Effect Of Phosphorous Calcined Gypsum On The Hydration And Shrinkage Characteristics Of Sulfoaluminate Cement Clinker

Calcined phosphogypsum to produce phosphogypsum calcined gypsum is one of the most suitable methods for the utilization of phosphogypsum at the present stage.Phosphogypsum is a kind of industrial solid waste generated from phosphoric acid production prepared by wet process.A large stacking of phosphogypsum destroys the surrounding soil environment,water environment and air environment,which brings human life and safety in danger.Realization of the resource utilization of phosphorus calcined gypsum can not only transform waste into valuable,protect the environment,promote the healthy and sustainable development of phosphorus chemical enterprises,but also produce cement-based materials with excellent performance.The effect of phosphorous calcined gypsum on hydration mechanism and the characteristics of shrinkage of calcium sulfoaluminate cement clinker was studied.The main conclusions are as follows:(1)The setting time of calcium sulfoaluminate cement clinker is significantly shortened by adding phosphorus calcined gypsum.With the increase of phosphorus calcined gypsum content,the setting time became shorter gradually,but the shortening range became slower.When the water-binder ratio was 0.6,the compressive strength of hardened cement paste with phosphorous calcined gypsum was higher than that of control sample,and these samples still increased with the increase of curing ages.When the content of phosphorous calcined gypsum was 15%,the compressive strength of hardened cement paste for 6 h developed rapidly.When the water-binder ratio is adjusted to 0.5 and the amount of phosphorus calcined gypsum was 20%,the strength of hardened paste reached 22.3 MPa at 6 h and 74.9 MPa at 90 d.(2)The hydration of cement was promoted by adding phosphorus calcined gypsum and the XRD peak of ettringite increased with the increase of the amount of phosphorus building gypsum.At 6 h of hydration,the characteristic peak of ettringite in the samples with phosphorous calcined gypsum increased significantly.At 28 and90 days,the content of ettringite in the samples with phosphorous calcined gypsum content less than 15% decreased because of ettringite decomposed.The content of ettringite continued to rise in the addition of 20% and 30% phosphorous calcined gypsum.Combined with the results of XRD and TG tests,the main hydration products of calcium sulfoaluminate cement did not change after adding phosphorous calcined gypsum.(3)With the increase of the amount of phosphorous calcined gypsum,the resistivity of cement paste increases gradually.And each hydration stage is unchanged,but the characteristic peak of each hydration stage changes.(4)According to the autoshrinkage development curve,autoshrinkage can be divided into five stages: plastic shrinkage stage,expansion stage,rapid contraction stage,fall stage and stable stage.Compared to the autoshrinkage,it can be found that the drying shrinkage reduces the expansion amount and prolongs the expansion time.(5)The early hydration of cement paste can be accelerated and the time interval between induction period and acceleration period was shorten by high temperature.With the increase of curing temperature,gypsum is consumed rapidly and insufficient in the later stage.Ettringite decomposed under a small amount of phosphorous calcined gypsum,and the decomposition of ettringite in the later stage can be reduce significantly by adding more phosphorous calcined gypsum.