Study On The Effect Of Silica Fume On Hydration And Microstructure Of Cementitious Materials By Numerical Simulation

Silica fume which consists of very fine spherical particles and has a very high content of amorphous silicon dioxide has been widely used in ultra-high performance concrete.It is always densified and compacted in order to improve the transport properties.So silica fume tend to be agglomerated and have some effect on hydration and microstructure of cementitious materials.In fact,it is difficult to control the agglomeration of silica fume in experiments.Therefore,the research of silica fume on the microstructure and properties of cementitious materials is still limited.Based on ?ic model,the new cement hydration model and cement-silica fume hydration model which considers four minerals of cement clinker,different stages of hydration process and pozzolanic reaction has been proposed in this thesis to study on the effect of silica fume agglomeration,content and water-cement ratio on hydration process and microstructure development of cementitious materials.In this model,cement particles are assumed to be composed of four main minerals.Whereas silica fume as spherical particle consists of silica and an inert phase.The filler and chemical effect of silica fume are modelled.The model is validated by comparing numerical results(hydration degree,calcium hydroxide content and porosity)with experimental data obtained by other authors.The reaction degree of silica fume and cement,hydration product content,porosity and microstructure development at different water-binder ratio were obtained by this new model.The effect of particle size and content of silica fume on cementitious materials with low water-binder ratio was studied.It was found that the agglomeration of silica fume plays a negative role on the improvement of cementitious materials.Silica fume with larger particle size have ineffectual or even counter-productive.Additionally,effect of silica fume content on cementitious materials also varied with the different particle size distributions.It provided a resonable explanation for the phenomenons that silica fume added to cementitious materials failed to get the expected result and the optimum content is uncertain.In conclusion,silica fume content in cementitious materials should control in certain range and pay attention to the dispersion of silica fume,so as to avoid larger agglomerated particle size which weaken the performance of cementitious materials.