Experimental Study On The Manufacture Of Green Composite Phase Change Concrete And Its Operation Performance As A Wall Material

Energy consumption in the building sector has accounted for an increasing share of total global energy consumption in recent years.In order to reduce the use of cooling,heating and ventilation and develop energy-efficient green buildings,there is an urgent need to optimize the efficiency of energy use and vigorously develop latent heat energy storage technology of phase change materials.The phase change materials,which were used in buildings,could automatically regulate the temperature and energy consumption of buildings.The research was based on the National Natural Science Foundation of China(41877240,41672280)and the National Key Research and Development Program of China(2018YFC1802300)In this research,five different composite phase change materials were prepared by vacuum adsorption method.Specifically,five porous materials including coral sand,steel slag,volcanic stone,expanded perlite and expanded vermiculite were used as carriers,and polyethylene glycol 1000 was used as phase change material.The thermal material properties and leakage properties of the five composite phase change materials after encapsulation were systematically studied.Then,the composite phase change materials were mixed into concrete to make green composite phase change concrete,and their compressive strength and thermal insulation properties were studied.Finally,numerical simulations of the indoor temperature and energy savings of the house models with phase change concrete and common concrete were carried out with COMSOL Multiphysics.Based on the test results,the following conclusions can be drawn:(1)The pore size and particle size of five porous materials were studied by mercury-inpressure(MIP)and gradation curves,and the loading rate and temperature control efficiency of five composite phase change materials were investigated by comparison with the former postmass calculation and water bath heating method.The test results show that the loading rate and temperature control efficiency of the five composite phase change materials were different due to the difference of pore structure of porous materials.The order of preference was: expanded perlite based composite phase change material,expanded vermiculite based composite phase change material,coral sand based composite phase change material,volcanic stone based composite phase change material,and steel slag based composite phase change material.(2)The microscopic morphology,thermal parameters,chemical compatibility,thermal stability and thermal cycling stability of the five composite phase change materials were studied by scanning electron microscopy(SEM),differential scanning calorimetry(DSC),Fourier infrared spectroscopy(FT-IR),X-ray diffraction analysis(XRD)and thermogravimetric analysis(TGA)tests.The test results show that all five porous materials had dense pore structure,and their pores and surfaces were well filled and adhered after the adsorption.The phase change enthalpy of five composite phase change materials all increased with the increase of loading rate,and the phase change temperature was in the phase change temperature interval of polyethylene glycol 1000.There was no chemical reaction between porous material and the phase change material in composite phase change materials.The thermal stability and thermal cycling stability of the composite phase change materials were good,and no thermal decomposition occurred in a conventional environment.After 500 phase change cycles,the phase change enthalpy loss of the expanded perlite based composite phase change materials was the largest at 13.8%,the phase change enthalpy drop of expanded vermiculite based composite phase change materials was 12.5% and the phase change enthalpy loss of the other composite phase change materials was within 10%.(3)The composite phase change material was encapsulated with cement slurry,and then the compressive strength of the composite phase change concrete was tested.The test results showed that compared with the composite phase change material before encapsulation,the mass loss of encapsulated composite phase change material significantly reduced,and the mass loss is less than 1%.The encapsulation effect was excellent.The 28-day compressive strength of concrete was greater than 30 MPa when the 50% coarse aggregate of concrete was replaced with the coral sand,steel slag or volcanic stone groups.The 28-day compressive strength of concrete was greater than 20 MPa when the 40% coarse aggregate of concrete was replaced with the expanded perlite and expanded vermiculite groups.The compressive strength of these concrete meeting the requirements of the Design of Concrete Structures.(4)Temperature control efficiency of phase change concrete and conmon concrete was compared by house models test.And the results showed that compared with the common concrete house models,the wall temperature and indoor temperature of each phase change concrete house models showed an increase and decrease in temperature peaks and troughs,and the increase and decrease were positively correlated with the content of phase change materials in the walls.There was also a time delay in the arrival time of the temperature peaks and troughs,and the length of the time delay was positively correlated with the content of phase change materials in the walls.The concrete walls of the expanded perlite group rose and fell with the greatest amplitude and the longest delay.The concrete walls of the steel slag group had the smallest rise and fall and the shortest delay.All groups of phase change concrete walls had certain insulation function and temperature hysteresis effect.(5)Simulations of the indoor temperature and wall temperature of a room model with phase change concrete and common concrete as wall material under the variation of ambient temperature as a sinusoidal function were carried out by COMSOL.The simulation results showed that compared with common concrete,the phase change concrete could better control the fluctuation of indoor temperature and could maintain room temperature within the comfortable range of human body.The phase change concrete save 11.297 k W-h of energy in72 hours for the overall house size of 400cm*400cm*300cm and the indoor size of340cm*340cm*240cm,which indicated that the phase change concrete has great potential for energy saving in the building.