Enhancing the compressive strength of thermal energy storage concrete containing a low-temperature phase change material using silica fume and multiwalled carbon nanotubes

Abstract

In this study, structural functional thermal energy storage concrete (TESC) containing Tetradecane which is a low-temperature phase change material (PCM) has been developed. The PCM was incorporated in the concrete using a porous lightweight aggregate (LWA). PCM–LWAs were fabricated using vacuum impregnation technique, and a dual–layer coating having high thermal conductivity. The epoxy of high thermal conductivity was applied on the surface of PCM impregnated LWAs to prevent leakage of PCM. Differential scanning calorimetry (DSC) and thermogravimetric analysis were used to evaluate the thermal performance of encapsulated PCM–LWA. The DSC results demonstrated that PCM–LWA had melting and freezing temperature 4.18 °C and 0.33 °C and corresponding enthalpies 18 J/g and 15 J/g, respectively. Thermal energy storing concrete was developed by replacing normal-weight aggregates with the PCM–LWAs in proportions of 50% and 100% by volume. The compression test results revealed that the strength of PCM–LWA concrete decreased significantly compared to normal concrete. The strength loss in the PCM–LWA concrete with replacement ratios of 50% and 100% were 29% and 39%, respectively. Due to porous nature and relatively low stiffness of LWAs, significant strength loss has been observed. To overcome the strength degradation, silica fume (SF) and multiwalled carbon nanotubes (MWCNTs) were added to the concrete mixture. The addition of SF/MWCNTs reduced the strength loss by 15% and 20%, respectively. The SEM results revealed that the SF/MWCNT addition in concrete resulted in denser microstructure. The XRD results confirmed that SF reacted with Ca(OH)2 to increase the growth of C-S-H. Therefore, the mechanical performance of TESC containing PCM–LWAs can be improved by adding SF/MWCNTs to the concrete mixture.