Synthesis of Shrinkage-Reducing Admixture with Different Branch Chain Structures and Its Effect on the Drying Shrinkage of Cement-Based Materials

Shrinkage-reducing admixtures (SRAs) can effectively mitigate the drying shrinkage of cement-based materials, but the influence of SRA structures with varying configurations on drying shrinkage remains unclear. This study mainly synthesized two types of SRA by using different shrinkage-reducing monomers and investigated the impact of SRA with distinct branch chain structures on the surface tension, contact angle, and viscosity of solution. Then, the drying shrinkage, mechanical properties, and microstructure of cement-based materials with SRA were further discussed. The findings indicated that Type II SRA with a complex branched-chain structure presents a greater steric hindrance effect, leading to a more significant decrease of surface tension and increase of solution viscosity and contact angle than that of Type I SRA. Meanwhile, samples with Type I SRA presented a smaller drying shrinkage, whereas Type II SRA showed a stronger reduction in surface tension, indicating the mechanism of SRA inhibiting the drying shrinkage is not limited to the reduction of surface tension. Pores below 50 nm are conducive to reducing drying shrinkage, and the pore volume of sample with Type I SRA was significantly reduced by 20.3%, which showed an excellent drying shrinkage inhibition effect.