The anti-dispersion mechanism of polyacrylamide on alkali-activated cementitious materials poured underwater

Alkali-activated cementitious materials (AACM) have remarkable potential for utilization in underwater engineering for both pouring and restoration endeavors. The predicament of anti-dispersion within AACM during underwater pouring (AACM-DUP) emerges as a pivotal technical impediment within this context. However, few researchers have focused on the effect and mechanism of polyacrylamide (PAM) on the anti-dispersion properties of underwater AACM. This study explored the effect of PAM on the anti-dispersion and rheological properties of fresh AACM paste. The mechanism underlying PAM-induced anti-dispersion in AACM-DUP was analyzed through total organic carbon (TOC) adsorption, Zeta potential, Conductivity, and X-ray photoelectron spectroscopy (XPS) tests. The results showed that the fresh paste's shear stress and plastic viscosity decreased first and then increased with the increase of PAM molecular weight and content. This is because PAM and water can form a network structure through hydrogen bonding, thus changing the viscosity of the paste. Additionally, the calcium ions (Ca2+) in the paste can be adsorbed by carboxylate ions after PAM hydrolysis, thus forming a new calcium bond. Moreover, the longer the molecular chain of PAM could adsorb more Ca2+, which made the anti-dispersion performance of AACM-DUP better. However, the excessive molecular weight of PAM could exacerbate viscosity, inducing adverse effects during underwater pouring. These results provided a theoretical cornerstone and technical backing for PAM as a remedy for ameliorating anti-dispersion issues within AACM for underwater engineering, ultimately advancing the application of AACM-DUP.