Effects of magnesium content and carbonation on the multiscale pore structure of alkali-activated slags

Abstract While CO2-resistant cement materials are crucial in oil and gas industries, the CO2 emissions associated with manufacturing oil-well cements have necessitated the development of lower-CO2 alternatives with enhanced carbonation resistance. A higher magnesium content blast furnace slag precursor for alkali-activated slag (AAS) has been shown to increase resistance to accelerated carbonation-induced degradation. This investigation assesses the effects of sample age, AAS magnesium content, and carbonation (exposure to 100% CO2) on the multiscale pore structure of AASs (nanometers to microns). The pore size distributions and diffusion tortuosities of ordinary Portland cement (OPC) and silicate-activated slag pastes are obtained through the techniques of nitrogen sorption, mercury intrusion porosimetry, and X-ray microtomography. These pore morphology properties show AAS to be more resistant to pore structural degradation following accelerated carbonation than OPC, and increased magnesium content in AAS is shown to improve its resistance to gel decalcification and capillary pore formation during carbonation.