The Basic Research On The Flexural Properties Of Ultra High Performance Concrete

Ultra-high performance concrete is a kind of cement-based composites with ultra-high strength,ultra high durability and low creep performance,compared with ordinary concrete,its strength is higher,toughness is better and durability is more excellent.Because of its superior material performance,The UHPC not only attracted the research and promotion of many scholars both at home and abroad,but also obtained many application in practical engineering,and achieved good results.The tensile property of UHPC material is one of the critical basic properties,it is the basic index to describe the anti-cracking performance of UHPC,and also closely related to the UHPC shear performance and impact resistance,so it is of great practical significance to study the tensile properties of UHPC materials.In this paper,with fiber type and fiber content as test variables,four-point bending test without notch is carried out,and three-point bending test with notch specimen is performed.Based on the obtained load deflection curves and the load crack width curves,a inverse analysis method is used to obtain the stress-strain curves and the stress-crack width curves of the material,the effect of fiber content and fiber type on the basic properties of UHPC materials was compared,the conclusions are as follows:(1)The compressive strength of UHPC c was significantly affected by fiber type and content,when the fiber content from 2%increase to 3.5%,the compressive strength is also increased,the end-hook fiber has the best effect on the compressive strength and the longest straight fiber is the worst.However,the effect of fiber type and dosage on the elastic modulus of UHPC materials is not significant.(2)Based on the load deflection curves of two kinds of bending tests,the UHPC material shows the flexural hardening characteristics under different fiber content and type.The effect of fiber content and type on the linear limit strength is lower,but the influence of the flexural tensile strength is greater,under the same fibre type,it increases with the growth of fiber content,and the mixed fibers have higher bending tensile strength,but the long straight fibers are lower.(3)According to the UHPC stress-strain relationship curves obtained by the inverted analysis method,the UHPC materials showed obvious low strain hardening characteristics,and the stress size of different fibers and dosage on the strain hardening platform section of UHPC stress and strain curves was more remarkable,and it became higher with the increase of fiber content,and the effect was better under 3%and 3.5%fiber content.Mixed fibers have better effect on strain hardening of UHPC materials due to their own fibre gradation effect.(4)According to the stress crack width curve,we can obtaine that when the crack width is small,the curve shows the obvious stress platform segment,its length grows with the increase of fiber increment.The crack width is about 2.5mm and the inflection point appears.When the crack width is about 5mm,the stress level of the specimen is close to 0.(5)Comparing the results of three-point bending test and four-point bending test,the results of two kinds of bending tests and the regularity of change are basically identical,so the test method is feasible.