Mohan et al found no improvement of the strength of

Mohan et al. [8] found no improvement of the strength of the bricks due to addition of waste RHA. Hossain et al. [9] collected RHA from a local rice mill, where rice husk was burnt in an uncontrolled environment, and then used for replacement of clay in brick production. With inclusion of RHA water CHIR-124 increases and crushing strength decreases in two different phases: higher rate upto 20% RHA addition, beyond that the strength decreases at lower rate. Agbede and Joel [10] investigated the effect of RHA on properties of fired clay bricks. RHA was collected from the heap of the rice husk being burnt at a rice mill and used for preparing test specimens of 40 mm × 40 mm × 40 mm. The test specimens were fired in an electric muffle furnace with a rise of 200 °C/h for 4 h. They found 6% improvement in compressive strength with 2% of RHA (having 49.8% SiO2). Strength improvements have not consistently found in previous studies, possibly, because waste RHA collected from different residual have different chemical properties. A systematic study on structural properties of fired clay bricks, manufactured at an industrial scale plant, together with chemical properties of waste RHA is necessary to identify a potential use of RHA wasted from brick firing process onto the brick manufacturing process, enhancing effective management of waste RHA by decentralization. Centralised waste management has known to fail at scale, largely because of the complexity while decentralised systems however run on smaller, but manageable scales [11]. The centralised waste disposal arrangements shift the waste management problem from the source of waste generation to waste disposal sites. Centralised mechanisms also involve long distance transportation of waste, with possible negative externalities and higher fuel consumption. Given Sri Lanka energy dependence, and continuing high oil prices, such an option would be enormously expensive. The decentralised community-based waste RHA management arrangements do not suffer from the above limitations. For example, waste RHA can be utilised near to the origin (i.e., at the brick kiln), eliminating the need for transport, landfill, or treatment at the waste disposal site. Decentralised community-based waste RHA management method will have a remarkable environmental and ecological gain. The fired clay bricks, which are popular as a walling material due to its low cost, are expected to have better structural, thermal and acoustics performances. To improve strength properties of clay bricks, chemical properties and behaviour of clay materials plays a significant role. De Silva and Crenstil [12] have investigated the chemical behaviour of clay materials under different ratio of SiO2/Al2O3 and found that the proper SiO2/Al2O3 can improve the strength characteristics of clay. The best form of RHA, suitable for masonry is in amorphous form, which is produced under controlled burning temperature. However, if controlled combustion is used, bulk production of RHA is not economical. Adding waste RHA, which contains high amount of silica, will be a cost-effective method to increase the SiO2/Al2O3 ratio in the clay mixture and improve strength characteristics of fired clay bricks. In a brick kiln, where the rice husk is used as a fuel, the temperature varies from 600 °C to 850 °C [13] and produced RHA is having about 90% of SiO2[14], [15], which are amorphous and reactive in nature [15]. However, utilization of this waste RHA on fired clay bricks has not investigated previously. Buildings scarcely control the internal environment to comfortable conditions without cross ventilation or mechanical air conditioning. Application of thermal insulator in the walls and roofs is the only technique to reduce the scale of air conditioning [16]. A few studies investigated thermal conductivity on bricks by estimating thermal resistance from density, but rarely conduct any specific tests. For example, Sutcua and Co [17] investigated thermal performance of walling material (i.e., hollow clay bricks) by FEM modelling. Santos et al. [18] performed numerical investigation on thermal performance of walls built with the new eco-efficient perforated clay bricks by using finite element model, which was calibrated and validated with experimental results. Better thermal performances in wall materials would be green and sustainable, although most of the investigation on wall materials, including masonry block and bricks, were limited for investigation on physical and mechanical properties.