Chloride Diffusion in Reinforced Concrete Beam Under Sustained loading

Abstract

The purpose of this paper is to determine the effect of mechanical loading on the transport properties of concrete. The test specimen (B1CL) used for chloride measurement, was a three-meter long reinforced beam kept in a loading state, in a confined salt fog (35 g/l of NaCl) for fourteen years. Because of corrosion of reinforcement, the characterization of mechanical loading was made on another old beam (B1T) cast at the same time but stored in a non-aggressive environment. The measurement of tensile concrete strains using strain gauges showed two parts in the bottom of the beam: the first one is characterized by an elastic behavior and the second one by non-elastic one which is still controlled by the steel reinforcement. Total chloride profiles in relation to the depth were measured in different locations of the tensile zone of reinforced beam B1CL. Until 15 mm depth, the chloride content is constant and corresponds to the maximum chloride content available, taking into account both concrete porosity (where free chloride content corresponds to 35 g/l of NaCl) and concrete binding capacity. Beyond 15 mm depth, total chloride profiles appear to be pure diffusion profiles allowing to calculate the effective diffusion coefficient by using a saturated model of chloride motion taking into account the non-linear binding capacity of concrete. The evolution of effective diffusion coefficient in the beam field (B1CL) is strongly correlated with the field of non-elastic strains in concrete (B1T) and can increase up to 40% in the part of the beam where the non-elastic damage is the more important.