Effect of magnesia expansion agent with different activity on mechanical property, autogenous shrinkage and durability of concrete

Abstract

The addition of Magnesia Expansion Agent (MEA) to reduce shrinkage of concrete has attracted attention gradually. In this study, three types of MEA with different activity, i.e. R, M, and S were added into concrete by 5% weight of cement. The effects of MEA on hydration, mechanical properties, shrinkage and durability of concrete were comprehensively evaluated. The results indicated that MEA has a certain delaying effect on hydration of cement and the effect is related to its activity. The addition of MEA exhibites a larger porosity at early curing age leading to negative effects on the mechanical properties of concrete. Later, the microstructure of concrete is refined due to the micro-expansion of MEA. As a result, the mechanical strength of concrete increases 5–20 % at 84 d. Meanwhile, the autogenous shrinkage of concrete with MEA of type R, M, and S decreases by 47.6 %, 49.7 %, and 23.8 % at 90 d, respectively. Because of the smaller MPPD and lower porosity, concrete with MEA of higher activity presents better resistance to chloride penetration. In addition, the models of shrinkage and chloride diffusion coefficient of concrete with MEA of different activity were proposed and verified, which can be used in the shrinkage and service life prediction of concrete with MEA. Furthermore, with the increase of MEA activity, the frost resistance of concrete decreases. On the contrary, the lower the MEA activity, the lower the sulfate resistance of concrete.