Degradation Mechanism of Nonaqueous Reactive Polymer Grouting Materials under Chemical Corrosion Environment

Nonaqueous reaction foam polyurethane (PU) grouting materials have found wide applications in civil engineering. However, degradation laws and mechanism of the strength performance of PU grouting materials in different corrosion environments are not clear yet. Here, the uniaxial compression test, scanning electron microscopy (SEM) characterization, Fourier-transform infrared (FTIR) spectroscopy test, and molecular dynamics (MD) simulations were conducted to investigate the influences of acidic and alkaline corrosion environments on the compressive strength, microstructure, molecular structures, and nanoscale mechanical properties. Results show that with the increase of corrosion time, the compressive strength of PU grouting materials decreases more and more. The deterioration effect of an acidic environment is stronger than that of an alkaline environment, and it is stronger when the acidic environment is with a lower pH value. At the microscale, the damage of carbamate esters and the breakage of ether bonds results in the fracture, hydrolysis, and dissolution of the long PU molecule chains, which is the main reason leading to the destruction of microfoams. Compared with sodium hydroxide solution, sulfuric acid solution produces more pronounced damage to molecular structures as well as microstructures, and thus more significant deterioration effect on compressive strength. At the nanoscale, the compressive strength, tensile strength, and shear strength of the amorphous PU elastomers after corrosion decreased by 26.7%–35.7%, 13.4%–27.9%, and 4.26%–12.73%, respectively, compared with the original model, illustrating the damaging effect of chemical corrosion on the nanostrength of the PU elastomer. MD simulation results also show that the length of the molecular chain has a great influence on compressive strength and tensile strength, and the absence of molecular fragments has a great influence on shear strength.