Effect of fibers on permeability and crack relaxation of cracked concrete

Splitting test and water permeability test were conducted. The effect of steel fiber, macro polypropylene fiber and micro polypropylene fiber were evaluated on crack relaxation ratio, splitting test toughness and permeability coefficients of cracked concrete. The results show that the addition of steel fiber and macro polypropylene fiber restrains crack propagation and improves toughness of concrete. They aid in converting the brittle failure of concrete into ductile failure. The crack relaxation increased with the use of steel fiber and macro polypropylene fiber. The permeability coefficients also decrease. The crack relaxation and impermeability increase with the increasing of steel fiber dosage. The permeability of concrete decreases by 87%, with steel fiber content increasing from 25 kg/m³ to 55 kg/m³. The hybrid use of steel fiber and macro polypropylene fiber shows significant positive hybrid effect. When unloading at crack width of 150 μm, the permeability of concrete reinforced by 25 kg/m³ steel fiber and 4 kg/m³ macro polypropylene fiber decreases by 60%, compared to that reinforced by 35 kg/m³ steel fiber. Micro polypropylene fiber has little effect on crack relaxation and permeability of cracked concrete.