Fiber Effects On Permeability Of Concrete With Cracks Under Loading

In recent years, with the develop of concrete structure, the concrete durability is even m-ore important than strength as the main criterion for judging the quality of the concrete, which has already been accepted as a consensus in construction industry. The permeability of concr-ete plays a critical role in controlling the properties and serviceability of concrete. How to re-duce the permeability of cracked concrete is the key to solve the durability problem while co-ncrete structures works with cracks in service, which is valuable in engineering. Mixing fibers in concrete is an effective manner to improve the mechanical properties over the plain concre-te. A fair amount of research has been performed to identify, investigate, and understand the mechanical traits of fiber-reinforced concrete like strength and roughness.etc. However relat-ively little research has been concentrated on the transport properties of concrete with cracks.The thesis which studies the fiber influence on the mechanical properties and permeabi-lity of concrete with cracks is consist of two parts:statics splitting test and hydro-mechanical permeability test.The standard splitting test has been enhanced so the one single controlled crack (up to 300μm) is generated in the species with different width levels. The analysis of the result conduct as the basis of the theory analysis of the permeability test. During the permeab-ility test which uses the independently improved device, the permeability coefficient is tested to compare different types, content and hybrid style of fibers’influence on the permeability of the cracked concrete.In the conclusion, our results indicate that:(1) In the splitting test, Steel fiber and macro polypropylene fiber contributes to incre-ase the ultimate splitting capacity and ductility. However the steel fiber is more effective; The micro polypropylene has no influence on mechanical properties during the test.(2) In the splitting test, Steel fibers and macro polypropylene fiber promote the crack width recovery which means that traditional permeability test after the splitting test is not sui-table for fibers.(3) The crack tortuosity is improved with the steel fiber content; The macro and micro polypropylene seems to have little effect on the crack tortuosity.(4) During the permeability test we found that the permeability coefficient of the crac-ked concrete the crack width, is decreased with the steel fiber content and the macro polypro-pylene fibers contributes to decrease the permeability coefficient of the concrete with cracks. (5) The fibers between the two crack fracture faces, which could transfer stress because of the bridging effect, prolong the concrete quit working path,considering as the crack tortuosity. It has been proved that the permeability of the concrete with cracks is proportional to the square of the tortuosity. The steel fiber decreased the permeability of the cracked concrete by improved the crack tortuosity.(6) The steel fiber and macro polypropylene could limit the crack development which has a stitch effect on the edge of the crack to reduce the effective area of the crack. As the eff-crack area reduced, the permeability of the cracked concrete decreased.