Research On Basic Properties Of Steel Fiber Composite Bars Reinforced Marine Sand Concrete Beams

As the coastal development and reef construction in our country, the shortage of river sand has appeared in some region, so marine sand has been increasingly used in constructions as fine aggregate instead of river sand.However chlorine salt in marine sand will cause serious corrosion of reinforcement in concrete, reducing the durability of structure. Steel fiber composite bars(SFCB) can provide a new method for the application of marine sand concrete due to its superior corrosion resistance and good rigidity. SFCB reinforced beams are studied in this paper.Good bond behavior between SFCB and marine sand concrete is the fundmental issue of reinforced concrete, therefore bond behavior between SFCB and marine sand concrete was firstly studied in this paper.66 pull-out specimens were made and tested in the experiment in order to obtain short-term and long-term bond behavior between each bar and each kind of concrete. 5%NaCl solution was made to simulate sea water and two different corrosion means which were dry-wet cycling with sea water at 20℃ and sea water soaking at 40℃ were used in the test. Bonding slip curve of each specimen, bonding failure mechanism and the ultimate bond strength of specimens were investigated in this paper. Flexual behavior of SFCB reinforced marine sand concrete beams was experimentally studied nextly.8 marine sand concrete were made to study the short-term flexural properties of SFCB beams and the long-term flexural properties of SFCB beams under the action of dry-wet cycling with sald solution and these SFCB beams were compared with steel reinforced marine sand concrete beams under the same condition. The long-term degradation rule of SFCB reinforced marine sand concrete beams was analysied by the aspects of bearing capacity, secondary stiffness, ductility and crack development.From the first test, excellent bond behavior was found between SFCB and marine sand concrete. The long-term bond behavior between SFCB and marine sand concrete was good and better than that between SFCB and river sand concrete under dry-wet cycling. The bond behavior between SFCB and marine sand concrete decreased rapidly under sea water soaking with high temperature, over high temperature will seriously reduce the durability of SFCB. The bond strength between steel and river sand concrete increased with corrosion age, however the bond strength between steel and marine sand concrete decreased due to serious corrosion of steel.From the second test, the mechanic properties of marine sand concrete beams were similar to river sand concrete beam, SFCB reinforced marine sand concrete beams had excellent short-term mechanic properties and obvious and stable secondary stiffness. Severe rusting occurred in steel reinforeced marine sand concrete beams after long-term conditioning. The stiffness after yielding of these beams decreased more rapidly with corrosion age, the ductility decreased as well, but the ultimate strength were not significantly affected. The surface of SFCB in SFCB beams have no obvious corrosion marks, but their seconday stiffness after yielding decreased, their ultimate strength decreased slightly as well. After long-term corrosion, the crack of steel reinforced beams became more sparse, the crack width increased largely. On the other hand, there were more branches in lower part of main crack of SFCB beams and crack spacing decreased, and the growing rate of the crack width was smaller.Life prediction of bond behavior between SFCB and marine sand concrete was done in this paper by time shift factor (TSF) method according to the test data. The basic anchorage length of SFCB in marine sand concrete was raised.The calculating formulas of bearing capacity and crack width of SFCB reinforced marine sand concrete were raised in this paper. The calculated results according to the formula were in good agreement with experimental values.