On leaching mechanisms of major and trace elements from concrete - Carbonation, exposure to deicing salt and external sulphates

Model simulations and tank leach tests are compared to investigate the surface release of major and trace elements from ordinary Portland cement concrete and how this is affected by carbonation, NaCl or Na₂SO₄ in the eluent. It is distinguished between surface dissolution processes and diffusion of species from inside the concrete. Whereas alkalis, Cr(VI) and Sr are mainly released by diffusion, Ca, SO₄²⁻, Al, V, Ba and Zn are primarily released by surface dissolution. Changes in the leaching of Cr(VI) and V from concrete exposed to carbonation, NaCl or Na₂SO₄ are explained by the solubility equilibria of ettringite in which SO₄²⁻ is substituted by CrO₄²⁻ or VO₄³⁻. Barite and strontianite control the release of Ba and Sr. It is likely that C–S–H with incorporated Zn controls the release of Zn.