Coupled effects of polymer-to-cement ratio and resting time on cold-joint degradation and interfacial mechanism of PAE cement-based coatings

Polyacrylic ester (PAE) latex cement-based coatings were prepared using P·O 42.5 ordinary Portland cement with polymer-to-cement (P/C) ratios ranging from 10% to 50%. The effects of P/C ratio and resting time before mortar overlay on the coatings’ crosslinking degree, adhesion strength, bonding performance, and corrosion resistance were systematically investigated. The P/C ratio significantly affected coating compactness and interfacial compatibility, with optimal performance achieved at a P/C ratio of 25%, where the bonding strength increased by 11% and the corrosion current density decreased from 9.31 to 0.35 μA·cm -2 , representing a reduction of nearly two orders of magnitude compared with bare rebar. Resting time was identified as a key factor governing interfacial evolution. At 3 h, sufficient migration of water and Ca 2+ ions from the subsequently cast mortar promoted continuous hydration, yielding a hydration degree of 45.8% and a dense C–S–H structure. Extending the resting time to 24 h resulted in excessive polymer crosslinking and densification, which restricted hydration-medium transport. Consequently, the hydration degree on the coating side decreased to 40.5%, the C–S–H fraction dropped to 29%, while CH content increased to 20%, leading to an approximately 50% reduction in bonding strength. This study elucidates the “polymer densification–hydration medium shielding” mechanism responsible for the interfacial cold-joint effect and provides quantitative insight into the coupled influence of P/C ratio and resting time. The findings offer a theoretical basis for optimizing polymer-modified cement-based coatings and controlling on-site construction timing. • Optimal P/C ratio of 25% ensures peak bond strength and corrosion resistance. • Bond strength decreases by 50% when resting time exceeds 10 h before casting. • Dense polymer film after 24 h blocks hydration and weakens interfacial bonding. • Cold-joint forms due to hydration gradient and phase imbalance in the ITZ.