Understanding the impact of polyacrylamide molecular weight on the workability of cement paste

Abstract

The impact of polymer admixtures on the performance of cementitious materials is certainly dependent on their molecular structures. This paper aims to elucidate the influence and mechanism of polyacrylamide (PAM) molecular weight on the workability of cement paste. The surface charge property and adsorption behavior of modified cement paste were quantified. Additionally, the assembly morphology of three molecular weight PAMs and the viscoelasticity of their solutions were monitored, so as to provide new insights into the underlying mechanisms. The findings indicate that the growth of PAM molecular weight causes a significant drop in fluidity and an improvement in plastic viscosity of modified cement paste. PAM with higher molecular weight can be adsorbed as a larger size of assembly aggregates on the cement particles, thus promoting the bridging effect. Besides, after the incorporation of PAM, the electrostatic repulsion between cement particles is decreased, whereas a higher PAM molecular weight causes a greater drop. Therefore, it is important to consider not only the dosage of PAM but also its molecular weight in practical engineering.