Acid attack on pore-reduced cements

Because the durability of high-performance cements is as important as their strength, the performance of pore-reduced cement (PRC) in aggressive media such as sulfuric, hydrochloric and ethanoic acids, was studied and compared with that of ordinary Portland cement (OPC). The effects of exposure to these media on these cements were monitored by periodic visual inspection and sample weighing. Specific interactions with regard to interconnected porosity were addressed and the corrosion products characterized. PRC is less susceptible than OPC against hydrochloric and ethanoic acids. However, sulfuric acid damages PRC and OPC to almost the same extent. It is shown by electron microprobe analysis that the hydrochloric and ethanoic acids quickly penetrate the interior of normal cement pastes by acid leaching of the interconnected porosity. The reduced porosity of PRC reduces the susceptibility to attack by this mechanism. Sulfuric acid exposure causes extensive formation of gypsum in the cement surface regions, which results in mechanical stress and ultimately leads to spalling. Thus fresh surfaces are exposed regularly and therefore the relatively closed microstructure of PRC is no hindrance to this kind of attack.