Research On Basic Properties And Application Of Layered Steel Fiber Reinforced Concrete

How to ensure strength and durability of pavement concrete synchronously is a hotspot topic. At present, it is one of the important research directions to choose material rationally. For example, steel fiber of high strength and high elastic modulus is mixed with synthetic fiber of low elastic modulus or flexible concrete, which can develop positive mixed effect on concrete properties and improve mechanics and enduring capability of pavement material.Based on the structure form of layered steel fiber concrete, together with plentiful tests and theoretical analysis, the paper studies the mechanical properties and pavement design methods of Layered Steel Fiber Reinforced Concrete (LSFRC), Layered Hybrid Fiber Reinforced Concrete (LHFRC) and Layered Steel Fiber Flexible Concrete (LSFFC).Main research work and important results are as follows:1. The paper discusses the influence of material property on bending-tensile strength of LSFRC, obtains the influence rule on LSFRC bending-tensile strength by mechanical and geometric parameters, and adhesion status between steel fiber and base material, holds that volume ratio of steel fiber is the best factor for improveing bending-tensile strength (up to 28.42% from 1.0% to 2.0%).2. Based on a series of experiments, the paper studies the performance of LSFRC,LHFRC and LSFFC under compression, tension and bending conditions. It holds that layered steel fiber concrete can improve the compressive strength and tensile strength by about 5%, the ultimate compressive stress by about 30% and the bending-tensile strength by about 40%, compared with that of plain concrete. The bending toughness index I₁₀ of LSFRC, LHFRC and LSFFC is 5.47, 7.04 and 10.32 times than that of plain concrete respectively.3. The reinforcing and collapse mechanisms of LSFRC, LHFRC are analyzed through crack developing procedure, collapse characteristics and cross section scan electricity photos(SEM) of bending test members. There are obvious plastic collapse characteristics. Four stages can be observed from loading to collapse, which can be described as microcosmic crack occurrence, crack development, crack transfixion and member collapse.4. Based on the systematic experiments and theoretical analyses, probability distribution of LSFRC and LHFRC is studied. It obtains fatigue life and double logarithmic equation under different failure probabilities. Damage regulations are researched. The effect on fatigue deformation curve of layered steel fiber concrete structure by steel fiber is discussed.5. Based on the systematic experiments and theoretical analyses, the main durability indexes of layered steel fiber concrete structure are studied, such as porosity rate, dry shrinkage, permeability resistance, freeze-thaw resistance, impact resistance, and wearing capacity. The mechanisms of durability enhancement are analyzed. The porosity ratio of LHFRC is 43.9% lower than that of plain concrete (C). Moreover, there are more pores with small diameter which distribute more evenly. After 180 days, the dry shrinkage of LHFRC is 26.9% lower than that of C, and the seepage height of LHFRC is 26.9% lower than that of C. After 75 freeze-thaw cycles, the compressive strength of LHFRC only reduces 1.9% and the relative dynamic elastic modulus of LHFRC decreases 19.1%. No mass is lost. The impact resistance of LSFRC is 127.85% higher than that of C. The wearing quantity in unit area of LSFFC is 26.31% higher than that of C.6. The paper sets up the bending-tensile constitutive model of LSFRC beam and presents the simulation results and collapse characteristics of LSFRC beam. The load-deformation curve and performance of LSFRC is compared with that of C, which shows that layered steel fiber can obviously increase long-term ductility. Mechanical properties of layered concrete with different parameters are discussed.7. Finite element analysis models of LSFRCP, LHFRCP and LSFFCP are set up. Under the traffic load and temperature variation, the bearing load capacity of pavement slab is studied, with consideration of different slab length, slab thickness, volume ratio of steel fiber and elastic module of basic concrete. Internal stress reduces with the increase of slab thickness. The stress of LHFRCP and LSFFCP can reduce 6% maximum with 2cm more in thickness. However, temperature stress increases at first and then reduces with the increase of slab thickness.8. The paper presents design methods of pavement slab of LSFRC, LHFRC and LSFFC and works out reference table of slab thickness with different length under different traffic grade. The slab thickness of layered concrete pavement is smaller than that of C. Furthermore, LSFFCP is the most economical solution under the same conditions.