Mechanism of Preferential Adsorption of Carboxylic-Vinyl Copolymer, Hydroxy Carboxylate and Sulfonation - Polyol in Cement Hydration Process

Abstract

In the ternary system of hydroxy carboxylate (HC), sulfonation-polyol (SP) and carboxylic-vinyl copolymer (PC), HC and SP preferentially adsorb on the surface of particles to shield the initial hydration. In this way, the ternary system has excellent dispersibility and holding dispersibility, and it has little effect on later hydration. By means of the chemical shrinkage, SEM and XRD analysis, the hydration mechanism of the hydroxy carboxylate (HC) and sulfonation-polyol (SP) has been discussed and the preferential adsorption model (PAM) has been established. The results show that HC delays the initial hydration of C3S and accelerates both the hydration of C3A and the formation of AFt; HC reduces the strength for 28 d with the addition of 0.2%; SP delays initial hydration of C3S and C3A; the ability of shielding hydration becomes weaker along with cement hydrating and the development of strength is normal. In the ternary system of HC, SP and PC, HC and SP with the electrostatic attraction of -SO3- and COO- and complexation of OH- preferentially adsorb on the surface of particles and active hydrating points. Then, reaction of active hydrating points was shielded and the growth of the hydration products slows. In this way, hydration of C3A and C3S are delayed, and the holding dispersibility of PC becomes better. The PC preferentially adsorbs on inert hydrating points and consumes slowly to provide dispersibility with steric hindrance. Along with hydrating going on, organic compounds are enwrapped by hydration products and the shielding ability becomes weaker and weaker. Then, the hydration becomes normal.