The effect of nano-MgO on the setting time, autogenous shrinkage, microstructure and mechanical properties of high performance cement paste and mortar

Many studies have targeted the application of micro-size MgO to reduce autogenous shrinkage in cement based materials. However, there is little knowledge the effect of nano-MgO on the mechanical, durability and microstructure properties of high-performance cement-based materials. In this paper, the properties of cement pastes and mortars with nano-MgO were experimentally investigated. 2.5%, 5.0% and 7.5% nano-MgO by weight of binder were used in mortar and paste mixtures. While the setting time and the volumetric autogenous shrinkage tests were carried out in paste mixtures, the heat of hydration, 7 and 28 days compressive strength, ultrasonic pulse velocity (UPV) and 28 days linear autogenous shrinkage test were carried out in mortar mixtures. In addition, Scanning Electron Microscopic (SEM) observations were also made to evaluate the effect of nano-MgO on microstructure. It was concluded that nano-MgO had a significant effect on the fresh and hardened properties of cement pastes and mortars. Generally, nano-MgO increased the compressive strength (about up to 8%). Nano-MgO decreased autogenous shrinkage and setting time decreased with an increased in use of nano-MgO. The final hydration heat of the control mixtures and the nano-MgO mixtures are almost the same. Nano-MgO can be used as an expanding additive.