Low-carbon MgO/hydromagnesite binders – effect of moisture state on the evolution of mechanical properties

We studied the mechanical properties of MgO/hydromagnesite mortars cured at 20 °C both in humid (98 %RH) and dry (57 %RH) environments. The linear storage Young's modulus was determined with quasi-static loading and dynamically by SIngle MOde Resonance Ultrasound Spectroscopy (SIMORUS) measurements. We measured the corresponding loss modulus and the nonlinear counterpart of the storage modulus. Humid environment adversely affected the evolution of the elastic properties, i.e. it caused a reduction of the linear storage Young's modulus and an increase of its nonlinear counterpart, the latter being a proxy of microstructural heterogeneity and potential damage. On the other hand, mortars cured at 57 %RH experienced a monotonous growth of the linear storage Young's modulus and decrease of the loss modulus. Similar trends were observed for compressive strength. We postulate that the lowering of mechanical properties upon moisture uptake is due to the intrinsic effect of adsorbed water on the microstructure.