About thaumasite formation in Portland-limestone cement pastes and mortars--effect of heat treatment at 95 deg C and storage at 5 deg C

摘要

Owing to the presence of finely divided calcite, mortars and concretes made with Portland-limestone cements are particularly susceptible to damaging thaumasite formation during sulfate attack at lower temperatures. This work reports the results of investigations on mortars made according to DIN/EN 196 and pastes (w/c ratio of 0.5) with CEM I 42,5 R, as well as with mixtures of cement with limestone filler. Some of the samples were heat-treated at 95 deg C. The length changes and resonant frequencies of the samples were measured during long-term water-storage at 20 and 5 deg C. There was no evidence from X-ray diffraction data of thaumasite formation in the samples. Only for pastes containing 30 wt. percent limestone filler were small areas found by SEM and X-ray microanalysis whose chemical analysis matched thaumasite or a thaumasite-ettringite solid solution.