ABSTRACT
ABSTRACT: Thaumasite is formed as a result of the reaction between sulfates, carbonates, and the calcium silicate hydrates present in old and new hydraulic mortars. Thaumasite formation is more prevalent in mortars exposed to low temperatures, high humidity and environments with high sulfate content. The present study aimed at ascertaining whether pH, type of aggressive solution and mortar composition may increase thaumasite formation. Thermodynamic modelling results (PHREEQCI program) have been considered for the evaluation of the potential risk of different ligands with less aluminates and silica fume addition causing thaumasite formation. Samples were immersed for 1 year in: CaSO4, MgSO4 and Na2SO4 (1500 ppm of sulphates). Thermodynamic results indicated that all solutions were in equilibrium with thaumasite. Samples immersed in MgSO4 solutions were also in equilibrium with magnesium silicate, silico-aluminate, and carbonates. Thaumasite only formed over the surface of the sample exposed 1 year to MgSO4 and CaSO4 solutions.
