Effect Of Rheological Properties On Stability Of Concrete

The performance of fresh concrete is required in terms of its ability to maintain adequate stability meanwhile showing good flowability during casting operations.However,the concrete stability problems are commonly observed during construction process,which cause the non-uniform distribution of coarse aggregates in the mortar,thereby affecting both the mechanical properties and durability of hardened concrete.Therefore,in this paper,the image analysis through colored aggregates was used to evaluate the stability of fresh concrete and the appearance of harden concrete,the orientation of aggregate was analyzed as well.The stability of concrete and the distribution of aggregates with different particle sizes could be evaluated by this method quantitatively and accurately.The effect of gradation of coarse aggregate on the rheological properties and stability of fresh concrete was studied by using the same mortar.It can be concluded that both distribution of coarse aggregate size and the specific surface area of them decided the shear thickening or thinning response of fresh concrete,when the volume of cement mortar was fixed.Fractal dimension could represent geometry properties of coarse aggregate correctly and the yield stress and viscosity approximately had a relationship with fractal dimension of aggregate.The stability of fresh concrete is greatly affected by the gradation of coarse aggregate,it was obvious that concrete with well graded coarse aggregate exhibited decrease of yield stress compared to that with gap grade aggregate.Meanwhile,the concrete with well graded coarse aggregate performed higher segregation resistance.The particles with larger size performed higher segregation tendency,and the gap graded aggregate with large proportion of largest size particles could result in the worst homogeneity.Therefore,under the condition of changing aggregate gradation,it was difficult to obtain the relationship between segregation and rheological parameters of concrete.The aggregate gradation and cementitious materials were consistent,the effect of rheological parameters and the interaction between aggregates on stability and appearance of cast concrete were investigated under different vibrating conditions.The results shown that in the case of light vibration or stand,the stability of concrete was affected by the yield stress and plastic viscosity;then with the strengthen of vibration,the plastic viscosity became the primary element to decide the stability of fresh concrete In addition,the appearance quality of the concrete after casting was affected by the rheological parameters,on contrary,the insufficient filling ability and segregation could resulted in the poorly appearance of cast concrete.Thus,the optimum region of rheological parameters could be conducted from control the stability and appearance quality of concrete effectively.The migration and redistribution of coarse aggregate were investigated by changing the rheological properties of concrete and the rotating speed of “Shearmeter”.The results shown that the “Shearmeter” could equivalent the aggregate migration under the shear rate gradient during the pumping.The migration of coarse aggregate is mainly governed by the rotating speed of the “Shearmeter” and the parameters of concrete.The higher yield stress and lower plastic viscosity and the higher rotating speed of the “Shearmeter” which cause a greater shear rate gradient of concrete.The results of pumping in the field is consistent with the migration law from the “Shearmeter”.however,the migration degree of coarse aggregate will be affected by the thickness of the shear layer at the same time.