Study On The Preparation Of High Strength Gypsum And Its Waterproof Property

? hemihydrate gypsum crystal is neat,colse-grained and has higher compressive strength.? hemihydrate gypsum is also known as high strength gypsum.But,the high strength gypsum can be decreased by its property of absorbing water,that restrict its application scope,To improve the strength and water resistance of gypsum is one of the problems that need to be solved urgently in industry today.This article was mainly study on the preparation of high strength and water resistant gypsum,and explored the mechanism.The main points were as follows:1.High strength gypsum was prepared by hydrothermal method under high pressure with nature gypsum as raw material,Using single factor experiment method with TG-DTA?XRD,the measurement of crystallization water content.Under the optimum condition,reaction temperature was 120??proportion of water was 50%?reaction time was 1h and stoving time was 110?,the compressive strength of high strength gypsum could reach42.62 MPa.2.The crystal morphology and its arrangement was the key factor of deciding the strength,and adding crystal modifier was one of the best solution.Based on the different types of crystal agent such as filtered aluminum sulfate,sodium citrate,etc,the results show that:organic acid had better effect than inorganic salt,and complex crystal modifier was the best.when add in 0.2% sodium citrate and 2% aluminium potassium sulfate,the crystal morphology of ? hemihydrate gypsum was short column,length to diameter ratio was2:1,colse-grained,the dry compressive strength was 51.36 MPa.3.Based on the preparation of high strength gypsum,study the effect of the different types of waterproofing agent such as paraffin emulsion,polyvinyl alcohol,alunite on high strength and water resistant gypsum.Using single factor method to determine the levels of factors.Through the orthogonal experiment method to optimize the best formula for composite waterproofing agent.The results show that,the best prescription of composite waterproofing agent was 4.5% paraffin emulsion,6% PVA emulsion and 6%alunite,thus,the 2h and 24 h water-absorption was 2.01% and 2.74%.Compared to the blank sample,water-absorption had decreased 93%.4.Waterproofing agent mechanism was discussed through SEM micrographs of the gypsum sample section.The study found that:the effect of paraffin emulsion and polyvinyl alcoholt on the morphology of the high strength gypsum crystals,which affects the strength,The incorporation of alunite could cause the hydration of high strength gypsum to be incomplete,which would decrease its strength.Paraffin emulsion,polyvinyl alcohol and alunite could reduce the gap between crystal and crystal,improve the compactness of high-strength gypsum,thus reducing its water absorption.