The pollution of construction and demolition waste (C & DW) to groundwater must be considered in exploring the applicability of C & DW aggregates as an alternative material for permeable pavement subbases. In this paper, two common C & DW recycled aggregates, namely, recycled brick aggregate (CB) and recycled concrete aggregate (RCA), were selected as research objects. The concentration of leached heavy metals and the release characteristics and rules of contaminants were examined, and the influences of factors such as mix ratio, liquid-solid ratio, pH value and others on the leached concentration of heavy metals were analyzed. Results demonstrated that in pure brick environment, the leached concentration of Cd, Cu, Ni, and Zn hit the lowest, while in pure concrete environment, the leached concentration of Cr and Pb minimized. As liquid-solid ratio varied, the leached concentration of Cd and Zn barely changed, implying that Cd and Zn reached equilibrium. With the rising of liquid-solid ratio, the leaching rate and volume of Cr and Pb both increased, whereas the leaching rate of Cu and Ni dropped. At different pH values, the trends of leached concentration of Cd, Ni, and Pb varying with time were similar in general: with the rising of pH value, the balanced concentration reduced. The leached concentration of Cr displayed a positive relation with pH value. The leached concentration of Cu and Zn surged at extreme pH values, presenting a U-shaped curve. In conclusion, C & DW recycled aggregates can be used as pavement filler as the concentration of heavy metals after leaching meets China's relevant specifications.
Key words
construction and demolition waste /
environment pollution /
recycled aggregate /
pavement filler /
heavy metals
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