Zeta potential testing, Fourier infrared spectroscopy, and total organic carbon analysis were employed in this manuscript to explore the flocculation mechanism of polyacrylamide (PAM) on slurry with a high content of polycarboxylate ether (PCE). Through the combination of assessments of chemical bond shifts, adsorption indicators, and intrinsic viscosity of high-molecular-weight polymer systems, the microscale flocculation mechanisms of different PAM dosages in cement suspensions were elucidated, showcasing stages of “adsorption–lubrication–entanglement”. Initially (PAM < 0.3%), with PAM introduction, the polymer primarily underwent adsorption interactions, including hydrogen bonding between the ester group, amine group, and water molecules; chelation between the ester group and Ca²⁺ and Al³⁺ on the cement surface; and bridging between PAM’s long-chain structure and cement particles. As the PAM content increased, the cement particles’ adsorption capacity saturated (PAM < 0.67%). The entropy loss of polymer conformation could not be offset by adsorption energy, leading to its exclusion from the interface and depletion attractive forces. Slurry movement shifted from inter-particle motion to high-molecular-weight polymer sliding in interstitial fluid, forming a lubrication effect. With further PAM content no less than 0.67%, the polymer solution reached a critical entanglement concentration, and the contact of the rotation radius of the long-chain molecules led to entanglement domination. By introducing bridging adsorption, depletion attraction, and entanglement forces, the cohesion of cement-based polymer suspensions was subsequently determined. The results showed a linear correlation between cohesion and PAM concentration raised to powers of 0.30, 1.0, and 0.75 at different interaction stages, and a multiscale validation from microscopic flocculation mechanisms to macroscopic performance was finally completed through a comparative analysis with macroscopic anti-washout performance.

To elucidate the impact mechanism of the interfacial characteristics of Calcium Silicate Hydrate gel (CSH)–Montmorillonite (MMT) at the nanoscale on the strength of cement-stabilized montmorillonite soil, this paper begins by examining the interfacial energy. Through Molecular Dynamics (MD) simulation methods, the energy at the MMT and CSH binding interface is quantitatively calculated, and the correlation between the interfacial energy and macroscopic strength is determined in conjunction with grey relational analysis. Finally, based on the characterization results from X-ray diffraction (XRD), the accuracy and sources of deviation in the MD simulation results are discussed. The study shows the CSH-MMT interfacial energy is composed of van der Waals forces, hydrogen bond energy, and electrostatic interactions, which are influenced by the migration of cations; there is a good consistency between the CSH-MMT interfacial energy and the unconfined compressive strength (UCS) of cement-stabilized soil (cemented soil), with the interfacial energy decreasing as the number of water molecules increases and first decreasing then increasing as the number of MMT layers grows; by adjusting the mix proportions, the magnitude of the CSH-MMT interfacial energy can be altered, thereby optimizing the strength of the cemented soil.

This article comprehensively investigates the scouring mechanism of underwater cement paste (UWP) through parameter calibration, flume erosion testing, numerical simulations, and force chain analysis. Building upon the established ARR constitutive model, concurrent calibration involving flowability and rheological parameter experiments confirms that when fluidity ratio, yield stress, viscosity below 3.5, 7.5, 3.5%, the discrete element method (DEM) can effectively simulate fresh UWP performance. A comprehensive analysis of the slurry anti-erosion characteristics was then conducted using a one-sided flow erosion apparatus and 3D image reconstruction technology. Through physical and numerical comparative analysis, the feasibility of simulating anti-erosion performance within an error range of 4.42–10.93% for Ha and Hm values was finally confirmed using the DEM-CFD coupling method. After that, an in-depth analysis of particle force chains and displacement field was further carried out to elucidate the UWP anti-washout mechanism under dynamic water conditions. The results indicate that as the coordination number of cement particles decreases from 5.98 to 4.11 and relative displacement reaches 3.5 times their diameter, cohesive force chains within the suspension dissipate, resulting in the dispersion of the entire cement slurry. The UWP erosion process under dynamic water conditions unfold in two stages, with approximately 74.0% of the force chains rapidly fracturing within the initial 10% scouring time, while the remaining force chains break apart gradually through a slow tearing process.

This study builds on the practice of using waste rubber to improve the ductility of cement mortar and further explores the potential of vinyl acetate-ethylene (VAE) in enhancing the ductility of rubber cement mortar (RM). It systematically analyzes the effects of VAE on the workability, mechanical properties, crack resistance, and microstructure of RM. Additionally, isothermal calorimetry was employed to investigate the mechanism of VAE’s influence on cement hydration heat. The results show that VAE significantly improves the flexural strength, tensile strength, and ultimate tensile strain of RM, while reducing its compressive strength and tensile elastic modulus, thereby markedly enhancing its flexibility and ductility. At a VAE content of 4%, the fluidity, 28-day flexural strength, tensile strength, and ultimate tensile strain of RM reached 240 mm, 4.83 MPa, 1.92 MPa, and 233 × 10⁻⁶, respectively, representing increases of 16%, 18.97%, 11.63%, and 62.94% compared to ordinary RM. However, when the VAE content exceeded 4%, both flexural strength and tensile strength began to decrease. Furthermore, the incorporation of VAE induced the formation of flexible polymer films within the RM matrix but also increased the porosity of the cement matrix, extended the induction period of cement hydration, and reduced the rate and degree of hydration. These findings provide valuable data to support the development of high-ductility and high-crack-resistance concrete repair materials.

Thermodynamic modeling helps to reveal insights into the basic chemical kinetics of dissolution and precipitation in cementitious materials, but relevant applications to cement-stabilized soils have seldom been reported. Based on the thermodynamic database of Cemdata18 and the pore solution composition of cement-stabilized soils, this study formulated a specialized thermodynamic model, using essential thermodynamic constants for soil minerals that were calculated to ensure the model’s accuracy. Two commercial admixtures of alkaline activator and polynaphthalene sulfonate were selected for the different modification mechanisms and plain and modified cement-stabilized soils were prepared. Compressive strength was tested to determine the specimens for pore solution analysis and the influences of the admixture type and dose on dissolution and precipitation were investigated by modeling the ionic activity products and saturation indexes. An X-ray diffraction (XRD) analysis was performed to verify and complement the thermodynamic results. The major research findings were that (1) thermodynamic modeling can be reliably applied to cement-stabilized soils by providing the essential thermodynamic data and an appropriate product model, (2) the pozzolanic reaction is accelerated by increasing the OH⁻ concentration in the pore solution, while the cement hydration is highly dependent on the dissolution of Ca(OH)₂ and the relevant complexes and (3) the dissolution equilibrium of Ca(OH)₂ is directly affected by the alkaline activator dissolution and is indirectly affected by the polynaphthalene sulfonate adsorption of the reactants.

To investigate the evolution of impermeability and pore structure in concrete under long-term service, systematic tests were conducted on submerged concrete from dam sections with over 75 years of service. Results show that the surface water permeation resistance index of concrete in the downstream section of the main dam is only 9.19 × 10⁻⁹, significantly lower than that of concrete from the upstream of the main dam (UMD), downstream of the main dam (DMD), upstream of the auxiliary dam (UAD), and upstream of the weir (UW). Moreover, its impermeability improves noticeably within the 0–100 mm depth range. Mercury intrusion porosimetry revealed that the median pore diameter, average pore diameter, pore content, and porosity in this region reach 306.7 nm, 55.4 nm, 35.64%, and 3.961 mm, respectively—all markedly higher than in other dam sections. Combined XRD and SEM/EDS analyses indicate that crystallization pressure from saline solutions in the coastal environment, together with long-term carbonation, leads to structural loosening and increased porosity in the downstream concrete of the main dam, ultimately degrading its impermeability performance.