Preparation and Properties of Eco-Friendly Aerated Concrete Utilizing High-Volume Fly Ash with MgO and CaO Activators

The associated MgO in limestone is believed to affect the volume stability of cementitious materials at room tem-perature,which limits the utilization of low grade limestone.In this study,MgO was used as an alkali activator instead of partial CaO to prepare the aerated concrete under hydrother mal conditions.The expansion process was studied to evaluate the influence of the raw materials on the gas forming stability of the slurry.The pore structure(porosity,pore size and its distribution)was analyzed by the image method.The physic mechanical properties(density,strength,thermal properties)of concrete with the addition of MgO were comprehensively investigated.Besides,the mineral compositions and morphology of the hydration products were analyzed to demonstrate the infuence mechanism of MgO on the mechanical properties.Experimental results show that the final expansion rate of the slurry decreases with MgO content.A reasonable MgO content,ie,MgO/(MgO+CaO)<20%,con-tributes to improve the compressive strength,attributing to an increased reaction rate to C-S-H gel and tobermor-ite.The addition of MgO causes the thermal conductivity and specific heat to increase.The pore structure is mainly related to the amount of air entraining agent.This study has a significance for the further utilization of magnesium-rich carbonates in the autoclaved building products.