Effect of pretreatment procedure on the properties of cementitious materials with limestone cured by CO2

Carbon sequestration in cementitious materials is an effective way to promote sustainable development of the cement industry. Traditionally, specimens are cast and then cured by CO2. Cement particles are first pretreated with CO2 and cast into specimens to study their performance properties are innovatively investigated in this paper. In this study, the carbonation depth, CO2 uptake amount, compressive strength, reaction heat, XRD and SEM/BSE of cementitious materials with and without pretreatment procedure were investigated. The results showed that the pretreatment procedure enhanced the CO2 uptake amount of paste samples and contributed significantly to the carbonation depth, but was not conducive to the development of compressive strength. As seen in the SEM/BSE images, a rim of dense nano-sized CaCO3 was produced around the clinker particle after pretreatment, which was identified as mainly calcite in combination with XRD analysis. The considerable reduction in cumulated heat release of the pretreated cement implied that the rim of dense CaCO3 hinder the subsequent hydration of unreacted clinker particle to some extent. The sample prepared with pretreated cement caused a rim of crack around the clinker particle after 1 day of CO2 curing and 27 days of subsequent water curing. 5%, 10% and 15% limestone powder were added in order to improve the degree of carbonation and hydration of cementitious materials. With the increase of limestone powder addition, the carbonation depth and CO2 uptake amount increased gradually. The compressive strength reached the maximum when its content was 10%. •Present a pretreatment procedure for the first time to promote the reaction process between CO2 and clinker particles.•The pretreatment procedure contributed significantly to the carbonation depth.•The rim of dense nano-sized CaCO3 around the clinker particle produced in the pretreatment procedure hindered the subsequent hydration.