In-situ growth of polymer drives time-evolving rheology of cement paste

In-situ growth of polymer has shown great promise in smart rheology control of cement-based materials, a critical demand for ‘construction-of-the-future’ applications. However, its mechanistic role in governing time-evolving rheology of cement paste remains unclear. Here, we show this role by investigating in-situ polymerization in cement pastes under varying initiator concentrations, revealing how polymer chain growth modulates rheological behaviors. Yield stress development is governed by the kinetics of in-situ polymerization and proceeds through two stages: an initial stage dominated by the increasing polymer concentration from polymerization, and a subsequent stage driven by polymer chain growth. Unexpectedly, longer polymer chains do not always enhance interparticle forces through bridging effect. Once chain length exceeds a critical threshold (~750 kDa), polymers adopt more contracted conformations, leading to self-shielding of potential adsorption sites for bridging contacts and increased particle separation distances, thereby diminishing attractive interparticle interactions. This result highlights a delicate balance between bridging-induced attraction and steric-induced repulsion in determining rheology of cement paste. In‑situ polymer growth shows strong potential for controlling cement rheology, but its exact influence on the time‑evolving behavior of cement pastes remains unclear. Here, the authors demonstrate a nuanced interplay between bridging‑induced attraction and steric‑induced repulsion that shapes the rheology of cement paste.