Design Of Calcium Sulfoaluminate Cement(CSA) Concrete And Mechanism For Regulating Its Shrinkage

Although compared with ordinary Portland cement(OPC),Calcium Sulfoaluminate(CSA)cement clinker is characterized by lower calcination temperature,better grindability as well as more solid waste consumption,delivers lower drying shrinkage of the formulated concrete,and produces less carbon dioxide emissions during the production process,there are some problems in its real-life use.To explore the engineering application of CSA cement,the preparation covering different strength grades and the study on the shrinkage regulation mechanisms of CSA cement concrete were carried out.The research consists of two parts: the first part focuses on the performance of cement paste and its modification,with an attempt to address an array of problems such as the accelerated setting of CSA cement concrete,intense heat release in early hydration phase,poor workability of fresh concrete,and coarse pores in hardened paste;the second part is centered on the composition of the cementitious material following the performance optimization as elaborated in the first part,intended to examine the shrinkage and regulation of CSA cement concrete prepared by it,as well as the mechanism of shrinkage regulation,with an attempt to solve the larger early autogenous shrinkage of CSA cement concrete,understand the law and mechanism of pre-absorbent ceramsite substantially reducing the shrinkage of CSA cement concrete.Compared with OPC,the reaction exothermic peaks of the first and second hydration of CSA cement are magnified by 16.8 and 3.1 times,respectively;the plastic viscosity of the fresh cement paste is increased 1.32 times,and it presents shear thickening behavior;the volume of coarse pores of hardened cement paste is greater.Through the optimization of mix proportions,the peak of hydration heat release of CSA cement is reduced,and the cumulative heat release is lowered;the plastic viscosity of fresh CSA cement paste is significantly reduced,and all of the cement paste becomes shear thinning fluids;the median pore size of the hardened CSA cement paste is dwindled,and the harmful pores larger than 100 nm and the pores larger than 1000 nm are reduced by big margins.Compared with OPC concrete,the shrinkage of CSA cement concrete mainly occurs in the humidity saturation phase.The initial two-hour shrinkage after pouring accounts for upward of 85% of the 28-day total shrinkage under dry conditions.Whether it is high-strength,super-high-strength,or medium and low-strength CSA cement concrete,the drying shrinkage value during the humidity decline period is very small,and the drying shrinkage ratio after 28 days is less than 5%,and the influence of factors such as w/b ratio,strength and internal relative humidity is not appreciable.The difference in volume stability of ettringite and CSH gel under humidity changes may be the main mechanism that the drying shrinkage of CSA cement concrete is much smaller than that of OPC concrete.A small amount of pre-absorbed ceramsite can notably reduce the shrinkage of CSA cement concrete,the higher the strength,the greater the reduction in shrinkage.The ceramsite internal curing test of CSA cement concrete by paraffin immersion,which substitutes pre-absorption water proves that the modulus of ceramsite has little effect on the early shrinkage of CSA cement concrete.In the ceramsite curing CSA cement concrete,the water release of the pre-absorbed ceramsite is synchronized with the shrinking and shrinkage reduction of concrete.Via the simulation test of the ceramsite connected with the glass tube,it is revealed that the greater the initial air content inside the pre-absorbed ceramsite in the cement paste,the more water will be removed from the ceramsite;the lower the w/b ratio of the cement paste,the more water will be removed from the pre-absorbent ceramsite.Combined with the ideal gas equation of state,the mechanism of the law of water release inside the ceramsite is initially explained.