Microscopic Thickening Mechanisms of Hydroxypropyl Methyl Cellulose Ether Anti-Washout Admixture and Its Impact on Cementitious Material Rheology and Anti-Dispersal Performance

The anti-washout admixture (AWA) serves as the primary constituent in the formulation of underwater non-dispersible concrete (NDC). In this study, hydroxypropyl methyl cellulose ether (HPMC) was chosen as AWA. Molecular dynamics simulations were employed to investigate the nanoscale thickening anti-washout mechanism of HPMC, while the impact of HPMC with varying viscosities on macroscopic behavior was examined by incorporating it into cement paste. Subsequently, NDC was prepared using HPMC, and its flowability, anti-dispersion properties, and rheological characteristics were assessed. The findings demonstrate that HPMC can establish stable Ca-O bonds with C-S-H, effectively mitigating water erosion and making it an ideal AWA. Additionally, the viscosity of HPMC significantly impacts its performance, with higher viscosities leading to enhanced thickening but reduced flowability. Thus, HPMC-15W emerges as a preferable AWA. The use of HPMC as an AWA in NDC results in a notable shear-thinning behavior, consistent with the modified-Bingham model, along with excellent resistance to underwater washout and self-compactness. In summary, this paper provides a deeper and more comprehensive understanding of the thickening mechanism of HPMC in cementitious materials through multi-level research.