Portland cement concrete can undergo attack by sulfate bearing solutions such as natural groundwater or those contaminated by industrial activity. Attack can result in expansion, strength loss, surface spalling and ultimately disintegration. The resistance that a cement matrix provides to sulfate attack depends on a number of factors which include: • nature of the reaction products formed with the sulfate solution and in particular, whether their formation results in disruptive expansion; • impermeability of the matrix (including the important paste-aggregate interfacial zone) which provides a barrier against penetration by sulfate ions; • concentration of sulfate ions (in this report expressed as g/l SO42-); • mobility of the sulfate containing groundwater; • nature of the accompanying cation e.g. Na+, Mg2+, Ca2+ etc; • pH of the sulfate bearing ground water/solution; • presence of other dissolved salts such as chlorides; • temperature of the exposure; • degree of pre-curing before exposure, although in the field this is only likely to affect the performance of the concrete surface; • presence of finely divided limestone (calcium carbonate) in the aggregate, or carbonate ions dissolved in the groundwater, which may promote the formation of thaumasite under low temperature conditions.
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