Effect of Carbonation Curing on Portland Cement MgSO4 Attack: Laboratory Characterization at 900 Days

Abstract

Sulfate exposure at low temperatures is known to accelerate chemical deterioration in limestone cement concrete by promoting thaumasite formation. Carbonation curing as an emerging CO2 sequestration strategy converts gaseous CO2 into mineral calcite, a key species that incurs thaumasite formation in conventional limestone cements. To clarify the risk of thaumasite sulfate attack after carbonation curing, this paper presents a laboratory characterization of carbonation-cured mortars stored in a MgSO4 solution at 6°C for up to 900 days. It was found that carbonation curing suppressed mortar swelling and enhanced material mechanical integrity and dimensional stability. The mineral thaumasite and gypsum were significantly lessened after carbonation curing. The maximum longitudinal expansion of mortar bars during MgSO4 exposure was lowered from ∼0.9% to less than 0.06% by carbonation curing. The compressive strength of carbonation-cured mortars remained higher than 60 MPa whereas the noncarbonated control decreased to less than 2 MPa. Moreover, mortar critical pore diameter after MgSO4 storage decreased from 52.3 nm (noncarbonated) to 12.5–15.8 nm (carbonation-cured), with the total pore volume lowered by 9%–11% resulting from carbonation curing. The pore densification led by calcium carbonate precipitation tends to limit MgSO4 ingress and prevent mortar interior damage. It was concluded that the calcium carbonate converted from CO2 through carbonation curing did not promote thaumasite formation, and material durability with respect to thaumasite sulfate attack could be further enhanced after carbonation curing.