Research On Hydration Kinetics Of Ultrafine Cement And Its Applications

Ultra-fine cement has shown excellent properties of high injectability,short setting time and high early strength due to its microfine particle size,and is widely used in microfine crack grouting reinforcement projects in construction,mines and oil wells.However,the effect of microfine cement particles on the kinetic process of its hydration reaction and the mechanism are still lack of in-depth research.Four types of silicate cements with particle size Dv_（90）of 54.3μm,28.5μm,20.3μm,and 11.2μm were prepared by grinding in a high-speed ball mill,which characterized the particle size distribution,particle morphology,and phase composition,and the degree of distortion of cement crystal structure was characterized by X-ray diffraction peak half-height width.The influence of particle size on the hydration process was analyzed;the influence of water-cement ratio on the performance of ultrafine cement grouting materials was studied and field grouting reinforcement tests were conducted.The main research results are as follows.With the decrease of cement particle size and increase of specific surface area,the intensity of X-ray diffraction peaks of tricalcium silicate minerals decreased and the half-height width increased.When the particle size was reduced to 11.2μm,the diffraction peak half-height width increased significantly by 8%～15.3%,and the crystal structure of cement particles was distorted due to ultrafine grinding.As the particle size decreases,the hydration processes all exhibit three stages controlled by crystalline nucleation growth（NG）,phase boundary reaction（I）and diffusion process（D）.When the particle size was above 20.3μm,the hydration parameters such as activation energy of hydration reaction,exotherm of hydration and hydration reaction constant decreased linearly;when the particle size was reduced to 11.2μm,the hydration parameters changed dramatically,the induction period was shortened by 1.5 times,the exotherm rate increased by 56.2%,the reaction constant of NG process increased by 85.5%,and the activation energy decreased by 39.72%,which obviously deviated from the linear law.The ultrafine cement particles undergo lattice distortion and require lower activation energy,which promotes the hydration reaction.The Ca²⁺concentration in the hyperfine cement slurry decreased faster,and the early hydration products of the nodular body were more abundant and the later microstructure was more dense.With the increase of water-cement ratio,the fluidity of ultrafine cement slurry increased,viscosity decreased,water precipitation rate increased,strength gradually decreased,and the maximum central reaction temperature decreased.Compared with the performance of ordinary grain size silicate cement,ultrafine cement still has good slurry stability under large water ratio;under the same water-cement ratio,and the hydration reaction of ultrafine cement slurry is faster and stronger.The field application shows that the ultrafine cement slurry has good diffusion performance,the fissure filling is dense,the anchor pulling force is improved significantly,and the deformation of the roadway surrounding rock is reduced.