Characterization of Concrete and Corrosion of Steel Fibers Embedded in Dry-Cast Concrete Pipe

Abstract Despite the low water to cementitious ratio used when preparing dry-cast reinforced concrete pipes, the concrete porosity of dry-cast reinforced concrete pipes has been found to range between 9 to 11 percent. These porosity values are higher than the porosity that is usually found on wet-cast concrete prepared with comparable low water to cementitious ratio. The high porosity could affect how chlorides are transported into dry-cast concrete. Recently, steel fibers have been suggested to reinforce dry-cast concrete pipes, replacing the traditional steel wire cage reinforcement. The corrosion resistance of steel fibers in this type of concrete is not known, nor the concrete durability to chlorides (marine) exposure. Steel fiber reinforced concrete pipes were prepared at a producers’ plant and cut segments were provided for this study. The goals of this investigation are: 1) characterize the transport properties of this concrete and 2) to assess a) whether the steel fibers are prone to corrosion, b) what is the chloride concentration that triggers corrosion, and c) to what depth into the concrete is corrosion observed. Rapid migration tests, modified rapid migration tests (e.g., longer exposure), and resistivity, porosity and sorptivity tests were used to characterize steel fiber reinforced concrete. Wet-cast concrete specimens with instrumented fibers were used to characterize the corrosion potential as the chloride builds-up around the fibers (via accelerated chloride transport). Selected specimens were terminated for forensic examination.