Ettringite and thaumasite formation in laboratory concretes prepared using sulfate-resisting cements

Four series of micrographs are presented illustrating the microstructures resulting from the long-term immersion (21 years) in sulfate solutions of concretes prepared using either a Type II or a Type V Portland cement. The effects of cement type (II or V), water-to-cement ratio (0.45 or 0.50) and the sulfate solution (Na2SO4 or MgSO4) on microstructural evolution were analyzed. Gradients were observed in sulfate-containing solids from the concrete surfaces inward. Such gradients are consistent with immersion in sulfate solutions in that the extent of sulfate attack was progressively diminished at locations increasingly remote from the surfaces. Although the samples were stored at ambient temperatures, extensive thaumasite formation was observed. (C) 2002 Published by Elsevier Science Ltd.