Monitoring the effect of MgO expansive additive on micromechanical properties of cementitious materials using a combined method of EDS-nanoindentation

The effect of MgO expansive additive (MEA) on micromechanical properties is significant for understanding both the expansive and the mechanical behavior of the shrinkage-compensating concrete containing MEA. This study monitored the stiffness of different phases appearing in the shrinkage-compensating cementitious material containing MEA by using a combined method of energy dispersive X-ray spectroscopy (EDS)-nanoindentation. The effect of MEA and hydration time on the calcium silicate hydrates (C-S-H) and portlandite was focused. The MEA weakened the micromechanical properties of C-S-H and portlandite mainly at early ages. Hydration is the main reason responsible for the elastic properties evolution of C-S-H. With a two-step homogenization scheme, the experimentally determined micromechanical properties of individual phases were successfully upscaled to the macroscopic elastic modulus of the material. This study is a pioneering study on uncovering the micro-mechanical signature of the shrinkage-compensating concrete containing MEA.