Hydration And Hardening Of High-flexural Strength Low-heat Slag Calcium Sulfoaluminate Cement

The high-flexural strength low-heat slag calcium sulfoaluminate（HFLH-CSA）cement is a new cementitious material with granulated blast furnace slag as main raw material and anhydrite and high belite sulphoaluminate mineral as activator.HFLH-CSA cement has the advantages of high flexural strength,low hydration heat,strong impermeability,alkali-free and strong resistance to sulfate attack.Its performance is based on the hydration hardening mechanism of HFLH-CSA cement.It provides a theoretical basis for scientific research and engineering applications of mass concrete.This paper intends to study the hydration mechanism and microstructure evolution of HFLH-CSA cement,explore the relationship between the composition-structure-performan--ce of the cement,and reveal its low-hydration heat release and strength development mechanism;Studying the hydration mechanism of HFLH-CSA cement and mineral admixture composite system;Carrying out HFLH-CSA cement hydration process and microstructure thermodynamic model（GEMS-PSI software）simulation;The hydration process,hydration products,microstructure and pore structure were characterized by microcalorimeter,XRD,TGA,SEM and MIP.The results show that:（1）The early strength of HFLH-CSA cement is slightly lower,and the late strength of HFLH-CSA cement increases rapidly;（2）The early hydration products of HFLH-CSA paste are mainly ettringite.With the development of hydration,the acicular ettringite rapidly increases,interlacing and interlacing in capillary pores.C-S-H gel fills the structure and plays a bonding function.The pores of hardened paste develop toward a small pores,the hardened paste forms a dense structure,and the strength increases rapidly.During the later stage of hydration,a large number of C-S-H gel is formed and hardened paste becomes denser,so the mechanical strength of HFLH-CSA cement increased further;（3）The hydration mechanism of HFLH-CSA cement is simulated by thermodynamic model.The early hydration of HFLH-CSA cement mainly forms ettringite.With the exhaustion of gypsum,the amount of ettringite formed do not increase.The amount of C-S-H gel formation begin to increase,and a small amount of OH-hydrotalcite and Al（OH）₃ gel are formed.The simulation results are close to the test results;（4）The total water demand of HFLH-CSA cement is 0.49 by thermodynamic simulation（GEMS-PSI）combined with the hydration cumulative heat of different water-to-binder ratios in HFLH-CSA cement.