High-Early-Strength, High-Resistivity Concrete for Direct-Current Light Rail

Abstract

Stray current from direct-current light rail systems can corrode underground metal pipes, potentially causing significant damage to utility lines. To address this problem, Seattle Public Utilities has adopted two preventative measures: use of a dielectric rubber boot and a high-resistivity concrete rail bed. In this work, a constructible, high-resistivity concrete mix was developed using supplementary cementitious materials. The concrete is highly workable, can be placed year-round, and has a high early strength to minimize road closures. In addition, the resistivity is 100 times greater than standard concrete. Based on these data, concrete mixes using Type III portland cement with ternary combinations of silica fume, slag, and Class F fly ash were evaluated. Fresh-state properties, including slump, air content, and density, were determined. Samples were subjected to curing conditions similar to the Seattle area. The compressive strength and resistivity of the mixes were monitored over time. In addition, the effect of temperature on the setting behavior was evaluated. The results indicate that a constructible, highly resistive concrete mix design can be achieved.