Potential Approach to Evaluating Soundness of Concrete Containing MgO-Based Expansive Agent

Abstract

This paper will discuss how MgO-based expansive agent (MEA) has increasingly been used to compensate for the effects of thermal shrinkage of concrete in China. Long-term soundness of concrete containing MEA attracts much attention; however, the autoclave test, which is used to assess the soundness of cement caused by excessive intrinsic dead-burnt MgO, seems to be inapplicable to the reactive lightly burnt MEA due to its harsh and unreliable autoclaving condition. This study seeks a reasonable accelerated approach for ascertaining the relevant soundness of concrete made with this admixture. The effects of temperature on accelerating the hydration of MEA are investigated by curing cement pastes containing three types of MEA at 25, 40, 60, and 80°C (77, 104, 140, and 176°F) in water, respectively. Results of the expansion measurement of cement pastes and X-ray diffraction analysis on the hydration products of MEA indicate that the hydration of MEA is accelerated most effectively at 80°C (176°F), and it is fully reacted within a short period. This provides a new possible accelerated method. Soundness of concrete prisms containing MEA is investigated under the accelerated condition of 80°C (176°F) and the feasibility of this new approach is discussed.