Strength and environmental behaviors of solidified fly ash under carbonation effect

The cemented solidification/stabilization has been widely adopted for fly ash around the world, since it can effectively enhance strength and restrict heavy metals. However, the carbonation effect has a significant impact on the performance of cement-based materials. Thus, the carbonation on strength characteristics and heavy metal toxicity of samples solidified with cement and chelating agent is evaluated. The test results show that the strength of samples after 28 d of standard curing has reached 3~6 MPa, which is 7.5 times more than that of cement soil. Besides, the carbonated specimens with chelating agent of 6% show the highest strength is more than those with 3% and 9%. Considering the leachability of heavy metals, the leaching concentration of Cd, Pb, Ni and Cr of cement-chelated solidified fly ash is only 2.0%, 1.0%, 19.2% and 14.1% of raw fly ash, respectively. Compared with the samples cured under standard condition, the carbonated specimens show higher leachability. Both of them reach the leaching standards and are environment-friendly. Furthermore, the carbonation depth increases with the curing time and is inversely proportional to the cement content.