Increased sulfate resistance of ggbs concrete in the presence of carbonate

Significant occurrence of the thaumasite form of sulfate attack (TSA) has only been identified in concrete containing carbonate aggregate, leading to a perception that the presence of calcium carbonate is undesirable in concrete exposed to sulfate attack. This paper reports on how the addition of a small percentage of calcium carbonate or calcium sulfate, affects the sulfate resistance of concrete containing ground granulated blastfurnace slag (ggbs). Three test methods were employed to assess sulfate resistance (all at 20 degreesC): Cubes were immersed in magnesium and sodium sulfate solutions and monitored for corner-loss and strength-loss, over six years. Mortar was sieved from fresh concrete and used to make prisms. These prisms were immersed in magnesium and sodium sulfate solutions and their expansions monitored for up to six years. In accordance with a draft of a European Standard for sulfate resistance, mortar prisms were prepared and monitored for expansion for one year. It was found that both calcium carbonate and calcium sulfate additions, had a consistent beneficial effect on the resistance of ggbs concrete to conventional sulfate attack, both in respect to expansion and in respect of disintegration. The paper discusses possible mechanisms for the improved resistance. (C) 2003 Elsevier Ltd. All rights reserved.