Overlay for Concrete Segmental Box-Girder Bridges

Abstract

Concrete overlay cracking and delamination were noticed on a concrete segmental box-girder bridge. Analytical investigation and field and laboratory examinations were conducted to identify the major factors causing the defects. The time-dependent stress distribution and its change in the overlay and along the interface between the overlay and the bridge deck were modeled through the finite-element method with the consideration of concrete age, shrinkage, and critical temperature gradients. Appropriate interpretation of the modeling results were verified through field and laboratory examinations. The primary factors causing the defects were identified and discussed. It was concluded that conventional concrete is applicable for a thin bonded overlay construction on concrete segmental box-girder bridges. Removal and replacement were recommended to repair the delaminations through a field test program. Low shrink conventional concrete with a maximum aggregate size of 25.4 mm (1.0 in.) was used without the application of bonding grout. The base deck surface was roughened (by hydroblasting) to a macrotexture of 2.0–2.8 mm (0.08–0.11 in.) on average. The substrata was not presoaked and was surface dry before placing of plastic concrete. Curing consisted of moist curing for 7 days, followed by chemical (curing compound) curing for 21 days. The successful experience gained can be applied to other similar projects.