The Effects Of Cement Particle Shape And Size Distribution On Hydration Process

Cement-based material is a typical porous material,and its microstructure is the foundation of mechanical properties,thermal and wet transmission characteristics.The hydration and hardening process of cement is a long-term and gradually developing process.In the past 20 years,according to the experimental data and reaction mechanism,researchers have put forward many hydration models.But most of hydration models regard cement particle as sphere,which is different from its real shape,and will certainly affect the accuracy of the simulation.Therefore,reconstructing an initial packing model with various morphological particles has great theoretical significance to study the influence of particle shape and size distribution on hydration process.The construction methods of various morphological particles is compared,and the cement aggregate is assumed to be ellipsoidal particle in this paper.The overlapping detection algorithm and phase assignment algorithm of ellipsoids is improved,and reconstructed packing models of ellipsoidal particles are applied to CEMHYD3 D hydration reaction.By comparing the simulation results and experimental results,the ellipsoidal particle with an aspect ratio of 3.0 is regarded as the best replacement of real shape.At the same time,the evolution process of microstructure is observed.It is found that the smaller particles have been hydrated completely after 28 days,while the larger particles are close to the original shape.The degree of hydration is proportional to the amount of heat release and chemical shrinkage,inversely proportional to the amount of porosity during the hydration process.Therefore,measuring one of the quantity is enough to calculate the other three quantities in experiment.Then,the influence of aspect ratio,aspect ratio distribution interval,water/cement ratio,particle size distribution on degree of hydration,fraction of connected solid,fraction of connected porosity is compared by control variable method,and the reason has been discussed.The results show that: 1)larger aspect ratio result in larger degree of hydration,earlier initial setting time and percolation blocking time;2)when the aspect ratio is subjected to the normal distribution with an average of 1.0,larger aspect ratio distribution interval result in larger degree of hydration,earlier initial setting time and percolation blocking time;3)larger water/cement ratio result in larger degree of hydration,later initial setting time and percolation blocking time;4)larger average equivalent diameter result in smaller degree of hydration,later initial setting time and percolation blocking time.Particle shape and size distribution influence the specific surface area of the packing model,which lead to the difference.