Research On The Application Of Polyoxymethylene Fiber In Airport Pavement Concrete

Cement concrete pavement is one of the airport pavement structure commonly used at present.Cement concrete is a kind of heterogeneous and brittle material with low tensile mechanical properties,high matrix shrinkage and poor flexibility.Under the action of complex environment and repeated aircraft load,the concrete slab surface of airport pavement is easy to crack,and the existence of cracks will weaken the bearing capacity,overall stability and durability of the pavement structure,bringing hidden dangers to the structure safety.One of the measures to overcome the above defects in concrete is to add fibers to the concrete with a view to changing it from brittleness to ductility or quasi-ductility,while improving mechanical properties and durability.Compared with traditional concrete,fiber reinforced concrete has superior properties,such as high compressive and tensile strength,high initial cracking strength,high fracture toughness,excellent energy absorption capacity and good impact and fatigue resistance.Polyoxymethylene（POM）fiber is a kind of new organic synthetic fiber with excellent comprehensive performance,the molecular structure of the fiber contains a lot of ether bond of carbon oxygen groups have certain polarity,is advantageous to the POM fiber and cement matrix form hydrogen bonds,and inorganic materials with high strength,good compatibility.These properties give POM fibers great potential as reinforced concrete fibers.In order to expand the application of POM fiber in the field of airport pavement engineering,and to provide a certain experimental basis for the reasonable design of POM fiber airport pavement concrete（PFAPC）structure,In this paper,the mechanical properties of PFAPC foundation,bending fracture properties and bending fatigue properties under dynamic loads of different orders of magnitude were preliminarily explored.The main experimental research work was as follows:（1）The orthogonal experimental design method was used to optimize the length and dosage of POM fiber.The results show that the PFAPC has better mechanical properties when the length of POM fiber is 12 mm and the dosage is1.2%of the concrete volume.（2）The influence of strain rate on the bending properties of PFAPC was studied by four point bending tests.The bending deflection,bending modulus,bending strength and toughness index of PFAPC at five different strain rates(10^-5～10^-1s^-1)were analyzed,and the microstructure of the fractured fibers was observed,and the failure modes of the fibers at different strain rates were summarized.The results show that PFAPC can absorb a large amount of energy under the impact of vehicles and aircraft,showing certain ductile failure characteristics and good bending toughness.（3）Based on the four-point bending toughness test and the three-point bending test of precast notched beams,the effects of different POM fiber content on the fracture performance of airport pavement concrete at different strain rates were studied.The load-crack opening displacement（P-CMOD）curve,double K fracture parameters and fracture energy were characterized,and the variation of the parameters with strain rate and fiber content was analyzed.The results show that the strain rate sensitivity of PFAPC fracture characteristic parameters decreases with the increase of POM fiber content,and 1.8%fiber content can effectively improve the cracking load,fracture energy and ductility index of concrete.（4）Four-point flexural fatigue tests of PFAPC with reference concrete（OPC）,0.6%and 1.2%fiber volumes were carried out under four stress levels.The variation law of flexural fatigue deformation with cyclic ratio（n/N）was analyzed,the two-parameter Weibull distribution test of flexural fatigue life was carried out,and the flexural fatigue life equation considering different failure probabilities was established.The results showed that the fatigue deformation of OPC and PFAPC showed three-stage curve characteristics.POM fiber can effectively improve the bending fatigue deformation ability of airport pavement concrete,but it has different degrees of negative influence on the fatigue life.