Abstract
The effect of CO2 curing on alkali-activated slag paste activated by a mixture of sodium hydroxide and sodium silicate solutions is reported in this paper. The paste samples after demolding were cured in three different curing environments as follows: (1) environmental chamber maintained at 85% relative humidity (RH) and 25 °C; (2) 3-bar CO2 pressure vessel; and (3) CO2 chamber maintained at 20% CO2 concentration, 70% RH and 25 °C. The hardened samples were then subjected to compressive strength measurement, X-ray diffraction analysis, and thermogravimetry. All curing conditions used in this study were beneficial for the strength development of the alkali-activated slag paste samples. Among the curing environments, the 20% CO2 chamber was the most effective on compressive strength development; this is attributed to the simultaneous supply of moisture and CO2 within the chamber. The results of X-ray diffraction and thermogravimetry show that the alkali-activated slag cured in the 20% CO2 chamber received a higher amount of calcium silicate hydrate (C-S-H), while calcite formed at an early age was consumed with time. C-S-H was formed by associating the calcite generated by CO2 curing with the silica gel dissolved from alkali-activated slag.
Highlights
Greenhouse gas emission, including CO2, is one of the causes of global warming, which increases the frequency and extent of natural disaster in the world
Alkali-activated slag pastes were cured in various CO2 curing environments, and Table 4 reports the effect on their compressive strength
The effect of CO2 curing for 3 h was compared in Figure 2a: the sample cured in the 20% CO2 concentration chamber (CO2-HC) showed the highest strength, followed byPEER
Summary
Greenhouse gas emission, including CO2 , is one of the causes of global warming, which increases the frequency and extent of natural disaster in the world. The construction industry has tried to reduce greenhouse gas emissions. The use of CO2 for accelerated curing of cement-based materials is one of the active responses to decrease CO2 concentration in the atmosphere. Calcium silicates such as alite and belite in Portland cement are spontaneously carbonated, which mainly results in the formation of calcium carbonate (CaCO3 ). Cement-based materials subjected to CO2 curing at an early age show a rapid development of their strength because in the process of CO2 curing, CaCO3 precipitates in pores of cast mortar and concrete. Densifying the pore refines their microstructure, including the cement paste matrix and the interfacial transition zone, which results in a higher strength at a rather early age [2,3]. Previous studies adopted a very low water-to-cement ratio (w/cm) ranging from 0.06 to 0.28 [4], 0.11 to
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