Leaching from Granular Waste Materials Used in Highway Infrastructures during Infiltration Coupled with Freezing and Thawing

Secondary materials such as bottom ash, slag, concrete debris, and other waste materials are being considered for use as substitutes for natural aggregates in highway applications due to suitable engineering and economic properties. This research investigated the effect of freezing and thawing on flow mechanisms and constituent leaching from recycled concrete during a scenario of infiltration. Laboratory flow column tracer and leaching studies coupled with freeze/thaw aging were performed on laboratory formulated concrete. Three material moisture contents including the optimum moisture content of the packed material and three levels of freeze/thaw aging were examined to simulate different extents of freeze/thaw exposure. Variation in flow through the columns was observed between the different levels of freeze/thaw cycling and moisture contents. The columns receiving the maximum number of freeze/thaw cycles demonstrated a lower release of calcium, sodium, potassium, chloride, and sulfate, especially at low LS ratios, which may be due to consolidation of the material during freezing and thawing action. Overall, no significant effect of freeze/thaw cycling was observed in the leaching of trace metals. Results were compared to columns subjected to more rapid freeze/thaw cycling. Additionally, a limited number of intermittent flow columns with F/T aging were run on both laboratory formulated concrete material and actual recycled concrete (construction debris) to simulate field-like conditions.