Age-Dependent Evolution and Synergistic Damping Mechanisms of XSBRL–Rubber-Modified Cementitious Composites

Incorporating viscoelastic inclusions enhances the damping capacity of cementitious composites, but is often hindered by strength degradation and weak interfacial bonding. This study addresses this trade-off by investigating the synergistic modification of a cement matrix using carboxylated styrene-butadiene rubber latex (XSBRL) and chlorinated rubber (CR) powder, focusing on the age-dependent evolution of their joint energy-dissipation mechanisms. Macroscopic mechanical and microscopic test results reveal a pronounced synergy between latex and rubber powder, governed by possible interfacial interaction. The XSBRL film formed during hydration improves the compatibility between chlorinated rubber and the cement matrix, while its active groups further strengthen the bonding with hydration products. This interfacial coupling transforms the conventionally brittle transition zone into a ductile, high-friction network that maximizes dynamic stress transfer. Moreover, the temporal evolution of damping is governed by the competitive kinetics between cement hydration and polymer-film coalescence, shifting from early-age restructuring (7 to 14 days) to late-stage stabilization (28 days). To balance mechanical and dynamic properties, a recommended formulation of 10% XSBRL and 10% chlorinated rubber is established. This work provides a reference for clarifying the structure–property relationship of high-damping cementitious composites and for optimizing their mix designs.