Red-mud geopolymer composite encapsulated phase change material for thermal comfort in built-sector

Abstract

In housing sector, large quantity of energy is expended on thermal comfort and other domestic routines which increase the energy consumption and drives up demand, thus, contributes to greenhouse gas emissions. The development of smart, energy-saving enhanced materials can reduce these energy consumption and emission. In this study, expanded graphite (EG) is used to encapsulate phase change material (PCM) to produce EG/paraffin composites. And the EG/paraffin composite was mixed with a geopolymer aggregates using the vacuum impregnation technique to produce enhanced thermal wall material for building and construction industry. Effect of EG/paraffin composite on the thermophysical properties, compressive strength and thermal behaviour of the geopolymer composite wall was investigated by thermal constant analyser, uniaxial compressive strength, differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The result of thermal conductivity, heat permeability, specific heat and density for the EG/PCM geopolymer composite are 46.4321 kj/kg, 2.4561 W/mk, 2.1834 Mj/m3k and 873.32 kg/m3 respectively. While the compressive strength for the EG/PCM geopolymer composite was 10.3 MPa. Thermophysical properties of the EG/PCM geopolymer composite increased with increased concentration of EG/paraffin composite in the geopolymer aggregate, however, the compressive strength is reduced. This is because of the low rigidity and strength of the EG/PCM composite inside the geopolymer aggregates. A 25% EG/PCM concentration inside the geopolymer aggregates was the optimal mixing concentration that is high enough for application in building and construction industries. The PCM and EG/PCM composite melting and crystallization temperature curves exhibited identical peaks, which implies a stable composite was formed. The melting enthalpy and crystallization enthalpy of the EG/PCM are 131.13 J/g and 126.77 J/g, respectively. Whereas, melting and crystallization specific heat value for the EG/PCM are 26.11 J/g and 17.42 J/g, respectively. The outdoor test result of the EG/PCM composite geopolymer wall material thermal ability demonstrated higher thermal storage performance than the conventional cementite, clay, and gypsum. The EG/PCM composite geopolymer wall average temperature was 51 °C during the day time and 36 °C all through the night till 7 am. EG/PCM geopolymer composite was thermally and chemically stable under varying solar conditions. The EG/PCM composite geopolymer aggregate can be an excellent thermal comfort material for building and construction industries.