The thermal properties of metakaolin geopolymer coated with MgO particles

The main objective of this study is to experimentally investigate the influence of MgO particles on the thermal properties of metakaolin geopolymer. Geopolymer was produced through alkali activated of metakaolin by adjusting the oxide molar ratios of the starting materials to the fixed value of SiO2/Al2O3 = 1.5, Na2O/SiO2 = 0.3 and H2O/Na2O = 10, and curing temperature at 70°C for 2 hours. The particle size of MgO was reduced by means of ball milling at 300 rpm for 5 hours and then painted on the surface of geopolymer before reaching its setting time. The variation of MgO mass relative to the mass of metakaolin were 0%, 1%, 2% and 3%. The resulting composite-like geopolymer-MgO materials were stored in open air for 28 days before commencing any thermal measurement. The structure of geopolymer-MgO was examined by using x-ray diffraction (XRD) and the results showed the presence of magnesium aluminum oxide phase as the MgO concentration increases. The thermal properties of the resulting materials were examined by means of thermal conductivity measurement, heat resistance at 750°C and fire resistance around 1000°C for 30 minutes. The results showed that the thermal conductivity of the samples decrease as the concentration of MgO on the surface of geopolymer increases. The thermal resitance measurements showed the development of cracks on the surface of the samples increased as the MgO concentration increase and hence reducing the density and the mechanical strength of the materials. The fire resistance measurements indicated that all samples were able to maintain their integrity up to 1000°C. It is concluded that MgO particles was able to improve the thermal resistance of geopolymer especially when it is exposed to intense fire.