Study On The Rheological Behaviour Of Cement Pastes With The Addition Of Nano-Metakaolin

With the development of marine engineering,the durability of concrete structures is becoming more and more important.Owing to the small size and crystal nucleus effects,nano-metakaolin(NMK)gives the cement-based materials excellent mechanical properties and high durability.However,the smaller particle size and higher specific surface area and energy of NMK result in the increase of the water demand of the fresh cement-based materials inevitably,which take a negative effect on its rheological properties.Based on the current research results reported worldwide,the rehological behavior of the NMK cement pastes were examined in the paper.The effects of environmental temperature,hydration time,water to binder ratio and superplasticizer were taken into consideration.Rheogical parameters were achieved by the rheological tests.The relation between NMK contents and rheological behaviour were discussed.A multi-factor model was then established for the prediction of rheological parameters.The principal research work is listed as follows:(1)Experimental study on the chloride resistance and mechanical properties of cement-based materials added with nano materials.Eight kinds of nano materials were prepared.The chloride permeability of the cement mortars with various nano materials were tested and compared respectively.Meanwhile,the construction cost was taken into account as well.The suitable NMK was then suggested.Afterwards,the mechanical property of the NMK cement pastes during the curing periods were tested and discussed.(2)Experimental study on the fluidity of NMK cement pastes.The traditional fluidity test was performed.The effects of water to binder ratio,superplasticizer on the flowability of NMK cement pastes were analyzed.The relationship between fluidity and NMK contents was proposed.(3)Experimental study on the rheological properties of NMK cement pastes.The effects of water to binder ratio,superplasticizer on the rheological properties of NMK cement pastes were investigated by rheological tests.The mechanism of NMK on the rheological properties of fresh cement paste was revealed.The rheological characteristics of NMK cement pastes were analyzed.The correlation between apparent viscosity,yield stress,plastic viscosity,hysteretic area and NMK contents were discussed in detail.The relationship between the flowability parameter and rheological parameters were achieved.(4)Experimental study on the effect of environmental temperature and hydration time on the rheological properties of NMK cement pastes.The rheological properties at various hydration time(10-90min)and environmental temperatures(8-45℃)were explored by rheological method.The development of the rheological parameters of NMK cement pastes under various of environmental temperature and hydration time were discovered.(5)Study on the rheological parameters prediction of NMK cement pastes.The modified Krieger-Dougherty model achieved high prediction precision for the viscosity of cement pastes with lower NMK contents(<3%).Based on BP neural network,a multi-factor prediction model,which taking the environmental temperature,hydration time,NMK contents and water to binder ratio into consideration,was established to predict the rheological parameters.The predicted results showed good agreements with the experimental results.