Research On Thermal Insulation Characteristics And Mechanical Properties Optimization Of Phosphogypsum-based Composite Cementitious Material

Phosphogypsum is the main industrial by-product in the phosphating industry.The existing pile has large stock and low utilization rate,which will pollute the natural ecology.The preparation of building materials from phosphogypsum is an effective way of its consumption.In this study,the mechanical properties,water resistance and thermal insulation properties of phosphogypsum-based composite cementitious materials(PGCs)were studied by adding quicklime,fly ash,cement,water reducing agent,retarder and other additives to phosphogypsum.The main research is as follows :(1)Study on the mechanical properties of PGCs.Based on the experimental results of single factor experiment and orthogonal experiment,the mechanical properties of PGCs were studied.The results show that the mass ratio of phosphorus building gypsum to water cement is a significant factor affecting the mechanical properties of PGCs.The effect of lime on the mechanical properties of PGCs was obvious in the early stage of hydration.Fly ash has a significant effect on the mechanical properties of PGCs in the later stage of hydration.(2)The water resistance of PGCs was studied.The water resistance of PGCs was studied by single factor experiment and orthogonal experiment.The results show that the water-cement mass ratio has the most significant effect on the water resistance of PGCs,and the main mechanism is achieved by affecting the degree of hydration and increasing pores.The amount of phosphorus building gypsum has a significant effect on water absorption,and the amount of lime has a significant effect on the softening coefficient.(3)Study on the thermal-mechanical cooperative working characteristics of PGCs.Based on single factor and orthogonal experiments,the influence mechanism of thermal insulation performance of PGCs was studied by means of SEM and other analytical methods.The results show that the water-cement mass ratio is the most significant factor affecting the thermal insulation performance of PGCs,which is mainly due to the large number of pores left by water evaporation,which increases the thermal resistance of PGCs.There is a negative correlation between thermal insulation performance and mechanical properties.The index membership degree is used to analyze the thermal insulation-mechanical cooperative working characteristics of PGCs,and the multi-index comprehensive performance of PGCs is qualitatively evaluated.(4)Study on thermal insulation properties and mechanical properties of PGCs after foaming.PGCs were foamed by different foaming methods,and the changes of thermal insulation and mechanical properties were studied.The results show that when the porosity is the same,the mechanical and thermal insulation properties of physical foaming specimens are better than those of chemical foaming specimens.The larger the pore size and the more connected pores,the more serious the stress concentration of the specimen under compression,and the compressive strength of the specimen is significantly reduced.The porosity of the specimen increases with the increase of the foaming agent content,but the decrease of the thermal conductivity is limited when the bubble aggregation occurs.