Experimental Research On The Flexural Performance And Fracture Property Of Steel Fiber-reinforced Concrete At Early Age

Because SFRC materials have many strongpoints,it has been applied to civil engineering.It has been approved that nonlinear of concrete and softening curve after peak load are improved obviously.Previous studies were based on the performance of SFRC at the age of 28 days or even longer,while the study is rare on mechanical properties in the hardening process of concrete.In this paper,around the mechanical properties of SFRC,the major research work has been done as fellows:First,54 cubic specimens and 27 small beams were designed and made,and the experiment on compressive resistance strength,split-tensile strength and bending strength were carried out.According to the comparison between two samples strength which was at different ages and with different fibers content,the fitting formula of the strength development at different ages was measured.The strength of the specimen at the age of 7 days is as high as 60%to 75%of the one's at the age of 28 days.Among them,the increasing range of flexural strength is higher than others.Second,36 small beam specimens were designed and made,and the experiment on flexural toughness of early-age SFRC was carried out.The evaluation of test result was made according to testing data,by means of ASTM C1018 toughness index and German fiber concrete standard DBV.The results showed that the early-age SFRC are of good ductility and toughness.Bending toughness index ratio is at the range of 1.95 to 2.20,which are close to 2(ideal elastic-plastic parameter).Remaining strength coefficient is at the range of 88.0 to 134.4,which indicates that SFRC has a good plastic property.The effect of age is not remarkable on the index of SFRC,while the effect of fibers content is greater,especially to the early-age SFRC.Third,36 small beam specimens with prefabricate cracks were designed and made, and the experiment on fracture properties of early-age SFRC were carried out.After having an evaluation of fracture toughness by fracture toughness and fracture energy, the formula about the relationship between fracture toughness,fracture energy and age were established,which are K_IC=2.Z35-10.57/(1+exp(x+10.876)/7.857) and G_F=1116.92 + 816.02x - 13.06x².Because of the resemble mechanism between splitting tensile failure and three-point bending tests,the relation formula between splitting tensile strength and fracture toughness was established,which are K_IC=-0.3361 + 0.7641f,- 0.0446f_t².After checking computation,the error is small. So,fracture toughness of early-age SFRC can be evaluated indirectly by split-tensile test.Finally,the numerical simulation software named MFPA^2D was used to simulate the flexural toughness of SFRC and the fracture failure process of three-point flexural specimen from the microscopic.The simulation results were close to the test results. What's the more important is that,from elastic modulus graph,stress graph and AE graph,the simulation results can show the micromechanical damage phenomenon which can not be observed in the lab.Flexural toughness and fracture properties are the important mechanical properties of SFRC.Along with the depth of the research going deeper,it is helpful to the long-term quality of SFRC project,if the development law of mechanical properties of SFRC can be mastered and some corresponding measures can be carried out.