Evaluation of compressed stabilized earth block properties using crushed brick waste

Construction and Building Materials 280 (2021) 122520 Contents lists available at ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat Evaluation of compressed stabilized earth block properties using crushed brick waste Pardhasaradhi Kasinikota ⇑, Deb Dulal Tripura Department of Civil Engineering, National Institute of Technology, Agartala, Tripura 799046, India a r t i c l e i n f o Article history: Received 10 November 2020 Received in revised form 15 January 2021 Accepted 23 January 2021 Keywords: Compressed stabilized earth blocks Crushed brick waste Sulfate attack Particle size Strength Water absorption a b s t r a c t This study investigates the engineering properties of compressed stabilized earth blocks (CSEBs) incorporating crushed brick waste as alternative to soil-sand mixture as well as sand. The work was undertaken in two phases: in first phase, the influence of crushed brick waste to replace soil-sand mix without jeopardizing the original performance along with resistance against sulfate attack has been highlighted. Further, microscopic studies were performed to examine the compounds developed. Then, the influence of crushed brick waste particle size and replacement ratio to replace natural sand has been studied. The results show that inclusion of crushed brick waste in soil-sand mixture significantly improved the block performance, especially under wetting–drying cycles and sulfate attack. The X-Ray Diffraction (XRD) and Scanning electron microscope (SEM) studies confirmed that inclusion of crushed brick waste leads to better resistant against external attacks. Crushed brick waste particle size and replacement ratio has significant influence on block strength and water absorption. The addition of 20% crushed brick waste with particle size 0/4.75 mm increases the compressive and flexural strength; beyond that the resistance decreases due to inferior properties of crushed brick waste. On the other hand, removal of powder content negatively affected the block strength. The replacement of sand with very fines content up to 20% is encouraging beyond that the strength decreases drastically due to higher porosity and water absorption of crushed brick waste. Irrespective of crushed brick waste particle size, water absorption increases with replacement ratio. Ó 2021 Elsevier Ltd. All rights reserved. 1. Introduction Since antiquity, bricks have been used for construction as sunbaked (unfired) bricks and fired bricks. Today brick is considered as one of the principal material in buildings [1]. Despite the superiority of fired bricks over traditional bricks, they are energy intensive. Especially, developing countries like India largely depend on fired brick for low cost housing resulting in unsustainable development [2]. With the development of modern construction materials like concrete and steel, the earth construction has been abandoned. Nevertheless, it is projected that more than two billion people presently lives in earthen houses across the world [3]. Now with growing concerns on environmental degradation and energy consumption associated with industrialized materials, the earth construction is gaining renewed interest as a sustainable building material [3]. ⇑ Corresponding author. E-mail address: pardhu.saradhi87@gmail.com (P. Kasinikota). https://doi.org/10.1016/j.conbuildmat.2021.122520 0950-0618/Ó 2021 Elsevier Ltd. All rights reserved. Earth buildings has several advantages over houses built with concrete and fired clay bricks such as low embodied energy, thermal comfort, environmental-friendly, locally available and economical [4,5]. Among the various construction techniques, the most prominent are adobe, cob, rammed earth, compressed earth block (CEB) and wattle and daub. CEB is modern form of the adobe brick, involves the static compaction of moist soil using manual or hydraulic press thus achieving densities in range between 1700 to 2300 kg/m3 [3,6]. However the inherent deficiencies of natural earth such as low strength, affinity to water are preventing its acceptance in modern construction society. In addition, lack of design standards for CEB and wide variation of soils depending on geographic location, limiting its dissemination [3,7]. The performance of CEB against water can be improved through soil stabilization. Cement is the most widely used stabilizer for fabrication of compressed stabilized earth blocks CSEBs as it provides higher strength and durability under different conditions [7,8]. Other stabilizers such as lime, gypsum and bitumen rendered satisfactory results [7,9,10]. Nonetheless, the knowledge of various types of soils is essential to select suitable stabilizer type. Studies reported increase in CSEB strength with increase in cement content; how- P. Kasinikota and Deb Dulal Tripura Construction and Building Materials 280 (2021) 122520 and high resource value for recycling and reuse. In India, most of the waste is dumped as landfill due to lack of specific treatment plants for segregation [29]. According to Ministry of housing and urban affairs (MoHUA) India, the construction industry is expected to grow at a rate of 7–8% in the next decade due to rapid urbanization [30]. The main raw materials such as sand, soil, aggregates and lime stone are natural resources have significant impact on environment and particularly sand is facing implications due to ecological imbalance whose conservation is of vital importance. Currently, in India the annual consumption of sand and soil are about 750 and 350 million tones. Despite of its abundant availability, soil is also depleting whose usage should be minimized through integration of various wastes and industrial by-products [1]. In 2018, Buildings Materials & Technology Promotion Council (BMTPC), MoHUA estimated that the annual production of construction and demolition waste in India is approximately 100 million tonnes [30]. It is confirmed that, construction and demolition waste can be reused in form of recycled concrete, ceramic and mixed aggregate to substitute the natural aggregate to develop a green building material [31]. Further, the particle size of recycled aggregate considerably influences the fresh and hardened properties of cement mortar [32,33]. Several studies endorsed the utilization of construction and demolition waste as a recycled fine and coarse aggregate in compressed earth blocks and rammed earth engendered comparable results. Taghiloha [34] developed a sustainable construction material for stabilized rammed earth construction by replacing natural sand and gravel in artificial soil with recycled aggregates. Soils were prepared by mixing different percentages of clay and silt, natural sand of 0/2 mm, 0/4 mm and gravel of 4/10 mm, 10/20 mm. Mixtures with recycled aggregates attained lower strength compared to reference samples although exceeded the minimum acceptable strength whilst the shrinkage increased yet within the limits. However, the effect of replacing natural sand explicitly with ceramic waste was not reported. Oti et al. [35] addressed the feasibility of brick dust waste 0.15/6 mm to partially replace the clay in production of unfired clay bricks stabilized with ground granulated blast furnace slag (GGBS) and lime. Bricks were made with brick dust waste of 0%, 5%, 10%, 15% and 20% percentages. Incorporation of brick dust waste up to 20% improved the compressive strength, while the water absorption, linear expansion and weight loss after freezing and thawing cycles increased with brick dust percentage. However, the optimum content of brick dust waste was not reported. Jayasinghe et al. [36] explored the properties of stabilized rammed earth with incorporating concrete waste of size 0/19 mm. It was shown that walls incorporated with concrete waste provided satisfactory results for single and double storey buildings. Seco et al. [37] examined the possibility of concrete and ceramic wastes of 0/4 mm to substitute clay soil in fabrication of unfired bricks using various stabilizers at 4–10% dosage. Based on the workability requirements, the maximum replacement levels of soil by concrete and ceramic wastes are established as 50% and 30%. Bricks incorporated with ceramic waste recorded higher compressive strength than control and concrete waste incorporated bricks for all types and combinations of stabilizers. While, bricks incorporated with concrete waste displayed superior freezingthawing resistance. Bogas et al. [7] investigated the physical, mechanical and durability performance of un-stabilized, 8% cement stabilized, 4% cement and 4% lime stabilized compressed earth blocks with 15% recycled aggregates as partial replacement of soil. The recycled aggregates employed consisted of concrete, fired brick and cement mortar with maximum particle size of 2 mm. It was pointed that CSEBs with partial substitution of recycled aggregates showed results comparable with conventional CSEB. Cement stabilization was more effective than the combination of lime and cement, which satisfied the minimum strength ever the cement content greater than 10% by soil weight is uneconomical [1,5,8,10]. The CEB performance is primarily governed by the soil characteristics and particle size distribution[3,11]. Each fraction has significant impact on the mechanical behavior. A slight variation in grading can vary the soil structure, plasticity, cohesion and permeability [12]. The recommended particle size distribution of soils for CEB has been stated by various earthen standards [13,14]. Extensive research has been undertaken on influence of soil grading on compressed stabilized earth block properties [8,9,11,15–20]. According to these studies the best results were obtained with soil fractions in following ranges: sand and gravel 55–75%, silt 15–30% and clay 10–30%, respectively. Addition of sand/ crushed sand/ crushed gravel to soils with excess clay or silt or lacking sand content is recommended [14]. In addition, soils with higher fines are unfavorable for CEB construction [13]. Conversely, bricks made of soil having 98% fines showed desirable strength and satisfactory durability performance when stabilized with cement and fly ash based geopolymerization [21]. Bachar et al. [22] reported soils with 91.3% fines stabilized with 30% dune sand and 12% cement achieved acceptable strength. Sekhar and nayak [23] achieved satisfactory strength for highly fine grained soil (88% clay/silt) with addition of 20% coarse grained granulated blast furnace slag and 6% cement. Eslam et al. [24] found soil with 88% fines was suitable for compressed earth blocks when stabilized with 40% coarse sand and 6% cement. Hallal et al. [25] found cement stabilized soils with 76% fines exhibited satisfactory strength. More recently, Limami et al. [26] evidenced reasonable strength for bricks using clay (less than50 lm). From the above studies, it was evident that highly fine grained soils are also suitable for CSEBs through either stabilizing with cement and/or sand addition. The potential use of stockpiled circulating fluidized bed combustion ash (SCFBCA) in CEB production was addressed [27]. Series of mixtures were prepared using grounded (finer) and ungrounded (0/10 mm) SCFBCA in combination with different proportions of sand, clay stabilized with various stabilizers. Mixtures with clay and grounded SCFBCA showed higher strength than with clay and ungrounded SCFBCA, attributed to effect of finer size SCFBCA. González-López et al. [10] studied the significance of granulometry of sand on un-stabilized and stabilized compressed earth block properties using different stabilizers and compaction forces. Blocks made by mixing clay and sand in which the sand gradation is varied initially to select the best composition. The results showed that by changing the granulometry of the clay-sand mix the compressive strength improved by 200% for the same binder dosage. Reddy and Latha [11] showed that fine grained soils prepared by blending soil with silt from manufacturing sand are superior to the coarse grained soils made of soil and natural sand at all proportions when stabilized with cement. Limami et al. [28] investigated the properties of unfired clay bricks using polymeric wastes as HDPE granules and PET flakes. Bricks were produced using clay soil with three types of grain sizes of HDPE and PET (d
1mm; 1 < d
3mm; 3 < d
6mm) at different percentages. Regardless of grain size, addition of polymer wastes reduced the compressive strength of bricks at all incorporation rates due to increase in porosity and reduction in clay fraction. Bricks with HDPE waste registered higher strength than PET samples. Furthermore, smaller the grain size and substitution ratio of waste the higher strength obtained compared to other types due to lower porosity. It was inferred that type of polymer, size and substitution ratio strongly influenced the brick performance. Literature clears that the particle size of constituents has significant influence on block properties. Currently, construction and demolition waste is becoming a serious environmental burden in many countries, significantly constitute of concrete and masonry debris with huge potential 2 Construction and Building Materials 280 (2021) 122520 P. Kasinikota and Deb Dulal Tripura mechanical properties and water absorption of CSEB with an aim to specify the optimum amounts of different sizes of crushed brick waste to replace sand with improved behavior. The results obtained after experimental and microscopic studies were analyzed, discussed and compared with the control mixture. requirement under saturated conditions. However, the effect of recycled aggregates separately was not studied. Jyothi et al. [38] examined the properties of soil-brick powder- lime pozzolanic cement geo polymer mixtures. Brick powder used was sieved through 90 l. The mix with soil-brick powder of 1:1 ratio and 10% lime pozzolanic cement achieved higher strength, which was attributed to pozzolanic reaction by brick powder and geopolymerization. Arrigoni et al. [39] investigated the mechanical, sustainability and hygroscopic properties of stabilized rammed earth with incorporation of recycled concrete aggregates (RCA). Cement stabilized mixtures were produced with locally available crushed limestone; engineered soil prepared using kaolin clay, sand, silica flour and gravel with RCA passed through 6/19 mm at 0%, 25%, 50% and 75% percentages. It was deduced that grain size distribution greatly influenced the strength rather than the RCA substitution. Mechanical resistance decreased with RCA substitution although did not affect the durability. Joshi et al. [40] presented the characteristics of cement stabilized adobe blocks using demolished brick masonry waste (DMW) passed through 4.75 mm as replacement to natural soil. The results indicated that the DMW in range of 60–80% provided superior performance. Except at 20% replacement, the compressive and flexural strength, dry density improved and initial rate of water absorption, water absorption and weight loss after wetting–drying cycles reduced with incorporation of DMW and the optimum percentage was 70%. Stress–strain characteristics indicated that the elastic modulus increased with addition of DMW, SEM studies revealed that the addition of DMW increased the concentration of hydrated products. Joshi et al. [41] examined the suitability of utilizing natural soil, crushed brick masonry powder and LD slag individually and combinations as alternative to natural sand (Zone II) in production of stabilized mud concrete. A wide range of mixtures were made with different combinations. It was noted that the mixtures with soil as fine aggregate offered most economical sustainable solution. In mixtures with combination of soil and construction and demolition waste, the mix with 100% mortar waste attained higher strength than with brick waste. In summary, although many studies addressed the characteristics of CSEBs with brick waste, only few researchers highlighted the influence of brick waste as substitute to soil-sand and sand to develop CSEBs. Especially, the knowledge on effect of brick waste particle size and replacement ratio as alternative to sand was scanty. Few studies shed light on sulfate resistance of CSEBs. Sulfate generally present in soils, seawater, ground water, industrial effluents, in acid rain or in air and can cause damage under cyclic wetdry conditions [42]. Reduction in block strength with duration of sulfate exposure was reported by [21]. In contrast, Increase in block compressive strength and reduction of tensile resistance was found after 12 days in sulfate medium [43]. In addition, increase in strength for coarse grained soils and decrease for fine grained soils after sulfate exposure was observed [44]. The performance of CSEB under external sulfate attack based on capillary absorption procedure was proposed and noted that higher sulfate concentrations greatly damaged the blocks [42]. Further, the author suggested mechanical tests while assessing the resistance against sulfate attack. Thus, bearing on literature the author felt the need to understand the properties of CSEBs with brick waste as a substitute to reconstituted soil (soil-sand) and sand. The study intend to address the specific objectives: the influence of crushed brick waste as a substitute to soil-sand mixture at both macro level through determination of mechanical (Dry and wet compressive strength, Flexural strength) and durability tests such as wetting–drying and sulfate attack and micro level using scanning electron microscope (SEM) and X-ray diffraction (XRD) analysis. Also, the effect of crushed brick waste particle size and replacement ratio on 2. Materials and methods 2.1. Soil The soil used was collected from west-side of Agartala, Tripura at a depth of 0.5–1.5 m below existing ground level. To assess the soil suitability particle size distribution, Atterberg limits, shrinkage limit, free swell index and standard proctor compaction tests were performed in accordance with IS 2720 [45–50]. The index properties of soil are outlined in Table 1 with liquid and plastic limits are 50.48% and 27.12%. The grain size distribution is illustrated in Fig. 1, indicating that the soil is highly fine grained with 97.35% clay and silt fraction. According to Indian standard soil classification system (ISSCS) the soil is classified as CH. To determine the mineralogical composition X-ray diffraction (XRD) was conducted using PANanlaytical X-ray diffract meter with Cu-Ka radiation. The data was collected in a 2h range 5°70°. XRD data in Fig. 2 revealed that soil is mainly dominated by kaolinite, Illite and quartz minerals. The activity of soil is 0.76 indicating normally active which is in consistent with the mineralogy data. The grain size distribution of soil fall outside the recommended envelope of IS 1725 [14] and AS HB 195 [13] for making compressed earth blocks. The optimum clay content of soil for CEB varied from 8.65% to 22% depending on soil type [11,16,17,20]. Further AS HB 195 [13] and IS 1725 [14] recommended a sand content of 30–75% and 50–80% suitable for CEB production. Very often the soil grading is altered by diluting with sand to improve the skeleton as well to reduce the shrinkage [19]. Thus, mixtures were prepared with different ratios of sand-soil to found the optimum mix ratio. A soil-sand mix of ratio 30:70 attained the maximum dry density is selected, which is compliant with earlier studies [8,16]. Muntohar [51] selected an optimum proportion of soil-sand (70– 30) mixtures based on proctor test results. CSEB made of highly fine grained soil with coarse sand 50–60% attained maximum density and compressive strength [24]. 2.2. Sand and crushed brick waste Locally available natural river sand of white color was used. Crushed brick waste was procured from local crushing plant. The particle size distribution for sand and crushed brick waste are Table 1 Properties of Soil and Reconstituted soil. Property Atterberg Limits Grain size distribution Proctor Test Swell Index Activity shrinkage limit IS soil classification 3 Liquid Limit Plastic Limit Plasticity Index Sand Silt Clay Optimum moisture content (OMC) Maximum dry density (MDD) Soil Reconstituted soil (RS) 50.48% 27.12% 23.36% 2.65% 67.21% 30.14% 18.83% 21.3% 15.8% 5.5% 70.41% 20.53% 9.06% 10.77% 1634 kg/ m3 3.4% 0.76 16.88% CH 1928 kg/m3 – – – SM P. Kasinikota and Deb Dulal Tripura Construction and Building Materials 280 (2021) 122520 Fig. 1. Particle size distribution of Soil, Natural sand, Reconstituted soil and Crushed brick waste. Fig. 2. XRD data of raw materials used; G- Gypsum, Q-Quartz, C-Calcite, K-Kaolinite, I-Illite, and crushed brick waste are primarily composed of quartz mineral with traces of calcite in sand. shown in Fig. 1. The physical properties ascertained by following IS 2386 and IS 383 [52,53] are presented in Table 2. Table 3 pictorially represents the details of different fractions of natural sand and crushed brick waste. XRD analyses in Fig. 2 shows that both sand 2.3. Cement The ordinary Portland cement of 43 grade confirming to IS 8112 [54] is used. All mixtures are cement stabilized with maximum 10% by weight of soil as greater contents are uneconomical [8]. Table 2 Physical properties of natural sand and crushed brick waste. Sl. No Property Natural sand Crushed brick waste 1 2 3 4 5 Fineness modulus Specific gravity Loose bulk density Compacted bulk density Water absorption 1.6 2.6 1410 kg/m3 1575 kg/m3 1.05% 2.2 2.5 1213 kg/m3 1381 kg/m3 12.26% 2.4. Determination of OMC and MDD The OMC for mixtures with and without crushed brick waste was determined following the IS 2720 part VII [49], as it indicates the moisture content at which a specific compaction force would 4 Construction and Building Materials 280 (2021) 122520 P. Kasinikota and Deb Dulal Tripura Table 3 Details of granular fractions of Natural sand and Crushed brick waste. Particle size fraction (mm) 4.75–0.6 0.6–0.3 0.3–0.15 < 0.15 Natural sand Crushed brick waste centage which may be attributed to the low clay content of soil (5.8%), which agrees with Seco et al. [37] reported that the maximum substitution of ceramic waste was 30% based on workability. This can be explained from the fact that soil containing low clay content may experience difficulties to handle the blocks immediately after pressing due to lack of initial cohesion [57]. provide the maximum dry density [5]. It is used as a reference such that a close relation with static compaction press optimum moisture content was noticed [4,7,19,55,56]. 2.5. Mixture proportions and nomenclature A total of 20 composite mixtures were prepared and categorized in two phases. In phase I, the soil-sand mixture was replaced by crushed brick waste at 6%, 12%, 18% and 24% respectively. In second phase the sand was replaced by three different particle sizes of crushed brick waste namely 0/4.75 mm, 0.15/4.75 mm and less than 0.15 mm at 20%, 40%, 60%, 80% and 100% respectively. The summary of production and test run of CSEB samples is given in Table 4. The material proportions of mixes are listed in Tables 56. The quantities of ingredients aforementioned are by weight proportion. The grain size curves of mixtures studied are presented in Fig. 3. 2.7. Tests scheme For each variation five samples were tested to determine the compressive strength, water absorption and three samples for flexural strength. Compression test was performed in a 200 ton capacity compression testing machine, capable of applying load uniformly to failure. Both dry and saturated (i.e. after immersed in water for 24 hrs prior to testing) compressive strengths were determined by placing the CSEB between two 15 mm thick steel plates and loaded. The compressive strength of block was calculated from its failure load and cross-sectional area. Three points flexural test was performed in accordance with HB 195 [13] to determine the flexural strength of CSEBs. The blocks were tested over a span of 230 mm using a 400 kN capacity universal testing machine (UTM) at a constant loading rate of 2.5 kN/min until failure. Water absorption of CSEBs after 24 hrs immersion was determined according to IS 3495 part II [58] which is similar to ASTM C67 [59]. To examine the durability, alternate wetting–drying and sulfate attack tests were carried out on phase I blocks. Alternate wetting– drying test was performed in accordance with IS 1725 [14] which is similar to ASTM D559-96 [60] with slight modifications. Prior to test, blocks were dried in oven at 60 °C till constant weight is attained and the initial dry weight is recorded. Then the blocks were soaked in water at room temperature for 5 h, followed by oven dried at 70 °C for a period of 42 h. Remove the blocks from oven and using wire brush scratch twice on all sides of blocks corresponding to a force of 1.5 kgf. The process of wetting–drying including abrasion constitute one cycle. Twelve such cycles were repeated, and then blocks are oven dried at 60° C till to reach constant weight. Finally, the dry weight of block is noted. The mass loss is determined based on the initial and final dry weight. To assess the sulfate resistance, blocks were exposed to 3% sodium sulfate (Na2SO4) solution at room temperature. The procedure proposed by Bezerra et al. [42] was adopted. Initially, the blocks were oven dried at 110 °C for 24 hrs and dry weights were 2.6. Production of CSEBs A hand operated manual press with a compaction ratio of 1.85 was used to manufacture CSEBs of dimension 290x140x100 mm as shown in Fig. 4(a). The dried soil is in lumps was pulverized manually using rammer then sieved through 1 mm sieve. The sand and crushed brick waste are also screened from 4.75 mm sieve. The quantities of air dried ingredients such as soil, sand, crushed brick waste and cement as obtained from calculations were weighed and mixed as follows. Initially, the soil and sand were mixed then crushed brick waste was added, further blending is continued, after that cement was added and thoroughly mixed until a homogeneous mixture was obtained. The quantity of water determined individually for each mix through proctor test is adopted for molding blocks. This requisite amount of water was sprinkled gradually on to the dry mixture and turn over several times to attain uniform distribution of moisture. The prepared wet mixture was then introduced into mould of press using scoop, any excess material was removed. The mix was then compressed manually by static compaction and the block was ejected immediately and placed carefully in a level surface, Fig. 4(b). The ejected blocks were weighed and cured for 28 days under wet gunny bags after 24 hrs of casting and were then air dried for 7 days in the laboratory before testing. In phase I, the incorporation of crushed brick waste was confined to 24% because the block starts to crumble beyond this per5 Phase Mix type/ Sample type Description Compressive strength IIb CS C6 C12 C18 C24 20CF 40CF 60CF 80CF 100CF 20CM 40CM 60CM 6 80CM 100CM 20CL 40CL 60CL 100CL Water absorption c(%) Alternate wetting–drying CSEB sample with 0% crushed brick waste CSEB sample with 6% crushed brick waste CSEB sample with 12% crushed brick waste CSEB sample with 18% crushed brick waste CSEB sample with 24% crushed brick waste CSEB sample with 20% crushed brick waste of full (F) particle size 0/4.75 mm CSEB sample with 40% crushed brick waste of full particle size 0/4.75 mm CSEB sample with 60% crushed brick waste of full particle size 0/4.75 mm CSEB with 80% crushed brick waste of full particle size 0/ 4.75 mm CSEB sample with 100% crushed brick waste of full particle size 0/4.75 mm CSEB sample with 20% crushed brick waste of medium (M) particle size 0.15/4.75 mm CSEB sample with 40% crushed brick waste of medium particle size 0.15/4.75 mm CSEB sample with 60% crushed brick waste of medium particle size 0.15/4.75 mm CSEB sample with 80% crushed brick waste of medium particle size 0.15/4.75 mm CSEB sample with 100% crushed brick waste of medium particle size 0.15/4.75 mm CSEB sample with 20% crushed brick waste of particle size lesser (L) than 0.15 mm CSEB sample with 40% crushed brick waste of full particle size lesser than 0.15 mm CSEB sample with 60% crushed brick waste of full particle size lesser than 0.15 mm CSEB sample with 80% crushed brick waste of full particle size lesser than 0.15 mm CSEB sample with 100% crushed brick waste of full particle size lesser than 0.15 mm Sulfate attack Microstructural analysis Dry Dry Dry Dry p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p p x x x x SEM, XRD x x x SEM, XRD x p p p p x x x x x p p p p x x x x x p p p p x x x x x p p p p x x x x x p p p p x x x x x p p p p x x x x x p p p p x x x x x p p p p x x x x x p p p p x x x x x p p p p x x x x x p p p p x x x x x p p p p x x x x x p p p p x x x x x p p p p x x x x x Note: a: Soil-sand mixture replaced with crushed brick waste, b: Sand replaced with crushed brick waste, c: Average of five samples, d: Average of three samples, CSEB: Compressed stabilized earth block, SEM: Scanning electron microscope, XRD: X-ray diffraction. Construction and Building Materials 280 (2021) 122520 80CL Flexural strength (MPa) Compressive Flexural strength c(MPa) strength d (MPa) Dry Wet Dry I (MPa) d Compressive Flexural strength d(MPa) strength c(MPa) a c P. Kasinikota and Deb Dulal Tripura Table 4 Production and test run of CSEB samples. Construction and Building Materials 280 (2021) 122520 P. Kasinikota and Deb Dulal Tripura Table 5 Mix proportions and standard compaction results of phase I. Phase I Mix Crushed brick waste (%) Soil-sand (%) Cement (%) Optimum moisture content (OMC-%) Maximum Dry Density (MDD- kg/m3) Coefficient of uniformity(Cu) Coefficient of curvature (Cc) CS C6 C12 C18 C24 – 6 12 18 24 100 94 88 82 76 10 10 10 10 10 10.45 11.11 11.93 12.15 12.7 1932 1909 1896 1886 1875 102.4 96.8 89 85.7 82.6 7.7 11.1 12.3 12.2 13.5 Table 6 Mix proportions of phase II. Phase II Soil (%) Sand (%) Crushed brick waste (%) Cement(%) 30 30 30 30 30 56 42 28 14 0 14 28 42 56 70 10 10 10 10 10 Mix 20CF/20CM/20CL 40CF/40CM/40CL 60CF/60CM/60CL 80CF/80CM/80CL 100CF/100CM/100CL Coefficientof uniformity(Cu) Coefficientof curvature (Cc) CF CM CL CF CM CL 105.6 111.2 119.5 132.2 152 107.8 122.7 142 168.7 207 95.1 78 63.7 - 0.91 0.56 0.37 0.30 0.24 8.2 7.7 7.2 6.9 6.9 0.42 0.45 0.86 - Fig. 3. Particle size distribution curves of mixtures. (a) Phase I- crushed brick waste as substitute to soil-sand mixture (0–24%) and (b) Phase II crushed brick waste as substitute to sand  0/4.75 mm (CF), (c) 0.15/4.75 mm (CM) and (d) less than 0.15 mm (CL). noted. The blocks were then placed inside the plastic container over the support bars and the prepared sulfate solution is poured gently till to reach a height of 2 cm from the bottom surface of block as depicted in Fig. 6. The solution was replaced to 2 cm at regular intervals, after 1 week the samples were taken out of the solution and weighted. The container was emptied and blocks 7 P. Kasinikota and Deb Dulal Tripura Construction and Building Materials 280 (2021) 122520 Fig. 4. HADUL PRESS- (a) CEB making machine (b) Blocks produced. Fig. 5. OMC and MDD characteristics of phase I and II mixtures. diffractometer with Cu-Ka radiation, the data was collected using 2h angle in the range of 5°–70°. was allowed to air dry for 2 weeks and weighted. In this study the number of cycles was limited to two. A minimum of five samples mean is reported as mass variation. After completion of wetting– drying cycles and sulfate attack, the blocks were tested to determine the compressive and flexural strength. X-ray diffraction (XRD) and scanning electron microscope (SEM) tests were performed on phase I blocks after different exposure conditions to investigate the mineralogical composition, microstructure and morphology. A (CARL ZEISS-SIGMA 300) FESEM was employed to examine the products formed. XRD measurements were taken on powdered samples using PANanlaytical 3. Results and discussion 3.1. OMC and MDD characteristics 3.1.1. Influence of crushed brick waste as substitute to soil-sand mixture The OMC and MDD of mixtures with 0%, 6%, 12%, 18% and 24% of crushed brick waste are depicted in Fig. 5(a). It can be deduced that 8 Construction and Building Materials 280 (2021) 122520 P. Kasinikota and Deb Dulal Tripura Fig. 6. Sulfate attack test. Fig. 7. Status of blocks after wetting –drying cycles. When the sand is replaced with crushed brick waste particle size between 0/4.75 mm (CF), the MDD and OMC values for 20%, 40%, 60%, 80% and 100% replacement ratios are ranging between 1875 kg/m3–1658 kg/m3 and 12.17–16.66%, respectively. Similarly, the values of MDD and OMC corresponding to the particle sizes 0.15/4.75 mm (CM) and less than 0.15 mm (CL) vary from 1860 kg/m31645 kg/m3 and 11.84–16.26%; 1848 kg/m3– 1540 kg/m3 and 12.71–21.60%, respectively as tabulated in Table 7. The highest MDD value obtained for the 20CF (20% of sand was replaced by crushed brick waste of particle size between 0/4.75 mm) whereas the lowest OMC was achieved for 20CM (20% of sand was replaced with crushed brick waste particle size between 0.15/4.75 mm). Especially, at all replacement ratios the MDD values are greater for CF mixtures and OMCs are lower for CM mixtures. The higher MDD values for CF mixtures are attributed to filling effect of fines. On the other hand, removal of fines leads to lower OMC in CM mixtures. addition of crushed brick waste decreases the MDD and OMC increases, respectively. This was due to lower density and high water absorption of crushed brick waste. As the crushed brick waste content varies from 0 to 24% the OMC increased from 10.45% to 12.70% and MDD decreased from 1932 kg/m3 to 1875 kg/m3 respectively. Tests results are listed in Table 4. 3.1.2. Influence of crushed brick waste particle size and dosage as substitute to sand in soil- sand mixture The influence of crushed brick waste particle size and replacement ratio on OMC and MDD of soil-sand-cement mixtures are shown in Fig. 5(b)-(d) and Table 7. For the three different particle sizes, the MDD decreases and OMC increases with crushed brick waste replacement ratio compared to control mix. The lower bulk density and high porous nature of crushed brick waste as well as change in particle size distribution and corresponding packing potential are the plausible explanations. Table 7 Summary of phase II optimum moisture content (OMC) and maximum dry density (MDD) test results. Mix OMC (%) MDD (kg/m3) Mix OMC (%) MDD (kg/m3) Mix OMC (%) MDD (kg/m3) 20CF 40CF 60CF 80CF 100CF 12.18 13.62 15.19 16.32 16.66 1875 1825 1756 1703 1658 20CM 40CM 60CM 80CM 100CM 11.75 13.22 14.75 15.67 16.26 1860 1804 1740 1694 1645 20CL 40CL 60CL 80CL 100CL 12.72 13.97 15.64 16.82 21.6 1848 1755 1707 1616 1540 9 P. Kasinikota and Deb Dulal Tripura Construction and Building Materials 280 (2021) 122520 with crushed brick waste of 0/4.75 mm size) increased initially for 20% replacement and then gradually decreased for further replacements. The dry and wet strength of 20CF block increases by 11.27% and 12.9% compared to control CSEB. For the crushed brick waste replacement ratios of 40%, 60%, 80% and 100% the dry strength decreases by 3.87%, 6.78%, 10.44% and 11.97%; wet strength reduced by 3.97%, 10.65%, 13.92% and 15.06% respectively. The increase in strength for 20CF was due to combined effect of pozzolanic properties and filing effect of crushed brick waste fines, this agrees with [33,37]. On the other hand the reduction in strength at higher substitutions can be attributed to increase in fines content that increase the porosity as well as inferior properties of crushed brick waste relative to sand. However, a microscopic study is warranted to confirm the conclusions. Similar trends were obtained for cement mortar with ceramic masonry aggregates [62,63]. Both dry and wet strengths of blocks containing crushed brick waste of particle size 0.15/4.75 mm (CM) decreases steadily with replacement percentage. The absence of crushed brick waste fines negatively affected the strength, as the increase in quantity of coarser particles with incorporation ratio appear to increase the voids. Similar observations when coarser ceramic aggregates used instead of finer sand in stabilized rammed earth by [34]. Arrigoni et al. [39] confirmed that specimens with 100% rammed recycled concrete aggregates showed higher porosity than traditionally stabilized rammed earth mixtures. For 100% replacement ratio (100CM) the dry and wet strength decreases by about 25.51% and 28.17% compared to control sample. As it can be clearly seen in Fig. 13(a) and (b), the substitution of sand with 20% crushed brick waste particle size less than 0.15 mm (CL) resulted in slightly higher strength and then decreases drastically with further replacement level. For 20% substitution, the block strengths in dry and wet state are 9.21% and 11.13% higher than the control. With further increase in substitution rate up to 100%, the corresponding decrease in dry and wet strengths are in the range of 9.36–55.01% and 11.13–68.59% respectively. Test results are included in Table 10. The dry and wet compressive strength of blocks produced with 20CF are higher than the 20CM blocks by 1.14 and 1.2 times. The improved strength in 20CF was anticipated because of presence of fines. In general, crushed brick waste fines less than 75 mm are reactive because of firing at high temperatures [31]. During this process, active siliceous and aluminous compounds were developed. These components chemically react with hydration products of cement to form additional calcium silicate hydrates leading to strength enhancement. Thus it is clear that fines had a considerable effect on block compressive strength as noticed by [33]. In addition, when compared to 20CM, the dry and wet strength of 20CL blocks increases by about 1.12 and 1.2 times respectively. Micro filling and pozzolanic reaction of fines in 20CL contributed to higher strength as pointed by [32]. However, beyond 40% the strength of CL blocks was much lower than CF and CM blocks, which may be attributed to increase in porosity and water absorption with incorporation of fines. This is in accordant with The highest OMC and lowest MDD was obtained when sand is completely replaced with crushed brick waste of particle size less than 0.15 mm (CL100) which is due to large surface area, water absorption and lower density of fine particles compared to sand. Overall, the MDD values are higher for CF mixtures followed by CM and CL whereas the OMC values are higher for CL followed by CF and CM respectively. 3.2. Dry and wet compressive strength 3.2.1. Influence of crushed brick waste as substitute to soil-sand mixture The dry and wet compressive strength results of CSEBs with and without crushed brick waste after 28 days curing are given in Fig. 10(a). It can be seen that the incorporation of crushed brick waste improves the compressive strength significantly compared to control sample; this observation agrees with the earlier studies [35,37,40]. The average dry and wet compressive strengths achieved were lies in range of 8.20–9.57 MPa and 7.16–8.43 MPa corresponding to 0–24% crushed brick waste contents, are included in Table 8 with standard deviation. This increase can be attributed to pozzolanic effect of crushed brick waste and better particle size distribution as reported by [35,37]. For better insight, the particle size distribution of mixtures is considered, the coefficient of uniformity and curvatures exhibit an obvious correlation with compressive strengths. While testing, two types of failure modes were mostly encountered. The typical hour glass failure shown in Fig. 9(b) developed due to platen restraint effect and in Fig. 9(c) the face failure generated due to uneven compaction force applied to block during production which is in consistent with [61]. The strength reduction after 24 h immersion was varying between 11.73 and 13.6%. The reason for this low strength reduction was expected due to filling the voids between the sand particles with crushed brick waste fines as well as decrease in clay content lead to improvement in effectiveness of cement with sand grains [8,23], whereas development of pore water pressure and liquefaction of un-stabilized clay minerals caused for strength decrement in soaking condition as explained by [8]. These results are in consistent with previous studies, where the loss of strength was between 10 and 23% for samples with 4–10% PC and 30% ceramic waste [37], 5–20% loss was documented for soil-sand-lime-rice hush ash mixtures [51] and 19–33% loss reported for cement stabilized soil- granulated blast furnace slag mixtures [23], respectively. Conversely, increase in strength after 12 days soaking in water was evidenced [43]. 3.2.2. Influence of crushed brick waste particle size and dosage as substitute to sand in soil- sand mixture The average dry and wet compressive strengths of blocks with three types of crushed brick waste at different replacement percentages are illustrated in Fig. 13(a) and (b). The results show that the strength of blocks incorporating three types of crushed brick waste decreases with increase in replacement percentage relative to control sample. However, the strength of CF blocks (produced Table 8 Summary of Phase I test results. Mix/Sample CS C6 C12 C18 C24 Dry compressive strength (MPa) Wet compressive strength (MPa) Flexural strength (MPa) Water absorption (%) Average SD Average SD Average SD Average SD 8.20 8.53 8.83 9.24 9.57 0.2 0.22 0.29 0.34 0.24 7.16 7.37 7.7 8.15 8.43 0.21 0.31 0.36 0.26 0.31 2.19 2.25 2.43 2.58 2.65 0.04 0.07 0.06 0.08 0.09 8.41 9.06 9.44 9.94 10.52 0.29 0.18 0.22 0.19 0.2 10 Wet-Dry strength ratio 0.87 0.86 0.87 0.88 0.88 Construction and Building Materials 280 (2021) 122520 P. Kasinikota and Deb Dulal Tripura Fig. 8. Status of blocks after exposed to sulfate medium. Fig. 9. Compression test of block: a) Test setup b) Hourglass failure; and c) Face failure. Fig. 10. Test results of phase I blocks. 11 P. Kasinikota and Deb Dulal Tripura Construction and Building Materials 280 (2021) 122520 Table 9 Results of Phase I samples underwent wetting–drying cycles and sulfate attack. Mix/Sample CS C6 C12 C18 C24 Wetting-Drying Cycles Sulfate Attack Dry compressive strength (MPa) Flexural strength (MPa) Average SD Average SD 11.24 12.09 12.98 13.56 14.05 0.78 0.86 0.74 0.8 0.77 2.22 2.51 2.88 3.07 3.16 0.05 0.09 0.06 0.05 0.08 Mass Loss (%) 0.94 2.55 3.09 4.43 4.72 Dry compressive strength (MPa) Flexural strength (MPa) Mass Gain (%) Average SD Average SD 10.63 11.29 11.7 12.46 12.95 0.48 0.59 0.68 0.76 0.87 2.54 2.79 3.05 3.25 3.38 0.07 0.05 0.07 0.07 0.08 1.05 0.18 0.25 0.43 0.53 Table 10 Summary of phase II test results. Mix/Sample 20CF 40CF 60CF 80CF 100CF 20CM 40CM 60CM 80CM 100CM 20CL 40CL 60CL 80CL 100CL Dry compressive strength (MPa) Wet compressive strength (MPa) Flexural strength (MPa) Water absorption (%) Average SD Average SD Average SD Average SD 9.13 7.88 7.65 7.35 7.22 7.97 7.81 7.59 6.75 6.11 8.96 7.43 5.63 4.88 3.69 0.3 0.29 0.39 0.31 0.6 0.21 0.28 0.27 0.51 0.3 0.47 0.49 0.37 0.11 0.14 8.08 6.87 6.39 6.16 6.08 6.79 6.2 6.11 5.66 5.14 7.95 6.13 4.76 4.16 2.25 0.22 0.36 0.67 0.47 0.16 0.34 0.18 0.21 0.37 0.3 0.37 0.14 0.22 0.38 0.15 2.51 2.07 1.96 1.88 1.74 2.14 2.11 1.98 1.94 1.85 2.03 1.73 1.37 1.16 0.89 0.07 0.09 0.08 0.09 0.08 0.04 0.03 0.06 0.09 0.06 0.13 0.11 0.09 0.08 0.08 10.95 13.41 14.92 15.85 17.14 11.64 13.83 15.1 16.24 18.16 10.62 14.02 17.54 22.89 28.03 0.59 0.48 0.43 0.33 0.56 0.47 0.35 0.38 0.55 0.59 0.54 0.66 0.55 0.67 0.55 Wet-Dry strength ratio 0.89 0.87 0.84 0.84 0.84 0.85 0.79 0.8 0.84 0.84 0.89 0.82 0.85 0.85 0.61 for better performance was the pozzolanic activity of crushed brick waste and better grain size distribution resulted in good bonding between crushed brick waste and cement-soil matrix. Apart from pozzolanicity other parameters such as shape and roughness of crushed brick waste also contribute for strength development [33]. All blocks failed by splitting into two halves under three point loading. The mean flexural strength of blocks was about 26–28% of mean compressive strength. Corinaldesi et al. [63] who showed that finer brick waste used instead of sand increases the porosity of mortar. These results affirm that the crushed brick waste particle size has notable influence on block strength. The particle size distribution of mixtures has also been taken in to consideration to explain the strength trend with crushed brick waste substitution rate. Although, the increase in compressive strength at low replacement rates indicate that there exist an optimum particle size distribution for CF and CL blocks. However, the coefficient of uniformity and curvatures for theses mixtures presented in Table 6 did not provide a definite correlation with strength, which agrees with Arrigoni et al. [39], found no clear correlation of particle size distribution with strength for stabilized rammed earth with recycled concrete aggregates. Overall, 20CF block achieved higher compressive strength in both dry and wet state, followed by 20CL whereas for 20CM the strength in dry state is slightly less than control but in wet condition decreased significantly. The wet-dry strength ratio for CF, CM and CL blocks differ between 0.84 and 0.89, 0.79–0.85 and 0.61– 0.89 respectively. 3.3.2. Influence of crushed brick waste particle size and dosage as substitute to sand in soil- sand mixture The flexural strength of blocks incorporating three types of crushed brick waste is summarized in Table 10 and Fig. 13(c). It is evident that except for 20CF block, the flexural strength of blocks comprising three types of crushed brick waste decreases with increase in replacement percentage. The highest flexural strength of 2.51 MPa was obtained for 20CF blocks, is 14.5% greater than the control sample strength. Beyond 20%, the strength of CF blocks decreases linearly for crushed brick waste contents of 40% to 100% and the percentage decrease ranges from 5.5 to 20.4% with respect to control. The reason for the initial increase was explained by pozzolanic reactivity and roughness of crushed brick waste and later decrease at higher replacements was due to increase in amount of higher fines well as inferior properties of crushed brick waste [33,63]. Just as analogous to compressive strength, the flexural strength of blocks produced with 0.15/4.75 mm decreased steadily with replacement ratio. The percentage strength reduction varies between 2.43 and 15.37% as the crushed brick waste content varies from 20 to 100%. However, the loss of flexural strength at 100% replacement (15.37%) was lower than that of compressive strength (23.50%) which indicates that the removal of fines less than 0.15 mm did not showed significant impact on flexural strength. 3.3. Flexural strength 3.3.1. Influence of crushed brick waste as substitute to soil-sand mixture The flexural strength results and their standard deviation of blocks corresponding to phase I, are provided in Table 8. Similar to behavior of compressive strength; the flexural strength of blocks incorporating crushed brick waste was higher than the control. As shown in Fig. 10(b), the highest strength 2.65 MPa was attained for blocks produced with 24% crushed brick waste. The increase in percentage strength lies in the range of 2.9% to 21.16% as the crushed brick waste content increased from 6 to 24%.The reason 12 Construction and Building Materials 280 (2021) 122520 P. Kasinikota and Deb Dulal Tripura Substitution of sand with crushed brick waste particle size less than 0.15 mm led to a decrease in flexural strength. When compared to control sample, the flexural strength of 20CL, 40CL, 60CL, 80CL and 100CL blocks decreases by 7.15%, 21.15%, 37.60%, 46.88% and 59.36%, respectively. Except for 20CL, the strength of blocks steeply decreased with further replacement due to increase in water requirement with higher percentage of crushed brick waste fines which are considerably weak and highly porous as compared to sand. This was justified by compaction characteristics that the percentage increase in OMC of CL blocks lies in range of 33.68–106.62% as substitution rate varies from 40 to 100%. The flexural strength of 20CF was 1.2 times greater than the 20CM. However, the strengths of 40CF, 60CF, 80CF and 100CF decreases by 1.74%, 1.18%, 3.26% and 5.94% respectively with respect to corresponding percentages of CM blocks, which corroborates the removal of crushed brick waste fines, had no considerable affect on flexural strength, in fact a slight increase was observed at higher replacements for CM blocks, but in both cases the strength decreases compared to control mix. The better performance of CM blocks was explained by angularity and roughness of crushed brick waste, which are beneficial for developing bonding between crushed brick waste and soil–cement matrix. On the other hand, crushed brick waste inherent porous nature led to a lower flexural strength. The flexural strength of CF and CM blocks are higher than the blocks produced with crushed brick waste size less than 0.15 mm (CL) by about 1.23–1.95 and 1.05–2.08 times as the replacement percentage varies from 20 to 100% respectively. This is attributed to presence of coarser crushed brick waste particles in CM and CF blocks, especially for greater than 40% replacement ratios, as witnessed in previous studies [63]. Among all the mixtures studied, the lowest strength was achieved for 100CL blocks, 0.89 MPa. It is evident that incorporation of very fine brick waste in larger quantities was detrimental to the flexural strength. Overall, the CSEBs exceeded the minimum flexural strength value, 0.25 MPa specified by NZS 4298 [64] for load bearing masonry. The flexural strengths of CF, CM and CL blocks were about 24–27%, 26–30% and 22–24% of corresponding compressive strength. It was summarized that on one hand removal of fines from crushed brick waste had no notable influence on flexural strength. On the other hand, crushed brick waste fines & its percentage replacement significantly influenced the block strength. The optimum strength was obtained for mix containing 20% of crushed brick waste with particle size 4.75–0 mm (20CF). Fig. 11. Water absorption of phase I blocks. water absorption with crushed brick waste replacement ratio up to 70%, thereafter increases with further incorporation. These differences may be because of sand being replaced with crushed brick waste in this study instead of soil. In blocks produced with 0.15/4.75 mm (CM), less than 0.15 mm (CL) the water absorption values are 38.50%, 64.54%, 79.62%, 93.2% and 116%; 26.37%, 66.82% 108.73% 172.36% and 233.5% respectively higher than the control, as the crushed brick waste substitution ratio varies from 20% to 100%. Reddy and Latha [11] noticed higher water absorption when soil was replaced with silt size stone dust than with sand. From the above results, it manifests that incorporation of finer size crushed brick waste leading to higher absorption. These results confirm the wet compressive strength behavior. Despite removal of powder content, the blocks produced with 0.15/4.75 mm (CM) showed slightly higher water absorption than the blocks produced with 0/4.75 mm (CF). The increase in water absorption values are approximately ± 6% as the replacement percentage varies from 20% to 100%. It appeared to be contradictory with respect to OMC values; however the presence of fines in CF mixtures improved the microstructure by filling the pores as well as reacting with calcium hydroxide leading to dense matrix that reduces the water absorption. Especially, it was found that the water absorption of blocks produced with CL was less than the CF and CM at 20% substitution. In fact, up to 40% substitution ratio the values are comparable to CF and CM mixtures. This could be owing to filling of voids with crushed brick waste fines that hinders the water entrance in block, whereas at replacements greater than 40% this effect was no more evidenced. Indeed, at higher replacement ratios the water absorption of these blocks increases drastically. Furthermore, beyond 60% replacement the water absorption of CL blocks is exceeding the recommended value of 18% prescribed in IS 1725 [14] and 20% stated in NBR 4892 [65] as well as ASTM C62 [66] for building bricks under different weathering conditions. This was primarily attributed to higher water absorption of finer particles compared to coarser particle of crushed brick waste. Overall, in one hand the removal of powder content did not show much variation in water absorption. On the other hand the finer size crushed brick waste resulted in higher water absorption, which confirms its dependency on particle size. 3.4. Water absorption 3.4.1. Influence of crushed brick waste as substitute to soil-sand mixture The water absorption of phase I blocks increases with increase in crushed brick waste content and varies from 8.41% to 10.52% as the crushed brick waste dosage increases from 0 to 24%, as shown in Fig. 11 and Table 8. Oti et al. [35] reported 2.62–8.37% for lime-GGBS stabilized earth bricks with brick dust content up to 20%. 3.4.2. Influence of crushed brick waste particle size and dosage as substitute to sand in soil- sand mixture The effect of crushed brick waste particle size and replacement ratio on water absorption of blocks is shown in Fig. 13(d). The result indicates that, irrespective of particle size the water absorption increases as the percentage replacement increases. As it can be seen in Fig. 13(d), for blocks produced with 0/4.75 mm (CF) the water absorption values of 20CF, 40CF, 60CF, 80CF and 100CF blocks are 30.30%,59.60%,77.55%, 88.60% and 104% higher than the control. In contrast, Joshi et al. [40] reported the decrease in 3.5. Durability tests In this section, the durability of CSEBs with incorporation of crushed brick waste (0–24%) as substitute to soil-sand mixture under different conditions are presented. 13 P. Kasinikota and Deb Dulal Tripura Construction and Building Materials 280 (2021) 122520 into cementitious material, it reacts with portlandite and aluminum phases to form gypsum & ettringite, which are basically expansive in nature [68]. However, during initial period of exposure these two compounds fill the pores in composite structure and make it dense that will contribute to strength enhancement. For blocks produced with crushed brick waste, the reaction between crushed brick waste powder and portlandite led to production of supplementary CSH gels resulted in a higher strength. Thus the reduction of amount of calcium hydroxide in matrix enhanced the resistance against sulfate attack. 3.5.1. Wetting-drying resistance After completion of test, blocks were examined for any cracks/ spalling. All blocks showed minor loss of surface particles and corner damages; however the blocks containing crushed brick waste exhibited better resistance against abrasion because of good adhesion between particles and matrix. Fig. 7 shows the appearance of blocks after 12 cycles. To evaluate the effect of accelerated weathering on the mechanical performance, these blocks were tested to determine compressive and flexural strength. The results are illustrated in Fig. 10(c) and (d), Table 9. As shown in Fig. 10(c), the compressive strength of blocks underwent wetting–drying cycles are higher than the initial values obtained at ambient curing. The highest strength of 14.05 MPa was achieved by block produced with 24% crushed brick waste (C24). It has been found that the strength of control block increases by 37% after wetting–drying test, similarly for blocks with crushed brick waste varying from 6 to 24% the strength gain lies in the range of 42–47%, respectively (Table 9). Results are in consistent with studies Chaibeddra and Kharchi [44] reported more than 100%; and up to 160% strength increment by Arrigoni et al. [67] after wetting–drying cycles. The compressive strength of blocks containing 6–24% crushed brick waste increases by 1.08–1.25 times as compared with control. These increments are attributed to acceleration of cement hydration as well as pozzolanic reaction of crushed brick waste under alternate wet and dry at 70 °C temperature leading to production of additional calcium silicate hydrate (CSH) gel that further improved the rigidity of matrix [9,25]. The flexural strength of blocks went through wetting–drying cycles improved compared to initial values as shown in Fig. 10 (d). The strength values were typically between 2.22 and 3.16 MPa for the blocks with 0–24% of crushed brick waste. Furthermore, when compared to control the flexural strength increases by about 1.13–1.42 times as the crushed brick waste increases from 6 to 24%. This improvement was explained by higher roughness and irregular shape of crushed brick waste than sand in addition to pozzolanic reaction. 3.5.3. Mass variation Mass variation of blocks containing 0–24% of crushed brick waste subjected to wetting–drying cycles and to two cycles of 3% Na2SO4 solution is illustrated in Fig. 12. The mass loss increases with increase in crushed brick waste content and varies between 0.94 and 4.72% as the crushed brick waste varies from 0 to 24% (Table 9). Except for control (CS) and 6% crushed brick waste (C6) block, the mass loss of blocks with 12%, 18%, 24% crushed brick waste is exceeding the limiting value of 3% specified by IS 1725 [14], however these values are less than the maximum value of 5% in rainy climate, as recommended by ASTM D559-96 [60]. The mass loss was due to detachment of soil particles by pore-water pressure after immersion and brushing process. Furthermore, the higher water absorption of crushed brick waste induces more swelling/shrinkage on wetting–drying resulted in higher mass loss. These results are complied with [9,17] evidenced mass losses up to ± 6.5% at 8% cement content with varying clay contents. Blocks exposed to sodium sulfate solution showed gain in mass, Fig. 12. It is worthwhile to mention that, unlike oven drying in wet/ dry cycles, the blocks are air dried after Na2SO4 exposure. The highest mass gain was shown by control sample of 1.05%. Though the mass gain increases with increase in crushed brick waste content, the block containing 24% crushed brick waste exhibited lower increase in mass than the control. This behavior is typically due to formation of more ettringite crystals in control block compared to blocks with crushed brick waste, which fill the pores and consequently led to increase in mass of control block. Table 9 lists the average values. 3.5.2. Sulfate resistance Typical aspect of blocks after sulfate attack is shown in Fig. 8. No visible damages/spalling appeared on the blocks. However, a thin layer of efflorescence developed on control block sides and faces. Whereas for blocks produced with crushed brick waste, no sign of efflorescence was observed. Fig. 10(c) and (d) presents the results of blocks with crushed brick waste content of 0–24%, before and after exposure to 3% sodium sulfate (Na2SO4) solution. All blocks exposed to sulfate attack showed higher compressive strength than the initial values noted at 28 days of air curing as depicted in Fig. 11(c). The highest strength was registered for the block with 24% crushed brick waste of 12.95 MPa. The compressive strength of control blocks (CS) increases by 29.65% after exposure to two cycles in Na2SO4 solution. Similarly, for blocks with 6–24% crushed brick waste the increase in strength after Na2SO4 exposure varies in the range of 32.43–35.37%, respectively (Table 9). This increase is in consistent with earlier studies [43,44]. Moreover, compared to control the increase in strength was about 1.06– 1.22 times as the crushed brick waste varies from 6 to 24%. The flexural strength of blocks exposed to 3% Na2SO4 improved compared to control sample. As the crushed brick waste content varies from 0 to 24% the strength values were between 2.5 MPa and 3.57 MPa as shown in Fig. 10(d). The flexural strength of blocks with 6%, 12%, 18% and 24% crushed brick waste increases by 1.10– 1.33 times than the control. The reasons for improved behavior are explained as follows: In case of control block, the strength improvement was induced by cement hydration effect as well as filler effect of ettringite. In general, when sulfate was introduced 3.5.4. XRD and SEM analysis To substantiate the mechanical performance and to identify the products formed, XRD and SEM analysis were performed on control block (CS) and sample with 24% crushed brick waste (C24), before and after subjected to wetting–drying cycles and sulfate attack. The results of XRD are presented in Fig. 14. The control block (CS) contained the phases such as quartz, portlandite, little Fig. 12. Mass variation of phase I blocks. 14 Construction and Building Materials 280 (2021) 122520 P. Kasinikota and Deb Dulal Tripura Fig. 13. Test results of phase II blocks. Fig. 14. XRD data of CS and C24 samples before and after wetting–drying cycles (WD), sulfate attack (SA); E-Ettringite, CAH- Calcium aluminate hydrates, P- Portlandite (CH), G- Gypsum, Q-Quartz, and CSH-Calcium silicate hydrates. amount of ettringite; calcium silicate hydrate (CSH) and calcium aluminate hydrates (CAH). In case of C24 block, the portlandite intensity was reduced due to pozzolanicity of crushed brick waste. This indicates the strength improvement in C24 was because of pozzolanic reaction between the crushed brick waste and portlandite. 15 P. Kasinikota and Deb Dulal Tripura Construction and Building Materials 280 (2021) 122520 homogeneous structure with CSH and CAH formation with a very few amount of ettringite. After wetting–drying cycles, Fig. 15(b) illustrates the microstructure was dominant with CSH crystals as well as the ettringite formation was apparent, this observation confirmed the findings of XRD analysis. When exposed to 3% sulfate solution, the microstructure shown in Fig. 15(c) was dominated by clusters of ettringite needles. The reason might be due to presence of calcium aluminate hydrate (CAH) and portlandite (CH) that reacts with sulfate medium to from ettringite [21]. These ettringite crystals are responsible for the mass gain and strength development by filling the pores of microstructure as suggested by [68]. Thus in this study the formation of ettringite is advantageous. The SEM image of unexposed C24 sample in Fig. 15(d) showed a more compact structure with well establishment of CSH and CAH compounds. The pozzolanic nature of crushed brick waste could CS sample subjected to wetting–drying cycles showed increase in the peak of ettringite and the reduction in portlandite due to formation of additional cementitious compounds during the curing process employed [9,44]. The above observation corroborates the experimental results presented in Table 9. No significant difference was noticed in C24 sample after wetting–drying cycles. In case of sulfate exposure, the formation of ettringite and gypsum was more pronounced in CS sample; this could be explained by decrease in the peaks of CAH and CH phases on reaction with sulfate. Unlike CS sample, the ettringite formation in C24 was much lower which was attributed to decrease in amount of portlandite (CH) by the pozzolanic activity of crushed brick waste leading to a higher resistance against sulfate solution. The SEM micrographs of samples in Fig. 15 are with and without crushed brick waste exposed to different environmental conditions. As shown in Fig. 15(a) the unexposed CS sample displayed a Fig. 15. SEM images of control (CS): (a)- (c) and 24% crushed brick waste (C24) samples: (d)-(f). 16 Construction and Building Materials 280 (2021) 122520 P. Kasinikota and Deb Dulal Tripura 0.15 mm with satisfactory strengths. However, it should be mentioned that the water absorption of 100CF and 100CM blocks and also CL blocks beyond 40% replacement were much than higher than control. Thus, further investigation is needed to assess the long term durability performance of blocks.  The microscopic studies substantiate the presence of ettringite formation in control samples when subjected to wetting–drying cycles and sulfate solution, while in C24 sample mild presence was noticed. be the possible explanation. The microstructure shown in Fig. 15(e) became much denser under W-D cycles due to additional curing. Particularly, the crushed brick waste particles uniformly distributed over the matrix and induced a strong bond with soil–cement matrix. This was attributed to rough and irregular surface of crushed brick waste lead to higher strength in C24 samples. In sulfate exposed sample Fig. 15(f), the microstructure remains undisturbed except the formation of a little amount of ettringite. 4. Conclusions The present study demonstrated that crushed brick waste has potential to replace soil-sand mixture and sand for the production of compressed earth blocks without compromising mechanical and durability performance by highlighting the influence of particle size and replacement ratio. However, further investigation is needed to assess the long-term performance such as ageing tests. A detailed experimental study was conducted to evaluate the influence of crushed brick waste to replace soil-sand mixture and its particle size and replacement ratio as a substitute to sand on the properties of compressed stabilized earth blocks. In addition, microscopic studies are also highlighted. The following conclusions drawn based on the experimental results: CRediT authorship contribution statement  The OMC increases and MDD decreases as the percentage of crushed brick waste increases. This is primarily due to higher water absorption and lower density of crushed brick waste compared to natural sand as well as change in particle size distribution and corresponding packing potential.  The compressive (wet-dry) and flexural strengths enhanced with crushed brick waste addition of up to 24%. After wetting–drying cycles, sulfate exposure the strengths further improved due to formation of additional compounds. Despite within the limits, the mass loss after wetting–drying cycles increases with the crushed brick waste percentage. Whereas, mass gain was noticed when exposed to sulfate medium, the highest mass gain was observed in control sample. The block containing 24% crushed brick waste reported the highest mechanical resistance and better durability performance.  Crushed brick waste particle size and replacement ratio significantly influence the OMC-MDD characteristics and mechanical properties. The removal of fines leads to decrease in OMC of mixtures than the other particle sizes. The highest OMC value of 21.60% is obtained for the 100CL mixture.  For the three different particle sizes, the compressive and flexural strengths of blocks decreases as the replacement level progressed to 100%, except for 20CF and 20CL blocks. The strengths of 20CF blocks is higher than the control, while for 20CL blocks the compressive strength was higher and flexural strength was lower compared to control.  The removal of fines less than 0.15 mm lowers the compressive strength compared to CF blocks and control sample, whereas no significant impact was observed on flexural strength. In fact, the strength was improved compared to CF at higher replacement levels.  Blocks prepared by replacing the sand with crushed brick waste fines less than 0.15 mm (CL) showed adverse effects beyond 40% replacement. Both the compressive and flexural strength decreases by more than 50% corresponding to 100% replacement, thus complete replacement of sand with crushed brick waste fines is not recommended.  In phase I and II, irrespective of particle size the water absorption of blocks increases as the crushed brick waste percentage increases. The highest water absorption of 28.03% was noticed at 100% replacement level of sand by finer crushed brick waste (100CL).  The optimum content of crushed brick waste to substitute sand with improved behavior is 20% for particle sizes 0/4.75 mm and less than 0.15 mm. The sand can be totally replaced with crushed brick waste 0/4.75 and 0.15/4.75 mm with acceptable strengths and up to 80% with crushed brick waste less than Kasinikota Pardhasaradhi: Formal analysis, Investigation, Methodology, Writing - original draft. Deb Dulal Tripura: Conceptualization, Resources, Supervision, Writing - review & editing. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgements The authors are grateful for the support provided by Central Research Facility, National Institute of Technology Agartala during the experimental program. Moreover, the authors thankfully acknowledge the Central Instrumentation Center, Tripura University for SEM testing. Funding This work was supported by Science and Engineering Research Board (SERB), Grant no: EEQ/2017/000001, Department of Science and Technology, Government of India. References [1] A.L. Murmu, A. Patel, Towards sustainable bricks production: An overview, Constr. Build. Mater. 165 (2018) 112–125, https://doi.org/10.1016/ j.conbuildmat.2018.01.038. [2] Y. Kulshreshtha, N.J.A. Mota, K.S. Jagadish, J. Bredenoord, P.J. Vardon, M.C.M. van Loosdrecht, H.M. 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