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

The effect of the exposure of concrete structural components to CO2, chloride and external sulphates on the leaching of major and trace elements (Al, Ca, K, Na, S, Si, Ba, Sr, Cr and V) was investigated for concrete made with OPC and fly ash using a tank leach test and the Dutch availability test NEN 7341. Concrete specimens were carbonated under natural and accelerated conditions (2 vol.% CO2) before testing. Exposure to chloride or external sulphates was simulated by adding NaCl (30 g/L) or Na2SO4(3or30gSO42-/L) to the tank leach test eluent. The results show that concrete leaching depends significantly on the abovementioned environmental factors. In particular, the cumulative release of Cr during the tank leach test increased proportionally to carbonation depth. More V was released from carbonated concrete. Replacement of the cement by a fly ash with more Cr and V had no discernible effect on Cr release, but resulted in additional V release in proportion to the level of cement replacement. Exposure of concrete to NaCl solution enhanced the release of Cr, but not V. Exposure to Na2SO4 solution increased the release of Cr and V considerably. It is suggested that the dissolution of CrO42- and VO43- substituted AFt/AFm governs the leaching of Cr and V.