Resistance to Sulfate Attack of Mixtures with Limestone-Portland Blended Cements

Synopsis:Blended binders based on limestone-Portland cements are very popular in Europe after the advent of the EN 197-1 European norm. However, according to some British researchers concretes with limestone-Portland blended cements would be more vulnerable to sulfate attack than the corresponding concretes with Portland cement when exposed to sulfate environment. In order to assess this hypothesis, the performances of cement mixtures with portland cement and limestone-portland blended cements containing two different percentages of ground limestone (15% and 30%) were studied. Sound and cracked specimens of cement pastes, all at a given water/binder ratio of 0.40, were exposed to a sulfate-rich aqueous solution (10% by Na2SO4) at 20°C and 5°C. There was no evidence of ettringite or thaumasite formation related to the sulfate attack in the sound specimens independently of the temperature and cement type. On the other hand, in the cracked specimens some ettringite and/or thaumasite was found into the cracks of the specimens kept at 5°C, particularly when they were prepared with blended cement at 30% of ground limestone. This appears to be merely related to a higher water-cement ratio at a given water-binder ratio.