Rheological characterization and microstructural features of a novel polymer-modified bentonite slurry for underground construction

During underground construction, complex conditions often degraded slurry rheological performance and compromised stability. A polymer-modified bentonite slurry was developed in this study using a novel composite polymer additive prepared by combining polyethylene oxide (PEO) and sodium polyacrylate (NaPAA). Rotational shear tests were conducted to systematically examine the effects of polymer dosage, bentonite content, and temperature on slurry rheological behavior. Comparative analyses were also carried out against slurries modified with conventional additives, including carboxymethyl cellulose (CMC), polyanionic cellulose (PAC), and polyacrylamide (PAM). In addition, particle-size analysis, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), zeta potential measurements, and scanning electron microscopy (SEM) were performed to clarify the microstructural evolution and the polymer-bentonite interaction mechanisms. Experimental results demonstrated that the composite polymer significantly enhanced the yield stress and apparent viscosity of the bentonite slurry, transforming the system from an approximately Newtonian fluid to a non-Newtonian fluid with pronounced shear-thinning characteristics. Unlike slurries modified with conventional additives, the polymer-modified slurry maintained relatively higher yield stress and apparent viscosity at elevated temperatures, indicating improved thermal stability and resistance to structural degradation. Microstructural analyses indicated that the composite polymer additive modified the dispersion and aggregation behavior of bentonite particles by regulating particle size distribution and surface charge characteristics. The combined PEO chain entanglement and NaPAA electrostatic regulation promoted the formation of a more continuous particle-polymer network, thereby improving the flow behavior and suspension stability of the slurry. These findings provided valuable guidance for the optimization of high-performance slurries used in underground construction.