Novel autoclaved fibre-cements utilising clay-brick waste

Publication Type:
Thesis
Issue Date:
2007
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NO FULL TEXT AVAILABLE. Access is restricted indefinitely. ----- Millions of tonnes of fired clay-brick waste are generated worldwide each year, a large portion of which is destined for landfill. This study is concerned with the utilisation of such alumina-silica rich material for the development of hydrothermally cured fibre-cement composites. The principal objective of this research was to establish the hydrothermal chemistry involved, and, evaluate the potential of using ground fired clay-brick as a raw material in the development and production of autoclaved fibre-cement prototypes. A carefully designed experimental program involving the evaluation of slurry, mortar and filter pad samples was conducted using a combination of analytical methods including XRD, DTA-TGA and NMR, in addition to physical characterisation. It was established that mullite, an aluminosilicate phase contained in fired clay-brick, promotes the formation of Al-substituted 1.1 run tobermorite, the main binder in most autoclaved calcium silicate products, with the release of Al₂O₃ occurring at or below 170°C. The formation of crystalline tobermorite was further enhanced by a reactive glassy phase and additional SiO₂, in the form of quartz and cristobalite, contained in fired clay-bricks. The addition of clay-brick fines up to 17.2 wt % was found to be beneficial to compressive strength; however, at Al/(Al+Si) ratios > 0.091 the formation of Al-(C-S-H) was promoted, decreasing the amount of Al-tobermorite. The study established that for the production of fibre-cement composites up to 12 wt % clay-brick fines could be used as quartz replacement in the cement-quartz matrix with no adverse effect to mechanical properties. With increasing amounts of Al-tobermorite formation, through the addition of clay-brick fines, the drying shrinkage and susceptibility to carbonation were found to decrease. Thus, the utilization of fired clay-brick waste for the production of hydrothermally cured fibre-cement products is a viable option for the future, affording economical, environmental and social benefits.
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