INCORPORATION OF PHASE CHANGE MATERIAL IN LIGHTWEIGHT CONCRETE FOR PASSIVE BUILDING APPLICATIONS

Abstract

Materials possessing structural as well as thermal properties are one of directions of the sustainable constructions. Phase change materials (PCMs) are the latent thermal storage materials that has the capacity to store large amount of thermal energy during its phase change from one state to another. In the past, the use of PCM in buildings was either in the form of non-structural panels or by incorporation in structural panels in its encapsulated form. The encapsulation is an expensive and a time consuming process so our research was mainly focused on the elimination of the macro-encapsulation layer from PCM impregnated aggregate and to make the non-encapsulated lightweight aggregate concrete structurally useable, thermally efficient and reliable. The PCM used for this research was paraffin wax that has melting point 23.46 ºC and latent heat storage capacity of 192.98J/g. PCM was intruded in LWA through vacuum impregnation that increased the absorption from 11% to 23%. Encapsulation layer was made with epoxy (1:1 of resin and hardener) mixed with graphite (10% by weight of epoxy). The compressive strength and elastic modulus, microstructure, thermal properties, thermal stability, chemical compatibility and thermal performance of two concretes i.e. Non-encapsulated Light weight aggregate concrete (PCM-LWAC) and encapsulated Light weight aggregate concrete (ME-LWAC) were investigated by compressive strength machine (CSM), Scanning electron microscopy (SEM), Differential scanning calorimetry (DSC), Thermogravimetric analyzer (TGA), Fourier transformation infrared spectrum analysis (FT-IR) and Thermal performance test (indoor and outdoor). From the in depth investigation of test results it can be concluded that the compressive strength of PCM-LWAC and ME-LWAC at 28 days was 22.41MPa and 21.51MPa respectively which is greater than the structural strength limit i.e. 17MPa, showing that both the types of concretes can be used in structural members. From FT-IR analysis the chemical compatibility of PCM with epoxy and LWA was ensured. TGA results showed that PCM-LWAC and ME-LWAC were thermally stable up to 150ºC. DSC curves showed that the melting point, freezing point and latent heat storage of PCM-LWA and ME-LWA are 26.13°C, 30.15°C and 20.14J/g and 22.78°C, 29.19°C and 12.5J/g respectively, concluding that both the developed materials are within the human thermal comfort zone (20°C to 32°C). Thermal Performance Test outdoor showed the temperature difference between LWAC and PCM-LWAC is 3.5°C, while for LWAC and ME-LWAC is 4.5°C. Thermal performance indoor results verified the results of outdoor. Since there are no marginal differences between thermal and mechanical properties of ME-LWAC and PCM-LWAC, hence the encapsulation layer can be removed.