167 / 2022-04-30 11:04:04

High-temperature performance of SCMs blended cementitious materials subject to CO2 curing

Supplementary cementitious materials; CO2 curing; Steel slag; High-temperature performance; Microstructure

Supplementary cementitious materials (SCMs) are increasingly used to partially replace cement in the construction industry due to the expected reduction in CO₂ emissions and improvement in the mechanical and durability performance. Meanwhile, the application of CO₂ curing in cement-based materials is garnering growing attention against a backdrop of current green and sustainable development trends However, the influence of CO₂ curing on the high-temperature properties of the SCMs blended cementitious materials remains largely unknown. This study seeks to understand the influence of CO₂ curing on the high-temperature performance of cement paste incorporated with different types of common SCMs (Fig. 1).



The results showed that for the cement paste containing SCMs, pure CO₂ curing reduced the 28-day compressive strength by approximately 10% compared with standard curing. Further standard curing of 2 days promoted the hydration of the unreacted cement and SCMs in the CO₂ cured specimens, compensating for the reduced compressive strength of the pure carbonated SCMs cement paste (Fig. 2).



Due to the simultaneous generation of CaCO₃ and hydration products, the samples carbonated for 2 days and then standard cured for 26 days (CS curing) had the best high-temperature resistance, which was reflected by higher compressive strength, lower water absorption and decreased water sorptivity (Fig. 3). BSE imaged revealed that the porosity of the CS cured ground granulated blast furnace slag (GGBS)-incorporated cement paste decreased by 7.93% after exposure to 600 ℃, corresponding to a 57% decrease in water sorptivity due to the transformation of large loose pores into more compact small pores (Fig. 4).



The DTG and XRD analysis demonstrated that Glass powder (GP) was inert in the cement matrix with no obvious pozzolanic reaction and negligible improvement of carbonation degree, leading to the lowest high-temperature performance; whereas, GGBS and fly as (FA) increased the generation of CaCO₃ by 19.05% and 15.08%, respectively (Fig. 5). Samples after two days of carbonation were completely carbonated, and subsequent standard curing further promoted the formation of CaCO₃, which was present as calcite and remained stable after exposure to 600 ℃.



Findings from this study well demonstrate that the combined use of early CO₂ curing and subsequent standard curing to treat the SCMs blended binders has great potential to reduce carbon footprint and improve elevated temperature resistance.