External sulphate attack by ground water

ABSTRACT Materials based on Portland cement react chemically with solutions containing sulphates, even at very low concentrations. The originality of the work described in this paper is to have characterised the kinetics of evolution of mineralogy and solution-material chemical exchanges, for a concentration 10.10−3 mol/L of sulphate, representative of underground conditions, which is a deep geological site made up of argillite. Under these chemical conditions which are maintained as constant as possible at the laboratory scale, the main experimental fact established is the precipitation of gypsum in the damaged zone for two cements with very different C3A contents, despite the low sulphate concentration of the aggressive solution. The gypsum forms immediately behind the dissolution front of portlandite, which itself spreads towards the core of the material at a rate of 0.15 mm.d−0.5. The amplitude of the precipitation of secondary ettringite is consistent with the C3A content of the cement. However, such mineralogical changes did not cause macroscopic alteration.