Study On The Design Method Of Concrete Aggregate Gradation Considering The Effect Of The Aggregate Shape

Aggregate is an important composition in concrete.Its properties,such as shape and gradation,have a great influence on both the workability of fresh concrete and strength and durability of hardened concrete.Now the aggregate shape has never been considered in the design of concrete mixture ratio,and only the size of aggregate has been mentioned on designing aggregate gradation in current standard specification.Therefore,it is of great significance to develop the design method of concrete aggregate gradation considering the effect of the aggregate shape.The main work focus on the influence of the aggregate shape on aggregate gradation in the study,and they are as follows:(1)Several kinds of fine and coarse aggregates have been analyzed using the Image Pro-plus analysis software to obtain the shape parameters denoting the shape of particles.(2)The flow time of sand particles have been tested using “outflow time method” to establish the relationship between flow time and every shape parameter.(3)The slump flow,height and angle of repose of the coarse aggregate have been obtained by tesing the liquidity of particles to build the relationship between them and shape parameters.(4)The shape factor has better correlation between coarse and fine aggregate’s liquidity than the other aggregate shape parameter,and it has been applied into the Bolomey curve to establish model of aggregate gradation curve considering the shape of aggregate.(5)Concrete samples have been prepared according to the above established model of gradation curve,and both workability and compressive strength of as-prepared concrete have been tested to optimize the model of gradation curve.(6)Software of the aggregate gradation curve model have been developed to consider the effect of aggregate shape.(7)The experiment that compares the traditional design method of the aggregate gradation with result of the software recommending is used to verify the feasibility of the result that the software recommends.Based on the above study,the mian conclusions are as follows:(1)Both the particles’ degree of thickness and the aggregate shape have an effect on the liquidity of fine aggregate.It is not prominent of the correlation between flow time and shape parameters.Parameter(M_x)~F can be obtained by combining the fineness modulus and shape parameter.When F is shape factor,the correlation index between(M_x)~F and flow time reaches up to 0.846 7,and the correlation is prominent.(2)By analyzing relatonship between the slump flow,height,angle of repose and shape parameters of both 5~20 mm and 20~40 mm aggregate particles,it can be concluded that the best correlation was found between aggregate shape factor and liquidity.That is to say,the shape of aggregate particles could be reflected by shape factor.(3)Based on the contrast analysis,shape factor is applied to the Bolomey curve,and the new model of aggregate gradation curve is eatablished.The expression form of aggregate shape in the model has been adjusted and optimized by testing the workability and compressive strength of concrete.The optimized model is as follows:(4)Both the automatic measurement of aggregate shape and recommendation of the best aggregate gradation curve,considering the influence of aggregate shape,have been realized using both matlab and Visual Basic softwares.And comparing with the traditional design method of aggregate gradation,the feasibility of this method is verified.