Effect of carbonation, chloride and external sulphates on the leaching behaviour of major and trace elements from concrete

Construction and demolition waste: Comparison of standard up-flow column and down-flow lysimeter leaching tests

“…For most elements the pH-dependent curves reflected typical behaviours reported in the literature for cementitious materials (e.g. Engelsen et al, 2010Engelsen et al, , 2009Müllauer et al, 2012;Onori et al, 2011;van der Sloot, 2000;Van Gerven et al, 2006;Van Gerven et al, 2003). In contrast with the results of Engelsen et al, 2010 who observed low leaching of Pb at pH > 6, the leaching of lead was relatively stable at pH < 10 and somewhat scattered at pH > 10.…”

“…Similarly for SO 4 , leachability at high pH (>11) was increased in aged materials, supposedly due to enhanced dissolution of alumina ferric oxide trisulphate (AFt) and alumina ferric oxide monosulphate (AFm) phases with increased carbonation (Engelsen et al, 2009). Calcium, lithium, strontium and barium presented a similar trend: CDW3 and CDW4 displayed lower leaching, especially at high pH, possibly because of lower solubility of the corresponding carbonates compared with the original sulphate species, as suggested by Müllauer et al (2012). Oxyanion-forming elements, such as V (and Cr and Mo, to a lower extent), showed a sharper V-shape at high pH for CDW1, CDW2 and CDW5, which is typical of fresher materials (Engelsen et al, 2010); the same V-shape was observed for SO 4 , confirming that oxyanions may partly substitute SO 4 in ettringite in fresher samples (Kumarathasan et al, 1990).…”

“…For instance, Si releases were higher for CDW3 and CDW4 at high pH, which is typical for aged samples, owing to the higher solubility of amorphous Si with respect to the original CSH phases (e.g. Müllauer et al, 2012). Similarly for SO 4 , leachability at high pH (>11) was increased in aged materials, supposedly due to enhanced dissolution of alumina ferric oxide trisulphate (AFt) and alumina ferric oxide monosulphate (AFm) phases with increased carbonation (Engelsen et al, 2009).…”

“…Leaching control related to various kinds of fresh and carbonated cementitious materials has been described in detail elsewhere (e.g., Garrabrants et al, 2004;Müllauer et al, 2012;Van Gerven et al, 2006). A few studies have focused on the release processes from construction applications of recycled concrete aggregates: investigate the release mechanisms of C&DW samples, and found that release at the material's own pH is controlled by calcium silicate and aluminate hydrates and hydrogarnet.…”

Monitoring of sulphate attack on hardened cement paste studied by synchrotron XRD

“…This is indicated by the correlation of profile depth of calcite formation and ettringite depletion. Observations on the ettringite formation and de-composition in presence of carbonate source were investigated thoroughly [8,[34][35][36][37]. Sulphates are bound by AFm resulting in the formation of the AFt phase ettringite, which be-comes unstable in the surface near layers by pro-longed sulphate attack and decomposes slowly.…”