Evaluation of the Impermeability of Bridge Deck Overlays using Embedded Wireless Moisture Sensors

Overlays are installed on concrete bridge decks to improve ride quality, and in the case of impermeable overlays, also protect the deck from exposure to moisture and chlorides. Moisture and chlorides can penetrate over time into reinforced concrete, allowing for the initiation and progression of corrosion, which shorten the service life of a structure. To evaluate whether impermeable overlays are truly keeping moisture from penetrating into the concrete deck, researchers have implemented wireless moisture sensors in several bridge decks to monitor the moisture content of the deck below the overlay. In this study, the four overlays that are being monitored are a hot-mix asphalt wearing surface with a thermoplastic additive, an epoxy polymer concrete overlay, a fabric-reinforced liquid membrane with asphalt wearing surface, and a thin-set urethane membrane with an asphalt wearing surface. The moisture sensors have been installed at various locations in each deck including near the bridge joints, overlay construction joints, drainage paths, and under wheel paths. Results indicate that the hot-mix asphalt wearing surface with thermoplastic additive overlay only has moisture penetrating in regions that are near the joints. Measurements also indicate that the polymer concrete overlay has been effective at preventing the penetration of moisture. The latter two overlays, a fabric-reinforced asphalt membrane and a thin-set urethane, were recently installed and some preliminary conclusions may be offered about their effectiveness based upon early results.