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This study proposes a novel method for managing surplus soil in urban construction projects by investigating the use of banana leaf powder (BLP) as an eco-friendly and efficient mud-soil stabilizer. This study is pioneering in its focus on the use of an agricultural waste product, BLP, as an alternative to conventional methods that frequently rely on cement or lime, which pose environmental concerns owing to their high alkalinity and carbon emissions. BLP, derived from dried and pulverized banana leaves, traditionally used in various industries, was evaluated for its suitability as a stabilizer against orange peel biopolymer (OBP) and fly ash (FA). The findings of this study are groundbreaking. BLP's water absorption capacity, Wab, although lower than that of OBP, was significantly higher than that of FA, demonstrating its potential as a mud soil stabilizer. BLP increased the compaction and strength of the treated clay, whereas OBP made it more challenging to compact the clay owing to gelatinization. The ease of compaction with BLP is attributed to the absorption of free water into the pores of the particles. These results suggest that differences in the stabilizer's water absorption mechanism affect the effectiveness of the post-treatment compaction process on the treated soil. An analysis of the impact of water absorption capacity on the cone index, qc, revealed a material-independent relationship between the parameter β (=Wab × A, where A denotes stabilizer addition content) and qc for BLP and FA. This is because, in contrast to OBP, BLP and FA did not gelatinize the free water that was not absorbed by the stabilizer and remained in the same form within the treated clay. This indicates that understanding the water absorption capacity and mechanism of organic- or inorganic-based stabilizers is important for predicting the strength of treated soil. The same relationship between β and qc holds true for the hybrid-treated clay using both BLP and FA, with β considered to be the sum of β for both BLP and FA. Furthermore, this study innovatively addresses the concern of BLP decay in treated soil by creating a hybrid stabilizer with FA and conducting experiments to accelerate BLP decay using fungal mycelia. These experiments revealed that the hybrid-treated clay exhibited a more gradual decrease in carbon content and stabilized pH levels, implying that FA could inhibit decay by fungal mycelia, improving the BLP-treated soil's long-term durability. These findings suggest that agricultural wastes with high organic content can be effectively used for soil stabilization and ground improvement in civil engineering construction and maintenance projects by combining inorganic materials and taking advantage of their properties, such as high water absorbency. This can address the issues (such as high alkalinity and high carbon dioxide emissions) associated with cement- and lime-based stabilizers, which were previously widely used.

This study aimed to address and overcome the inherent challenges associated with the influence of primary curing on the consistency, compaction, and strength attributes of clays treated with biomass ash, specifically palm kernel shell ash (PKSA) and rice husk ash (RHA), for stabilization. Primary curing refers to the time from the addition of PKSA or RHA to the clay until its use for fill or backfill purposes. This study explores the effect of curing on the water absorption capacities of PKSA and RHA to elucidate the treatment mechanisms that shape the characteristics of the treated clays. Wab, which is the amount of water absorbed by 1 g of each stabilizer, was determined using the suction filtration technique. PKSA exhibited a significant increase in Wab with an increase in the curing period t. Wab of RHA showed no significant variation with t. The water absorption mechanisms of each stabilizer were successfully demonstrated using scanning electron microscopy (SEM) images and X-ray diffraction (XRD) patterns. It was also observed that the impact of primary curing on the limit states, compaction, and strength of the clays treated with PKSA and RHA differed significantly. The observed differences are consistent with the variation in Wab with respect to t between PKSA and RHA. The test results also suggest that changes in the free water content of the clays owing to water absorption by PKSA and RHA are closely related to changes in the properties of the PKSA- and RHA-treated clays. Parameter β represents the product of Wab and the addition ratio of each stabilizer, A, relative to the mass of the dry clay. The contributions of β to the limit states, compaction, and strength attributes of PKSA- and RHA-treated clays were much more significant than those of A.

Major challenges are encountered when using high-water-content clays as construction materials owing to their low shear strength and high compressibility. Processes, such as sun drying and stabilization using chemical agents, can address the problems met with these clays during their conveyance and reuse. However, natural dehydration is a time-consuming process, and chemical stabilization can lead to an increase in the hydrogen ion index (pH) of the surrounding environment. Thus, the aim of this study is to improve the performance of high-water-content clay using a combination of green and byproduct materials, specifically bamboo chips and fly ash, which are cost-effective and eco-friendly. No previous study has attempted to design a mixture for the purpose of improving the performance of clay based on the water absorption and retention performance of stabilizers. In this study, the water absorption and retention rate (Wab), which is the mass of the water absorbed and retained by 1 g of each stabilizer, was measured by removing the unabsorbed and unretained water through filtration under vacuum suction. A series of Cone Index tests were conducted on clay, separately treated with bamboo chips and fly ash, and the tests demonstrated a correlation among the Cone Index (qc), Wab, and amount of stabilizer added (Ast). A novel mixture design was proposed for hybrid-treated clay, using the two types of stabilizers in the composite, based on parameter β, which is defined as the sum of the product (Wab/100)×(Ast/100) of each stabilizer used in the hybrid-treated clay. The results of the Cone Index tests performed on the hybrid-treated clay showed that the proposed mixture design can predict the combinations of certain amounts of each stabilizer needed to attain the target qc with minimal errors. The results of pH measurement tests indicated that the hybrid-treated clays produced by the proposed mixture design were more eco-friendly than fly ash-treated clays. Furthermore, the theoretical maximum CO2 fixation capacities of the hybrid-treated clays were evaluated to assess their feasibility as CO2-fixing materials.

In this study, a novel testing method was developed to evaluate the water absorption and retention of waste-based stabilizers using suction filtration. Suction filtration was seen to remove most of the unabsorbed and unretained water from the waste-based stabilizer without losing any waste-based stabilizer particles. Therefore, oven-drying of the wet stabilizer, which can deteriorate the stabilizer, was not necessary. In addition, a formula was introduced to estimate the residual free water in the stabilizer after suction filtration based on the particle size. This estimate was used as a correction to determine the water absorption and retention rate (Wab) of the stabilizer. Subsequently, newly developed tests were conducted on fly ash (FA), a paper sludge ash-based stabilizer (PSAS), biomass ash (BMA), and the PSAS–BMA hybrid to evaluate Wab. The results show that the PSAS exhibited the highest Wab, followed by the BMA and FA. This is attributed to the CaO content of each stabilizer, which may have initiated hydration reactions. The Wab of the PSAS–BMA hybrid was similar to that of the PSAS, which is attributed to the synergistic effects of the components of each type of waste. Finally, the strength development of the FA, PSAS, BMA, and PSAS–BMA hybrid-treated clays was investigated via cone index tests. In addition to the stabilizer addition ratio (A), the Wab of the stabilizers is suggested to be an essential indicator for predicting the strength development of clays treated with waste-based stabilizers. Parameter β, which is the product of Wab and A, governs the cone index qc of the treated clays instead of A and Wab. Thus, the modified water content, w*, which considers the absorbed and retained water as a solid instead of a liquid, was applied to the cone index test results. The results show that the qc of the treated clays is more correlated to w* than to the measured water content. An empirical relationship for predicting cone index qc using w* was also proposed.

In an attempt to reduce environmental impact, paper sludge ash (PS ash) has recently been studied for its complementary reuse with cement for soil stabilization. In order to establish the optimal mixture design for combining PS ash and cement in soils, a detailed investigation into the stabilizing mechanism is required. To assess the combined effects of PS ash and cement on the strength development of stabilized clay soil, referred to as PS ash–cement-treated clay, a new critical parameter, the unabsorbed and unretained clay-water/cement ratio W*/C, was proposed. To determine W*/C, a new testing method for evaluating the water absorption and retention performance of PS ash was developed. It was revealed that the water absorption and retention rate Wab of PS ash increased with curing time. Unconfined compression tests conducted on the PS ash–cement-treated clay with various water-cement–PS ash mixture proportions and different curing times affirmed that the strength development was fundamentally governed by the parameter W*/C. This suggests that the water absorption and retention rate Wab obtained by the developed method is an essential material parameter in the mixture design for the PS ash–cement-treated clay. It was also found that the effect of the hybrid treatment method, which uses both cement and PS ash, was better than that of the method which uses cement alone, particularly under high W*/C conditions. This indicates that the water absorption and retention performance of PS ash can be fully utilized when the mixture has sufficient unabsorbed and unretained water for cement hydration.