In-situ polymerization induced toughening of cement pastes: Multiscale experimental and molecular dynamics insights

The intrinsic brittleness and poor crack resistance of cement-based materials severely limit their structural reliability under complex loading conditions. In this study, an in-situ polymerization strategy was developed to construct organic-inorganic interpenetrating networks within cement pastes for improving fracture resistance. Three water-soluble monomers with different functional groups, including acrylamide (AM), sodium acrylate (AAS), and 2-acrylamido-2-methylpropanesulfonic acid sodium (AMAS), were individually polymerized within cement pastes to form PAM, PAAS, and PAMAS networks, respectively. The influence of polymer molecular structure on fracture resistance was elucidated by correlating macroscopic mechanical behavior with microstructural evolution and polymer-CSH interfacial interactions through multiscale experiments and molecular dynamics simulations.The results demonstrated that in-situ polymerization effectively transformed cement paste from a brittle material into a deformation-tolerant composite. Among the investigated systems, PAM exhibited the highest toughening efficiency, increasing the flexural strength from approximately 4.45 MPa to 8.79 MPa and the flexural toughness from about 110 J/m 2 to nearly 800 J/m 2 at 28 d. Experimental and simulation results revealed that the enhanced fracture resistance originated from the synergistic effects of polymer-induced crack bridging, stress redistribution, and stable polymer-CSH interfacial bonding. Molecular dynamics simulations further demonstrated that polymer chains could bridge type-I crack regions, bridge crack surfaces, and delay crack propagation. The crack-bridging capability and interfacial interaction strength followed the order PAM > PAAS > PAMAS, consistent with the experimental toughening behavior. These findings provide molecular insights into the design of high-toughness cement-based composites through in-situ polymerization.