Synthesized hydrogel co-polymerized with hydrophobic n-butyl methacrylate and its impact on shrinkage mitigation and crack resistance of cement paste

Internal curing using super-absorbent polymers (SAPs) is an effective method to mitigate the autogenous shrinkage of cement paste . However, conventional SAPs, such as acrylamide/acrylic sodium copolymer , often leave voids in situ after water release, causing significant strength reduction. To address this issue, we developed a low-shrinkage hydrogel (BMH) synthesized using hydrophobic n -butyl methacrylate, which prevents volume collapse by enhancing polymer network stability and maintaining stable interfacial bonding with the cement matrix . Adding just 1 % BMH nearly eliminated autogenous shrinkage at 7 days by significantly reducing capillary stress and resulted in a 64.1 % reduction in crack area compared with conventional SAPs. The no-collapse characteristic of BMH ensures a wider and more uniform distribution of the internal cured region, effectively avoiding in-situ void formation and reducing strength loss (low as 20.7 %), and the conventional SAP leads to 34.9 % strength loss with 1 % SAP addition . The utilization of engineered hydrogel with hydrophobic component provides a novel strategy to reduce deformation and cracking sensitivity of cement-based materials without severe strength reduction.