Experimental Study On Mechanical Properties And Durability Of Ultra-high Performance Concrete With Coarse Aggregate

With the development of engineering structures towards ultra-long,ultra-large,and ultra-high,ordinary concrete is more and more difficult to meet the needs of modern engineering.Therefore,in recent years,research on cement-based materials with high durability and high strength has become one of the main research directions in the field of concrete materials.Ultra High Performance Concrete(UHPC)is a new type of cement-based material with excellent characteristics such as high strength,high durability,high toughness,good chemical resistance,and low porosity.However,UHPC has the problems of large amount of gelling material,high production cost,complicated process,and large initial shrinkage.Studies have shown that by incorporating coarse aggregate into UHPC,on the basis of improving some of its defects,ultra-high performance concrete with coarse aggregate(UHPC-CA)with excellent mechanical properties and high durability can be prepared.This paper takes the coarse aggregate content and the steel fiber content as the test variables for the experimental study.The volume ratio of the coarse aggregate content is:0%,15%,30%,40%,and the volume ratio of the steel fiber content: 0.5%.,1%,1.5%,2%.According to the above two variables,a total of 16 groups of specimens were designed for mechanical performance test(compressive strength test and splitting strength test)and durability test(freeze-thawing cycle test and sulfuric acid corrosion test),and the influence of crude aggregate volume ratio and steel fiber volume ratio on the performance of UHPC-CA was analyzed.The fluidity of UHPC-CA decreases with the increase of steel fiber and coarse aggregate content.When the coarse aggregate content is 40%,the UHPC-CA expansion is less than 500mm;when the steel fiber content are 1.5% and 2 % And the coarse aggregate content exceeds 30%,the UHPC-CA extension is less than 500 mm,then the coarse aggregate content should not exceed 30%.Basic mechanical tests show that the effect is best when the volume ratio of steel fiber is 1.5%,and the compressive strength is respectively increased by 25.6%,13.6%,and 5.4% compared with other groups for the cubic compressive strength of UHPC-CA.When the blending amount is no more than 15%,the compressive strength of coarse aggregate to UHPC-CA is slightly increased,and when it exceeds 15%,the compressive strength is reduced.For the split-tensile strength of UHPC-CA,the effect is best when the volume ratio of steel fiber is 2%,which is 86.9%,52.9%,and 55.4% higher respectively than those of other groups.However,the incorporation of coarse aggregate will reduce the UHPC-CA cleavage strength by up to 44.6%.In terms of damage morphology,the appropriate amount of steel fiber is very significant to reducing the number of cracks in the test block,and the UHPC-CA matrix exhibits plastic damage when it is compressed.The durability test shows that the increase of the steel fiber content can enhance the durability of UHPC-CA,and the coarse aggregate will have a certain negative effect on the durability of UHPC-CA.In terms of freeze-thaw resistance,the effect is better when the volume ratio of steel fibers is 1.5% and 2%.In terms of sulfate resistance,the effect is best when the volume ratio of steel fiber is 1.5%.Introducing the grey system theory,the correlation value between the durability of ultra-high performance concrete containing coarse aggregates and freeze-thaw resistance as well as sulfate corrosion is calculated.The greater the correlation value,the better the comprehensive durability.