Elucidating the dominant and interaction effects of temperature, CO2 pressure and carbonation time in carbonating steel slag blocks

Abstract

Abstract As an industrial by-product of the steel-making process, steel slag was produced in large quantities but with relatively low utilization rate. Previous studies indicated the feasibility of steel slag blocks using accelerated carbonation technique, owing to the enhancement of mechanical strengths and the availability of CO2 storage. Among all the factors affecting the carbonation reaction, temperature and CO2 pressure are highly critical but not well-investigated. This study is carried out to investigate the dominant and interaction effects of temperature, CO2 pressure, and carbonation time on the compressive strength, Ca conversion, mineralogy and microstructure of carbonated steel slag blocks through a parametric analysis. Dry-mixed blocks with 100% steel slag powder were fabricated and cured with CO2 under accelerated conditions (30–90\xa0°C, 0.05–1\xa0MPa, 30-360 mins). Experimental results indicate that the effects of temperature and CO2 pressure were time-dependent. In the early stage (30 mins), moderately elevated temperature and CO2 pressure promote strength development and Ca conversion, while over-threshold temperatures and pressures impose opposite effects. It was found that, in high-temperature scenarios (90\xa0°C), the extensive water loss and low CO2 solubility were responsible for the negative effect; as for the high-pressure cases (1\xa0MPa), the rapid calcium carbonate (CaCO3) precipitation on the surface, which fills up the pores and blocked the inward CO2 diffusion, resulting in lower strength compared to optimum pressure (0.55\xa0MPa). In the later stage (>120 mins), CO2 solubility became the limiting factor of carbonation reaction, the ultimate compressive strength and Ca conversion had no significant disparity when the temperature and CO2 pressure were in the range of 30–70\xa0°C and 0.2–1\xa0MPa respectively.