In subgrade engineering, silty clay often deforms and fails due to poor strength and water stability. This study investigates the compaction and shear properties of high-moisture-content silty clay modified by quicklime. Through compaction tests and direct shear tests, the effects of different lime admixture levels and curing conditions on the compaction and shear properties of the modified soil were analyzed. The results show that the maximum dry density of the modified soil decreases linearly with the lime admixture, while the optimal moisture content increases quadratically with the lime admixture. Excessive lime admixture cannot effectively improve the optimal moisture content of the modified soil, the compaction performance of the modified soil is optimal when the lime admixture is 7 %. The incorporation of lime significantly improves the cohesion and internal friction angle of the soil. Cohesion increases with the lime admixture, while the relationship between the internal friction angle and lime admixture is not significant. Curing conditions have a significant impact on the mechanical properties of the modified soil. Under low lime admixture, immersion curing conditions significantly deteriorate the shear strength of the modified soil, while under high lime admixture (7 %, 9 %), the modified soil exhibits good water stability. Moreover, the modified soil exhibits better shear strength and water stability under higher vertical stress. The research findings reveal the mechanical and deformation characteristics of lime-modified silty clay and provide important guidance for its practical engineering application.

The additions of microbial organic fertilizer (MOF), a microbial inoculant (MI), and quicklime (Q) are considered to be sustainable practices to restore land that has been damaged by continuous cropping of pepper (Capsicum annuum L.). However, the combined effects of these three additives on pepper yield, soil chemical properties, and soil microbial communities were unclear. The experimental design consists of 13 treatment groups: the untreated soil (control); soil amended solely with three treatments for each of MOF (1875-5625 kg ha-1), MI (150-450 mL plant-1), and Q (1500-4500 kg ha-1); and soil amended with combinations of MOF, MI, and Q at three comparable concentrations. A significant increase in pepper fruit diameter, length, yield, and soil available nitrogen, phosphorus, and potassium contents occurs upon exclusive and combined applications of MOF, MI, and Q. Pepper yield was greatest (29.89% more than control values) in the combined treatment with concentrations of 1875 kg ha-1 MOF, 150 mL plant-1 MI, and 1500 kg ha-1 Q. The application of Q increased soil pH and reduced soil-fungal richness. The application of MOF, MI, and Q increased the relative abundance of bacterial genera and the complexity of bacterial and fungal co-occurrence networks compared with control levels. The combined application of MOF, MI, and Q resulted in the greatest microbial network complexity. A Mantel test revealed the key role of soil available nitrogen content and bacterial diversity in the regulation of pepper growth and yield. We conclude that the combined application of MOF, MI, and Q improves soil nutrient availability and modifies soil microbial community composition, significantly promoting plant growth and pepper yield during continuous cultivation.

The hydrocarbonated shale (HCS) is a voluminous by-product in coal mines. It is useless and generates adverse impacts on environmental issues. This paper aims to utilize the waste hydrocarbonated shale (HCS) from the Tazareh Coal Mine in nano-scale particles to enhance the mechanical properties of low-strength kaolin clay (KC). The HCS is chemically rich in pozzolanic requirements. Its nanoparticles proportionally (5, 10, 15, and 20wt%) contributed to designing 10 mixes, which were cured until the ages of 3, 7, and 28 days. As an alkali activator, 3wt% of quicklime was added to mix designs. The nano HCS decreased the plasticity index (PI) and maximum dry density (MDD) of KC while it increased the optimum moisture content (OMC). The greatest decrease in PI values (threefold) and MDD occurred when 15wt% nano HCS and 3wt% quicklime were mixed with KC. The unconfined compressive strength (UCS) test results showed that mixing 15wt% nano HCS with KC, in the presence or absence of 3wt% quicklime, increased the UCS values by 4.8 and 3.6 times higher than the control sample after 28 days of curing, respectively. Also, the modules of elasticity (E50) increased by 5.4 times when similar additive proportions were added to the KC, leading to a more brittle behavior. New crystal phases, including dolomite, albite, and fayalite, enhanced the strength of KC after 28 days of curing. Developing the amorphous phases of polymeric bonds improved the strength of KC. The growth of stable minerals modified the textural fabrics of KC to a denser structure mainly by solid solution reactions.

Quicklime (CaO) or reactive magnesia (MgO) could be utilized as a novel activator of ground granulated blast-furnace slag (GGBS) to produce the geopolymer. The geopolymer was used to solidify soft soil, showing a significant environmental benefit over conventional Portland cement. In this study, the geopolymers were made according to the weight ratio of CaO/MgO to GGBS of 1:9 and 2:8 and were further used to solidify silty clay. The engineering and microstructural characteristics of the solidified silty clay were investigated through various physicochemical, mechanical, and microscopic tests. The results indicated that the unconfined compressive strength of the solidified specimens increased with the increase of activator ratio and curing period. The CaO-GGBS (CG)-solidified soil had a higher unconfined compressive strength than the MgO-GGBS (MG)-solidified soil after 7-day curing, while the MG-solidified soil showed good mechanical properties in the long run. The pH and electrical conductivity of the solidified soils gradually decreased with the decreasing binder dosage and the increasing curing period, and these values of MG-solidified soils were lower than those of CG-solidified soils. Based on XRD analysis, the CSH and hydrotalcite were confirmed to be the main hydration product of both CG/MG-solidified soils in filling the large pores, and the reinforcement mechanism model for the soil treated with CG/MG geopolymers was also proposed. The research results demonstrated that CG/MG geopolymers can be used as a binder to solidify soft soils.

Alternative building materials, such as adobe and rammed earth, can help reduce construction costs and carbon-dioxide emissions, making them an important part of sustainable building practices. Rammed earth building walls are substantial, long-lasting, heat-resistant, and recyclable because they are constructed by compressing naturally damp soil between temporary forms. Using mud in contemporary buildings presents several challenges, including durability and strength. This study investigated the impact of incorporating regular portland cement, quicklime (calcium oxide), and a self-polymerizable acrylic-based resin (a transparent bonding agent) into a soil mixture to address these problems. The optimal moisture content that maximizes compressive strength was also investigated. The results demonstrated that the optimum moisture content for maximum compressive strength and dry density was identical as the soil content in a mixture increased. The increase in the compressive strength and reduction in cracking can be attributed to the optimal proportions of regular portland cement, self-polymerizable acrylic-based resin, and quicklime. This study can serve as a guide for mixing appropriate proportions of materials that would yield the optimum mechanical properties for rammed earth construction in hot arid regions.