WEATHERING OF IRON SULFIDES AND CONCRETE ALTERATION - THERMODYNAMIC MODEL AND OBSERVATION IN DAMS FROM CENTRAL PYRENEES, SPAIN

The concrete of the Graus and Tabescan darns present significant durab ility problems. The cement paste is altered to expansive phases such a s ettringite and gypsum, following fractures and aggregate-paste inter faces. The alteration is initially attributed to the acidic solution p roduced by the weathering of the pyrrhotite contained in the aggregate fragments. A chemical model, based on ion association and thermodynam ic equilibrium, permits the calculation of the mass transfer between t he solids and the pore solution, and the prediction of the progress of the acidic attack. The results of the calculations have been compared with the alteration features observed in concrete of these dams. Desp ite the simplifications, this model is able to predict the observed al teration stages, and confirms the hypothesis of acidic-sulfatic altera tion of the cement. (C) 1998 Elsevier Science Ltd.