Experimental Study Of Coarse Aggregate On Rheological And Mechanical Properties Of Fresh Concrete

The volume of coarse aggregate in fresh concrete accounts for about 70%,and changes in its morphology,gradation,particle size and other characteristic parameters have a very important influence on the rheological properties and mechanical properties of fresh concrete.The research on the influence of aggregate properties on the rheological and mechanical properties of fresh concrete is of great significance for guiding the practical application of concrete structures.In this paper,the coarse aggregate morphology,particle size,gradation,type and other aggregate characteristics are the research objects.The morphology of coarse aggregate was systematically quantified and characterized by ultra-depth-of-field microscope,and the rheological characteristics and mechanical properties of fresh concrete were tested using experimental devices such as concrete rheometer and press.Using a combination of theoretical analysis and experimental research,the effect of aggregate properties on the rheological properties and mechanical properties of fresh concrete was studied.The main research results are as follows:(1)The morphology of coarse aggregate was systematically characterized.Eight parameters,such as sphericity,acicularity,flatness,volume ratio,angularity,convexity,roundness and roughness,were selected to quantitatively characterize the outline shape of coarse aggregate particles and the angularity of coarse aggregate particles.(2)The influence of coarse aggregate morphology,particle size and gradation on the rheological properties and mechanical properties of fresh concrete was clarified.The changes in the morphological characteristics of coarse aggregates,the size of coarse aggregates and the percentage of large aggregates in the gradation of coarse aggregates have profoundly changed the rheological properties of fresh concrete.The size of aggregate particle size affects the mechanical properties of concrete,but it is not a decisive factor affecting the mechanical properties.The increase of aggregate roughness and the percentage of aggregate with large grain size in gradation can improve the mechanical properties of concrete.(3)The influence weight of sand ratio,coarse aggregate morphology and gradation on the rheological properties and mechanical properties of fresh concrete was clarified.The results show that sand ratio is the most important factor affecting yield stress,plastic viscosity and flexural strength,and coarse aggregate morphology is the most important factor affecting compressive strength.(4)The influence of recycled coarse aggregate on the rheological properties and mechanical properties of fresh concrete was clarified.Under the same water-cement ratio,the fluidity and cohesiveness of concrete mixed with recycled coarse aggregate become worse,and the strength is slightly lower than that of the gravel coarse aggregate group.When the water-cement ratio is 0.35,the fluidity of the concrete mixed with recycled coarse aggregate will increase,the overall cohesiveness will be further deteriorated,and the mechanical properties will decrease significantly,with an average decrease of over30%.(5)The model of rheological properties and mechanical properties of fresh concrete expressed by coarse aggregate morphology parameters was established.The influence of different aggregate morphology parameters on rheological properties and mechanical properties of concrete was evaluated by multi-parameter linear regression analysis.The rheological properties parameters(yield stress,plastic viscosity)and mechanical properties parameters(compressive strength,flexural strength)were characterized by three characteristic parameters: flatness,angularity and roughness.This paper consists of 33 figures,12 tables and 75 references.