Page 539 - Handbook of Thermal Analysis of Construction Materials

510 Chapter 12 - Clay-Based Construction Products

Figure 14. DTA of some clays. [24]

3.4 Bloatability of Clays

Clays form an important group of raw materials for the production
of lightweight concrete. In practice, the clay pellets are fired to a temperature
1000–1300°C for a short period when the pellets suddenly increase in
volume, called bloating. Various materials present in the clay are reported
to be responsible for the bloating phenomenon. The gas-producing agents
are variously given as hematite, pyrite, carbonates, sulfates, alkali earths,
graphite, lignite, and micaceous minerals. The gases responsible for bloat-
ing are oxygen, sulfur, sulfur dioxide and trioxides, carbon dioxide, water,
hydrocarbons, and entrapped air either alone or in combination with others.
Ramachandran, et al., [26] mixed several potential bloating agents with
montmorillonite and a synthetic aluminate silicate corresponding to illite.
The agents, such as hematite, calcite, molasses, pyrites, gypsum, siderite,
magnesite, dolomite, saw dust, fly ash, talc, and muscovite, were mixed
with the clay fired at 50°C intervals from 1100 to 1300°C. Figures 15 and
16 show the DTA curves of some of the bloating agents. The temperature,
intensity, and the endothermal/exothermal nature of the peaks were used to
determine the mechanism and the efficiency of bloating of various agents.