An Experimental Study Of A Gypsum Self-leveling Material

With the rapid development of the construction industry,more and more new green building materials are coming to the market.Under the background of large-scale civil construction,a large number of civil building construction has increased the demand for floor materials.The application of a large number of self leveling materials in the ground leveling layer has become a high-value and large-scale trend.At the same time,the performance requirements of self leveling materials have been continuously improved.At present,the traditional self leveling materials are mainly cement-based materials.The cement production process consumes a lot of resources and energy and emits a lot of CO₂.At the same time,desulfurization gypsum,phosphogypsum and other industrial by-products are mainly stored on the ground,wasting land and endangering water sources,with high potential safety hazards.In this project,two industrial by-products of desulfurization gypsum and phosphogypsum are used,and a new type of ultra-high fluidity,high levelness,crack free,high-strength and sand free gypsum self leveling material is developed.The physical properties such as mineral composition and three-phase composition of industrial by-product treated gypsum were studied.The hydration mechanism of gypsum and the crystal morphology of hydration products are analyzed by XRD and SEM.It is obtained that the main components of hydration products are dihydrate gypsum(Ca SO₄·2H₂O).After hydration and hardening,the crystal shape is mainly long plate crystal,disorderly interwoven,there are many voids in the hardened body and the structure is relatively loose.Combined with the hydration characteristics of gypsum,a polycarboxylic acid superplasticizer powder(PCE-G)for gypsum substrate was prepared by orthogonal test and single factor variable test.The molecular structure and functional groups were analyzed by infrared spectroscopy(FTIR).Test PCE-G in the water reduction rate of?-hemihydrate gypsum is 46.1%,and that of phosphogypsum is 41.1%.The application of PCE-G in gypsum self leveling material has more remarkable water reduction effect and better plasticity.The orthogonal tests of polycarboxylic acid water reducer powder,polyether defoamer,modified amino acid gypsum retarder,sodium gluconate and hydroxypropyl methylcellulose L₁₆(4~5)were designed,and the effects of five admixtures on?-gypsum self leveling on properties of materials.The effects of p H regulating component,water retaining component and latex powder on the mechanical properties,working properties and wear resistance of self leveling materials were studied,and the type and content of each component were determined.Through the study of different cementitious material systems,the best cementitious material mix proportion is obtained:?-hemihydrate gypsum 90%+portland cement 5%+silica fume 2%+mineral powder 3%,and the hydration products of the best mixture ratio were analyzed by XRD diffractometer.Multicomponent coupling regulation?-gypsum self leveling material has the characteristics that the initial fluidity exceeds 150 mm,the fluidity exceeds 145 mm in 30 minutes,the compressive strength value reaches 21 MPa in 28 days,and the shrinkage rate is less than 0.04%.The best mix proportion compound material is applied in Jinan Zhonghai Huashan project,?-gypsum self leveling material has high construction efficiency,large fluidity,smooth hardened surface,high levelness and no cracks.The coupling regulation of multi-component of phosphogypsum based self leveling material was further studied.The orthogonal test of polycarboxylic acid water reducer powder,polyether defoamer,p H regulator and redispersible emulsion powder L₉(3~4)was designed.The effects of four additives on the properties of phosphogypsum self leveling material were analyzed,and the basic ratio of phosphogypsum self leveling material was determined.The effects of cementitious material components,water retaining agent components and retarder components on the properties of phosphogypsum self leveling materials were studied.Silica fume in cementitious material system can reduce fluidity,but can improve strength;Fly ash can increase fluidity,but it will affect the smoothness of hardened surface;The addition of mineral powder can increase the fluidity and significantly improve the later strength.The single factor variable test and L₉(3~3)orthogonal test of three different water retaining thickeners were carried out to determine the optimal dosage.When the content of retarder is in the range of 0.03%,the retarder will not affect the later strength growth of phosphogypsum self leveling material,and can achieve the best retarding effect of self leveling material.Under multi-component coupling control,phosphogypsum self leveling material has the characteristics of initial fluidity exceeds 150 mm,30 min fluidity exceeds 140 mm,28 day compressive strength of 21 MPa and tensile bond strength of more than 1.0 MPa.The adaptability of?-gypsum self leveling material to negative temperature environment was studied.By adding salt antifreeze,the adaptability of the material to negative temperature environment is explored,and the optimized water binder ratio is 0.50.In order to improve the serious bleeding and frost heaving during negative temperature construction,hydroxypropyl methylcellulose with different dissolution characteristics and viscosity values was introduced.Through the characterization test of digital display viscometer,the slow solution HPMC-5.5W compound was determined?-gypsum self leveling material meets the standard requirements under negative temperature.The negative temperature gypsum self leveling material provides a new solution for the construction and application of negative temperature(winter)engineering.