Comparison of Moisture Content and Electrical Conductivity of Lightweight and Normal-Weight Concrete Bridge Decks: Instrumentation and Monitoring

Abstract

The objective of this research was to measure both the in-situ moisture content and diffusivity (in the form of electrical conductivity) of both lightweight and normal-weight concrete bridge decks over time. Two lightweight concrete bridge decks and two normal-weight concrete bridge decks constructed as part of the Interstate 15 Corridor Reconstruction project in northern Utah were selected for instrumentation and monitoring. Sensors that could measure volumetric moisture content, electrical conductivity, and temperature were installed in each bridge deck prior to placement of the concrete, and air content, slump, and wet unit weight measurements were obtained during concrete placement. Sensor readings were taken frequently throughout the next approximately 2 years, and laboratory compressive strength and rapid chloride permeability tests were also performed. The measurements of 28-day compressive strength indicate that both the lightweight and normal-weight concrete mixtures exceeded the specified design strength and were also similar to each other. In rapid chloride permeability testing, both types of concrete changed from “high” chloride permeability at 28 days to “very low” chloride permeability at 6 months and 1 year, but the amount of current passed by the lightweight concrete was 25, 45, and 79 percent higher than that passed by the normal-weight concrete at 28 days, 6 months, and 1 year, respectively. The sensor readings showed that the lightweight concrete bridge decks were 33, 18, 33, and 19 percent wetter, on average, than the normal-weight concrete bridge decks at 28 days, 6 months, 1 year, and 2 years, respectively. The sensor readings also showed that the lightweight concrete bridge decks were 4 percent less conductive than the normal-weight concrete bridge decks at 28 days but became 107, 177, and 267 percent more conductive, on average, than the normal-weight concrete bridge decks at 6 months, 1 year, and 2 years, respectively.