The combined attack of sulfates and carbonates below 15°C can lead to deterioration of cementitious building materials due to the dissolution of C-S-H and formation of thaumasite. To avoid damage to concrete constructions, it is necessary to understand the mechanisms responsible for the formation of thaumasite. In this study, mixtures of synthetic cement clinker phases and mineral additions were examined during exposure to sulfates and carbonates. Besides temperature, the effect of C/S ratio and alkali equivalent were considered. The investigations show that thaumasite probably forms along the following routes. a) Ettringite acts as an activator for the crystallization of thaumasite. Due to the similarity in structure, thaumasite uses existing ettringite crystals as nuclei and grows epitaxially on the ettringite. b) Thaumasite forms by homogeneous nucleation directly from the solution. Small amounts of, for example, aluminate are necessary.     «

The combined attack of sulfates and carbonates below 15°C can lead to deterioration of cementitious building materials due to the dissolution of C-S-H and formation of thaumasite. To avoid damage to concrete constructions, it is necessary to understand the mechanisms responsible for the formation of thaumasite. In this study, mixtures of synthetic cement clinker phases and mineral additions were examined during exposure to sulfates and carbonates. Besides temperature, the effect of C/S ratio and...     »