Sulfate saline soil is considered as an inferior subgrade construction material that is highly susceptible to damage from salt heaving and dissolution. Polyurethane/water glass (PU/WG) is an efficient grouting material widely used in underground engineering; however, its application in saline soil reinforcement has not yet been reported. In this study, PU/WG was used to solidify sulfate-saline soils. The influence of the dry density, curing agent ratio, and salt content on the strength was evaluated. The mechanical properties of the solidified soil were determined by conducting uniaxial compression strength tests, and crack development was detected using acoustic emission technology. The reinforcing mechanism was revealed by scanning electron microscopy tests and mercury intrusion porosimetry. The results indicated that the peak stress, peak strain, and ultimate strain increased with increasing dry density and PU/WG content, whereas they decreased with increasing salt content. The relationship between the peak stress, density, and PU/WG can be described using linear functions. The relationship between the peak stress and salt content can be described by a second-order polynomial function. The larger the dry density and the higher the PU/WG content, the steeper the stress-strain curves and the lower the ductility. Further, the higher the salt content, the higher the ductility. Soil with a higher dry density, more PU/WG, and less salt content exhibited higher brittleness. Thus, PU/WG can fill in the original disorganized and large pores, thereby increasing the complexity of the internal pore structure via organic-inorganic gel reactions.

In order to solve the problem of low comprehensive utilization rate of industrial solid waste, this article focuses on the three problems of slag, which are steel slag, reuse of silica fume, and the strength enhancement and microscopic mechanism of slag-steel slag-silica fume composite material; analyzes the macro strength of the mixture under different curing ages from the two indexes of unconfined compressive strength and splitting tensile strength; and conducts microscopic tests such as X-ray diffraction, scanning electron microscopy, and Fourier transform infrared. The internal mechanism of hydration product formation and strength change of slag and steel wollastonite cementitious material under the excitation of sodium hydroxide and sodium silicate mixed solution as alkali activator was discussed. The strength results show that when the optimum mixture ratio of slag: steel slag: silica fume is 6:3:1, the modulus of lye is 1.2, the content of lye is 6 %, and the compressive strength of slag-steel slag-silica fume base polymer reaches 2.44 MPa under the standard curing condition of 28 day. The results show that the hydration products of geopolymer mainly consist of calcium-silicate-hydrate (C-S-H) gel and a small amount of ettringite (AFt) crystal. The addition of slag reduces the calcium/silicon ratio and increases the aluminum/silicon ratio, which makes the gel polymerization degree increase. C-S-H gel can be formed by the reaction of calcium hydroxide and silicon dioxide produced by steel slag hydration. Silica fume can provide highly reactive silicon for the system, and its seed effect and pozzolanic effect can accelerate the hydration process of the system.

In order to investigate the mechanism of mechanical performance enhancement and the curing mechanisms of acrylate emulsion (AE) in cement and magnesium slag (MS) composite-stabilized soil (AE-C-M), this study has conducted a comprehensive analysis of the compressive strength and microstructural characteristics of AE-C-M stabilized soil. The results show that the addition of AE significantly improves the compressive strength of the stabilized soil. When the AE content is 0.4%, the cement content is 3%, and the magnesium slag content is 3% (AE4-C3M3), the strength of the formula reaches 4.21 MPa, which meets the requirements of heavy traffic load conditions in the construction of high-speed or main road base layers. Some reactive groups on the polymer side chains (-COOH) engage in bridging with Ca2+ and RCOO- to form a chemically bonded interpenetrating network structure, thereby enabling the acrylate emulsion to enhance the water damage resistance of the specimens. The notable improvement in strength is attributed to the film-forming and solidifying actions of AE, the binding and filling effects of C-S-H gel, and the reinforcing effect of straw fibers. FT-IR and TG-DSC analysis reveals the presence of polar electrostatic interactions between AE and the soil matrix. AE enhances the bonding among soil particles and facilitates the attachment of C-S-H gel onto the surfaces of the straw fibers, thereby increasing the strength and toughness of the material. The application of MS in conjunction with straw fibers within polymer-modified stabilized soil serves to promote the recycling of waste materials, thereby providing an environmentally friendly solution for the engineering application of solid waste.

Geopolymers assume an irreplaceable position in the engineering field on account of their numerous merits, such as durability and high temperature resistance. Nevertheless, geopolymers also demonstrate brittleness. In this study, geotextiles with different layers were added to geopolymer to study its compressive strength and stability. Laboratory materials such as alkali activators, geotextiles and granite residual soil (GRS) were utilized. The samples were characterized via XRD, TG-DTG, SEM-EDS and FT-IR. The results indicate that the toughness of geopolymer is significantly enhanced by adding geotextiles, and the strength increase is most obvious when adding one layer of geotextile: the strength increased from 2.57 Mpa to 3.26 Mpa on the 14th day, an increase of 27%. Additionally, the D-W cycle has a great influence on geotextile polymers. On the 14th day, the average strength of the D-W cyclic sample (1.935 Mpa) was 1.305 Mpa smaller than that of the naturally cured sample (3.24 Mpa), and the strength decreased by 40%. These discoveries offer a novel approach for further promoting the application of geopolymers, especially in the field of foundation reinforcement.

This study aims to solidify sodium sulfate saline loess by biomineralization of reactive magnesium oxide (MgO) binder. The impact of Na2SO4 concentration on the viability and urease activity of S. pasteurii, the mechanism and products of biomineralization of MgO, and the effectiveness of the biomineralization-MgO binder in solidifying saline loess with varying salt content (1%, 3%, and 5%) were investigated. Results showed that low and moderate concentrations of Na2SO4 favored bacterial proliferation. However, the presence of Na2SO4 inhibited bacterial urease activity, and the inhibition was more significant at higher Na2SO4 concentrations. In addition, low and moderate concentrations of Na2SO4 decreased the specific urease activity, whereas high concentrations of Na2SO4 significantly increased specific urease activity. S. pasteurii was able to use carbonate ions formed by urea hydrolysis for the mineralization of MgO and to form magnesium carbonate minerals dominated by rosettelike dypingite and hydromagnesite crystals. The primary mechanism involves microbial cells and extracellular polymeric substances leading to partial dehydration of Mg2+ ions from the Mg2+-H2O complex and allowing for further association with carbonate anions to from Mg-bearing carbonates. Unconfined compressive strength tests conducted on the saline loess samples after 7 days of curing revealed a significant influence of urea concentration on the strength of the solidified soil. The optimal urea concentration to obtain a better 7-day UCS ranged from 4 mol/L to 5 mol/L. Furthermore, solidified soil with 5% salinity yielded the highest 7-day UCS and soil with 3% salinity exhibited the lowest 7-day UCS at the same urea concentration. XRD and SEM analysis of the solidified soil samples indicated that the formation of magnesium carbonate minerals in the soil matrix by the biomineralization-MgO binder was responsible for the UCS enhancement. The remarkable 7-day UCS of saline loess solidified with biomineralization-MgO binder demonstrates the effectiveness of this material in curing saline loess.