The incorporation of PCMs in energy piles holds significant potential for revolutionising thermal management in construction, making them a crucial component in the development of next-generation systems. The existing literature on PCM-integrated energy piles largely consists of isolated case studies and experimental investigations, often focusing on specific aspects without providing a comprehensive synthesis to guide future research or practical applications. To date, no review has been conducted to consolidate and evaluate the existing knowledge on PCMs in energy piles, making this review the first of its kind in this field. Up until now, this gap in research has limited our understanding of how PCM configurations, thermal properties, and integration methods impact the thermal and mechanical performance of these systems. Through thoroughly analysing the current research landscape, this review discovers key trends, methodologies, and insights. The methodology used here involved a systematic search of the existing SCI/SCIE-indexed literature to ensure a structured review. Based on the SLR findings, it is evident that current research on PCMs in energy piles is focused on improving thermal efficiency, heat transfer, and compressive strength. Furthermore, precise adjustments in melting temperature significantly impact efficiency, with PCM integration boosting thermal energy extraction by up to 70 % in some cases, such as heating cycles, and saving up to 30 % in operational costs. PCMs also reduce soil temperature fluctuations, improving structural integrity through minimising axial load forces. However, challenges remain, including reduced mechanical strength due to voids and weak bonding, high costs, and complexities such as micro-encapsulation. We acknowledge that there are gaps in addressing certain key factors, including thermal diffusivity; volume change during phase transitions; thermal response time; compatibility with construction materials; interaction with soil, creep, and fatigue; material compatibility and durability; and the long-term energy savings associated with PCM-GEP systems.

This study assesses the hygrothermal performance of the Photovoltaic External Thermal Insulation Composite System (PV ETICS), using a thick layer of mortar with Phase Change Material (PCM) granules as a passive heat sink. The experimental scenario involved the wall system exposure to real outdoor climate conditions during a 20-month long measurement period. Measured data were compared with results from the hygrothermal modelling. The findings reveal that with carefully designed diffusion channels the PV ETICS demonstrated no accumulation of moisture behind the vapour-tight PV panel. Long term hygrothermal modelling for PCM mortar moisture content with a previously calibrated model predicted stable moisture content around 0.03 m(3)/m(3), significantly lower than the moisture content during first 2 years. Relative humidity behind the PV panel falls into the hygroscopic range on the second spring after the construction. The annual maximum temperatures for PCM mortar during two summers were 69 degrees C, occurring in mid-August. Risk analysis was conducted with historic climate data to understand, whether higher PCM temperatures could be reached in the same climate for different years. Overall, the wall system showed no signs of extensive moisture damage during the testing period, but slight discolouring of the PCM mortar was recorded. This study contributes valuable insights into the practical viability of PV ETICS with PCM mortar, reaffirming its potential for application on larger scale on real building facades.

During winter construction of earthworks such as earth dams and embankments, the structural properties of the soil may deteriorate due to freeze-thaw cycles. A new measure to combat freeze-thaw damage, incorporating phase change materials (PCMs) into the soil to regulate temperature, has been verified and applied in roadbed and pavement engineering. However, the law of deterioration from freeze-thaw cycles for this novel construction material is not clear yet. This study investigated the characteristics and mechanism of deterioration of clay mixed with paraffin-based PCM (PPCM-clay) through freezing and thawing using freeze-thaw tests, unconfined compression tests, permeability tests, and macro-micro structural analysis. The results show that the freeze-thaw resistance of PPCM-clay is better than that of pure soil. The amount of PPCM added is proportional to the effect of inhibiting soil strength and permeability degradation. Under the same number of freeze-thaw cycles, the compressive strength of PPCM-clay is greater than that of pure soil. Micropore expansion and frost heave are also not significant in PPCM-clay. This indicates that the low initial water content, relatively large porosity, thermal hysteresis, frost contraction, hydrophobicity, and high viscosity of PPCMs are the main reasons for the improvement in PPCM-clay freeze-thaw resistance. These findings provide a theoretical basis for the potential application of PPCM-clay as a dam or embankment material for weakening soil frost damage in winter construction in cold regions.

In order to reduce heat loss and diffusion of underground heating pipelines, this research incorporated phase change material (PCM) into the controlled low-strength material (CLSM) to prepare a pipeline backfill material with temperature control performance. In response to the problem that PCM leaks easily, a new type of paraffin-rice husk ash composite PCM (PR-PCM) was obtained by adsorbing melted paraffin into rice husk ash. Through mixing PR-PCM with dredged sediment (DS) and ordinary Portland cement (OPC), a controlled low-strength material (CLSM) with temperature control performance was prepared. The flowability, mechanical properties, microscopic characteristics, thermal characteristics, and durability of CLSM were analyzed through flowability, unconfined compressive strength (UCS), X-ray diffraction (XRD), scanning electronic microscopy (SEM), differential scanning calorimetry (DSC), and phase change cycle tests. The results show that when water consumption is constant, as the PR-PCM content increases, the flowability of CLSM increases, and the strength decreases. The CLSM has an obvious paraffin diffraction peak in the XRD pattern, and its microstructure is dense with few pores. The melting point of CLSM is 50.65 degrees C and the latent heat is 4.10 J/g. Compared with CLSM without PR-PCM, the maximum temperature difference during the heating process can reach 3.40 degrees C, and the heat storage performance is improved by 4.1%. The strength of CLSM increases and the melting point decreases after phase change cycles. CLSM containing PR-PCM has the characteristics of phase change temperature control, which plays a positive role in reducing heat loss by heating pipelines and temperature change in backfill areas.

To prevent the cracking of silty clay under cyclic wet-dry cycling (W-D), which leads to the increase of deformation and strength attenuation of silty clay, microencapsulated phase change material (mPCM) was used to improve it. The deformation and strength characteristics of silt with different dosages (1 %, 2 % and 4 %) of mPCM and their changing patterns were analyzed and studied by indoor compaction test, crack observation test, consolidation test and straight shear test, and compared with silt without modifier. The results showed that with the increase of mPCM dosage, the optimum water content of silt and the maximum dry density decreased. A 2 % dosage of mPCM inhibited the development of silty clay cracks, reduced crack width and deformation, and increased the compression modulus of the soil samples by nearly 2.3 times. Under dry and wet cycling conditions, the cohesion decay of silty clay is greater than the angle of internal friction. The addition of 2 % mPCM significantly increased the shear strength of silty clay, cohesion by nearly 2.1 times, and internal friction angle by 1.4 times. The mPCM inhibits crack development mainly by regulating the internal temperature field of soil samples, thus improving soil strength. This study provides a reference for inhibiting soil cracking from a new temperature perspective.

Microencapsulated phase change materials (mPCM) can absorb or release heat by transforming their core phase. This study investigated the effect of mPCM on the thermal and mechanical properties of silty clay in seasonally frozen strata. It analyzed and researched the thermal and mechanical properties of silty clay blended with different contents (2%, 4%, and 6%) of mPCM, as well as its changing rules, using the DSC thermal cycling test, the specific heat capacity test, the freeze -thaw (F -T) cycling test, the no -limit compressive strength test, and the microscope observation test. In addition, this study utilized hyperspectral equipment to assess the applicability of improved silty clay soils in practical engineering on seasonally frozen ground. The results show that mPCM has no supercooling phenomenon and has stable and reversible transformation characteristics, which improves the thermal stability of silt. The specific heat capacity of silt increased with the increase of mPCM dosage. The unconfined compressive strength of silty clay increased to 162.5 kPa at 2% dosage, which was 16.8% higher than that of silty clay, while the unconfined compressive strength of silty clay at 6% dosage decreased to 119.1 kPa, which was 14.4% lower than that of silty clay after freeze -thaw cycles. Adding mPCM reduces the microscopic damage to the pore structure of silty clay soils caused by the freeze -thaw process and mitigates the macroscopic attenuation of their mechanical strength. The mPCM can effectively reduce the solar radiation reflectivity of silty clay, thus providing long-term utility for winter projects.

High temperatures leading to thaw settlement deformation of soil are the primary cause of damage to road structures in permafrost regions. In this study, phase change material (PCM) is prepared by adsorbing tetradecane, and epoxy resin composite phase change material (ERPCM) is prepared by combining epoxy resin with PCM. ERPCM is applied to geotextile to create phase change geotextile (PCG) with energy storage and impermeability characteristics. The impact of epoxy resin content and freeze-thaw cycles on ERPCM performance is analyzed using Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA). The results show that epoxy resin enhances the thermal stability and freeze-thaw resistance of ERPCM. When the mass ratio of epoxy resin to PCM is 0.8:1, ERPCM exhibits its highest enthalpy values both before and after freeze-thaw cycles, reaching 81.5 J/g and 72.6 J/g, respectively. The energy storage modulus of ERPCM decreases with increasing epoxy resin content. Temperature regulation experiments demonstrate that PCG under different structures can adjust the sample temperature within the range of 6 to 16 degrees C. Higher quantities of ERPCM could store more energy in the PCG. The temperature regulation effect is more pronounced when PCG is placed at greater depths. Increasing the number of PCGs improves the overall temperature regulation effect but reduces the individual temperature regulation effect of each PCG. This study has theoretical significance and practical value for promoting the further application of PCM in permafrost subgrades.