| The application of self-compacting concrete (SCC) is becoming increasingly widespread?in construction. SCC's properties include no vibration, low noise, casting speed, short construction period and so on. Viscosity modified agent is an important part of self-compacting concrete, and it can decrease the risk of bleeding and improve the role of cohesiveness. Although all kinds of thickening agent have been used in concrete works, the influence of the properties of cement is lack of systematic research. As a representative of the thickening agent, the influence of polyacrylamide (PAM) on the cement paste including the water consumption for normal consistency of cement, setting time, resistivity, microstructure, viscosity, shrinkage and strength properties has been studied in the paper.Studies have shown that the water consumption for normal consistency of cement increased with the increase of the content of PAM, and the setting time of cement paste was significantly prolonged. The viscosity of cement paste significantly increased when the PAM content is below 0.1‰, and the viscosity of the growth rate slowed while PAM dosage is between 0.1‰to 0.8‰. It indicated that the compounds containing ionic bonds, which are formed by the carboxyl-containing copolymer of hydrolyzed PAM and metal ions, caused the cross-linking of PAM molecules. PAM had little effect on the early resistivity of the cement paste, but the late electrical-resistivity increased with the increase of PAM content, so did the rate of the change of electrical-resistivity. The incorporation of PAM increased the closed pore in the cement paste, refined and compacted the needle structure of hydration products ettringite (AFt), local structure of paste was denser and more compact, and thus the space and ratio of inter-connected pores reduced. It could reduce the shrinkage rate when PAM content is not more than 0.5‰; in the cases of PAM content is not more than 0.8‰, the strength of specimen didn't appear to decrease significantly. |
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