Unraveling the role of superplasticizer in cement paste modified by in-situ polymerization: Competitive adsorption and intermolecular interaction

PCE lowers yield stress and viscosity of IPC, with stronger effects at higher dosages. • PCE adsorbs on particles first, forming a barrier that limits PAM adsorption and bridging. • PCE reduces PAM thickening by promoting coiled chains and disrupting PAM associations. In-situ polymerization is a promising strategy for enhancing both the mechanical performance and durability of cementitious materials. However, rapid polymerization at early age causes severe flowability loss, adversely affecting construction processes such as pumping and casting. Herein, we explore the possibility of improving the fluidity of in-situ polymerization modified cement paste (IPC) by incorporating polycarboxylate ether (PCE) superplasticizer, with emphasis on elucidating their interaction mechanisms. Rheological tests reveal that adding 0.5% PCE remarkably reduces the dynamic yield stress by 64% at 30 min, validating its contributing role in mitigating workability loss. Mechanistic experiments uncover the dual roles of PCE: 1) prior to the occurrence of in-situ polymerization, PCE molecules occupy the adsorption sites on particle surfaces to form a blocking layer, reducing PAM adsorption from 5.1 to 1.2 mg/g at 30 min and preventing interparticle bridging; and 2) the existence of PCE molecules in the interstitial solution drives the non-adsorbed PAM to adopt more coiled configurations by competitive solvation and disrupts PAM associations by breaking ion-mediated interactions, both of which undermine the thickening effect of PAM. Furthermore, the flexural strength of PCE-containing composites at 28 d reaches 14 MPa, remaining comparable to that of PCE-free counterparts. Our work provides a feasible route to mitigate workability loss in IPC, and the discovery in this work offers fundamental insights into the interaction mechanisms between PCE and in-situ polymerized polymers.