The influence of reactive MgO on the hydration and carbonation performance of slag-rich cement system

Abstract

To enrich the choice of minor addition for cement production, the paper investigated the influence of reactive MgO on the long-term hydration and carbonation behavior of slag-rich cement paste. Three different mixtures (cement-slag-MgO, C3S-slag-MgO, and cement-slag) were adopted in the study, and specimens were sealed cured for 90 days, followed by a six-month accelerated carbonation test. It was found that the addition of MgO did not modify the phase assemblage evolution and microstructure development of slag-rich cement paste fundamentally during hydration and carbonation. Brucite occurred as the main hydration product of MgO. As for its carbonation product, Mg-containing carbonate phases and magnesium silicate hydrates were found to agglomerate with each other in the matrix. Compared with cement-slag mixture, cement-slag-MgO blend exhibited a slightly higher carbonation depth and a lower CO2 binding capacity. Brucite did bind some CO2; however, it cannot compensate the reduction of C–S(A)−H gel phase and portlandite due to the substitution of cement clinker with MgO. Therefore, the addition of MgO reduced the carbonation resistance of the corresponding system from a long-term perspective.