Sustainable building material from CO2 mineralization slag: Aggregate for concretes and effect of CO2 curing

Carbonation curing for cement-based materials can be applied as a green concrete production technology, which provides a promising route to economic CO2 sequestration. The substitution of cement by industrial solid waste could further reduce the carbon footprint of concrete. This study proposed a sustainable building material of CO2 mineralization slag (CMS) from the wet process. Based on the accelerated carbonation experiment of Portland cementitious materials, the feasibility of blending CMS as enhanced addition is evaluated. This study discussed the effects of CMS aggregate on CO2 sequestration capacity and mechanical property during CO2 curing, and further investigated the related physicochemical mechanisms. It is revealed that the increase of CaCO3/SiO2 ratio would promote the nucleation and crystallization of CaCO3 microcrystal and result in higher CO2 uptake. With optimum CMS addition ratio of 30% and CaCO3/SiO2 ratio of 4:1, the carbonation degree can be increased by 74.2% in comparison with pure cement paste. Unlike natural curing (28d), a significant strength increment of 40% is observed after pure CO2 curing at 40℃ and 1.5 MPa with a 20% addition of CMS. It is considered that the strength gain is primarily contributed by the intensifying of the interfacial transition zone after CO2 curing. The Klinkenberg permeability tests verified the densification effect of carbonation. These findings provide a guidance for the industrial application of CO2 mineralization slag as the sustainable building material.