Influence of carbonation and carbonation methods on leaching of metals from mortars

Mortars with varying water-to-cement (w/c) ratio were spiked with heavy metals. After hardening, some samples were carbonated in a CO2 chamber, others were carbonated using supercritical CO2 (SCC). Porosity and carbonation depth of treated and untreated samples were compared. Leaching was tested using the diffusion (NEN 7345) and extraction test (based on DIN 38414-S4). The results show that carbonation decreases the porosity of the samples. The decrease is more important with increasing w/c ratio. Carbonation runs deeper into the monolith with increasing w/c ratio. In the supercritical method, not all samples were carbonated to the same extent. The diffusion test shows that carbonation decreases leaching of Na, K, Ca, Ba, Cu, and Pb and increases leaching of Mg. Ni leaching depends on the pH induced by carbonation. Influence of pH and formation of metal carbonates is evaluated with the extraction test and enhances understanding of metal leaching in the diffusion test. (C) 2003 Elsevier Ltd. All rights reserved.