The lead (Pb) content of concrete is often a concern to project managers and environmental regulators. Waste reduction policies give an incentive to limit landfilling of demolition debris, but many material recycling scenarios involve some environmental exposure to crushed concrete.
The objective of this project was to determine the mobility of residual Pb content in crushed demolition concrete in the environment when exposed to rainfall.
This study used a demolition project to investigate relative Pb concentrations and solubility of Pb in runoff water. Painted walls were sampled before demolition, mass of concrete was calculated, and a projected Pb concentration for total demolition debris was calculated. An extraction experiment was designed to mimic the environmental performance of using crushed concrete as a paving material for parking lots.
This experiment showed that, for expected levels of Pb, little of the heavy metal moved. Levels of Pb in runoff water remained below drinking water standards. In addition, after exposure to a simulated two years of rainfall, the concrete retained high alkalinity, which limits the action of acidic rain.
Given the low concentrations of Pb in the recycled concrete aggregate (RCA) samples tested relative to regulatory limits and the buffering capacity of concrete, this study concluded that the environmental risk from Pb-containing crushed concrete applied to land is negligible. Moreover, the uses for crushed concrete as road base or fill conveys little risk of environmental or human exposure; in such cases, the RCA would be placed underneath thick layers of soil or paving materials, thus limiting environmental and human exposure.