Gas‐producing agents in the production of lightweight aggregates

Abstract

An investigation into the bloating phenomenon in an illitic clay was studied by subjecting the clay to different treatments and employing techniques such as differential thermal analysis, X-ray diffraction, chemical analysis and gas chromatographic analysis. The results indicate that both organic matter and calcium carbonate behave as gas-producing agents. l h e hydroxyl water, entrapped air in thc pores and ferric oxide do not significantly contribute to the bloating.

Production of lightweight aggregates from mining and industrial wastes

“…The endothermic peak at 575 C (P4) could be due to the transformation from a-to b-quartz (Chopra et al, 1964), and the sharp endothermic peak at 750 C (P5) (associated with a significant weight loss) in sample W100, which decreases as the sewage sludge in the mixture increases, is due to the decarbonation of calcium carbonate. Pure calcium carbonate shows an endothermic peak at around 850 C-900 C, but, in the presence of impurities, the temperature of the peak is known to decrease by 100 C (Chopra et al, 1964). The last endothermic peak, at approximately 1140 C (P6), is believed to be due to the gas evolution produced in the reaction of Fe 2 O 3 .…”

“…5a) and in the mixture with the clay-rich sediment (Fig. 5e) is caused by the dehydroxylation of the clay minerals, such as kaolinite and illite (Chopra et al, 1964) (Table 2). The endothermic peak at 575 C (P4) could be due to the transformation from a-to b-quartz (Chopra et al, 1964), and the sharp endothermic peak at 750 C (P5) (associated with a significant weight loss) in sample W100, which decreases as the sewage sludge in the mixture increases, is due to the decarbonation of calcium carbonate.…”

“…5e) is caused by the dehydroxylation of the clay minerals, such as kaolinite and illite (Chopra et al, 1964) (Table 2). The endothermic peak at 575 C (P4) could be due to the transformation from a-to b-quartz (Chopra et al, 1964), and the sharp endothermic peak at 750 C (P5) (associated with a significant weight loss) in sample W100, which decreases as the sewage sludge in the mixture increases, is due to the decarbonation of calcium carbonate. Pure calcium carbonate shows an endothermic peak at around 850 C-900 C, but, in the presence of impurities, the temperature of the peak is known to decrease by 100 C (Chopra et al, 1964).…”

Use of clay in the manufacture of lightweight aggregate

“…Initial [20]  m m  m m m Clay and FeCr slag [23]      Clay and granite waste [24]     m  m m Silt-clay waste and sewage sludge [25]      …”

“…The production of clay derived LWA requires processing in a temperature range where pyro-plastic deformation, gas generation and gas retention occur simultaneously. The main sources of gas generation in clay-containing minerals at high temperatures are dissociation or reduction of ferric oxides, combustion of organic matter, release of interlayer water molecules and thermal decomposition of carbonates [24,25]. The temperatures at which gases are generated vary and this influences/controls the bloating behaviour [26].…”