Coal fly ash–carbide lime bricks: An environment friendly building product

• Strength controlling equations for coal fly ash–carbide lime bricks are proposed.
• Strength is governed by ratio involving porosity and volumetric binder content.
• Increasing curing temperature produces gains in strength up to a threshold.
• Energy required for heating (for curing at 40 °C, 60 °C and 80 °C) is assessed.
• Preferred strategies for attaining target strength are proposed.

Coal fly ash and carbide lime are industrial by-products of coal combustion in thermal power plants and of manufacture of acetylene gas, respectively, available in profusion in southern Brazil. Research has been carried out to search for possible use of such materials to produce environmental friendly bricks that have high compressive strength. This study aims to evaluate strength controlling parameters of coal fly ash–carbide lime mixtures, as well as to show that porosity/carbide lime (η/Lv) ratio (corresponding to porosity divided by the volumetric carbide lime content) can be used to predict compressive strength (qu). The controlling parameters evaluated here are carbide lime content, porosity, curing temperature, curing time and porosity/carbide lime ratio. A number of unconfined compression tests were carried out. The results show that a power function adapts better the relation qu versus η/Lv, in which Lv is adjusted by an exponent (in this case 0.11) for all coal fly ash–carbide lime mixtures studied. Equations that control the compressive strength for each curing period and curing temperature examined can be formulated using this unique ratio. Preferred strategies for varying ranges of qu are also proposed based on the energy required for heating, considering distinct curing periods and temperatures.