With the increasing utilization of underground space, engineering muck has become a potential urban risk. This study employed a waste-to-waste strategy to promote its low-carbon recycling by using rice husk ash (RHA) as a stabilizer, with a focus on elucidating the stabilization mechanisms through multi-scale analysis. The results showed that RHA synergized with cement, enhancing unconfined compressive strength and water stability, while reducing the specific surface area and swelling potential of the engineering muck. The optimal RHA dosage was found to be between 4 % and 6 %, with cement content ranging from 3 % to 9 %. The multi-scale analysis demonstrated that the stabilization mechanisms of RHA-cement stabilized soil were governed by two main factors: structural enhancement and surface modification, both of which were driven by the promotion of novel hydration products through the incorporation of RHA. Specifically, the needle-like and columnar minerals effectively filled soil pores, forming a dense, robust skeletal structure that enhanced the mechanical properties of the stabilized soil. Meanwhile, the honeycomb-like C-S-H gel adhered to soil particle surfaces, repairing cracks and reinforcing interparticle bonding, thus improving the overall structural integrity. AFM analysis further revealed that the honeycomb-like C-S-H gel consisted of rod-like nanoparticles that were regularly arranged on the soil surface. This feature increased surface roughness, reduced fractal dimensions, and created a multi-scale structure of micro-papillae and nano-hairs with a lotus leaf effect, significantly enhancing the hydrophobic properties of the soil.

This research compares the stabilization efficiency of kaolinite and montmorillonite clayey soils using two industrial and agricultural by-products, namely fly ash (FA) and rice husk ash (RHA), activated by sodium hydroxide (NaOH). To this end, various proportions of FA and RHA (i.e., 0%, 5%, 10%, 15%, and 20%), along with NaOH solutions at 2 M and 4 M concentrations, are utilized to treat both low-and high-plasticity clayey soils. The resulting geopolymers are then subjected to a wide range of mechanical and micro-structural tests, including standard compaction, unconfined compressive strength (UCS), ultrasonic pulse velocity (UPV), swelling potential, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). Results show that incorporating both FA and RHA into kaolinite and montmorillonite clays up to their respective optimal contents significantly enhances all their mechanical properties. However, FA-based geopolymers exhibit superior mechanical properties compared to RHA-based ones under similar additive contents and curing conditions. Accordingly, the optimal FA content is found to be 15%, while for the RHA-based geopolymers, the peak UCS is observed at 15% and 10% RHA for kaolinite and 10% and 5% RHA for montmorillonite when treated with 2 M and 4 M NaOH solutions, respectively. The results also suggest that FA is more effective than RHA in controlling the swelling potential of both kaolinite and montmorillonite soils. Microstructural analyses further corroborate the findings of macro-scale experiments by showcasing the comparative occurrence of geopolymerization, as well as the formation of cementitious gels, and synthesis of new chemical products.

This study examines the use of low-value rice husk ash as a stabilizer to optimize the mechanical performance and strength of compressed earth blocks made with local soil from the Cauquenes Province, Chile. The use of locally sourced earth construction materials in Chile is limited by their lower compressive strength compared to conventional fired bricks, along with the demanding seismic conditions of the region. To address these limitations, this study details the methodology for collecting, preparing, and mixing raw materials to manufacture compressed earth blocks, compacted under 10 MPa using a novel cylindrical polylactic acid mold designed for miniaturized samples. Fourteen different samples representing nine mixtures of rice husk ash and soil were evaluated using an optimized experimental design. The resulting mechanical properties, including fracture analysis correlated with performance, were assessed through statistical analysis to determine the significance of the optimum mix and the observed trends in strength, modulus of elasticity, yield strength, and associated plastic work. The maximum compressive strength achieved was 3.3 MPa. Notably, the optimum mix of rice husk ash-stabilized compressed earth blocks exhibited a 60% increase in strength compared to pure soil compressed earth blocks, demonstrating the potential of rice husk ash as a cement substitute.

Black cotton soil's notable swelling and shrinkage contribute to structural damage. This study examines the impact of nano rice husk ash (nRHA) variants on this soil: One synthesized in 60 h and another through 7 h combined dry-wet milling method. The primary objective is to assess the effects of nRHA treatment on the soil's index properties, engineering characteristics and swelling behavior. Laboratory tests including free swell index, Atterberg's limits, swelling potential, swelling pressure, unconfined compressive strength and consolidation tests were conducted on black cotton soil samples treated with both nRHA variants. Results indicated that the 7-h nRHA treatment led to lower plasticity and reduced swelling compared to the 60-h variant. Specifically, the 7-h treated soil showed decreased swelling pressure, compression index and rate of primary swelling, along with increased pre-consolidation pressure and unconfined compressive strength. The free swell index also decreased by 21% with the 7-h nRHA treatment. The superior performance of the 7-h milled nRHA is likely due to its higher calcium and reactive silica content, enhancing its stabilizing effect. This research highlights the 7-h nRHA as a more effective stabilizer for black cotton soil, offering a promising solution to mitigate its problematic volumetric behavior.

Two common waste by-products in Thailand, rice husk ash (RHA) and coir fiber (CF), were used alongside lime (L) to stabilize laterite soil and create a sustainable subbase material for pavements. The mechanical properties of the laterite soil mixed with RHA, lime, and CF were evaluated through compaction characteristics, unconfined compressive strength (UCS), California bearing ratio (CBR), scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX) analyses. The dry soil mass was replaced with 10% and 20% RHA, and CF was added at 0.5%, 1%, and 1.5%. Additionally, based on the initial consumption of lime (ICL) test, 8% lime was incorporated into the mixture. The samples were cured for 7 days (short-term) and 56 days (long-term) before undergoing various tests. In terms of compaction, results showed that increasing the content of RHA, CF, and lime led to a decrease in maximum dry unit weight and an increase in optimum moisture content. The 10RHA8L and 20RHA8L mix designs demonstrated the highest UCS and CBR values after 56 and 7 days of curing, respectively. EDX analysis revealed the formation of calcium silicate hydrate (C-S-H) and calcium aluminate hydrate (C-A-H) gels on the particle surfaces, leading to a denser and more cohesive structure. Based on these findings, the mixture containing 20% RHA and 8% lime exhibited the most favorable properties for use as a subbase material in road and embankment construction.

Highway, road, and airfield construction on weak soils is costly endeavor. Re-use of agricultural waste is widely employed as a stabilizing agent to improve engineering properties of these soils. In this study, rice husk ash (RHA), a by-product of incineration of husk from rice production, was used as a potential stabilizer. The water absorption and retention rate of the stabilizer, denoted as W-ab, is determined by measuring the amount of water that is absorbed and retained by the stabilizer in relation to its initial dry mass. The study involved treatingAo clay, imitating a dredged soil with highwater content, at various addition ratios (ARHA). Diverse curing periods were applied to assess the liquid limits (w(L)), plastic limits (w(P)), and cone index (q(c)) of the treated clays. Compaction characteristics were also determined for several ARHA and different curing periods. The test results show an increase in both w(L) and w(P) with decrease in plastic index (I-p) with increase in ARHA, but no remarkable change in w(L) and w(P) associated with curing. Compaction characteristics show a decline in rho(dmax) and increase in wopt with increase in ARHA, but no notable changes in rho(dmax) and wopt with cured samples. Increase in q(c) with ARHA, but no noteworthy change in q(c) with curing was discerned through cone index test. The trends for curing observed in the above test results were consistent with that observed for W-ab. The results were then modified based on the W-ab of stabilizer. The measured water content (w) and liquidity index (IL) were modified to account for absorbed water (w*), which gave a better correlation with q(c) than w. The compaction characteristics were also modified based on Wab, ARHA and the results suggest that treated clays were able to achieve modified dry density (rho(dmax)*) at the same values of modified water content (w(opt)*).

The United States' top provider of long-grain rice is Arkansas. The burning of the outer shell of paddy under controlled circumstances generates rice husk. A significant portion of the ash created during the rice-milling process is silicate, which is a pozzolanic substance that may enhance the strength of poor soils. By examining two local subgrade soils from Arkansas, the primary goal of this study is to determine the optimal amounts of hydrated lime, Rice Husk Ash (RHA), and RHA + lime. Various tests, including the Atterberg Limits, Modified Proctor, Unconfined Compressive Strength (UCS), California Bearing Ratio (CBR), pH, and Free Swell (FS), were performed on the treated soils. The findings of the tests indicate that the maximum dry density and plasticity of the soil are decreased by both RHA and lime. On the other hand, adding either RHA or lime improved the treated soils' strength characteristics. According to the FS results, the soil's swelling was decreased by both RHA and lime. But it was shown that lime was more successful than RHA in lowering the FS of soils. RHA has no discernible impact on soil pH; however, lime causes a significant rise in pH. It was found that the best dosages for treating both soils were 6% RHA and 3% lime. The swelling potential may be decreased, and the strength properties could be enhanced by the combination of RHA and lime. Based on laboratory test findings, it is recommended to stabilize poor subgrade soils using 4% RHA + 1% lime.

The increasing volume of surplus soil generated from excavation works in infrastructure projects such as roads, railroads, and subway facilities poses significant environmental and logistical challenges, particularly in terms of its disposal. Therefore, the development of engineering technologies that promote the effective use of surplus soil has intensified. Among surplus soils, clay is soft and must be treated when used as a backfill or fill material. Cement-based stabilizers are commonly used for soil treatment; however, the production of cement involves high carbon-dioxide emissions, which conflicts with Japan's carbon-neutrality goals. This study investigates the use of alternative stabilizers derived from biomass waste, specifically palm kernel shell ash (PKSA) and rice husk ash (RHA), to treat clayey soils intended for use as a backfill material in road construction. Experiments are conducted to evaluate the compaction and consolidation properties of clayey soils treated with PKSA and RHA. The results indicate that both stabilizers reduced the maximum dry density and increased the optimum water content of the treated soils. PKSA and RHA treatments enhanced compaction control, particularly on the wet side above the optimum water content, thus facilitating the achievement of a high compaction degree of 95 % under high initial water contents. Consolidation test results indicate that treatment with PKSA and RHA increases the consolidation yielding stress and reduces the volume compressibility, and that these effects are more pronounced at higher compaction levels. These results suggest that adding PKSA or RHA can expand the load range that exhibits elastic settlement and may reduce the consolidation settlement. At the same addition rate, PKSA treatment increases the consolidation yielding stress more significantly than RHA treatment. Additionally, PKSA treatment improves the stiffness and reduces the hydraulic conductivity at lower consolidation pressures compared with RHA treatment, thus indicating the greater effect of PKSA. Based on results of scanning electron microscopy, the enhancement in the stiffness and permeability afforded by PKSA is attributed to the formation of needle-like ettringite crystals, which strengthened the soil structure. By contrast, RHA treatment results in densely packed particles, which is attributable to limited hydration reactions caused by low CaO and high SiO2 contents. Thus, different mechanisms can result in different consolidation parameters of PKSA- and RHA-treated clays. However, both the PKSA- and RHA-treated clays indicate reduced coefficients of volume compressibility and permeability at a compaction degree of 95 %, with a stabilizer-to-clay ratio of up to 15 % by dry mass. Because neither PKSA nor RHA require high addition rates to improve the properties of surplus soft clays, these results suggest that PKSA and RHA can effectively enhance the compaction and consolidation properties of clayey soils. PKSA and RHA treatments are sustainable alternatives to the conventional cement-based treatments and support the environmental goals of construction projects.

This study investigates the enhancement of strength, durability, and shrinkage parameters of poorly graded silty sand through stabilization using local wastes. Brick kiln dust and rice husk ash were utilized as additives alongside cement as the primary stabilizer. The strength assessment included unconfined compressive strength and indirect tensile strength tests, while durability was evaluated through wet-dry cycles. Shrinkage effects were studied over a 28-day curing period in a humidity chamber maintained at constant relative humidity. Microstructural analysis involved particle size and elemental characterization of stabilized soil mixtures. Results demonstrate significant improvements in both strength and durability when using the admixtures. The combination of cement with brick dust and rice husk ash proved effective in enhancing the engineering properties of the silty sand. Specifically, the 7-day unconfined compressive strength results indicate potential for replacing granular sub-base layers in low volume road construction. In conclusion, the study recommends the use of brick kiln dust and rice husk ash as suitable admixtures for stabilizing poorly graded silty sand, offering sustainable solutions for infrastructure development with improved performance characteristics.

Thailand's highway development project and expansion of the main road are currently being built or planned. The development of stabilizing techniques in soils with various agents has been adopted since the early days due to the insufficient availability of local materials and their unsatisfactory engineering properties. Rice husk ash's (RHA) partial replacement of geopolymers in road-based applications received less attention. This study examines the engineering properties of clay (C) treated by kaolin-rice husk ash geopolymer (K-RHAGP). The ordinary clay is activated by sodium hydroxide solution. The appropriate proportion of kaolin:rice husk ash (K:RHA) of 70:30 stimulated by a sodium hydroxide solution of 8 molars exhibits the highest unconfined compressive strength (qu). Clay is treated by kaolin-rice husk ash geopolymer (K-RHAGP) with various ratios of C:K-RHAGP by weights of 90:10, 80:20, 70:30, 60:40, and 50:50. The results showed that the optimal C:K-RHAGP proportion of treated clay is 70:30, which yielded the highest qu at 7 days under curing temperatures of 70 degrees C and 50 degrees C, resulting in values of 9352 and 4557 kN/m2, respectively. The highest split tensile strength under 70 degrees C and 50 degrees C curing temperatures was 1182 and 576 kN/m2, respectively. The relationship between the modulus of elasticity at 50% strength, E50, and qu is expressed as E50 = 4.531qu. After wet and dry processes, the samples with the C:K-RHAGP ratio of 70:30 exhibit the highest strengths of 2445.89, 1670.55, and 1218.68 kN/m2 for 3, 9, and 12 wet-dry cycles corresponding to the lowest weight loss. The C:K-RHAGP weight loss of 70:30 in cycles 1 to 12 was 1.5 to 7.2%. The authors believe that the proposed K-RHAGP stabilization could be used as an effective replacement for cement-based soil stabilization in road-based construction.