This research aims to isolate and identify calcite-precipitating bacteria and investigate whether they can be used in concrete to enhance its mechanical qualities and self-healing capabilities. Microbial-induced precipitation of calcium carbonate is a new technique for making cement concrete stronger. The present study aims to compare cement concrete's compressive and split-tensile strengths to those of conventional concrete to examine the possible use of alkaliphilic bacteria to improve its qualities and ability to self-repair hairline cracks in concrete. Through conducting experiments on concrete samples at ages 7, 28, and 56 days, to which the isolated bacteria were added and characterized at the molecular level using the AccuPrep Genomic DNA Extraction kit, amplified, and subjected to agar gel electrophoresis, the sequences were obtained and compared with those in the GenBank database using the BLAST tool in the NCBI-GenBank database. Using PCR and scanning electron microscopy, it was confirmed that the isolated alkaline bacteria had a 99.69% identity rate. The bacteria Alkalibacterium iburiense were used at different concentrations of 105and 108. Additionally, 2% of recycled coarse aggregate and 10% & 20% was used. It was found that the concrete properties were improved. It was determined that the optimum improvement in mechanical properties was with the addition of bacteria at a concentration of 108 and a total recycled aggregate ratio of 10% after 56 days. The compressive, tensile, and flexural strengths increased by 25.75%, 17.27%, and 19.4%, respectively.

In recent years, owing to the advancement of highway infrastructure, modified asphalt has been extensively employed in pavement engineering. Asphalt mixture will invade the soil under high-temperature conditions, affecting soil cracking. Cracking characteristics caused by dryness of the mixed samples of modified asphalt and soil accounting for 0%, 2.5%, 5%, and 7.5% of the total weight were investigated in this paper. According to the water loss situation, the degree of cracking was determined. The crack development was quantitatively analyzed by digital image processing technology, so as to analyze the influence of modified asphalt on soil cracking under different contents. The results show that the soil was relatively better than the normal state. Under the same conditions, the moisture content of modified asphalt soil with 2.5%, 5%, and 7.5% increased by 30.17%, 63.49%, and 110.37% compared with that without modified asphalt. At the same time, due to its special bonding properties, it can effectively improve the cracking of soil. The cracking rate of modified asphalt soil with 2.5%, 5%, and 7.5% content is reduced by 11.58%, 20%, and 31.58%, respectively. The soil added with modified asphalt can effectively increase the total porosity of the soil, thus improving the ability of water absorption, and also can well inhibit the rate of soil evaporation and reduce cracking. Modified asphalt can be rationally applied not only to have soil mechanical properties improved but also to have waste asphalt utilized to reduce environmental pollution.

Strongly alkaline dispersive soils pose a significant global challenge to both engineering applications and agricultural production, particularly in arid and semi-arid regions. Conventional soil modifiers used to address this issue not only present environmental and economic concerns but also fail to effectively improve soil alkalinity. This study investigates the potential application of acidic desulfurization gypsum (DG) as a soil modifier for dispersive soils, aiming to achieve high-value utilization of industrial solid waste. The dispersibility of soil under hydrostatic and dynamic conditions are studied using the mud ball test and pinhole test. The engineering properties and modification mechanism of DG consolidated soils were revealed by combining the unconfined compressive strength (UCS), Brazilian split tensile strength (BTS), microstructure, and mineral evolution. Results show that 3% DG significantly reduces soil dispersibility and improves disintegration and erosion resistance, with UCS and BTS increases of 210% and 94%, respectively. The mechanism involves DG releasing hydrogen ions to reduce soil alkalinity, which in turn activates cation activity of DG, replacing sodium ions on the soil surface and forming a binding hydrate within 7 days. Tests on natural dispersive soil from check dams confirmed effectiveness of DG. Advanced machine learning techniques quantitatively analyzed the impact of DG on soil dispersibility, highlighting the relationship between soil dispersibility and chemical/mechanical properties. This study establishes a novel link between hydraulic erosion parameters, mechanical parameters, and soil stressstrain relationships, providing valuable insights for future soil stabilization. The results show potential of waste acidic DG in practical engineering applications and contribute to the sustainable advancement of dispersive soil stabilization technology. Alkaline dispersive soils also aid in regulating the acidity and alkalinity of DG and controlling toxic emissions.

Steel slag (SS) is a byproduct that comes from the production of crude steel in alkaline oxidation furnaces. Resource utilization of steel slag, a calcium-silicon solid waste, is an urgent problem. This paper investigates a solid waste disposal method that applies different steel slag contents to modify dispersive soil. The engineering properties and modification mechanisms of dispersive soil specimens are studied and revealed by performing microstructure, mineral evolution, unconfined compressive strength (UCS), and tensile strength analysis. The pinhole test, mud ball crumb test (BCT), and mud cube crumb test (CCT) were carried out to determine the dispersivity of the soil specimens. Results show that when the steel slag content increases from 1% to 10%, the unconfined compressive strength and tensile strength increase by 176.05% and 75.40%, respectively. For soil specimens without curing time under 50 mm water head, the weight loss of the specimen with 10% steel slag content decreases by 72.03% compared to specimens with 1% steel slag content. Microstructural and mineralogical analyses indicate that the hydration reaction of steel slag changes the ionic composition of the soil and generates reaction products with effects such as filling and connection. To sum up, steel slag effectively improves water stability and mechanical properties of dispersive soil.