Evaluation of rice husk ash and vermiculite materials in the production of ceramic tiles

The challenging issues in ceramic tiles are low mechanical strength, thermal discomfort and high production costs. Apart from strength the technical functions of floor tiles based on thermal insulation is very important in buildings with human occupation where thermal comfort is required. The objective of this work was to investigate the potential of rice husk ash (RHA) and vermiculite materials in production of ceramic tiles. Initially, a typical ceramic body composed of the mixture of vermiculite and RHA batched with clay, feldspar, quartz and kaolin was prepared. Ceramic bodies were then obtained from this ceramic mixture by pressing samples at a forming pressure of 35 MPa. These bodies were then fired at 1180°C in a laboratory furnace and finally the changes in the physical and mechanical properties caused by the introduction of vermiculite and RHA were tested and evaluated. The chemical composition of the raw samples was analysed by X-ray fluorescence (XRF) while the phase composition was investigated using X-ray diffraction (XRD). The morphology of the powdered samples was studied by using Scanning electron microscopy (SEM). The bulk density and open porosity of the sintered ceramic bodies were evaluated using Archimedes ‘principle while the flexural rupture strength was determined by the three point bending test method. The major chemical compounds in vermiculite raw sample were SiO2, Al2O3 and Fe2O3 while RHA sample was found to contain mainly SiO2. From the XRD analysis, vermiculite sample had crystalline vermiculite while RHA sample had amorphous silica at low temperature below 900oC and crystallized (tridymite) above 900oC. The results from physical, mechanical and thermal properties tests show that with addition of vermiculite and RHA, the percentage of porosity, water absorption, linear shrinkage and thermal insulation capacity were increasing while the bulk density, bending strength, thermal conductivity and effusivity of the fired ceramic bodies decreased. Among the studied compositions apart from the reference sample, tile bodies made from blend containing 20 wt. % vermiculite, 5 wt. % RHA and fired at 1180oC were found to have the best properties for the production of ceramic tiles. For this combination the values for water absorption, porosity, and linear shrinkage, bulk density, bending strength, thermal conductivity and effusivity were 7.60 %, 12.08 %, 3.29 %, 1.88 g/cm3, 18.54 MPa, 0.82 W/m.K, and 1284.33 W1/2/m2K4 respectively. These values were close to the required standards for wall and floor tiles applications. This is an indication that vermiculite and RHA are suitable raw materials for the production of ceramic tiles with a required strength and thermal comfort.