CO2 activation of magnesium slag for the preparation of unburned aggregate: Performance evaluation, CO2 absorption, and ecological benefits

Abstract

For the development of unburned aggregate, accelerated carbonation technology is deemed to be a significant curing method. In this paper, accelerated carbonation was applied in preparing magnesium slag unburned aggregate (MSUA). The effects of curing time on physical property, phase evolution, CO2 absorption, microstructure and stability of MSUA were explored by employing XRD, TGA, MIP and SEM-BSE characterization techniques. According to the results, with the increase of carbonation time, the mechanical strength and apparent density of MSUA prepared by accelerated carbonation technology enhance, while the water absorption rate declines. The predominant form of the carbonation product is calcite (CaCO3), accompanied with amorphous silica gel. The amount of CO2 absorption has positive correlation with time, exhibiting an absorption rate of 18.5 % at 168 h of carbonation. On the other hand, with 3 h CO2 curing of MSUA, the alkali-silica reaction (ASR) expansion can be completely suppressed. As observed from MIP analysis, the increase of carbonation time reduces the porosity of aggregates. SEM analysis also reveals that gel pores are filled with carbonation products, leading to a denser structure of the aggregate matrix, which is possibly a crucial factor for the suppression to ASR expansion. Based on these findings, MSUA is demonstrated to have enormous potential in substituting natural aggregates and reducing carbon emissions.