Expansion Performance Of Calcium Sulphoaluminate Cement

Cracks and capillary pores are easily caused by volume shrinkage of ordinary cement inthe process of gelation,which results in poor durability,the micro expansion property of calcium sulphoaluminate cement can effectively compensate the shrinkage,make the concrete structure more compact,and the service life of concrete structure is extended.It is of great importance to study the adjustable expansion performance of calcium sulphoaluminate cement.Expansion performance of calcium sulphoaluminate composite cement blends was studied in this paper,by changing the fineness of calcium sulpoaluminate cement clinker and the amount of gypsum and calcium hydroxide,and using XRD,TG/DTG and so on,hydration products of the system with different ages were analyzed qualitatively and quantitatively,then effects of its hydration products and strength on expansion ratio were fully studied,and summarize the change rules of expansion ratio of calcium sulphoalumiante composite cement system,in order to provide theoretical reference for application in engineering practice.The main achievements of this paper are as follows:(1)Calcium sulphoalumiante cement with different amount of gypsum was studied,by changing the molar ratio of gypsum and calcium sulphoaluminate.We found the expansion ratio of specimens will increase significantly,with the molar ratio of gypsum and calcium sulphoaluminate reaches 2.0 and above,and the expansion duration is also prolonged.The expansion ratio of specimens is related to the growth rate of AFt and strength,specimens with larger AFt growth rate and a bigger strength get a larger expansion,a larger strength would restrict the expansion of specimens.(2)Calcium sulfoaluminate cement clinker-gypsum system(abbreviation: CG system)and calcium sulfoaluminate cement clinker-gypsum-calcium hydroxide system(abbreviation:CGL system)were were studied,we found the production of AH3 in the CGL system was more than that in the CG system,with the presence of calcium hydroxide.Adding calcium hydroxide would reduce the early strength development of the specimens,where the compressive strength of specimens of CGL system could catch up with or even surpass the specimens of CG system specimen later.Expansion duration of specimens of CGL system had a degree of extension,and the growth rate of AFt and expansion ratio at 1d-3d of CGL system were different from CG system.In CG system,growth rate of AFt and expansion ratio at early age both showed an increasing trend with the increase of gypsum,but in CGL system,the growth rate of AFt and expansion ratio at early age were exactly the opposite,both showed a decreasing trend.(3)The calcium sulphoaluminate cement system with different amount of gypsum or anhydrite were studied,we concluded that adding anhydrite was more efficient to promote the strength development than adding gypsum.(4)Two kind of calcium sulphoaluminate cement with different fineness were studied,in which the average particle diameter of samples CGB was smaller than that of samples CGA.We found that the compressive strength of samples CGB was higher than that of samples CGA,and both two samples showed a contraction of strength in the late.Besides,that had no difference between the expansion duration and final expansion ratio of samples CGA and CGB.The total weight loss of samples CGB was larger than that of samples CGA,but AFt content in hydration products of samples CGB was not higher than that of samples CGA.