| Phase change composite materials play an important role to achieve thermal energy and temperature control.Gypsum-based self-leveling mortar is a kind of self-compacting ground mortar that flows by its gravity.Thus,it is widely used in the field of the covering layer of"floor heating".In order to reduce costs of gypsum-based self-leveling mortar,phosphogypsum building or anhydrous phosphogypsum prepared from industrial solid waste phosphogypsum is usually used as raw to manufacture the self-leveling mortar instead of type-?high-strength natural gypsum as raw.However,in the"floor heating"cycle heating process,the phosphogypsum-based self-leveling floor has some disadvantages,such as temperatures fluctuation,energy waste and so on.Thermal energy storage can not only effectively reduce the mismatch of energy supply in time and space,but also enable effective management and utilization of thermal energy.In the heat storage process,the phase change of the material is used to absorb heat when the solid phase changes to the liquid phase within a specific temperature ranges,then it releases heat when the liquid phase changes to the solid phase,thereby achieving the purpose of energy storage.Therefore,the phase-change composite materials can be introduced into the phosphogypsum-based self-leveling mortar,which hardened to form a phosphogypsum-based floor with a heat storage function,to reduce the temperature fluctuation.First,Phase-change composite materials with three different carriers of capric acid-palmitic acid/perlite,paraffin-hexadecane/clay,paraffin/activated carbon were prepared by porous adsorption method.The microstructure,stability and thermal properties of pearl,clay,activated carbon and different carrier phase-change composites were analyzed by using SEM,BET,FT-IR,XRD,and DSC.The results showed that the perlite,clay,and activated carbon have an excellent pore structures,which can load the phase change materials,and the phase change materials were evenly distributed inside the pores of the perlite,clay,and activated carbon.Phase change composite materials with three different carriers have good thermal properties and latent heat values.The melting temperature of capric acid-palmitic acid/expanded perlite was 24.3?-31.7?,and the latent heat value was 64.16 J·g-1.Paraffin-hexadecane/clay melting temperature was 15.6?-44.37?,and latent heat value was54.54 J·g-1.The melting temperature ranges of paraffin/activated carbon was from36.8?-50.5?,and the latent heat value was 77.61 J·g-1.Secondly,phosphogypsum-based self-leveling mortar was prepared by anhydrous phosphogypsum?AP?from calcining phosphogypsum,type-?high-strength gypsum??-HH?,quartz sand,and admixtures as raw.The effects of calcination temperature on the phase composition and strength properties of phosphogypsum,the effects of the amount of type-?high-strength gypsum on the mechanical properties of anhydrous phosphogypsum,and the effects of the amount of admixtures on the properties of phosphogypsum-based self-leveling mortar were analyzed.The results showed that properties of calcined phosphogypsum at 500?were as follow,the setting time 87 minutes,and the 28d strength 13.6 MPa.Type-?high-strength gypsum could increase the mechanical strength of anhydrous phosphogypsum.The ratio of cement to sand could improve the flow performance of phosphogypsum-based mortar.When the amount of PE retarder was 0.01%?0.02%,the initial setting time was more than 60 min,and the strength loss was less than 5%.When the amount of melamine?MSF?water reducing agent was between 0.1%and0.2%,the mechanical strength of the mortar gradually increased.However,when the amount of water reducing agent was more than 0.2%,the strength of the mortar decreased.Hydroxypropyl methyl cellulose?HPMC?water-retaining agent could reduce the bleeding performance of phosphogypsum-based mortar.When 42%anhydrous phosphogypsum,28%?high-strength gypsum,30%quartz sand,0.01%PE,0.2%MSF,and 0.1%HPMC were used to prepare phosphogypsum-based self-leveling mortar,its performance indicators met the requirements of JC/T 1023-2007"Gypsum-based self-leveling mortar".Finally,the Phosphogypsum self-leveling mortar with thermal adjustment properties was prepared by anhydrous phosphogypsum from calcining phosphogypsum,type-?high-strength gypsum,paraffin/activated carbon phase change composite and admixtures.The effects of the amount of paraffin/activated carbon phase change material on the fluidity,setting time,mechanical properties,shrinkage rate and thermal conductivity of phosphogypsum-based self-leveling mortar with phase change composites were studied.The effect of paraffin/activated carbon phase change composite materials on the thermal regulation performance of phosphogypsum-based floor was analyzed.The thermal properties and morphology of the hardened phosphogypsum-based floor with the composite materials were analyzed by DSC and SEM.The results showed as the amount of paraffin/activated carbon phase change material increases,the fluidity,mechanical strength and shrinkage of phosphogypsum-based self-leveling mortar decrease,while the setting time and thermal conductivity increase.When 54%anhydrous phosphogypsum,36%type-?high-strength gypsum,10%paraffin/activated carbon,0.01%PE,0.2%MSF,0.1%HPMC were used to prepare phosphogypsum-based self-leveling mortar,its performance indicators met the requirements of JC/T 1023-2007"Gypsum-based Self-leveling Mortar".Phosphogypsum-based floor composite with paraffin/activated carbon has good temperature regulation performance.When the content of the paraffin/activated carbon is 10%,the surface temperature of the phosphogypsum-based floor is reduced by 3.4?during the heating process and the surface temperature is increased by 4.6?during the cooling process.With the paraffin/activated carbon phase change material increased,the internal voids and phase change material particles of the hardened phosphogypsum composite materials increased.Phosphogypsum-based floor with the phase change composite materials had good thermal properties,the melting temperature 37.1?-38.8?,the latent heat value 15.51J·g-1,and the latent heat loss by 1.5 J·g-1 after 1000 cycles. |
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