Evaluating soundness of concrete containing shrinkage-compensating MgO admixtures

Abstract Reactive MgO admixtures are available to counteract drying shrinkage of concrete. However, since excess amounts of MgO in the form of periclase in cements can cause unsoundness, there is a concern whether these admixtures can result in unsoundness. Hence, the volume stability of paste and concrete specimens partially substituted with up to 10 and 15% wt of r-MgO, respectively were subjected to 23, 38, 60, and 80 °C moist curing conditions and expansion monitored for six months. In addition, the ASTM C151 autoclave expansion test (AET) used to assess the soundness of cements was conducted but was found to underestimate the 6-month expansion of cement pastes containing r-MgO admixtures. And, the impact of the MgO admixtures on compressive strength of the concrete cylinders was evaluated at different curing temperatures. It was found that with sufficient moist curing, r-MgO admixtures can effectively limit the drying shrinkage of concrete.