Improvement in the freeze-thaw resistance performance of concretes by a composite phase change material

Concrete is a widely used material for buildings, and its production reached approximately 10 billion m3 in 2022. Half of concrete-related buildings suffer seasonal freeze-thaw action, which causes frequent engineering damage, short service life and enormous economic loss. To improve the freeze-thaw resistance and durability of concretes, we used expanded graphite (EGC14) to encapsulate n-tetradecane (C14) and thus prepared a composite phase change material (EGC14). Scanning electron microscopy (SEM), differential scanning calorimetry (DSC), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) tests indicate that the EGC14 is chemically stable and has excellent phase change capability. Then, five mass ratios of the EGC14 to concrete aggregates were designed to produce phase change concretes (PCCs), named as PCCEGC14s (0%, 1%, 2%, 3%, and 4%). The PCC-EGC14s ' freeze-thaw resistance performances were systematically tested at different freeze-thaw cycles (FTCs). The test data demonstrate that the EGC14 could effectively keep the transition and capillary pores in the PCC-EGC14s from expanding into easily FTC-damaged macropores. Moreover, the more EGC14 the PCC-EGC14s contain, the less mass loss, and the larger dynamic moduli of elasticity (MOEd) and compressive strengths the PCCEGC14s have. According to the strength requirement of C20 concretes, the PCC-EGC14 (3%) has the optimal freeze-thaw durability. Therefore, it is suggested for actual engineering applications. Of course, the mix design principle and experimental data of the new PCC-EGC14s in this work are helpful to comprehend the freeze-thaw process and mechanism of concretes and could also provide a critical reference for practical production.