Corrosion And Protection Of Steel Fiber Reinforced Concrete

Concrete is widely used as building material. But the concrete will become fragile with the increasing of its strength. Fiber can greatly improved strength, toughness and crack resistance of concrete material. And steel fiber reinforced concrete(SFRC) has more excellent bearing capacity than other synthetic fiber reinforced concrete, which is very fit for bearing high loads. So it develops very quickly in the fields of transportation, architecture and irrigation works, etc. But in worse marine environment, corrosion will occur in SFRC, and reduce the performance of the structure.Some tasks were finished in the paper: The reinforcement mechanism and corrosion mechanism of SFRC was studied, and the corrosion effect on interface and mechanical property was the focus; A new zinc phosphate chemical treatment was put forward, which can improve corrosion-resistance ability of the steel fiber; The corrosion effect on property of ZnPh steel fiber reinforced concrete was studied; Strength calculation mode of SFRC beam was put forward.The following conclusions were obtained:1. Based on the analysis of SFRC structure and the experimental results, it was found that the interface characteristics is the most important to the performance of SFRC, and marine corrosion will affect the interface bond between steel fiber and cement matrix.Interface bond property is the guarantee for SFRC maintaining excellent work performance, but it is also the weakest of steel fiber reinforced concrete composite. It was observed that interfacial structure and interface bond strength had great difference before and after corrosion in marine environment. After corrosion, the interfacial layer obviously became thick, and the micro-hardness was decreased. Corrosion environment reduced the interfacial layer, and the difference between layer and cement matrix became greater.In marine corrosion environment, the average bond strength of interface between steel fiber and cement was reduced about 20%, and the energy of pulling-out fiber from cement was obviously declined about 40% after the steel fiber was corroded.2. By contrast tests, it was found that the change of rupture strength and flexural toughness of SFRC beam before and after corrosion in the simulated seawater was great.Steel fiber improved the lower tensile strength of concrete. When the matrix of SFRC cracked, the steel fibers bridging cracks started to be in action, and the steel fibers continued to undertake the stress transferred from concrete. With the development of cracks, steel fiber’s effect increased gradually. After fiber was pulled out, the curve of load and displacement declined. Fine cracks were first appears in pure bending section for all the specimens which was corroded or not corroded. With the load increasing, wider cracks appeared and went upward, which formed a main fracture. While the bearing capacity of the specimen decreased significantly. The steel fiber was pulled out from concrete and the beam was broken when the crack extended to certain degree.After the corrosion of SFRC, there was surface rust but no concrete stripping of SFRC beams. Bond property between steel fiber and concrete was greatly reduced, and steel fiber didn’t give its full efficiency because of being pulled out early. When the steel fiber volume rate is at 0.5% ~ 1.0%, the rupture strength of SFRC beam reduced about 26% ~ 38% because of corrosion. After corrosion, the toughness of SFRC beam was also reduced, and the bending capability coefficient is down about 29%. The reinforcement efficiency of steel fiber was weakened after corrosion.3. According to the research results on the SFRC interface and macroscopic mechanical properties, it was confirmed that the corrosion resistance of steel fiber itself is the guarantee for the interface bond strength and the component strength. After studying anticorrosive measures of steel in concrete and engineering practicability, the method of zinc phosphate modified steel fiber(ZnPh fiber) was put forward. The result of accelerated corrosion test showed that zinc phosphate modified steel fiber had good corrosion resistance to salt water.4. Because the good interfacial bond is always the guarantee for good working performance of SFRC, the interface experiment and macroscopic mechanical test were done to test interfacial microstructure , bond strength between ZnPh fiber and concrete, strength and toughness of ZnPh fiber reinforced concrete beam. Experimental results showed that the ZnPh fiber not only had good corrosion resistance, but also had good interfacial characteristics with cement matrix, while ZnPh fiber reinforced concrete beam had good mechanical property. After corrosion, the strength and toughness of ZnPh fiber reinforced concrete beam didn’t decreased.5、Combining the strength theories, a new strength calculating mode of SFRC with considering corrosion was put forward from the view of engineering practicality. The mode has simple form, in which the parameters have clear physics meaning. This style can be applied commonly. The result of calculation fit with the test data well.