Hydration products in two aged cement pastes

Thermal decomposition of asbestos-containing materials

“…Calcite was formed as a result of the long-term ageing of the cement-asbestos samples. It was possibly formed not only on portlandite carbonation, but also from other compounds, such as amorphous carbonate or CSH gel [41]. For the ACB sample, the thermal effect associated with calcite decomposition was the strongest.…”

“…A wide temperature range of CO 2 release may indicate a different degree of crystallinity of the calcite or the presence of other carbonate minerals in the tested samples [33]. The weak effect from H 2 O at 600°C on the EGA curve may come from the thermal decomposition of chrysotile asbestos and/or more complicated CSH phase components [41,43].…”

“…The wide temperature range of these effects may indicate a different degree of crystallinity of calcite, the presence of other carbonate minerals [33] or the thermal decomposition of other cementitious phases. Stepkowska et al [41] stated that the rest of the sorbed water escaped from aged cement pastes between 500 and 700°C, possibly upon dehydroxylation of the jennite-like compound (9CaOÁ6SiO 2 Á11H 2 O). At a higher temperature (in the range of 800-900°C), the decomposition of carbonates takes place, especially of calcite (CaCO 3 ) [42].…”

“…On the EGA curves of all the tested samples, a peak which came from the released water vapour is clearly visible in this range. This is adsorbed water and water from the thermal decomposition of the hydrates CSH phase [41]. Next, in the temperature range of 200-400°C, small mass loss (*2 mass%), which may have come from combustion of organic material traces [37], was observed for all of the samples.…”

“…Due to the much smaller amount of samples in this measurement as compared to the DTA analysis (32 vs. 500 mg), the temperature of the maximum peak is shifted towards lower values of temperature. At a higher temperature (in the range of 500-750°C), decomposition of carbonates, especially calcite (CaCO 3 ) [41], takes place. This is indicated by a clearly visible loss of mass.…”