Carbon-based Reinforced Structural-functional Integrated Phase Change Energy Storage Cement-based Materials

Owing to phase change materials?PCMs?have many advantages,such as high energy storage density and isothermal processes of storage and discharge heat,it can be utilized to store or release thermal energy.Mixing PCMs with concrete to fabricate structural-functional integrated phase change energy storage concrete?SFPCESC?can significantly increase the building's heat storage capacity and improve the efficiency of building's use of renewable energy such as solar energy so as to reduce building energy consumption.However,according to current research results,it can be seen that due to the low strength of PCMs,the mechanical properties of SFPCESC would lead to a significant decrease when mixing PCMs with concrete.In addition,the poor thermal conductivity of PCMs also could affect low heat transfer efficiency of SFPCESC which limited the application of composite materials in construction.In order to solve this problem,this project focus on developing a structural-functional integrated building materials which has both high-efficiency phase change energy storage and good mechanical properties:?1?Using high thermal conductivity?expanded graphite and graphene sheets?as supporting materials to prepare a shape-stabilized PCMs and fabricating SFPCESC;?2?Figuring out the mechanism of the synergism effect of nanosilica?NS?and carbon fiber?CF?to strengthening the mechanical and thermal properties of microencapsulated phase change cementitious materials?MPCCM?;?3?Studying the strengthening effect of graphene oxide?GO?on cement paste and exploring the effect of GO on the mechanical and thermal properties of MPCCM.According to experiments,the following conclusions are summarized:?1?Two porous carbon-based materials?expanded graphite and industrial-grade multilayer graphene sheets?and paraffin was respectively used as support materials and phase change material to develope shape-stabilized PCMs with high latent heat capacity.Differential scanning analysis?DSC?calculates the latent heat values of expanded graphite/paraffin and industrial grade multilayer graphene sheets/paraffin to be 152.8 J/g and 51.84 J/g,respectively.Experiments have shown that the components within the shape-stabilized PCMs are chemically compatible with each other.Moreover,they can meet the requirements for thermal stability and thermal reliability.?2?According to the results of hydration heat,incorporating porous carbon-based shape-stabilized PCMs into cement paste not only can effectively reduce the total heat of cement hydration,but also can effectively reduce the heat release rate of hydration heat.Through the analysis of the infrared thermal image analysis results,it can be concluded that the thermal performance of the cement based materials containing PCMs is more superior.?3?After the addition of graphite-modified microencapsulated phase change materials,the flexural strength and compressive strength of MPCCM decrease 41%and 48%at 28 days,respectively.However,the mechanical properties of MPCCM showed a rise trend when incorporating NS and CF on it.Compared to the control group,the flexural strength of MPCCM increase 17%while the compressive strength decrease 20%at 28 days after incorporating 1.5%CF and 2%NS.Moreover,as the amount of CF increases,the thermal conductivity of MPCCM improve 17.8%.The results of the room model and infrared thermal image analysis show that CF can considerably improve the heat exchange efficiency of MPCCM.?4?In order to enhance the mechanical properties of cement-based materials,the study about multi-layered graphene oxide?GO?reinforced cement-based material was developed.Under the premise that GO is uniformly dispersed in the alkaline environment,the mechanical properties of cement paste is proportional to the quantity of GO.The results of X-ray diffraction?XRD?,thermogravimetric analysis?TGA?and solid-state nuclear magnetic resonance(²⁹Si MAS-NMR)explained that the increase of strength gets benefit from that GO promotes hydration process rather than GO modify the structure of calcium silicate hydrate?C-S-H?.Moreover,the addition of a small amount of GO has little effect on the mechanical properties and thermal conductivity of MPCCM.