Tensile And Bending Behavior Of Ultra High Performance Concrete And Its Bending Damage Process Investigation With Acoustic Emission Technology

Since the ultra-high performance concrete(UHPC)was introduced in the 1990 s,researchers from all over the world have worked together to overcome difficulties in preparation,lack of fluidity,lack of toughness,and other issues,have now developed into an ultra-high specific strength.Cement-based materials with high toughness and excellent durability.Today,this smaller,thinner,stronger and more resilient building material is increasingly used in engineering.The outstanding toughness of UHPC is mainly attributed to the bridging effect of high-strength matrix and fiber with low water-to-rubber ratio.Characterization is often performed by bending tensile properties.The subject first selects the UHPC mix ratio and curing system through fluidity and flexural compression resistance tests.The dog-bone test specimens and thin-plate specimens are molded separately for uniaxial tension and three-point bending test.Acoustic emission technology is used to collect data in real time.Supplemented by analysis.The uniaxial and three-point bending stress-strain curves and acoustic emission characteristics of UHPC were studied from two perspectives of water-binder ratio,steel fiber type and volume content.The efficient coordination mechanism between high-strength matrix and high-strength fibers was verified.The main conclusions are as follows:(1)The decrease of water-binder ratio and the increase of steel fiber content will reduce the fluidity of UHPC,which is beneficial to the increase of flexural strength and compressive strength.When the proportion of PVA fiber in the blend increased,the fluidity of the mixture decreased significantly,and the flexural strength and compressive strength decreased in varying degrees.(2)The stress-hardening ability of UHPC,whose ratio of water to binder is 0.16,total fiber content is 2 and steel fiber is 2:1,is more prominent under uniaxial tension and three-point bending load,which indicates better toughness.When the content of steel fiber decreases and the content of PVA increases,the stress-deflection curve level decreases.(3)UHPC with 0.16 water-binder ratio in the process of loading,the accumulative ringing count and accumulative energy have obviously accelerated rising and leveling stage,which shows the dynamic balance between macroscopic crack propagation and new crack formation in the process of loading.When the content of steel fiber decreases and the content of PVA fiber increases,the balance is broken.(4)The shear cracks of UHPC specimen with low water glue are more under threepoint bending load.When the amount of steel fiber is increased from 1% to 2%,the ratio of tensile cracks and small amplitude events increases,which means that UHPC with 2% steel fiber content can effectively avoid the continuous expansion of a single macro crack and produce more fine tensile cracks.Later to the shear fracture development resulting in fracture.(5)When the rigid fiber and PVA fiber are mixed in a reasonable proportion,the steel fiber and PVA fiber have a good synergistic effect,and the de-bonding strength of the fiber and the strength of the matrix can also achieve a better synergistic effect.The dynamic equilibrium is achieved between the propagation of macroscopic cracks and the formation of new cracks during the loading process of the specimen.Therefore,I propose that the most reasonable damage process of specimen is from micro-tensile fracture to shear fracture.In this paper,the effects of water-binder ratio and fiber on the stress-deflection curves of UHPC under tensile and bending loads are studied,and the acoustic emission characteristics of UHPC under three-point bending load are analyzed,so as to reduce the failure process and crack mode of UHPC.The results provide a basis for the further study on the evaluation of UHPC toughness by acoustic emission technology.