Leaching of heavy metals from concrete pavers containing waste-to-energy bottom ash as an aggregate

Treated bottom ash (BA) from aeb Amsterdam's waste-to-energy (WtE) plant was used to partially replace conventional aggregates in concrete pavers. To evaluate the effect of weathering and recycling on the leaching of heavy metals, two pavers were first carbonated in an incubator (20 vol% CO2, 30°C). After 14 days one of the pavers was crushed and the resulting 0-31.5 mm granulates were put back in the incubator for another 17 days to simulate second life. The other carbonated paver and an untreated equivalent were submitted to a diffusion test, whereas the granulates sampled at regular time intervals were submitted to batch and column leaching tests. The element concentrations in the eluates were measured with ICP-OES. The results of the diffusion tests showed that the elution of heavy metals from the paver was very low. The elution of sulphates and chlorides from the carbonated tile was significantly lower than the elution from the non-carbonated tile and decreased exponentially over time. For both pavers, the measured cumulative elution after 64 days was below the Dutch legal limit values. The batch leaching tests of the granulates showed that the leaching of most heavy metals showed no trend over time, but for the leaching of Zn and Sb that decreased and increased, respectively, which could be linked to pH changes. Colum tests showed that all granulates complied with the Dutch legal limit values for use of waste as uncontained construction material, confirming that BA can be used safely as aggregate in concrete pavers at the considered level even if the paver is recycled.