Research On High Strenrth-High Flowability Concrete Based On Optimization Of Integrated Particle Gradation

High strength concrete has low water binder ratio and high viscosity.It is easy to cause distress due to its poor flow performance.It is an important research direction to improve the fluidity of concrete at present to improve the particle size distribution of concrete,improve its compactness,reduce the internal void ratio and release more free water based on the compact packing theory.But the domestic and foreign research often concentrates on the cementitious system or aggregate system to carry on the single system research,seldom studies from the entire concrete system.In addition,in engineering practice and many studies,the flow properties of concrete are roughly evaluated by experiments such as collapse and expansion,but the rheological analysis is not carried out.On the other hand,the fluidity of concrete can be significantly improved by adding fly ash,but with the shortage of high-quality fly ash resources,looking for an alternative admixture has important practical significance.In South China,limestone resources are abundant,limestone powder has the advantages of low water requirement and easy grinding,making the wide application of ultra-fine limestone powder in concrete possible,but its research in high-strength concrete is relatively less.In this paper,based on the rheological characteristics of concrete from the cementitious system,aggregate system to optimize the gradation of the whole particle,and explore the feasibility of the application of ultra-fine limestone powder in high-strength concrete.For this purpose,the following work has been carried out in this paper:It was found that the effect of compound admixture was better than that of single admixture.Fly ash had the best water reducing effect,followed by limestone powder and the worst mineral powder.The particle size distribution of cementitious system is not only related to the amount of each powder,but also affected by its particle size distribution.The smaller the particle size of limestone powder,the better the effect in a certain range of dosage.In aggregate system,fine aggregate is divided into three particle sizes: 0-0.6 mm,0.6-1.18 mm and 1.18-4.75 mm,coarse aggregate is divided into three gradations: 5-10 mm,10-15 mm and 15-20 mm,and different particle gradations are obtained by adjusting the proportion of the three particle sizes.It is found that the aggregate system with large bulk density and small specific surface area can be obtained by optimizing aggregate particle size distribution,which can effectively improve the flowability and mechanical properties of concrete.The addition of appropriate amount of limestone powder(less than 20%)in concrete can play a better micro-filling effect,reduce porosity,improve pore structure,reduce cement hydration heat release,and have a certain retarding effect.XRD analysis showed that limestone powder also participated in the hydration reaction in the late hydration stage,and was not a completely inert material.Therefore,the application of ultra-fine limestone powder in high strength concrete is feasible,to a certain extent,improves the performance of concrete,and has a good application prospect.