Insights into Early-Age Interfacial Bonding Improvement of Polymer-Modified Sulfoaluminate Cement Mortar: Roles of Polymer Film Formation and Hydration Regulation

In this study, a polymer-modified fast-hardening and early-strength cement-based repair material was proposed, using the polymer cellulose ether (HPMC), polymer dispersible polymer powder (VAE) and silica fume. The optimal mixing ratio of the three polymers was designed by an orthogonal test by combinational evaluation of the fresh performance and mechanical properties, complemented by the observation of the changes in the macroscopic properties by XRD and SEM analysis. The results showed that the content of HPMC has a more significant effect on fluidity, consistency and water retention than other factors, and the content of silica fume has a more significant effect on setting time. The content of HPMC is the most important factor affecting the compressive strength and flexural strength. The content of HPMC and VAE has a more significant effect on the interfacial bonding performance, the 1-day interfacial bond strength was significantly higher than that without polymer. According to the SEM results, it was observed that, the porous structure of Ca(OH)2 induced by VAE, and the polymer film formed by HPMC covering the hydration product, the two polymers work together to significantly improve the interfacial bond strength of cement mortar. The optimal mixing ratio of the two interface bonding methods is the same, so the optimal mixing ratio of three factors is obtained: 0.2% of cellulose ether, 0.6% of redispersible polymer powder, and 10% of silica fume strong and fluid repair material.