Thermal performance and mechanical properties of phase change cement paste with Nano-SiO2 grafted straw-paraffin

Abstract

In paraffin-based phase change concrete, rice straw can be used as the carrier for paraffin, however, the compatibility between rice straw and cement matrix is poor. In this study, Nano-SiO2 was grafted on straw-paraffin to improve the interfacial compatibility, and its influences on thermal performance and mechanical properties of phase change cement paste were investigated. Firstly, the phase change potential heat and tensile property of Nano-SiO2 grafted straw-paraffin were tested. Then, the thermal performance and mechanical properties of cement paste with Nano-SiO2 grafted straw-paraffin were tested. The results indicate that: (1) The melting temperature of Nano-SiO2 grafted straw-paraffin (PRS-1%) is 51.15℃, 0.39% lower than paraffin-straw without Nano-SiO2(PR), the enthalpy value is 85.64 J/g, 8.74% higher than PR. (2) The tensile strength of PRS-1% is 38.63 MPa, which is 18.63% higher than PR. After 100 phase change cycles, its tensile strength is 23.98% higher than PR. (3) The Nano-SiO2 grafting can reduce the volume of pores and cracks at straw-paste interface, decrease the content of Ca(OH)2 and increase the content of C-S-H gel at the interface. (4) Compared with cement paste with PR, the compressive strength and flexural strength of cement paste with PRS-1% increase by 21.05% and 16.55%, respectively. (5) The Nano-SiO2 grafting (1%) can increase the specific heat capacity and thermal conductivity of straw-paraffin based phase change cement paste by 2.24% and 9.64%, respectively.