X-ray diffraction characterization of the superficial attack of cement pastes in sulfate solutions

Samples of cement pastes were submitted to sulphatic attack. The X ray diffraction analysis of their surfaces allowed the identification and the location of the different phases present through the alteration thickness. So it was confirmed that a thin film of ettringite arises between crystallised gypsum, on the surface, and the unattacked zone of the hydrated cement bulk. This phase profile explains the kinetic of the process which varies according to the acidity of the aggressive agent. It must be underlined that this layer is thin and that it can constitute a protective barrier against further corrosion. Therefore, the size of the corroded area depends on the surface roughness. It will increase with the micro-porosity or the micro-cracking of the cement paste.