Supercritical carbonation of calcareous composites: Influence of curing

Abstract

This paper reports the effect of curing on the susceptibility of cementitious composites to carbonation using supercritical carbon dioxide. Samples made using a compression moulding technique were cured in water before and/or after carbonation and the effect on porosity, microstructure, solid phase assemblage and flexural strength was determined. In terms of development of mechanical strength, no benefit was gained from any period of pre-or post-carbonation curing regime. Yet samples cured prior to carbonation underwent minimal chemical reaction between supercritical carbon dioxide and calcium hydroxide, unhydrated cement or C-S-H. Thus there was no correlation between chemical degree of reaction and strength development. The effects responsible for the marked strength gain in supercritically carbonated samples must involve subtle changes in the microstructure of the C-S-H gel, not simple pore filling by calcium carbonate as is often postulated.

Rationalizing the impact of aging on fiber–matrix interface and stability of cement-based composites submitted to carbonation at early ages

“…Early carbonation contributes to decrease these voids around the cellulose fibers. Farahi et al [35,36] also observed very little porosity at the interface between aggregate particles and groundmass when composites were submitted to supercritical carbonation. Santos et al [25] observed changes in the nanostructure in the vicinity of the fiber by energy-dispersive X-ray spectroscopy maps in extruded cement-based composite after early supercritical carbonation and before accelerated aging.…”

Carbonation of cement paste: Understanding, challenges, and opportunities

“…It seems that, in early hydration stages, the C-S-H becomes intermingled with carbonates, generating an amorphous calcium-silicatehydrocarbonate binding phase [116], while CH is converted to CaCO3 [109]. In fact, effects responsible for marked strength gain probably include subtle changes in C-S-H microstructure, not only simple pore filling by CaCO3 as often stated [121,122].…”

Modification of cementitious building materials by treatment with CO2

“…Apparently, the carbonaceous aggregate providedas opposed to quartz sanda surface for the crystallization of carbonate phases during treatment, thus improving the connection between the aggregate particles and the hardened cement paste matrix at the contact zone. Farahi et al [18] also noted an increase in the flexural strength of mortar specimens with calcitic aggregate after scCO2 treatment. In earlier investigations [20], it has been found that an increase in the strength of hardened cement paste specimens with w/c = 0.6 can be produced after a 48 hour treatment at only 3 bar and 20 °C.…”

“…Short et al [14] have noted that the relative humidity during the preliminary storage of hardened cement paste specimens affects the treatment process with scCO2, the most favourable relative humidity for storage before scCO2 treatment being about 35 % for maximum phase changes. In addition, positive effects of scCO2 treatment on strength are reported for cement-bonded glass fibres [16], wood fibreboard [17] and specimens with a cement-lime binder produced by pressing [18].…”