| As an important geotechnical material,cement concrete is widely used in roads,airports,dams and other engineering construction fields.About 90%of the newly built pavements of airport runways in my country are constructed with cement concrete.Cement concrete is a kind of brittle material,and its ability to resist deformation is poor.Under the repeated action of aircraft load,it is easy to cause fatigue fracture of cement concrete slab and reduce the operational safety of airport pavement.In order to improve the anti-deformation ability of airport cement concrete materials,mixing with an appropriate amount of high-performance fiber can effectively improve the anti-cracking performance of concrete.Based on the construction project of Beijing Da Xing International Airport,the paper mixes modified polyester fiber(FC),polyvinyl alcohol fiber(PVA)and polypropylene fiber(PP)into cement concrete to prepare high-performance fiber concrete.Tests,flexural toughness tests and fracture performance tests are carried out to study the fatigue characteristics of high-performance fiber concrete,and the fatigue performance,flexural toughness and crack resistance of three high-performance fiber concretes are compared and analyzed.The paper uses the response surface optimization design method to determine the optimal mix ratio of the benchmark concrete,and at the same time obtains the optimal content of the ultra-high-strength modified polyester synthetic fiber(FC fiber).Static load tests were carried out on FC fiber concrete with 1.0kg/m~3,1.2kg/m~3,1.4kg/m~3 and 1.6kg/m~3 to test the effect of high-performance fibers on the mechanical properties of concrete.Carry out indoor trabecular fatigue test and bending of 1.4kg/m~3 modified polyester fiber(FC)concrete,2.6kg/m~3 polyvinyl alcohol fiber(PVA)concrete and 3.0kg/m~3 polypropylene fiber(PP)concrete Toughness test and three-point loading notched beam fracture performance test,comprehensive analysis of the fatigue characteristics of different types of synthetic fiber concrete,the main results are as follows:(1)Using the reference mix ratio optimized by the response surface design method,the obtained fiber concrete has good working performance,and the prepared concrete beam specimens all meet the design requirements of the specification for the flexural strength of not less than 5MPa.(2)According to the results of the static load strength test,it is concluded that high-performance fibers mainly improve the toughness of concrete,but are very limited in improving the compressive bearing capacity of concrete.(3)According to the results of the fatigue performance test,the three high-performance fibers have effectively improved the fatigue life of concrete.Among them,FC fiber has the most obvious effect on the improvement of concrete fatigue life,and the fatigue life is about 2to 3 times that of plain concrete.(4)The statistical method is used to sort out and analyze the fatigue test results,which proves that the two-parameter Weibull distribution can better describe the fatigue life distribution of the three fiber concretes;the average life curve of the three fiber concretes and the curve considering the survival probability are given.And the fatigue equation,the fatigue ultimate strength of three kinds of fiber concrete is obtained through the equation,and the effect of three kinds of synthetic fibers in improving the fatigue resistance of concrete is obtained by comparison:FC>PVA>PP.(5)Compared with plain concrete,the flexural toughness and fracture performance indexes of FC fiber concrete,PVA fiber concrete,and PP fiber concrete:the flexural toughness value increased by 125.8%,118.4%and 87.1%,and the peak strength increased by20.5%,18.8%And 16.7%;fracture energy increased by 87.1%,73.2%and 55.6%,and unstable fracture toughness increased by 45.1%,39.3%and 31.5%.In the experiment,the fiber content is selected,and the toughening effect of synthetic fiber on concrete is:FC>PVA>PP.(6)Comprehensive fatigue test,bending toughness test and fracture performance test,FC fiber has a significant improvement in the fatigue resistance of concrete compared with the commonly used PVA fiber and PP fiber on airport pavement,and the effect of toughening and cracking resistance is obvious.It is suitable for airport pavement construction.It can be used to prepare high-durability and long-life airport pavement fiber concrete.(7)The results of this research are expected to have reference value for the structural design of airport cement concrete pavement and predict the service life of cement concrete pavement.It can further enrich the content of the code and have certain reference value for the next revision of the code. |
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