Effect Of Fibers On The Toughness And Permeability Of Concrete

Concrete, as the most significant engineering constuction material, is widely used in civil, industrial and defense engineering buildings. Different constructions and structure of buildings have different requirements in concrete. Most scholars and engineering designers have already not only considered the compressive strength of concrete as the sole criterion to judge the quality of concrete, but also have paid great deal of attention on other mechanical and physical properties of concrete. Fiber-reinforced concrete as an efficient way to modifying concrete matrix, can limit the development and expansion of cracks, improve the ability of deformation of concrete and transform the form of ordinary concrete brittle failure pattern to ductile failure pattern.Fiber-reinforced shotcrete is a form of mixture by adding fibers to ordinary shotcrete for improving the crack resistance, ductility, toughness, durability, etc. In underground space, New Austrian Tunneling Method(NATM) often use hanging steel mesh to ameliorate brittle failure pattern of shotcrete. However, a variety of problems exist in this method, like hollow and loose areas behind steel mesh, low bonding strength between shotcrete and surrounding rock, and other defects. Fiber-reinforced shotcrete alternative to traditional hanging steel mesh shotcrete can solve the problems above, by transforming the brittle failure pattern and better meet the requirements of NATM. So, fiber-reinforced shotcrete is an ideal supporting material in underground space.The ductility of concrete, measuring the energy absorption in deformation process of the concrete structure loading to the failure, is a significant indicator to measure the mechanical properties of fiber-reinforced concrete. This article, referring to the European EFNARC plate ductility test and the German DBV beam ductility test, compares and analyses the ductility indexes of different steel fiber content of fiber-reinforced concrete and rebar reinforced concrete at the early-age(8-10h) and the hardened age. The indexes include the load-displacement curves, energy absorption values, the flexural strength, the flexural ductility, the equivalent flexural strength, the residual strength indicators, etc.Permeability is an important indicator to evaluate the durability of concrete. Generally, the uncracking concrete have a high permeable resistant. But, in engineering construction the concrete is easy to form cracks under the actions of internal and external stress. As soon as the concrete cracks, the cracks become the main channel for harmful water seeping into the concrete to cause the corrosion of rebar and fibers, resulting in structure deterioration. Therefore, study of permeability of cracked concrete is the key to research the durability of concrete. In this article, splitting tensile test is used to introduce the artificial controlled cracks in round cake specimens, self developed permeability instrument is used to measure the permeability coefficient of round cake specimens with different crack widths. Furthermore, this article compares and analyzes the effects of different crack widths and different types and contents of fiber on permeability coefficient.