13This paper presents both experimental and multi-physics studies on the carbonation and heavy 14 metal retention properties of cement-solidified fly ashes. Cement-solidified fly ash samples 15 with 40% and 60% fly ash ratios were tested for carbonation depth after being supercritically 16 carbonated. Tests were also carried out for compressive strength and retention capacity of heavy 17 metals of the samples before and after supercritical carbonation. Using CO2 absorption instead 18 of calcium carbonate to measure carbonation degree, a multi-physics model was developed and 19 combined with a leaching model to study the impact of carbonation on Cu and Pb leaching from 20 the cement-solidified fly ash. The results show that supercritical carbonation has both positive 21 and negative impacts on the strength and retention capability of heavy metals of the cement-22 solidified fly ashes, which suggests that both the carbonation conditions and the amount of fly 23 ash recycled in cementitious materials should be properly controlled to maximize potential 24 positive effect. 25 26 27

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Curing early age concrete (hereinafter referred to as EAC) with CO2 as a new method for capturing and storing CO2 can not only result in energy savings and emission reductions, but can also improve the performance of early age concrete and shorten the curing time, which leads to various application prospects. In this paper, we collect the existing research results at home and abroad to explain the reaction mechanisms of early age CO2-cured concrete (hereinafter referred to as EACC); summarize the effects of external factors such as carbonation time, CO2 pressure and concentration, and intrinsic factors (such as the active admixture, the water/cement ratio, and the water content) on the carbonation effect of early age CO2; detail the existing theoretical and numerical models of EACC; investigate the technology of EACC in four fields, i.e., precast concrete, cast-in-place concrete, recycled concrete, and fibre-reinforced concrete; and summarize the problems faced by existing research in application.

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