Studies On Mechanical Properties Of Ultra High Performance Concrete With Coarse Aggregate

Ultra high performance concrete(UHPC)is a kind of cement-based composite material with high strength,high toughness and excellent durability.For the problems of large amount of cementitious material and early high cost of Ultra High Performance Concrete,the UHPC system was mixed with coarse aggregate and river sand instead of quartz sand,the preparation of UHPC with coarse aggregate of excellent mechanical properties is successful and the effect of the coarse aggregate content and the length of the steel fiber on the mechanical properties of the UHPC with coarse aggregate were studied.Achieved the following results:(1)When the coarse aggregate content is less than 400kg/m3,with the increase of coarse aggregate,the cube compressive strength and axial compressive strength of long fiber UHPC have been improved,flexural strength and first crack strength of long fiber UHPC and cube compressive strength and axial compressive strength of short fiber UHPC change little,the flexural strength of short fiber UHPC decreased greatly.When the coarse aggregate content is greater than 400kg/m3,the compressive strength,axial compressive strength,flexural tensile strength and first crack strength of the long and short fiber UHPC were reduced to some extent.When the content of coarse aggregate is 400kg/m3,with the increase of fiber length,the compressive strength,axial compressive strength and first crack strength of UHPC are changed little,but the flexural strength of UHPC increased.(2)Cube compressive strength failure of UHPC with coarse aggregate still belongs to the splitting failure,but toughness is good,appeared cracked but not broken phenomenon,prism compressive test appeared an oblique main crack significantly with failure,obvious shear failure.There is no multiple cracking phenomenon of UHPC without coarse aggregate in bending failure,also no obvious cracks;with coarse aggregate content increase and long fiber content decreased,UHPC flexural failure multiple cracking phenomenon gradually disappear,the micro cracks of become less and the main crack is more obvious.(3)With the increase of coarse aggregate content,the elastic modulus of UHPC increased almost linearly,and the length of steel fiber had little influence on the UHPC elastic modulus of different coarse aggregate.(4)The contents of coarse aggregate have significant effect on the flexural toughness of UHPC.With the increase of coarse aggregate content,the energy consumption of elastic stage,strain hardening stage and strain softening stage decreased,the peak strength,first crack deflection and peak deflection decreases.When the content of coarse aggregate is 400kg/m3,with the increase of the length of the fiber,the energy consumption of the elastic phase changed little,and the energy consumption of strain hardening stage and strain softening stage decreased increase in the process of bending.