Application Of Phase Change Materials In Construction Materials And Its Energy Storage Mechanism Research

Building energy consumption accounts for 51.3%of China’s total emissions,and the solution to the high energy consumption status of the building industry has become a research hotspot under the background of carbon peak and neutrality targets.Phase change materials can use heat absorption and exothermic effect when they undergo a phase change to achieve energy storage and autonomous release for energy utilization,which is highly potential in building materials applications.Because of their poor compatibility and low thermal efficiency after encapsulation,this paper explores three aspects,including the energy storage mechanism of polyethylene glycol in cement-based materials,the preparation and application of phase change light aggregates,and the optimization of the application effect of phase change materials.The fluidity,mechanical properties,thermal properties,hydration process,and hydration products of polyethylene glycol with a molecular weight of 600（PEG-600）cement paste were investigated by TAM,XRD,FTIR,DSC,MALDI,etc.The results showed that a large dosage of PEG-600 leads to slow setting or even non-setting of the cement paste;with the increase of admixture,the mechanical properties decreased,and when the PEG-600 dose increases to 10%,the compressive and flexural strengths decrease by 19%and 18%,respectively;PEG participates in the hydration reaction of cement,firstly depolymerizing and subsequently forming a complex with Ca²⁺,so the phase change point of both PEG-600 cement paste and PEG-800 cement paste decreases to 10-15°C,and the enthalpy of phase change is about 6 J/g,and PEG can be added directly into cementitious materials without encapsulation directly into the cementitious material.A novel phase change lightweight aggregate with PEG incorporated in the shell layer and paraffin wax in the core was prepared by the core-shell spheroid formation technique.The results showed that PEG did not have a significant effect on the thickness and mechanical properties of the shell layer.There were two phase change points of the phase change lightweight aggregate,at 15°C and 50°C,respectively.The secondary encapsulation of the phase change light aggregate was directly coated with the permeable crystalline material solution,and the leakage rate decreased to 1.3%and 1.5%at 60°C for 6h and 24h,respectively,and 1.4%for a single cycle and 1.6%for five cycles.Lightweight concrete containing phase change lightweight aggregates has a higher percentage of solid-phase early,especially after 24hours,resulting in higher early strength and less dry shrinkage.At the same time,there was no significant change in the chloride ion permeability coefficient and other functionalities of phase change lightweight concrete,and such phase change lightweight aggregates and phase change lightweight concrete are very promising for application.The study carried out the simulation calculation of the one-dimensional heat transfer model of the wall by the explicit difference method using the Nanjing climate conditions.The study shows that the optimal phase change point of the temperature control material is related to the indoor temperature,and the average heat flux of the wall decreases by 44.0%when the phase change storage material with a phase change point of 27°C is used in the innermost layer of the wall at a controlled indoor temperature of 26°C in summer,and by 43.0%when the phase change storage material with a phase change point of 16°C is used in the innermost layer of the wall at a room temperature of 18°C in winter.When the thickness of phase change energy storage material layer reaches 15mm in summer,the average heat flux decreases the most when all walls choose insulation material in the innermost layer,37.6%,47.9%,49.1%;when the thickness of phase change energy storage material layer reaches 15mm in winter,the average heat flux decreases the most when all walls choose wall innermost layer as phase change energy storage material,48.6%,45.4%,42.1%.When the thickness of the phase change energy storage material layer reaches 10mm in spring and autumn,the average heat flux decreases the most when all walls choose the outermost layer of insulation as the phase change layer,28.6%,27.8%,and 32.2%.Phase change energy storage wall material phase change stage equivalent specific heat capacity of 3000J/（kg·K）to achieve effective temperature control under the harshest conditions in winter and summer.