Experimental Research And Preparation Of Concrete Expansive Agents From Phosphogypsum

With the development of society,the demands of the performance of concrete become higher in industry.The concrete expansive agents can be used to compensate the shrinkage of concrete,make the concrete structure more compact,increase the strength of concrete to a certain extent.So it is more and more used in high performance concrete.Concrete expansion agents sold on the markets are produced with natural gypsum,other high grade ores and non renewable resources,what's more higher requirements on the processing technology are needed,which not only consumes a large amount of non renewable resources,but also improves the production cost.Therefore,to improve the production process and the use of solid waste gypsum instead of natural gypsum to produce high performance concrete expansive agent is one of the important development trend of expansion agents.Preparation of high performance concrete expansive agents using phosphogypsum instead of natural gypsum is not only opens up a new way for the utilization of solid waste residue in the phosphate mining industry,but also reduces the dependence of non renewable resources on related enterprises agent produced expansive agents.And this achieves the goal of utilization of waste resource,saving natural resources,meets the requirements of the sustainable development,it is of great economic and social benefits.There are also a series of problems in the production of high performance concrete expansive agents from phosphogyps instead of natural gypsum.Due to the dispersion of phosphorus chemical enterprises in our country,different production process,technology and stockpiled situation,result in the different impurities contents(F-,P2O5,organic and so on)in different stockpiled places or the same stockpiling locations in different positions.This increases the difficulty of resource utilization of phosphogypsum.In this paper,solid waste phosphogypsum are used as raw material.The high content of CaSO4·2H2O in phosphogypsum(the content of CaSO4·2H2O can be as high as 90%after removal of free water)are made full use of to produce high performance concrete expansive agent.The calcium oxide calcium sulphoaluminate composite clinker was used as the main expansion source and the limestone was used to fill the pores of concrete hydration.This paper makes the following researches:(1)The effects of the ratio of three kinds of expanded clinker,phosphogypsum and limestone,on the properties of expansive agent were studied.The best ratio of expansive clinker:phosphogypsum:Limestone is 45:20:35.In this condition,the confined expansion of 7 d and 28 d is 0.038%and-0.014%,respectively.(2)On the basis of the best ratio of raw materials,the effects of free water,phosphorus and fluorine on the properties of expansive agent were studied,and the maximum impurity content index of the expansion agent were determined.The results showed that the water content of swelling agent was 2%,the fluorine content was about 1.8%,and the content of phosphorus was about 5%.(3)The effects of modification methods,such as calcination and washing,on the properties of expansive agent were studied.The results showed that the modification of water swelling agent was the most effective.(4)The effects of phosphogypsum slurry concentration,crystal seed,conversion agent,pH,reaction time and temperature on the morphology and length diameter ratio of hemihydrate gypsum were studied with control variate method.The best react conditions were as follows:the reaction temperature was 130?,the slurry concentration was 3.0%,the pH was 6.0,content of seed was 10%,the reaction time was 4 h,and crystal agent content was 3.0%.Hemihydrate gypsum of high purity,smooth surface was prepared with the ratio of length to diameter of 329.2.(5)The influence of the morphology of gypsum on the properties of expansive agent was studied.Concrete expansion agent with different length diameter ratio of(6)hemihydrate gypsum instead of phosphogypsum was produced.The results show that the morphology of gypsum does not affect the performance of expansive agent.