Research On Resource Utilization Technology Of Industrial Waste Gypsum

At present,with the continuous development of building materials science,the application of industrial by-product gypsum in the field of building materials has received extensive attention.Using gypsum raw materials to prepare mortar is an effective way for the comprehensive utilization of industrial solid waste resources.At the same time,it can also reduce engineering costs and achieve green development.It has multiple benefits and important meanings in society,environment and economy.At present,there are relatively many researches on desulfurization gypsum-based mortar,and phosphogypsum is used more and more widely at home and abroad.However,due to its poor quality,mortar prepared with it as a base material has a short setting time and strength.Low,resulting in low utilization of phosphogypsum.Based on this,this article prepares mixed gypsum-based leveling mortar based on the proportion of desulfurized gypsum-based mortar,and explores the influence of fly ash,silica fume and metakaolin on the physical mechanics,water resistance and shrinkage properties of the mortar,and uses microscopic tests.Methods The microscopic composition,structure and thermal stability of mortar hydration products were analyzed to provide a theoretical basis for resource utilization of phosphogypsum.the result shows:(1)When the ratio of phosphogypsum to desulfurized gypsum is 1:1,the performance of mixed gypsum-based leveling mortar is better.The best mix ratio is: desulfurized gypsum 22.5%,phosphogypsum 22.5%,cement 5%,aggregate 35%,heavy calcium powder 15%,water reducing agent 0.3%,retarder 0.2%,cellulose ether 0.05%,defoamer0.9%.Performance indicators basically meet the requirements of JCT1023-2007 "Gypsum-based self-leveling mortar".(2)The admixture can enhance the compressive,flexural strength and water resistance of the mortar at various ages.Among them,mineral powder,first-grade fly ash and silica fume increase the strength of the mortar relatively significantly.The 28 d strength increases nearly 1.5 times compared with the benchmark sample(admixture content 0).The mineral powder improves the strength of the mortar most significantly,28 d The strength is increased by nearly 2.0 times,followed by secondary fly ash and metakaolin;mineral powder and secondary fly ash have a significant improvement in the water resistance of the mortar,with a softening coefficient of about 0.54,and the softening coefficient of the benchmark sample is only 0.31,followed by First-grade fly ash,silica fume and metakaolin have a softening coefficient of about 0.45.(3)With the help of modern test methods such as X-ray diffraction analysis(XRD),scanning electron microscopy(SEM)and comprehensive thermal analysis(TG-DCS),the mortar hydration products and structural characteristics have been studied.The research results show that: admixture The replacement rate is in the range of 15%～25%.The ettringite content in the mortar system is more,the voids in the hydration phase are filled,the microstructure is relatively dense,the strength is increased by nearly 1.4 times,and the softening coefficient reaches about 0.5.The water resistance has been significantly improved;the gelling system has an obvious endothermic peak between 100℃ to 200℃and 700℃ to 800℃,and accompanied by the thermal decomposition of ettringite,resulting in a large loss of mortar quality.Among them,the weight loss rate of mineral powder modified mortar is relatively large,followed by metakaolin.In the modified mortar with high weight loss rate,the content of ettringite is more,which promotes the significant improvement of the mechanical strength and water resistance of the mortar.(4)The hydration process of mortar was studied with the aid of hydration heat analysis.The results showed that: the highest heat release peak of hydration of mortar modified with admixtures was significantly lower than that of mortar without admixtures,and admixtures promoted the mortar.Secondary hydration.In the heat of hydration curve,the exothermic peak first appears within 2h,the mortar hydration reaction is violent,and begins to set and harden,and the exothermic peak appears again within 8-10 h,the activity of the mineral admixture is activated,and the mortar occurs twice.Hydration.As time goes by,the mortar hydration gradually enters a stable period,in which silica fume and metakaolin can effectively promote the secondary hydration reaction of the mortar.(5)Mineral admixtures can effectively improve the working performance of the mortar,and enhance the water resistance and mechanical properties of the mortar.Among them,the effect of single-mixed mineral powder and single-mixed silica fume is significant.Considering the requirements of mortar construction,basic performance and durability,it is recommended that the replacement rate of fly ash is 15% to 20%,the replacement rate of silica fume is 10% to 15%,and the replacement rate of metakaolin and mineral powder is20% to 25%.At this time,the mixed gypsum-based leveling mortar has excellent performance.After comprehensive benefit analysis,it is recommended to choose silica fume or metakaolin to prepare modified gypsum-based leveling mortar,and the economic benefits of the mortar are better at this time.