Permeability of Stressed Concrete and Role of Fiber Reinforcement

Abstract

The primary purpose of this paper is to study how externally applied stress influences the water permeability of concrete, while also evaluating the effects of fibers. To achieve this, the authors measure the water permeability of both plain and fiber reinforced concrete, with and without an applied compressive stress. A novel test is used to measure permeability under stress, involving one cylinder tested with stress while the other is tested without stress. Identical flow conditions are applied to both cylinders. Flow equilibrium is achieved early in the test via the use of a special design of the permeability cell that eliminates leakage. The stressed specimens are examined under two levels of applied stress -- 0.3f and subscript u and 0.5f and subscript u, where f and subscript u is the ultimate strength of concrete in compression. Collated cellulose fiber at volume fractions of 0.1, 0.3, and 0.5% is also used. Results show that fiber reinforcement reduces the permeability of concrete while in the unstressed state. However, for stressed concrete, results initially show that with an increase of the applied stress, there is an observed reduction in the permeability of both plain and fiber reinforced concrete. However, this observed reduction occurs only at a certain threshold value of stress. Beyond this stress threshold, plain concrete experiences a rapid increase in permeability. For fiber-reinforced concrete, there is also an observed increase in permeability beyond the threshold value of stress. However, the authors note that permeability still remains below that of the unstressed level.