Retardation and bridging effect of anionic polyacrylamide in cement paste and its relationship with early properties

Abstract

Deep understanding of the influence and mechanism of A-PAM on the early properties of the cement-based materials is of both scientific and practical importance. In this paper, the effects of anionic polyacrylamide (A-PAM) with different mass ratios on the early properties of cement, including hydration, structural build-up, setting time and early strength development were studied. The interaction between A-PAM and cement particles was also investigated. The relationship between the adsorption, retardation of A-PAM and the early properties of cement paste was then discussed. The results showed that the retardation and bridging effect generated from A-PAM jointly affect the early performances of cement. A-PAM can be adsorbed onto the surface of cement particles until a saturation point is reached. When the A-PAM dosage is below the saturation point, A-PAM mainly acts as flocculant, bridging cement particles and increasing the connection between cement particles. This accelerates the structural build-up and setting of cement paste. When the A-PAM dosage is above the saturation point, the dominant role of A-PAM is retarder, which highly retards the cement hydration and setting, thus slows down the structural build-up and reduces the early strength.