| In this paper,a hydraulic calcium aluminophosphate(CAP)crystal was prepared and its formation kinetics,hydration kinetics and hydration products were studied.The calcium aluminum phosphoaluminate mineral is a main ore phase in aluminophosphate cement,and the phosphoaluminate cement is a cement material having high gelling properties,high durability and versatility.This study can provide a theoretical basis for the design,development and improvement of new cementitious materials.The main work and results of this article are as follows.(1)The formation conditions and formation kinetics of CAP minerals were studied.The results showed that when the calcination temperature was 1590°C,the calcium aluminophosphate minerals began to form,and the amount of the minerals of calcium aluminophosphate increased gradually with the increase of the holding time;the formation of CAP was mainly controlled by diffusion at 1590°C,and the activation energy parameters were formed.470.6456 kJ/mol.(2)The hydration kinetics of CAP minerals was studied.Using the Kondo hydration kinetics model and the hydration heat test of CAP minerals with a hydration ratio of 0.35,the results show that the CAP hydration process can be divided into the initial hydration stage,induction stage,acceleration stage,deceleration stage,and stabilization stage.The period can be divided into two stages,and the deceleration period can be divided into three stages.In the acceleration phase,the reaction rate constant of phase 1 is 0.004402,the reaction rate constant of phase 2 is 0.083043;in the deceleration phase,the reaction rate constant of phase 1 is 0.028153,the reaction rate constant of phase II is 0.067089,and the reaction rate constant of phase 3 is 0.006801.(3)The hydration process of CAP minerals and the evolution of hardened slurry over time are studied.Using scanning electron microscopy and X-ray computed tomography(XCT),the hydration behavior of CAP hydration minerals was monitored at 2h,5h,8h and 12 h ages.When the age is 2h,the crystal morphology can still be discerned in the hydratable slurry.With the increase of the age,the crystals in the complete morphology of the slurry gradually disappear,and the crystal is covered by the gel and adhered into a whole.The XCT technique can be used to in-situ detect early hydration of CAP minerals,observe changes in the same position in the sample as the age increases,and quantitatively analyze the change in the volume ratio of unhydrated particles and pores in the sample: when water When the age of the larvae changed from 8h to 12 h,the proportion of unhydrated granules decreased from 75.4% to 71.8%,and the pores decreased from 1.67% to 1.33%.(4)The mechanism of adsorption of chloride ions by CAP minerals was studied.Using the isothermal adsorption law of chloride ions for the chloride binding ability of calcium aluminophosphate minerals,it was found that the calcium aluminophosphate minerals are more suitably described by the Freundilich nonlinear adsorption law in the process of chloride ion binding,but for the chemical binding part On the other hand,Langmuir's non-linear sorption laws with applications at the limit are more reasonable.(5)The nano-indentation technique was used to test the calcium aluminophosphate mineral paste.Combined with SEM-EDS analysis,there were three different hydration product phases in the hydration slurry of the calcium aluminophosphate mineral: high-P gel phase,The P gel phase and the low P gel phase have three indentation moduli of 25.59 GPa,31.58 GPa and 47.78 GPa,respectively. |
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