Evaluating Cr(VI) Leaching from Recycled Waste Concrete Aggregate Using Acceleration Tests

摘要

Cement based secondary materials, such as waste concrete aggregates and cement stabilized wastes, are often utilized as geo-materials. Their physical and chemical properties may change in field due to the loss of soluble chemicals and/or the surface wearing. Thus, the laboratory testing protocol for evaluating their in situ leaching behavior needs to be developed. In this study, three different acceleration tests, wetting-drying test, freezing-thawing test and abrasion test, are conducted for several waste concrete aggregates (WCAs) to evaluate the effects of the exposure to these conditions, which may actually occur in field conditions, on the leaching behavior of hexavalent chromium (Cr(VI)) contained in the mortar of WCA. Leaching amounts obtained are compared and correlated with those in the conventional batch leaching test. Exposure to these accelerated conditions, particularly the wetting-drying process, promotes the leaching of Cr(VI). Leaching amounts from granular WCA exposed to these conditions are no more than that in the conventional batch leaching test which is conducted for WCA crushed with < 2 mm in grain size. This finding supports that the Cr(VI) leaching amount of WCA exposed under environmental conditions can be conservatively estimated by the conventional batch leaching test.