimens. The highest strength value was obtained by the specimens with 1.5% polyester fiber and 8% cement, for both 7 and 28 days tests. On the contrary, the lowest strength value was attained by the specimens with vetiver-polyester mix and 8% cement for 7 days test and specimens with 1.5% vetiver fiber and 4% cement for 28 days test. As the fiber is not a pozzolanic material, the enhancement of the strength properties is dependent on the distribution of fibers and their interaction with the soil particle. Knotting and clumping of the fibers in the soil matrix resulted in the reduction of unconfined compressive strength for the specimens with fiber reinforcement than the control specimens. But the specimens with vetiver-polyester mix showed better strain behavior for both 7 and 28 days test. Because the presence of both the fibers influenced strong adhesion with the soil matrix and the voids were reduced greatly due to polyester fiber. This helped in forming the bridging effect more soundly and led to better ductility than other specimen types. For the STS test, specimens with 1.5% polyester fiber and 8% cement content exhibited the highest strength value for 7 and 28 days tests. On the other hand, specimens with 1.5% vetiver and 4% cement exerted the lowest tensile strength value for both 7 and 28 days tests. Fiber incorporation developed the formation of cracks, resulting in improved ductility in the specimen. Polyester fiber having a thin formation, occupied a particular space in a greater number in the soil matrix than vetiver fiber and adhered with the soil more firmly and hence, developed the crack generation during the implication of the diagonal stress. Also, specimens with polyester fiber showed better ductility among all three types in the split tensile strength test because multiple polyester fibers took up the same amount of area as one vetiver straw fiber did. This led to the strong adhesion of polyester fiber with the soil and the reduction of pores in the soil matrix, developing an improved bridging action. Eventually, the sample with polyester fiber represented better ductility than the other two fiber combinations. Specimens with vetiver-polyester mix also showed better strain behavior than specimens with vetiver fiber and the peak stress value for this specimen resided in between the values of specimens with the other two fiber combinations. Increased water absorption in CSEBs causes durability problems and decreases strength. For different water absorption values between the specimens with different fiber combinations in this study, specimens with polyester fiber at 8% cement content showed better outcomes because of better bonding with the soil matrix and reducing the pores in it. The presence of vetiver fiber in the soil matrix created larger voids, which enhanced the water intrusion through the voids due to capillary action and resulted in a larger water absorption value. Specimens with vetiver-polyester mix had shown water absorption value in between the specimens with the other two fiber combinations because even if polyester fibers were present, voids had still appeared in the soil due to the presence of vetiver fiber. For this, the water absorption value for this specimen prevailed between the specimens with the other two fiber types. The SEM images revealed that vetiver-polyester conjugate fiber in CESBs resulted in a more uniform and isotropic soil matrix with fewer voids. These fibers, coated with attaching clay particles, generated a stronger composite material by improving the bonding ability and friction between the soil matrix and the fibers, which resulted in better ductility for specimens with vetiver-polyester mix among the specimens with the other two fiber combinations for UCS test. Cement formed C-S-H gel with soil when they were mixed with soil. This gel reduced the pores in the specimen and helped in making the bond between the fiber and soil matrix, which increased the ductility of the specimen. In recent years, interest in earthen building has grown because of its economic, social, and environmental sustainability. According to the outcomes of this study, strong and durable CSEBs can be comprised of an optimum percentage of vetiver-polyester mixture and cement as stabilizing materials. The CSEB blocks with the fiber mix can be more suitable for load bearing walls because of the higher compressive strength of the specimens with vetiver-polyester mix. However, the split tensile strength test result suggests that polyester fiber contributes more to ductility and strain resistance. However, the fiber mix can enable a balanced improvement in strength and flexibility by reducing brittle failure and improving crack resistance. This makes the CSEB specimens with fiber mix an ideal solution for earthquake prone regions. Also, if the vetiver fiber is properly treated, it could aid in preventing erosion of the CSEB matrix. Moreover, the use of vetiver-polyester combination could lower the material cost compared to purely synthetic fiber. However, further strength enhancements are necessary to achieve all specifications, involving the use of specific cementitious materials. Long-term durability studies are needed to ascertain the real-world application. Other limitations may include the lack of standardized construction guidelines, susceptibility to insect attacks, unidentified thermal properties, etc. Resolving such limitations is essential for increasing the viability and acceptance of vetiver-polyester conjugate fiber-reinforced CSEBs in buildings. These need continued research to create an ecologically friendly, cost-effective construction material with more improved strength and ductility. Declarations Funding The authors did not receive support from any organization for the submitted work. CRediT authorship contribution statement Fayeq Tazwar: Conceptualization, Methodology, Formal analysis, Investigation, Data curation, Writing - original draft preparation, Writing - review and editing. Saidis Salekin Aninda: Conceptualization, Methodology, Resources, Writing - review and editing, Supervision, Resources. Mohammad Shariful Islam: Conceptualization, Methodology, Resources, Writing - review and editing, Resources. Declaration of competing interest All authors certify that they have no affiliations with or involvement in any organization or entity with any financial interest or non-financial interest in the subject matter or materials discussed in this manuscript. Data availability Data will be made available on request. Acknowledgements The authors would like to express their heartfelt gratitude to Bangladesh University of Engineering and Technology (BUET) for supporting them with the research work. Also, the authors would like to express their gratitude to Shantanu Paul for his incessant guiding throughout the research endeavor. The authors acknowledge the contribution of Department of Biomedical Engineering (BME) for obtaining the SEM images. The authors would also like to thank Abdullah Muhammad Asif and Sazid Alam Surid for their conducive approach throughout the study. References Tirelli D, Besana D (2023) Moving toward Net Zero Carbon Buildings to Face Global Warming: A Narrative Review. In Buildings (Vol. 13, Issue 3). https://doi.org/10.3390/buildings13030684 Guest Article: Building Materials – A Hidden Heavyweight for Climate Action | SDG Knowledge Hub | IISD. (n.d.). Retrieved April 4 (2024) from https://sdg.iisd.org/commentary/guest-articles/building-materials-a-hidden-heavyweight-for-climate-action/ Malkanthi SN, Wickramasinghe WGS, Perera AADAJ (2021) Use of construction waste to modify soil grading for compressed stabilized earth blocks (CSEB) production. 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Pertanika J Sci Technol, 19 (1) Thanushan K, Yogananth Y, Sangeeth P, Coonghe JG, Sathiparan N (2021) Strength and Durability Characteristics of Coconut Fibre Reinforced Earth Cement Blocks. J Nat Fibers 18(6). https://doi.org/10.1080/15440478.2019.1652220 Danso H, Martinson DB, Ali M, Williams JB (2015) Physical, mechanical and durability properties of soil building blocks reinforced with natural fibres. Constr Build Mater 101. https://doi.org/10.1016/j.conbuildmat.2015.10.069 Danso H, Martinson DB, Ali M, Williams J (2015) Effect of fibre aspect ratio on mechanical properties of soil building blocks. Constr Build Mater 83. https://doi.org/10.1016/j.conbuildmat.2015.03.039 Bouhicha M, Aouissi F, Kenai S (2005) Performance of composite soil reinforced with barley straw. Cem Concr Compos 27(5). https://doi.org/10.1016/j.cemconcomp.2004.09.013 Cai Y, Shi B, Ng CWW, Tang C (2006) sheng. Effect of polypropylene fibre and lime admixture on engineering properties of clayey soil. Engineering Geology, 87(3–4). https://doi.org/10.1016/j.enggeo.2006.07.007 Begum HA, Tanni TR, Shahid MA (2021) Analysis of Water Absorption of Different Natural Fibers. J Text Sci Technol 07(04). https://doi.org/10.4236/jtst.2021.74013 Additional Declarations The authors declare no competing interests. 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. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6655978","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":456004845,"identity":"5ce1f7b1-c888-4f5e-99a0-81bc808baac6","order_by":0,"name":"Fayeq Tazwar","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA7ElEQVRIiWNgGAWjYBACNvbGBoOEHzVy/A0MbHBBBh48Wvh4Dh8o+NhzzFjiAFiLAWEtchJpCR9nsDEnbnAgVgsbzxnDzTw8bOkb2BvYHvNU/GHgbz/A9uANXr/0GBvzWMjkbuA5wG7Mc8aAQeJMArvhHPy2mBkDbcndIJHAJs3bBnTYDQY2abwOk8gx/83DxpxuIP8AqOWfAYM8YS1pCYZA7ycYRABV8jYYMBgQ1AIMZANgIBvOOJPYbjjnmDGPIZiBR4t8OyQq5fnbDx978KZGTk7uOIiBRwsSYGwAkTwwxigYBaNgFIwCCgAA6QJFjF4f0dAAAAAASUVORK5CYII=","orcid":"https://orcid.org/0009-0009-0683-7358","institution":"Bangladesh University of Engineering and Technology","correspondingAuthor":true,"prefix":"","firstName":"Fayeq","middleName":"","lastName":"Tazwar","suffix":""},{"id":456005950,"identity":"3dc59d6c-83df-4e2d-a348-a5f2ee9b9719","order_by":1,"name":"Saidis Salekin Aninda","email":"","orcid":"https://orcid.org/0000-0002-9208-0524","institution":"Bangladesh University of Engineering and Technology","correspondingAuthor":false,"prefix":"","firstName":"Saidis","middleName":"Salekin","lastName":"Aninda","suffix":""},{"id":456005951,"identity":"5c3fea6b-07cc-422b-8150-9bebe87bdcf2","order_by":2,"name":"Mohammad Shariful Islam","email":"","orcid":"https://orcid.org/0000-0001-9620-2413","institution":"Bangladesh University of Engineering and Technology","correspondingAuthor":false,"prefix":"","firstName":"Mohammad","middleName":"Shariful","lastName":"Islam","suffix":""}],"badges":[],"createdAt":"2025-05-13 13:36:29","currentVersionCode":1,"declarations":{"humanSubjects":false,"vertebrateSubjects":true,"conflictsOfInterestStatement":false,"humanSubjectEthicalGuidelines":false,"humanSubjectConsent":false,"humanSubjectClinicalTrial":false,"humanSubjectCaseReport":false,"vertebrateSubjectEthicalGuidelines":true},"doi":"10.21203/rs.3.rs-6655978/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6655978/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":82857068,"identity":"586c8c4f-2475-4ed0-b730-443932a4cb76","added_by":"auto","created_at":"2025-05-16 05:34:08","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":22299,"visible":true,"origin":"","legend":"\u003cp\u003eDry density vs optimum moisture content graph.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-6655978/v1/8e84213d2dc504f0793910ff.png"},{"id":82857069,"identity":"1a5b77f0-7b5c-41d1-94b3-09f8b96cc499","added_by":"auto","created_at":"2025-05-16 05:34:08","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":41393,"visible":true,"origin":"","legend":"\u003cp\u003eTest setup for (a) unconfined compressive strength test\u003cstrong\u003e \u003c/strong\u003e(b)\u003cstrong\u003e \u003c/strong\u003esplit tensile strength test.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-6655978/v1/c910dbf0a52e3a0df3f0aee1.png"},{"id":82857070,"identity":"65f2e4d1-5187-4cdc-bbdc-9701552571d8","added_by":"auto","created_at":"2025-05-16 05:34:08","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":41013,"visible":true,"origin":"","legend":"\u003cp\u003e7 days unconfined compressive strength test result of specimens containing (a) 4% cement and (b) 8% cement.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-6655978/v1/37c2a1a8cb8835def01b96f9.png"},{"id":82857072,"identity":"74258f15-c223-4e60-9cb9-2c6ef21d3f45","added_by":"auto","created_at":"2025-05-16 05:34:08","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":46632,"visible":true,"origin":"","legend":"\u003cp\u003e28 days unconfined compressive strength test result of specimens containing (a) 4% cement and (b) 8% cement.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-6655978/v1/18406b222f5c17bd443aa986.png"},{"id":82857079,"identity":"44ca0f8a-2c6e-4fe1-8a1e-8a3f86f4eb03","added_by":"auto","created_at":"2025-05-16 05:34:08","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":1085114,"visible":true,"origin":"","legend":"\u003cp\u003eFailure pattern due to unconfined compressive test: (a) P1.5% specimen with 4% cement, (b) P1.5% specimen with 8% cement, (c) V1.5% specimen with 4% cement, (d) V1.5% specimen with 8% cement, (e) V 0.75%+P 0.75% specimen with 4% cement, (f) V 0.75%+P 0.75% specimen with 8% cement.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-6655978/v1/e78df3fcb6a11a4a91e25e23.png"},{"id":82857073,"identity":"9bd7c343-cbf7-4458-9474-8e597f2fe579","added_by":"auto","created_at":"2025-05-16 05:34:08","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":44456,"visible":true,"origin":"","legend":"\u003cp\u003e7 days split tensile strength test result of specimens containing (a) 4% cement and (b) 8% cement.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-6655978/v1/7219dce8f8e5a0903398c492.png"},{"id":82857521,"identity":"0aabf5a8-dcb8-467a-b16b-9b05cf89848e","added_by":"auto","created_at":"2025-05-16 05:42:08","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":45977,"visible":true,"origin":"","legend":"\u003cp\u003e28 days split tensile strength test result of specimens containing (a) 4% cement and (b) 8% cement.\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-6655978/v1/3a7ce8412a0e97810e614318.png"},{"id":82857077,"identity":"9623bb14-dc53-45d1-aae1-6154699655f4","added_by":"auto","created_at":"2025-05-16 05:34:08","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":2198247,"visible":true,"origin":"","legend":"\u003cp\u003eFailure pattern due to split tensile strength test for (a) P1.5% specimen with 4% cement, (b) P1.5% specimen with 8% cement, (c) V1.5% specimen with 4% cement, (d) V1.5% specimen with 8% cement, (e) V 0.75% + P 0.75% specimen with 4% cement, (f) V 0.75% + P 0.75% specimen with 8% cement.\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-6655978/v1/a241ff84272717d856b4d361.png"},{"id":82858472,"identity":"57678d55-dc40-448a-98f6-d24b80e72983","added_by":"auto","created_at":"2025-05-16 06:06:08","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":42882,"visible":true,"origin":"","legend":"\u003cp\u003eWater absorption test result with different cement percentages for (a) 7 days and (b) 28 days.\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-6655978/v1/8abbc3eecb3add30c9cfe253.png"},{"id":82857081,"identity":"feacd5c3-e274-4ea0-af8b-ca5963ede4fa","added_by":"auto","created_at":"2025-05-16 05:34:08","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":921116,"visible":true,"origin":"","legend":"\u003cp\u003eSEM images of V1.5%28D specimens with 8% cement content.\u003c/p\u003e","description":"","filename":"10.png","url":"https://assets-eu.researchsquare.com/files/rs-6655978/v1/f3614e9db746f0faa7d9b25b.png"},{"id":82857074,"identity":"9eb5eacb-ad36-433a-b06d-cc25a8bb6335","added_by":"auto","created_at":"2025-05-16 05:34:08","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":962204,"visible":true,"origin":"","legend":"\u003cp\u003eSEM images of P1.5%28D specimens with 8% cement content.\u003c/p\u003e","description":"","filename":"11.png","url":"https://assets-eu.researchsquare.com/files/rs-6655978/v1/6acce9da240a96d5e86eb042.png"},{"id":82857525,"identity":"e2f96365-cfc5-4cc5-8e2a-c1b3643b331c","added_by":"auto","created_at":"2025-05-16 05:42:08","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":801779,"visible":true,"origin":"","legend":"\u003cp\u003eSEM Images of V (0.75%) + P (0.75%) 28D specimens with 8% cement content.\u003c/p\u003e","description":"","filename":"12.png","url":"https://assets-eu.researchsquare.com/files/rs-6655978/v1/46df79500accbfe101eaa9ce.png"},{"id":82858475,"identity":"b901c91b-8183-42c8-803c-1fab9d8aec39","added_by":"auto","created_at":"2025-05-16 06:06:17","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":6845455,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6655978/v1/ec15334d-38bc-4592-9f24-cc7455274008.pdf"}],"financialInterests":"The authors declare no competing interests.","formattedTitle":"\u003cp\u003e\u003cstrong\u003eEffectiveness of Agro-Industrial Conjugate Fibers in Improving Mechanical Properties of Compressed Stabilized Earth Blocks\u003c/strong\u003e\u003c/p\u003e","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eThe global construction industry is a crucial interruption in achieving the three most important Sustainable Development Goals (SDGs) that are- affordable and clean energy, climate action, and sustainable cities and communities. Buildings have a significant role in CO\u003csub\u003e2\u003c/sub\u003e emission, accounting for 38% of global emissions [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e], which is a major contributor to environmental instability, directly linked to the progression of global warming. Traditional construction materials require high energy consumption for production, which contributes to significant greenhouse gas emissions. Production of building materials and construction activities are already responsible for 10% of global energy-related greenhouse gas emissions [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. This number of emissions will surely impact adversely on the environment; to be more specific, it will lead to the incremental impact of the greenhouse effect.\u003c/p\u003e \u003cp\u003eHence, a sustainable alternative to these traditional industrial materials is necessary for reducing environmental impact and promoting long-term development. For centuries, the use of earth as a building material began with plain mud and straw with low strength and durability until it grew into fired clay bricks with mass rapid production in the kiln [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Nowadays, raw-earth constructions are an area of growing interest as they possess lower thermal conductivity and therefore contribute to a greener environment by reducing greenhouse emissions [\u003cspan additionalcitationids=\"CR5\" citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Earth brick is a masonry unit made primarily from the soil, and its variants include adobe bricks, fired bricks, compressed earth brick (CEB), compressed stabilized earth brick (CSEB), stabilized earth brick (SEB), etc [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. CSEBs are promising options to replace fired burnt bricks since they take less energy to produce, are less expensive, and have a reduced carbon impact [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Unlike typical clay blocks, which are weaker and more prone to deformation, CSEB's compressive strength is increased with the use of stabilizers like cement or lime, making them appropriate for load-bearing constructions [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. CSEBs are made from locally available soil and require minimal energy for production, making them an affordable and sustainable alternative to conventional building materials such as burnt clay bricks and concrete. The production costs are typically 20\u0026ndash;30% lower due to the use of local materials and simplified production techniques. CSEB also has patronizing environmental characteristics such as efficiency in energy use, recyclability, biodegradability, etc [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. The CSEB blocks offer better thermal insulation, reducing the necessity for artificial heating and cooling, which can improve indoor air quality and reduce respiratory problems [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. The blocks have lower carbon emissions as they require minimal energy for production and reduce the need for transportation of construction materials. It has been examined that Concrete blocks and burnt clay bricks both emit 143 and 200 kg of CO₂ per ton respectively, whereas CSEB only produces 22 kg of CO₂ per ton [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. CSEB technology can help to mitigate the global housing shortage, particularly in low-income communities. Considering its low cost and minimal impact on the environment, CSEBs are quickly becoming a popular new method for constructing low-rise structures [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. Though CSEB can contribute to multiple SDGs, its effectiveness in achieving specific goals may vary according to the local context, execution strategies, and complementary initiatives. In most cases, CSEB produces greater strength than other earthen construction techniques like adobe, cob, and rammed earth [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. Other advantages include faster production and easier construction methods that generally require less skilled labor [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. Furthermore, it has been established that, when CSEBs are properly manufactured and used, they offer good load-bearing capacity and durability [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eNevertheless, CSEBs have shortcomings such as low ductility, low compressive and tensile strength, and susceptibility to weather [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. To lessen these difficulties, stabilization is essential and is usually accomplished by adding chemical stabilizers such as cement, lime, additional cementitious materials, and fiber reinforcing [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. However, stabilizers cannot completely mitigate these issues. Hence, the need for reinforcement materials arises. Reinforcing materials to be used in CSEB depends mostly on their purpose of use. Supplementary cementitious materials (SCM) such as WCP [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e], Rice husk [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e], Fly ash [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e], Blast furnace slag [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e], Silica fume [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e], Metakaolin [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e], Geopolymer [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e], etc are used when strengthening is required. However, these SCMs fail to provide ductility to the material. Extreme brittle behavior of the blocks leads to sudden failure during overloading. To overcome this issue fibers have been used as the most popular reinforcing member in CSEB production. Fiber reinforcement in most cases strengthens CEBs but also improves their ductility, toughness, tensile strength, and overall durability [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. However, fiber incorporation should be in the optimal range to amplify the strength value. Beyond that optimal range, the strength value decreases with the increase in fiber percentage [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. Shear stresses in the soil mobilize tensile resistance in the fibers, which in turn imparts greater strength to the soil [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. Numerous research works have been carried out throughout the years for amplifying the mechanical and durability properties of CSEB with fiber incorporation. Specimens stabilized with various natural and synthetic fibers and cement provided an effervescent performance in enhancing the properties mentioned earlier. Paul et al. [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e] incorporated areca fiber in the CSEB specimens and found an increment in compressive strength (107.04\u0026ndash;436.38%), split tensile strength (208.66\u0026ndash;358.08%), and flexural strength (16.49\u0026ndash;82.47%), along with the improvement in durability properties too. Paul et al. [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e] also studied that volumetric shrinkage and bulk density have decreased in the vetiver straw fiber-reinforced CEBs, according to their physical characteristics. Moreover, the research study illustrated that, in terms of the strength-ductility behavior, the ductility of the CEBs was significantly enhanced by the Vetiver straw fibers. However, the increase in strength was not too great, and it did not exhibit much variation over time. The results also depicted decreased water absorption and increased wear resistance. The compressive strength of the composite soil increases up to 1% of coir content and a further increase in coir quantity results in the reduction of the values. Prasanna \u0026amp; Kumar [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e] and Anggraini et al. [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e] perceived from their studies that the percentage of water absorption increases with an increase in the percentage of coir. The tensile strength of coir-reinforced soil (oven-dry samples) increases with an increase in the percentage of coir. In the unconfined compressive strength (UCS) test, Kumar et al. [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e] examined extremely compressible clay using flat and crimped polyester fibers at 0%,0.5%,1.0%,1.5%, and 2.0%. The findings showed that the UCS value will rise with increasing fiber length and/or fiber content. Fiber crimping results in a small rise in UCS. These outcomes closely resemble those discovered by Tang et al. [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. However, the axial strain of the samples due to fiber and cement incorporation was less than that of the control specimen at peak load. Hence, there was a reduction in the ductility of the specimen after implying fiber in the specimen. The variation in physical and mechanical properties of earth block specimens for incorporating synthetic fibers also have been assessed in numerous studies. Puppala and Musenda [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e] confirmed that Polypropylene fiber reinforcement increased the UCS of the soil and reduced both volumetric shrinkage strains and swell pressures of the expansive clays. Consoli et al. [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e] showed that adding Polyester (PET) fiber to fine sand for a particular percentage increases the material's peak and ultimate strength along with ductility. But employing natural and synthetic fiber incorporation may result in negative strength as well. Philip et. al. [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e] implied hemp fiber in the earth block specimen and found positive effects on the strength and ductility. But with flax fiber, he found negative results regarding strength values. In both cases, he found improved ductility after incorporating fiber in the specimen. Houben, H. and Guillaud [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e] found that, because of inadequate fiber-matrix bonding and incorrect fiber dispersion, the addition of several natural fiber types to CSEB did not considerably increase its compressive strength and, in some cases, slightly decrease it. Also, Richardson et al. [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e] examined the effects of artificial fibers on concrete. The findings demonstrated that the clumping of synthetic fibers and the resulting voids in the matrix caused a loss in compressive strength when the volume of fibers was significant. Moreover, Prasad et al. [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e] investigated the effects of coir and sisal natural fibers on the characteristics of mortar. The research discovered that although these fibers improved the flexural strength and toughness, they decreased the compressive strength because of voids and uneven fiber distribution. Safiuddin et al. [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e] also studied the effects of carbon fiber on mortar. He found that an increased amount of carbon fiber percentage caused a drop in compressive strength, which was attributed to micro void formation and fiber-matrix instability. The result also portrayed that, the ductility of mortar increased as the incorporation of carbon fiber. While these previous studies have illustrated the benefits of fiber reinforcement in improving ductility, they have largely overlooked the potential of combining natural and synthetic fibers to improve both strength and ductility in CSEBs. This research addresses this gap by investigating the effects of vetiver-polyester conjugate fiber mix in the CSEB specimens.\u003c/p\u003e \u003cp\u003eThe above studies investigate the effectiveness of different fibers in CSEB independently but fail to address the effects if a mixture of various fibers were to be used in production. Few previous works have discussed such effects of conjugate fibers in concrete and mortars, but no such work is available for CSEB. For example, Madhavi et al. [\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e] observed that the compressive strength and flexural strength of concrete with a composite mix of jute and polypropylene are enhanced by about 22% and 1\u0026ndash;2 MPa, respectively. Sen \u0026amp; Reddy [\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e] confirmed that Sisal fabric reinforced polymer composite system achieved better increment in its flexural strength and improvement in load-deflection behavior. Hence, increasing the ductility behavior. These studies highlight the need for investigating such work in CSEB production as well. To bridge this literature gap in this research endeavor, a mix of vetiver and polyester fiber was used in CSEB production. The research not only focuses on the strength and ductility behavior of reinforced CSEBs but also compares the findings with samples containing vetiver and polyester fibers independently. The reason for choosing vetiver fiber is because, among other natural fibers, vetiver grass is an intriguing option for using as a reinforcing filler in polymer composites [\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e]. Moreover, it exhibits some creditable attributes such as density and volumetric shrinkage are reduced in vetiver fiber reinforced CEBs which is mentioned above. Also, strength-ductility behavior is improved in vetiver straw fiber reinforced CEBs [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. On the other hand, among synthetic fibers, polyester fiber is utilized because it enhances the sample\u0026rsquo;s peak and ultimate strength [\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e]. Also, polyester is readily available, and it has a low cost [\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e], so collecting polyester fiber is not a problem. Moreover, as polyester fiber is a synthetic fiber, it has a low water absorption capacity [\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e], which can be beneficial for enhancing the durability property. All the above characteristics have led to the selection of polyester fiber.\u003c/p\u003e \u003cp\u003eFor this research work, the primary focus was centered on assessing the ductility and strength properties of CSEB specimens reinforced with vetiver-polyester conjugate fiber. These were evaluated in terms of unconfined compressive and split tensile strength tests. The durability of the specimens was examined through a water absorption test. Also, microstructural analysis was performed on the specimens to get an outlook on the interaction between soil and reinforced fibers inside the specimens.\u003c/p\u003e"},{"header":"2. Materials and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1. Primary constituents of CSEB: soil and stabilizers\u003c/h2\u003e \u003cp\u003eThe three main components of CSEBs are soil, stabilizer, and water. The features of a CSEB sample are determined by the kind and quantity of elements used in combination with compaction effort [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e].\u003c/p\u003e \u003cdiv id=\"Sec4\" class=\"Section3\"\u003e \u003ch2\u003e2.1.1. Soil properties\u003c/h2\u003e \u003cp\u003eThere are presently insufficient comprehensive criteria for selecting suitable soil to produce CSEB specimens. But there are guidelines on soil particle size for shaping CSEB specimens. The particle sizes must be 2 mm for sand and less than 5 mm for laterite soil to ensure the binding between all materials when mixed [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. Comprehensive research has been carried out to uncover the influence of soil grading on earth block properties. According to these studies, the best results were obtained with soil fractions in the following ranges: sand and gravel 55\u0026ndash;75%, silt 15\u0026ndash;30%, and clay 10\u0026ndash;30%, respectively [\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e]. It is advised to add sand, crushed sand, or crushed gravel to soils that are deficient in sand or have an excessive amount of silt or clay [\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e]. Sekhar and Nayak [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e] obtained a strength that was sufficient for extremely fine-grained soil (88% clay/silt) after adding 6% cement and 20% coarse-grained, granulated blast furnace slag. Eslam et al. [\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e] discovered that 88% fine soil, stabilized with 40% coarse sand and 6% cement, was appropriate for compressed earth blocks. Hallal et al. [\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e] observed that soils stabilized with cement and containing 76% particles showed enough strength. Recently, Limami et al. [\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e] showed acceptable strength for clay-based bricks (less than 50 \u0026micro;m). The above-mentioned research made it clear that extremely fine-grained soils can also be stabilized with cement or by adding sand to create CSEBs. Since the main raw material for CSEB production is soil, the clay content in the soil greatly affects the strength and durability [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Aninda \u0026amp; Islam [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e] suggested that the ideal proportions of soil should not be more than 75% sand and gravel and no more than 30% silt and clay. The soil used for this study was obtained from Dhaka and collected between two and three meters below ground level. Different laboratory tests were conducted according to the ASTM standard to characterize the soil, and its properties are listed below in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. According to Prakash and Sridharan [\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e], the type of the soil sample according to their mentioned modified version of the USCS classification system was SC-SMN. Also, as Bangladesh is situated within this dynamic landscape, where rivers deposit over 2.5\u0026nbsp;billion tons of silty material annually, as part of the vast Ganges-Brahmaputra-Meghna delta, while a sizeable amount of these sediments is removed for fishing and navigation, a significant portion is left unused [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. Therefore, riverbed sand was used in this investigation to change the clay soil's gradation. Various soil to sand ratios were tested to identify the optimal mix. By thorough examination, it was discovered that a soil-sand mixture at a ratio of 1:3 could reach the highest dry density, which was consistent with the findings from earlier research.\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\u003eProperties of soil\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"2\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSoil Property\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eValue\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSpecific gravity, GS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2.68\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGravel (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSand (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e79.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFines, Passing No. 200 sieve (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e20.7\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMean particle size, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{d}_{50}\\)\u003c/span\u003e\u003c/span\u003e (mm)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.026\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLiquid Limit, LL of fines (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e35\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePlastic Limit, PL of fines (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e18\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePlasticity Index, PI (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e17\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eOptimum moisture content (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e14.8\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMaximum dry density (kN/m\u003csup\u003e3\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e17\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section3\"\u003e \u003ch2\u003e2.1.2. Stabilizer properties\u003c/h2\u003e \u003cp\u003eCompressed earth blocks that are unstabilized generally display low tensile and compressive strength, decrease in ductility, and they are susceptible to unfavorable weather conditions. Different chemical stabilizers such as cement, lime, and other cementitious materials are added to the earth mixture to overcome these issues. These stabilizers are essential for improving the engineering qualities of CSEBs, which increases their durability and applicability [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. Cement stabilized CSEBs show better strength and durability compared to lime stabilized CSEBs [\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e]. However, the addition of lime to cement stabilized CSEB and earthen mortar can improve compressive strength when the soil used has greater clay content [\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e]. In this study, ordinary portland cement (OPC) type I was utilized as cement stabilizer at two different percentages (4% and 8%) with respect to the total mass of the specimen. According to the ASTM C109 code [\u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e54\u003c/span\u003e], the compressive strength of the cement sample at 28 days was found to be 47.8 MPa. The cement particles had a fineness of 240 m2/kg and a specific gravity of 3.15. Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e summarizes the chemical composition of the cement used.\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\u003eChemical composition of OPC type 1 cement [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"2\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCompound\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePercentage by Weight (%)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eC\u003csub\u003e3\u003c/sub\u003eS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e57.2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eC\u003csub\u003e2\u003c/sub\u003eS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e17.6\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eC\u003csub\u003e3\u003c/sub\u003eA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e9.2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eC\u003csub\u003e4\u003c/sub\u003eAF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e7.8\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\u003e3.1\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\u003e2.8\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eIgnition Loss\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFree CaO\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.0\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 \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.2. Fiber properties\u003c/h2\u003e \u003cp\u003eCompressed earth Blocks are reinforced with vetiver, polyester, and vetiver\u0026ndash;polyester conjugate fiber to enhance the specimens' strength and durability. Variation in the fiber length and content in the soil results in an improvement in the strength characteristics of the soil [\u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e55\u003c/span\u003e]. So, the length of fibers plays a significant part in the compressive strength improvement of soil.\u003c/p\u003e \u003cdiv id=\"Sec7\" class=\"Section3\"\u003e \u003ch2\u003e2.2.1. Vetiver straw fiber\u003c/h2\u003e \u003cp\u003eVetiver straw, derived from the vetiver grass (Chrysopogon zizanioides), holds a unique position in having versatile applications, including use in mulching, roof thatching, biofuel production, etc [\u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e56\u003c/span\u003e]. Vetiver, a hardy perennial grass, is distinguished by its robust, fibrous, and lengthy root system. [\u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e57\u003c/span\u003e]. Vetiver plant thrives in diverse climates and plays a pivotal role in infrastructure protection, stabilizing flood, and coastal embankments, and riverbanks, and aiding in soil and water remediation efforts [\u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e58\u003c/span\u003e]. Vetiver straw fiber has some important mechanical properties, which makes this fiber a sensible element for incorporating in CSEB. These properties are tensile strength and flexibility, erosion control performance, binding and stabilization, and handicrafts and weaving. These properties improve the strength, reduce shrinkage and cracking, and enhance insulation when vetiver fiber is used as a reinforcing agent. For this study, the vetiver straw fiber was directly collected from a local farm near Gabtoli, Dhaka. The fiber was cut into 25 mm and the aspect ratio of the fiber was 20, to ensure efficient distribution in the soil matrix.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section3\"\u003e \u003ch2\u003e2.2.2 Polyester fiber\u003c/h2\u003e \u003cp\u003eBangladesh is standing in a paramount position of producing and exporting polyester fiber and textiles. That\u0026rsquo;s why, managing of polyester fiber is relatively straightforward and does not require significant effort. The chemical composition of polyester fiber, specifically PET, consists of repeating units of ethylene glycol and terephthalic acid [\u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e59\u003c/span\u003e]. Polyester fibers are known for their environmental challenges which denote their production, use, and disposal [\u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e60\u003c/span\u003e]. The adverse influence that wasted polyester fiber yield is continuously affecting the environment. Polyester fiber, when not effectively managed, contributes to microplastic pollution, occupying valuable landfill spaces and potentially releasing harmful chemicals during degradation [\u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e61\u003c/span\u003e, \u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e62\u003c/span\u003e]. Hence, it is essential to prioritize recycling and reusing the fiber, to impede the adverse influence. Polyester fiber can be assimilated in numerous ways such as, during manufacture, consumer waste, post-consumer waste, etc [\u003cspan citationid=\"CR63\" class=\"CitationRef\"\u003e63\u003c/span\u003e]. Polyester fibers possess several mechanical properties, including high tensile strength, good dimensional stability, and resistance to stretching and shrinking [\u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e64\u003c/span\u003e]. Moreover, Polyester fiber is a synthetic fiber that can be used in pavement construction to prevent micro cracking and enhance the flexural and compressive strength of the pavement along with preventing drying shrinkage as well [\u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e65\u003c/span\u003e]. Consoli et al. [\u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e66\u003c/span\u003e] demonstrated that incorporating PET fiber in fine sand improves both peak and ultimate strength which is dependent on fiber content. From this concept, incorporating this fiber in CSEB could be a supplementary way of reusing the fiber and mitigating its impact on the environment. Therefore, this very fiber was chosen in our research study for implying in the earth block specimens. Polyester fiber was collected from a local marketplace. The average length was obtained by using a vernier caliper as 30 mm and thickness obtained from scanning electron microscope (SEM) images was 70 \u0026micro;m respectively. The polyester fiber received from the market was soaked in cold water for one day to remove any impurities before being used in the CSEB specimens.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e2.3. Methods of preparing samples\u003c/h2\u003e \u003cp\u003eA total of three fiber combinations involving 1.5% vetiver straw, 1.5% polyester fiber, and vetiver-polyester conjugate mix with 0.75% for each of the fiber were integrated into the CSEB specimen. The percentages of the fibers represent their portion relative to the total specimen weight. For each of the three fiber combinations, cement content of 4% and 8% of total specimen weight were utilized in the CSEB specimens. For preparing the cylindrical specimens, at first, the sand and clay samples were oven dried for 24 hours and then screened to trim any objectionable elements. In accordance with ASTM D698 [\u003cspan citationid=\"CR67\" class=\"CitationRef\"\u003e67\u003c/span\u003e], a standard proctor compaction test was performed, to measure the mixture's optimal moisture content (OMC). This approach called for the use of a conventional mold with a diameter of 4 inches (101.6 mm). Three layers of materials that passed through a No. 4 sieve were compacted, and each layer was tamped 25 times with a 5.50 lb-f (24.465 N) hammer held 12 inches (304.8 mm) above the ground. To determine the link between dry density and moisture content, this process was repeated for different molding water contents. The soil sample contained OMC of roughly 14.8% and a maximum dry density of 17 kN/m3, according to the compaction curves displayed in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e by the standard proctor compaction test. Studies on the relationship between the fiber-bond strength and the grain size of specific soils indicate that finer sand particles have more fiber bond strength than coarse grained soils and silts have even better performance [\u003cspan citationid=\"CR68\" class=\"CitationRef\"\u003e68\u003c/span\u003e]. That\u0026rsquo;s why in our work, sand to clay proportion was 3:1; to keep larger sand proportion in the specimens and enhance the bond strength of the soil matrix. The clay sample was then crushed and ground to a finer powder with a hammer. Then adequate amount of sand and clay was mixed properly according to the ratio. After that, each of the three fiber combinations and required amount of cement were properly weighted and mixed homogeneously in dry condition for preparing the specimens. Then, the required amount of water attained by the OMC in the standard proctor compaction test was added to the soil-fiber mixture. After adding water to the sample, the mixture was mixed circumstantially unless a homogenous mix was prepared. Next, the inside surface of the unconfined compression mold was greased to prevent the specimens getting stuck in the mold during the time of taking out. The type of mold was cylindrical in shape (50 mm. diameter and 100 mm. height). Afterward, the soil mix was poured into the mold in three layers. During the preparation of the specimens, compaction was done by a metal rod weighing 279 g with a drop height of 25 cm, and the blow counts per layer were 25. The amount of compaction energy employed for sample preparation was calculated using the following Eq.\u0026nbsp;(1) suggested by ASTM D 698\u0026ndash;12.\u003c/p\u003e \u003cp\u003e \u003cem\u003eCompaction energy required =\u003c/em\u003e \u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e\\(\\:\\frac{No.\\:of\\:layers\\times\\:No.\\:of\\:blows\\:per\\:layer\\times\\:weight\\:of\\:hammer\\times\\:drop\\:height}{volume\\:of\\:the\\:mold}\\)\u003c/span\u003e \u003c/span\u003e (1)\u003c/p\u003e \u003cp\u003eAfter the completion of compacting the top layer, the undulated surface was leveled off with a straightedge. Following that, the sample was taken out of the mold with proper caution. The samples were then kept in a plastic container to avoid moisture loss and were left in a moist room and water was sprinkled daily in reason of curing for 7 and 28 days at a mean temperature of 25\u0026thinsp;\u0026plusmn;\u0026thinsp;1◦C with a relative humidity of at least 96%. The mixture percentage of different materials with the cement stabilizer considered in preparing the samples along with the codes of the samples are presented 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\u003eMixture proportions for sample preparation\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\u003eSpecimen ID with Fiber\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCement (wt.%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eWater Added (%)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eP 1.5%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e14.8\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eV1.5%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e14.8\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eV (0.75%)\u0026thinsp;+\u0026thinsp;P (0.75%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e14.8\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eP 1.5%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e14.8\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eV1.5%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e14.8\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eV (0.75%)\u0026thinsp;+\u0026thinsp;P (0.75%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e14.8\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"3\"\u003e[N.B: For Sample ID, C stands for Cement content, P 1.5%/V 1.5%/V 0.75%+P 0.75% stands for Polyester/Vetiver/ Polyester-Vetiver combination with their percentages, 7D/28D Stands for 7 days/28 days test]\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e2.4. Unconfined compressive and split tensile strength test\u003c/h2\u003e \u003cp\u003eStrength characteristics of all specimens were assessed in terms of unconfined compressive strength (UCS) and split tensile strength (STS) test. The UCS test was performed according to ASTM D5102 [\u003cspan citationid=\"CR69\" class=\"CitationRef\"\u003e69\u003c/span\u003e]. After curing for 7 days and 28 days, the specimens were gathered for testing. The specimens remained for 24 hours in an oven set to 110\u0026thinsp;\u0026plusmn;\u0026thinsp;1◦C. After that, both testing procedures were allowed to cool for four hours before they started. The bedding surface was thoroughly cleaned before the test started to guarantee uniform contact and loading. To make loading easier, there were two plates- one at the top and one at the bottom, were used. The specimens were carefully positioned with respect to the testing machine's center before testing to prevent any eccentric loading. Readings of axial force and deformation were taken for each specimen test, and the axial deformation rate of 1% per minute was maintained [\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e]. The STS test was performed according to ASTM C496-96 [\u003cspan citationid=\"CR70\" class=\"CitationRef\"\u003e70\u003c/span\u003e]. The cylindrical specimens were placed horizontally and loaded to failure with a deformation rate of 0.50 mm/min. A schematic diagram for the two tests is sequentially attached below in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e2.5. Water absorption test\u003c/h2\u003e \u003cp\u003eThe water absorption test was performed to give an insight into the durability of the specimens. The test was conducted according to ASTM C67 [\u003cspan citationid=\"CR71\" class=\"CitationRef\"\u003e71\u003c/span\u003e]. After curing for 7 and 28 days, the samples were oven dried for 24 hours to acquire their dry weight. The weight of the oven dried samples (W1) was traced. Then the samples were totally immersed in water, keeping the top of the sample at least 2 mm below the water surface. After that, the entire system was left like this for 24 hours and the final saturated weight of the sample (W2) was measured. The water absorption of the samples was then, calculated from Eq.\u0026nbsp;(2):\u003c/p\u003e \u003cp\u003eWa (%) = \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\frac{(\\text{W}2\\:-\\:\\text{W}1)}{W1}\\times\\:100\\%\\)\u003c/span\u003e\u003c/span\u003e (2)\u003c/p\u003e \u003cp\u003eWater absorption was quantified with respect to the samples\u0026rsquo; oven dry weight. The test's objective was to evaluate the moisture resistance after spending a full day in the water, which will provide a notable insight into the suitability for construction in varying environmental conditions.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e2.6. Microstructural analysis\u003c/h2\u003e \u003cp\u003eThe scanning electron microscope (SEM) analysis was performed for microstructural examination and the test was carried out on three types of samples with 8% cement content at 28 days, containing 1.5% polyester, 1.5% vetiver straw fiber and vetiver-polyester conjugate mix of 0.75% of both fibers. The equipment to conduct SEM analysis was Zeiss Sigma 300 VP from Oberkochen, Germany. After being dried for 24 h in the oven, one prismatic piece was detached from each type of sample and positioned onto a stud. Subsequently, these samples were introduced into the chamber of the SEM machine. The working lengths were maintained within the range of 2 and 4.6 mm, with the acceleration voltage set at 2 kV.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results and discussions","content":"\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003e3.1. Strength and ductility behavior\u003c/h2\u003e \u003cdiv id=\"Sec15\" class=\"Section3\"\u003e \u003ch2\u003e3.1.1 Unconfined compressive strength\u003c/h2\u003e \u003cp\u003eThe unconfined compressive strength test results of CSEB specimens stabilized with three fiber combinations and cement after 7 and 28 days of curing are sequentially illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. The figures show that specimens reinforced with polyester fiber showed the highest strength value among all the fiber combinations for both 7 and 28 days. But when the specimens containing polyester, vetiver, and vetiver-polyester mix, were compared with the control specimens for 7 days test results with 4% cement content, it was observed that specimens with polyester fiber achieved the highest compressive strength value as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(a).\u003c/p\u003e \u003cp\u003eHowever, there was a significant reduction in the strength value compared to the control specimens for the remaining results. The reason behind this outcome can be attributed to the knotting and clumping of the reinforced fibers in the soil matrix. That\u0026rsquo;s why there persisted less cohesion between the fiber and the soil and hence, the soil-fiber composite weakened. Which led to the reduction of strength value in the specimens. Guo et al. [\u003cspan citationid=\"CR72\" class=\"CitationRef\"\u003e72\u003c/span\u003e] also stated identical reasoning in response to compressive strength reduction for Basalt fiber reinforced concrete. Moreover, the fibers were regarded as a filler in the mortar matrix when subjected to compressive loading. However, the effect of knotting and clumping of the fibers created discontinuities and voids in the matrix and lowered the strength of the specimens as a result. Ismail \u0026amp; Yaacob [\u003cspan citationid=\"CR73\" class=\"CitationRef\"\u003e73\u003c/span\u003e] also pointed out similar reasoning for the effect in strength due to the presence of fiber. Furthermore, the presence of fiber reduced the overall cement percentage of the soil matrix. So, there existed less coating for each fiber and consequently, the bonding between the fiber and soil matrix became weak hence, leading to a reduction in compressive strength, which resembles the explanation of Thanushan et al. [\u003cspan citationid=\"CR74\" class=\"CitationRef\"\u003e74\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eInspection of the deformation characteristics was performed through stress-strain response under axial loading. A considerable improvement in strain value was observed for all the specimens with fiber reinforcement, in comparison to the control specimens. This is because, apart from the knotting and clumping of fibers inside of the specimens, fibers and the soil matrix worked together to resist the propagation of cracks in the specimen by forming bridges across cracks, which improved the strain of the specimens consequently. Danso et al. [\u003cspan citationid=\"CR75\" class=\"CitationRef\"\u003e75\u003c/span\u003e] also theorized a similar conception regarding this phenomenon. Moreover, it is seen from Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e that the vetiver-polyester mix performed significantly better than the control, vetiver, and polyester incorporated specimens individually in terms of greater strain for each case. Because the presence of both the fibers adhered to the soil matrix more firmly and the voids in the soil were reduced greatly due to polyester fiber, which influenced the bridging effect intensively and the strain behavior of the specimen increased. Therefore, from a ductility point of view, specimens with vetiver-polyester mix sustained more efficiently than specimens with vetiver and polyester fiber and enhanced the ability to deform under compressive stress, preventing sudden failure.\u003c/p\u003e \u003cp\u003eThe failure of fiber reinforced specimens appeared with multiple fine cracks, and the failure was gradual with the fiber combination to the cracks being formed. Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e represents the failure pattern of the specimens with 3 fiber combinations which shows that specimens with polyester fiber for both cement percentages wielded bulging or lateral expansion, which corresponds to the ductility behavior of the specimens. Again, the type of cracks that appeared in the specimens with vetiver fiber corresponds to shear failure. Lastly, for specimens with polyester-vetiver mix, specimens with 4% cement content showed bulging failure and the one with 8% cement content demonstrated shear failure. The types of failure for all the specimens above demonstrated improved ductile behavior.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section3\"\u003e \u003ch2\u003e3.1.2 Split tensile strength\u003c/h2\u003e \u003cp\u003eThe split tensile strength test results of the specimens with three fiber combinations are illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e. The test results for the specimens are somewhat similar to the unconfined compressive strength test. Except for the fact that the ultimate tensile strength value of the specimens with the vetiver-polyester mix is in between the stress values of the specimens with the other two fiber combinations, for both 7 and 28 days tests. The maximum tensile strength was obtained for specimens containing polyester fiber because the interfacial bonding between the soil matrix and polyester fiber was stronger than vetiver fiber. A single vetiver fiber occupies more space than polyester fiber in a soil matrix. This led to a weaker bond between the soil matrix and vetiver fiber because of the presence of larger voids, resulting in less tensile strength generation. Therefore, during the implication of diagonal stress, when the fibers tended to reduce the cracks through adhesion with soil particles and resisting the splitting up of the specimen diagonally, polyester fiber having greater surface bonding with the soil matrix, did the work more profoundly than other two fiber combination types, which was seen from the SEM images during the microstructural analysis later. Here, the cracks formed vertically from top to bottom before failure for all the specimens which are represented in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e.\u003c/p\u003e \u003cp\u003eFor the compressive strength test, specimens with vetiver-polyester mix exhibited maximum longitudinal strain value in all cases. However, for the split tensile strength test, specimens with polyester fiber were higher in terms of diagonal stress and strain value, which indicated an improvement in the ductility behavior of the specimen. This can be theorized as more polyester fiber was available in a particular soil matrix than vetiver straw fiber, the bonding between polyester fiber and soil matrix induced an extensive bridging effect during crack formation and hence, the tensile resistance was also greater than all the three specimen types. The SEM images also unveiled that polyester fiber having a slender structure, adhered to the soil particles more firmly than the remaining two fiber types and reduced the voids in the soil. The frictional resistance between polyester fiber and the hardened soil matrix accelerated due to the large number of C-S-H gels during the curing phase, reducing the formation of cracks when the load was subjected to the specimen. This phenomenon resulted in greater diagonal strain value and increased ductility for specimens with polyester fiber. So, the failure happened more gradually and resembled a ductile material. This finding is in good agreement with the findings of Danso et al. [\u003cspan citationid=\"CR76\" class=\"CitationRef\"\u003e76\u003c/span\u003e], Bouhichaet al. [\u003cspan citationid=\"CR77\" class=\"CitationRef\"\u003e77\u003c/span\u003e], and Cai et al. [\u003cspan citationid=\"CR78\" class=\"CitationRef\"\u003e78\u003c/span\u003e]. Also, specimens with vetiver-polyester mix showed better results in tensile strength and diagonal strain value than specimens with vetiver fiber. The presence of both fibers in the specimens with vetiver-polyester mix aided in the adhesion with the soil matrix more effectively, which resulted in better ductility for the specimens.\u003c/p\u003e \u003cp\u003eThe failure pattern from Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e depicts that for all the specimens with three fiber combinations and both the cement contents, there persists a continuous diagonal crack in the specimens which represents improved ductile behavior for the specimens with fiber reinforcement.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003e3.2. Durability property\u003c/h2\u003e \u003cdiv id=\"Sec18\" class=\"Section3\"\u003e \u003ch2\u003e3.2.1. Water absorption\u003c/h2\u003e \u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e illustrates the water absorption test results of all the specimens containing each of the three fiber combinations with both cement percentages. Figure\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e demonstrates the graphical illustration of the results of the water absorption test of the specimens. The graphs from Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e(a) and Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e(b) show that the increment of cement content of the specimens by 8% resulted in a reduction in water absorption than specimens with 4% cement content. This is because cement content forms C-S-H gel with soil particles, which leads to the formation of C-H plates, and these plates reduce the pores inside the cement-soil mix. Therefore, more amount of cement was present in specimens with 8% cement content, which reduced the pores in the soil matrix largely than the specimens with 4% cement content. So, the water absorption was also less for the specimens containing 8% cement content. Moreover, vetiver fiber is a natural fiber and has a higher water absorption capacity than polyester fiber. Hence, it absorbed some of the water when water permeated into the specimen. The value of water absorption results of specimens with vetiver-polyester mix prevails in between the results of specimens with polyester and vetiver fiber. This can be hypothesized as both fibers were present in the specimen, the vetiver fiber took part in soaking up the water as it is a natural fiber [\u003cspan citationid=\"CR79\" class=\"CitationRef\"\u003e79\u003c/span\u003e]. On the contrary, polyester fiber, being a synthetic fiber, did not participate in absorbing water as much. So, the water absorption persisted in the mid-range for this vetiver-polyester fiber combination. This leads to the outcome of better durability of the vetiver-polyester specimens than with the specimens of vetiver fiber.\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\u003eWater absorption test results with different cement content\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\u003eSpecimen ID\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eWater Absorption (4% cement)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eWater Absorption (8% cement)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eP1.5% 7D\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e5.51\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e4.28\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eP1.5% 28D\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e4.81\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2.96\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eV1.5% 7D\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e6.98\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e5.43\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eV1.5% 28D\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e5.63\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e4.07\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eV (0.75%)\u0026thinsp;+\u0026thinsp;P (0.75%) 7D\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e6.28\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e4.96\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eV (0.75%)\u0026thinsp;+\u0026thinsp;P (0.75%) 28D\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e5.47\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e3.27\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 \u003c/div\u003e \u003cdiv id=\"Sec19\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Microstructural analysis\u003c/h2\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e, Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e, and Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e represent the SEM images of the three types of specimens with 8% cement content which was conducted at 28 days. Because, at 28 days, the UCS and STS tests exhibited maximum stress-strain values for all types of specimens. The images demonstrate that the distributed fibers build a three-dimensional lattice within the soil, which aids in interlocking the soil grains. This interlocking system helps in forming a cohesive matrix. The interlocking not only binds the soil particles but also evenly distributes stress throughout the matrix. This helps in resisting localized failures, which is mostly important for the unconfined compressive strength test. When these reinforced specimens were subjected to lateral stress, the fibers acted as bridges across the developing microcracks which efficiently restrained tension-induced fracture development and restricted soil-fiber matrix displacement. This bridging effect delayed the propagation of fractures, thus reducing the displacement between the fiber and soil matrix. Moreover, the bridging effect is one of the main reasons the fiber reinforced specimens exhibited better ductility than the control specimens because the fiber in the soil matrix helps the materials absorb more energy before falling.\u003c/p\u003e \u003cp\u003eThe images also depict that for all types of specimens, C-H plates are formed in the soil matrix, which is a clear indication of the composition of C-S-H gels in the soil. C-S-H is a primary product in cementitious systems, and its presence in the soil matrix suggests the improved bonding between the fiber and soil. This improved bonding directly contributes to both strength and ductility, as the matrix becomes more resistant to debonding under stress. For this reason, CSEB specimens with fiber reinforcement showed better results in ductility than the control specimens in the unconfined compressive strength test which is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. The SEM images of V1.5%28D specimens in Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e(a) and Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e(b) show that several clay particles stick to the surface of the vetiver straw fiber. This adhesion is important for the enhancement of bonding and frictional force between the soil matrix and the fiber. Also, there persist voids in between the vetiver fiber and the soil matrix interface which reduces the ductility behavior of the specimen when they are subjected to lateral and diagonal stresses.\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e shows the SEM images of the P1.5%28D specimen. When the images of Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e and Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e are compared, it is seen that as much space one vetiver straw fiber takes up, multiple polyester fiber occupies the same space. Figure\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e(b) also shows that polyester fibers are attached to the soil matrix strongly and there is no void present between the fiber-soil matrix interfaces. This has driven a greater bond formation between the polyester fiber and soil matrix and eventually increased the ductility behavior greater than specimens with vetiver straw fiber. Lastly, Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e represents the SEM images of V (0.75%)\u0026thinsp;+\u0026thinsp;P (0.75%) 28D specimen. As both the fibers are present in this type, polyester fiber along with vetiver fiber attaches with the soil matrix firmly and ensures more rigid bonding and frictional force with the soil matrix than the other two types of specimens which are visible in Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e(b). Also, the presence of polyester fiber assisted in filling up the pores which has made the specimen more rigid. So, when the specimen is subjected to vertical stress, due to the enhancement of the bridging effect, it induces maximum ductility among all three types.\u003c/p\u003e \u003c/div\u003e"},{"header":"4. Conclusions","content":"\u003cp\u003eThe research's scope was to examine the strength and durability properties of the specimens containing vetiver-polyester mix and the findings were compared with the results of specimens containing other two fiber combinations. In this study, fiber and cement was utilized as stabilizers in the earth block specimens. This study can be concluded with the following outcomes:\u003c/p\u003e \u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003eConsidering the strength properties, it was observed that for the UCS test, fiber incorporation did not affect the unconfined compressive strength greatly, and in some cases, it had an adverse impact, showing a decrease in compressive strength when compared to the strength of control specimens. The highest strength value was obtained by the specimens with 1.5% polyester fiber and 8% cement, for both 7 and 28 days tests. On the contrary, the lowest strength value was attained by the specimens with vetiver-polyester mix and 8% cement for 7 days test and specimens with 1.5% vetiver fiber and 4% cement for 28 days test. As the fiber is not a pozzolanic material, the enhancement of the strength properties is dependent on the distribution of fibers and their interaction with the soil particle. Knotting and clumping of the fibers in the soil matrix resulted in the reduction of unconfined compressive strength for the specimens with fiber reinforcement than the control specimens. But the specimens with vetiver-polyester mix showed better strain behavior for both 7 and 28 days test. Because the presence of both the fibers influenced strong adhesion with the soil matrix and the voids were reduced greatly due to polyester fiber. This helped in forming the bridging effect more soundly and led to better ductility than other specimen types.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eFor the STS test, specimens with 1.5% polyester fiber and 8% cement content exhibited the highest strength value for 7 and 28 days tests. On the other hand, specimens with 1.5% vetiver and 4% cement exerted the lowest tensile strength value for both 7 and 28 days tests. Fiber incorporation developed the formation of cracks, resulting in improved ductility in the specimen. Polyester fiber having a thin formation, occupied a particular space in a greater number in the soil matrix than vetiver fiber and adhered with the soil more firmly and hence, developed the crack generation during the implication of the diagonal stress. Also, specimens with polyester fiber showed better ductility among all three types in the split tensile strength test because multiple polyester fibers took up the same amount of area as one vetiver straw fiber did. This led to the strong adhesion of polyester fiber with the soil and the reduction of pores in the soil matrix, developing an improved bridging action. Eventually, the sample with polyester fiber represented better ductility than the other two fiber combinations. Specimens with vetiver-polyester mix also showed better strain behavior than specimens with vetiver fiber and the peak stress value for this specimen resided in between the values of specimens with the other two fiber combinations.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eIncreased water absorption in CSEBs causes durability problems and decreases strength. For different water absorption values between the specimens with different fiber combinations in this study, specimens with polyester fiber at 8% cement content showed better outcomes because of better bonding with the soil matrix and reducing the pores in it. The presence of vetiver fiber in the soil matrix created larger voids, which enhanced the water intrusion through the voids due to capillary action and resulted in a larger water absorption value. Specimens with vetiver-polyester mix had shown water absorption value in between the specimens with the other two fiber combinations because even if polyester fibers were present, voids had still appeared in the soil due to the presence of vetiver fiber. For this, the water absorption value for this specimen prevailed between the specimens with the other two fiber types.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eThe SEM images revealed that vetiver-polyester conjugate fiber in CESBs resulted in a more uniform and isotropic soil matrix with fewer voids. These fibers, coated with attaching clay particles, generated a stronger composite material by improving the bonding ability and friction between the soil matrix and the fibers, which resulted in better ductility for specimens with vetiver-polyester mix among the specimens with the other two fiber combinations for UCS test. Cement formed C-S-H gel with soil when they were mixed with soil. This gel reduced the pores in the specimen and helped in making the bond between the fiber and soil matrix, which increased the ductility of the specimen.\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e \u003cp\u003eIn recent years, interest in earthen building has grown because of its economic, social, and environmental sustainability. According to the outcomes of this study, strong and durable CSEBs can be comprised of an optimum percentage of vetiver-polyester mixture and cement as stabilizing materials. The CSEB blocks with the fiber mix can be more suitable for load bearing walls because of the higher compressive strength of the specimens with vetiver-polyester mix. However, the split tensile strength test result suggests that polyester fiber contributes more to ductility and strain resistance. However, the fiber mix can enable a balanced improvement in strength and flexibility by reducing brittle failure and improving crack resistance. This makes the CSEB specimens with fiber mix an ideal solution for earthquake prone regions. Also, if the vetiver fiber is properly treated, it could aid in preventing erosion of the CSEB matrix. Moreover, the use of vetiver-polyester combination could lower the material cost compared to purely synthetic fiber. However, further strength enhancements are necessary to achieve all specifications, involving the use of specific cementitious materials. Long-term durability studies are needed to ascertain the real-world application. Other limitations may include the lack of standardized construction guidelines, susceptibility to insect attacks, unidentified thermal properties, etc. Resolving such limitations is essential for increasing the viability and acceptance of vetiver-polyester conjugate fiber-reinforced CSEBs in buildings. These need continued research to create an ecologically friendly, cost-effective construction material with more improved strength and ductility.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors did not receive support from any organization for the submitted work.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCRediT authorship contribution statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFayeq Tazwar:\u003c/strong\u003e Conceptualization, Methodology, Formal analysis, Investigation, Data curation, Writing - original draft preparation, Writing - review and editing. \u003cstrong\u003eSaidis Salekin Aninda:\u0026nbsp;\u003c/strong\u003eConceptualization, Methodology, Resources, Writing - review and editing, Supervision, Resources. \u003cstrong\u003eMohammad Shariful Islam:\u0026nbsp;\u003c/strong\u003eConceptualization, Methodology, Resources, Writing - review and editing, Resources.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDeclaration of competing interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll authors certify that they have no affiliations with or involvement in any organization or entity with any financial interest or non-financial interest in the subject matter or materials discussed in this manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eData will be made available on request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors would like to express their heartfelt gratitude to Bangladesh University of Engineering and Technology (BUET) for supporting them with the research work. Also, the authors would like to express their gratitude to Shantanu Paul for his incessant guiding throughout the research endeavor. The authors acknowledge the contribution of Department of Biomedical Engineering (BME) for obtaining the SEM images. The authors would also like to thank Abdullah Muhammad Asif and Sazid Alam Surid for their conducive approach throughout the study.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eTirelli D, Besana D (2023) Moving toward Net Zero Carbon Buildings to Face Global Warming: A Narrative Review. 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Cem Concr Compos 27(5). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.cemconcomp.2004.09.013\u003c/span\u003e\u003cspan address=\"10.1016/j.cemconcomp.2004.09.013\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCai Y, Shi B, Ng CWW, Tang C (2006) sheng. Effect of polypropylene fibre and lime admixture on engineering properties of clayey soil. Engineering Geology, 87(3\u0026ndash;4). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.enggeo.2006.07.007\u003c/span\u003e\u003cspan address=\"10.1016/j.enggeo.2006.07.007\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBegum HA, Tanni TR, Shahid MA (2021) Analysis of Water Absorption of Different Natural Fibers. J Text Sci Technol 07(04). \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.4236/jtst.2021.74013\u003c/span\u003e\u003cspan address=\"10.4236/jtst.2021.74013\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"Bangladesh University of Engineering and Technology","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":"CSEB, Vetiver, Polyester, Fiber, Strength, Ductility","lastPublishedDoi":"10.21203/rs.3.rs-6655978/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6655978/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis study explores the creative use of a mixed reinforcement method that combines polyester and vetiver straw to overcome the constraint of limited strength and ductility of conventional Compressed Stabilized Earth Blocks (CSEB). Although the individual use of vetiver straw and polyester fiber in soil reinforcement has been previously recognized in different scholarly literatures, this research attempts to thoroughly investigate a novel aspect of study concerning the specific role in enhancing the ductility feature of CSEBs using a conjugate mix of vetiver and polyester as a reinforcing agent. The results depicted that, specimens with polyester fiber showed better results in unconfined compressive and split tensile strength tests. However, a notable finding was that specimens with vetiver-polyester mix exerted better strain behavior for the unconfined compressive strength test. Also, the diagonal strain was improved for specimens with vetiver-polyester mix, which showcases the improved ductile attribute of the vetiver-polyester conjugate specimens, aligning with this study\u0026rsquo;s research scope. Microstructural analysis unveiled a more homogenous and isotropic soil matrix with fewer voids for the specimens with vetiver-polyester mix. This indicated a stronger bond formation between the fiber-soil interfaces. The water absorption test result also showed that specimens with vetiver-polyester mix exhibited improving results for 28 days test, which suggests that the durability of the specimen with fiber mix gradually increases over time. Ultimately, this study highlights the potential of the vetiver-polyester mix as an effective reinforcing component in cement stabilized CSEBs, for producing environmentally viable and sustainable building materials.\u003c/p\u003e","manuscriptTitle":"Effectiveness of Agro-Industrial Conjugate Fibers in Improving Mechanical Properties of Compressed Stabilized Earth Blocks","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-05-16 05:34:03","doi":"10.21203/rs.3.rs-6655978/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":"692e84f3-9792-42d6-8581-b31e920444c2","owner":[],"postedDate":"May 16th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":48471662,"name":"Civil Engineering"},{"id":48471663,"name":"Geology"},{"id":48471664,"name":"Environmental Engineering"}],"tags":[],"updatedAt":"2025-05-16T05:34:03+00:00","versionOfRecord":[],"versionCreatedAt":"2025-05-16 05:34:03","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6655978","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6655978","identity":"rs-6655978","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}