Laboratory Evaluation of Corrosion Resistance of Steel Dowels in Concrete Pavement

An extensive investigation was carried out on the corrosion performance of several types of steel dowels embedded in concrete beams, to develop recommendations for their use in different environmental conditions. Specimens were exposed to concentrated chloride solutions to accelerate corrosion. The types of dowel bars evaluated in the study were: bare carbon steel, stainless steel clad, grout-filled hollow stainless steel, microcomposite steel, carbon steel coated with flexible epoxy (green color code), and carbon steel coated with non-flexible epoxies (two types: purple and gray color codes). Half-cell potential measurements (indicative of the probability of corrosion activity),and Linear Polarization Resistance, LPR (for determining corrosion rate) were used. Every epoxy-coated bar examined had one or more defects on the coating, especially along the edges at the ends. The study was conducted in three phases. Phase I: Dowels were cast in concrete beams with joints and then subjected to a corrosive environment. Half-cell potential was monitored for six months. Phase II: similar to phase I, but using a more permeable concrete and accelerated corrosion for a period of 18 months. Half-cell potential tests, LPR curves, visual inspections, chloride content analyses, and scanning electron microscopic investigations were carried out to evaluate the corrosion performance. Phase III: consisted in testing concrete slabs with transverse joints from a DBR project in Washington State. The slabs and dowels were subjected to half-cell potential tests, LPR curves, chloride content tests, and visual inspections. Measurement of chloride contents of these and other concrete cores we used for comparison of the laboratory and field conditions. The following main recommendations are drawn. 1. Uncoated carbon steel dowels should not be used. 2. Epoxy dowels present some risk of corrosion. It is recommended that: a) Quality control checks to control holidays should be implemented, b) Bar ends should be coated with epoxy, and care must be taken during shipping, storage, and installation. 3.It is recommended that the use of stainless steel clad, hollow stainless steel, or microcomposite steel dowels should be considered for locations with high risk of high chloride exposure (such as on mountain passes and marine environments).