Leachability of trace metal elements from fly ash concrete: Results from column-leaching and batch-leaching tests

Abstract

This paper deals with the effect of leaching conditions on the leachability of trace metal elements from concrete incorporating two fly ashes. The data from the column-leaching tests to simulate wetting and drying, and batch-leaching tests using buffered acetic acid and synthetic acid rain as leachants, are discussed. The United States Environmental Protection Agency (EPA) Regulatory Method 1311 - Toxicity Characteristic Leaching Procedure (TCLP) was used as a reference. The results indicated that, regardless of the type of the fly ash used, the percentage of fly ash, and the water-cementitious ratio (w/cm) of the concrete, none of the trace metals analyzed (As, Cd, Cr, Cu, Pb, Se, and Zn) in the leachates from the fly ash concrete samples exceeded the regulated concentration levels specified in the TCLP leaching test. The concretes incorporating the fly ashes are, therefore, considered stable. In the batch- and column-leaching tests, the leached trace metal levels from the fly ash concretes were also well below the regulatory levels for the leachate quality criteria. The fly ash content and w/cm did not appear to have significant effect on the leachability of the trace metal elements when using column-leaching tests and the 24-week batch-leaching test. The observed concentrations of metals leached using synthetic-acid rain were less than that observed for the buffered acetic acid. This is consistent with the pH dependence of the leachability of the metals. For Se, all measured values of the leachates from the four different types of tests were at or below the detection limit. Cadmium, Cr, Ni, Pb, and Fe in the leachates from the fly ash concretes were also measured at or near detection limits or at levels below or similar to those of the control portland cement concrete. Arsenic, and to a lesser extent Cu and Zn, were the only metals that showed any significant leaching trends in the tests. Arsenic showed a correlation between the metal content in fly ash and the concentrations of the metals leached from the fly ash concrete. Similar correlations for Zn and Cu were not observed.