Mechanical and durability properties of fly-ash cement sand composite bricks: an alternative to conventional burnt clay bricks

Burnt clay brick is one of the most widely used construction materials in developing countries. However, the extensive use of burnt clay bricks has resulted in some drawbacks such as the loss of fertile land used for clay extraction and environmental problems associated with unregulated burning processes of brick kilns. This study evaluates the mechanical and durability properties of an alternative, i.e. un-burnt fly-ash bricks in comparison with conventional burnt clay bricks. The study was performed in two phases. In the first phase, the effect of type of aggregate (fine sand, coarse sand, stone dust, and stone aggregate) and forming method (press forming and vibro-compaction) on the compressive strength and water absorption of small-scale cylindrical fly ash–cement–sand compacts was studied. Using the best aggregate type and forming method found in phase I (coarse sand and press forming), full-size un-burnt fly-ash bricks were prepared in phase II and their performance was assessed in terms of mechanical (compressive strength and modulus of rupture) and durability (efflorescence, water absorption, initial rate of water absorption and sulphate resistance) properties and compared with the results of conventional clay bricks and different standards. The results showed that un-burnt fly-ash bricks can be used as an alternative material to conventional burnt clay bricks with comparable mechanical and durability properties.