Practical Solution to Diminish Restrained Shrinkage Effects in Bridge Decks

Regents Of The University Of Michigan - Ann Arbor, Ann Arbor MI

Investigators

Abstract

Abstract The project will focus on a practical solution to diminish early-restrained shrinkage cracks in bridge decks. Current practice shows that service life of a reinforced concrete deck slab can be much shorter than the design life of the bridge. Observed deterioration scenarios indicate that degradation process of bridge decks is very often initiated by shrinkage cracks. These early, small cracks develop in time due to freeze and thaw cycles, application of dynamic load and evolution of restrained shrinkage. It is proposed to address the main source of problems, a restrained shrinkage, which is the main reason for the initiation of cracks. It is proposed to create initial stresses in the deck, of opposite sign to those caused by restrained shrinkage and thus to eliminate the problem. The initial stress will be induced by a camber created in the girders at the beginning of construction process, and by adjusting it during the first period of concrete maturing when shrinkage rapidly increases; than, the camber will be gradually released. Prior to pouring of concrete slabs, camber is induced using hydraulic jacks. The proposed research will be initially focused on developing of a mathematical model for calculation of the restrained shrinkage in concrete bridge decks composite with steel girders. The model will be based state-of-the art knowledge on free shrinkage of concrete, the design of a typical highway bridge composite cross section, the behavior of shear connectors to provide the continuity in deformation of composite cross section or possible slip at shear studs. The model will allow for longitudinal strain/stress computations in the early phase of concrete maturing. These values will be calculated according to restrains induced to the free shrinkage development by a connection with girders. After the evaluation of possible restrained shrinkage stresses, a practical solution will be proposed to decrease the early tensile stresses in deck caused by shrinkage. The theoretical analysis will be followed by lab tests to validate the proposed solution. This economical and technically viable method could substantially decrease tensile stresses caused by restrained shrinkage and effectively eliminate early cracks in concrete bridge decks. The proposed method can result in significant savings in bridge maintenance costs. The method to limit early tensile cracks in concrete decks will be easy to use and possible without any changes in typical deck design. It will not require any longer traffic interruptions than during a typical deck construction process.