Page 140 - Handbook of Thermal Analysis of Construction Materials

Section 9.0 - Durability Aspects 123

temperatures (200–600°C) and lignite exhibits three exothermal peaks
caused by oxidation. Opal shows an endothermic peak at 80°C for the loss
of water and another at 170°C due to a structural transformation. Marcasite
manifests three exothermal peaks at 450, 470, and 520°C.

Figure 37. DTA of harmful constituents in aggregates.

The causes leading to the failure of concrete near the construction
joints have been evaluated by TG. [70] The concrete sample exhibited peaks
at 705–745°C and 905–940°C caused by the decomposition of calcite and
dolomite, respectively. The slopes of the weight loss plot prior to the
dolomite and calcite decompositions correlated with the field performance.
In general it was found that in durable dolomite aggregate, carbon dioxide
loss occurs at 570°C and continues up to 705°C for the decomposition of
magnesium carbonate. Carbon dioxide from calcium carbonate is driven off