Application of carbon nanotubes in coal ash-plastic bricks

The use of waste materials, by-products and natural feedstocks as replacement of conventional binders and aggregates in building materials has received much interest. Furthermore, river sand and rock aggregates are finite resources. Thus, alternative sustainable materials are required in the built environment industry. In this study, waste plastics (low-density polyethylene) and coal fly ash, a coal combustion by-product reinforced with carbon nanotubes (CNTs) were used to make sustainable bricks. The CNTs were functionalized through acid treatment to improve their dispersibility in the bricks. The mechanical strength of the bricks increased from 11 to 25 MPa with an increase in the CNT loading from 0.01 to 0.1 wt%. All the bricks had compressive and split tensile strengths that exceeded the acceptable standards of 4 MPa and 1.2 MPa, respectively. The reinforcement mechanism by CNTs was found to be due to the bridging effect as well as through micro-void filling which improved the microstructure of the bricks by densifying their structures. This allowed crack deflection rather than microcrack propagation when load was applied. Furthermore, the densified structures of the bricks reduced their porosity and consequently the water absorption and deformation. The optimum CNT loading was found to be 0.05 wt% for the bricks made in this study.