A novel shrinkage-reducing polycarboxylate superplasticizer for cement-based materials: Synthesis, performance and mechanisms

Abstract

The incorporation of polycarboxylate superplasticizers may increase the risk of shrinkage cracking of cement-based materials. Co-adding shrinkage-reducing admixtures (SRAs) may decrease the compressive strength or arise the incompatibility problem. Designing a novel superplasticizer with excellent shrinkage-reducing function by modifying molecular structures of polycarboxylate superplasticizers can be a promising approach.This study aims to synthesize a novel shrinkage-reducing polycarboxylate superplasticizer (SR-PCA) possessing shrinkage-reducing and water-reducing functions and to investigate its performance and working mechanisms in cementitious systems. The results indicate that SR-PCA improves the fluidity of cement paste and has a distinguished fluidity retention capability. SR-PCA prolongs the cement hydration induction period, hinders the nucleation and growth of C-S-H in the acceleration period, while enhances hydration degree and refines the pore structure at later ages. Moreover, it can also be deduced that most PCA adsorbs on the cement surfaces, however, SR-PCA is mainly in the pore solution. The shrinkage-reducing mechanism of SR-PCA in cement-based materials is attributed to lowering the surface tension of the pore solution, due to the presence of the unreacted esterification macromonomers (AA-C4-PE-600) and the unadsorbed SR-PCA molecular.