Study On Hydration Characteristics And Maturity Of Calcium Sulfoaluminate Cement-based Materials

The calcium sulfoaluminate cement has high temperature sensitivity.Ettringite,the hydration product,is susceptible to the influence of the curing temperature,thereby affecting the performance of hardened cement paste.In this paper,calcium sulfoaluminate cement,silica fume and Class C fly ash were used as raw materials.The effects of curing temperature such as 20,30,40 and 50 ℃ on heat of hydration,electrical resistivity,chemical shrinkage,and compressive strength of calcium sulfoaluminate cement-based materials were investigated.The hydration kinetics process of calcium sulfoaluminate cement-based materials was established,and the apparent activation energy was calculated.In addition,a compressive strength prediction method based on the maturity equation was proposed.The main results can be concluded as follows:(1)The hydration heat of cement-based materials is mainly concentrated in the first 24 h.The incorporation of silica fume and Class C fly ash can effectively promote the hydration process and reduce the maximum rate of hydration heat.Higher temperature significantly accelerates the hydration process of the cement paste,and increases the accumulative heat at 24 h.With the increase of the content of mineral admixture,the difference of accumulative heat at 24 h decreases gradually.(2)The electrical resistivity of cement-based materials increases with the hydration time.The incorporation of silica fume and Class C fly ash can increase the electrical resistivity at initial time and decrease at 24 h.Higher temperature can decrease the electrical resistivity at intial time and 24 h,advance the characteristic points of the electrical resistivity curve.With the increase of curing temperature,the maximum rate of electrical resistivity increases first and then decreases,reaching the maximum at 40 ℃.(3)The chemical shrinkage of cement-based materials increases with the hydration time,mainly concentrated in the first 24 h.The incorporation of silica fume and Class C fly ash can decrease the chemical shrinkage at 72 h.Higher temperature can advance the characteristic points of the chemical shrinkage curve,significantlyincrease the maximum rate of chemical shrinkage,but decrease the chemical shrinkage at 24 h.(4)The compressive strength of the hardened cement paste within 28 d at different curing temperatures differs greatly.At 20,30 and 40 ℃,it can be divided into4 stages.At 50 ℃,the compressive strength will shrink and can be divided into 5stages.The compressive strength at 50 ℃ get the smallest at 28 d.(5)The hydration kinetics equation of calcium sulfoaluminate cement is (?).The hydration process of calcium sulfoaluminate cement can bedivided into 5 stages.The acceleration stage and deceleration stage are controlled by crystallization nucleation growth,and stable period by the diffusion reaction,whose called NG–D process.The incorporation of silica fume can promote the transformation of ettringite during deceleration,and the incorporation of Class C fly ash can inhibit the ettringite during deceleration.(6)The maturity equation of calcium sulfoaluminate cement is (?).The relationship between compressive strength and maturity is (?).With the increase of curing temperature,the limitcompressive strength gradually decreases,and the constant of reaction rate increases first and then decreases,reaching the maximum at 20% Class C fly ash addition.(7)According to the curing temperature,the heat of hydration,compressive strength,electrical resistivity and chemical shrinkage at 24 h can be predicted.Higher curing temperature can acquire a higher value of accumulative heat and compressive strength at 24 h,a lower value of electrical resistivity and chemical shrinkage at 24 h.