CAUSE AND CONTROL OF TRANSVERSE CRACKING IN CONCRETE BRIDGE DECKS

Many concrete bridge decks develop transverse cracking and most of these cracks develop at early ages, some right after construction and some after the bridge has been opened to traffic for a period of time. Transverse cracks usually occur when concrete is set and widen with time. These cracks have been observed in most geographical locations and on many superstructure types. It is estimated that more than 100,000 bridges in the United States develop early transverse cracks. These cracks are typically full depth, located 1-3 m (4-12 ft) apart along the length of the span, and usually observed over transverse reinforcement. It has been reported that transverse cracking is the predominant form of deck cracking. These cracks reduce the service life of the structure and increase maintenance costs, which is of paramount importance in highway maintenance activities. Transverse cracks accelerate reinforcement corrosion, especially in regions where deicing chemicals are applied. Corrosion damage has been observed even on epoxy coated reinforcing bars. Freeze-thaw cycles of water in cracks and leakage of water to supporting structures may also reduce service life of structures. Cracks in concrete occur when a restraint mass of concrete tends to change volume. Volume change in concrete depends on the properties of its constituents and their proportions as well as environmental conditions such as ambient temperature changes and humidity. Restraint, which is basically due to composite action of deck and girder, depends on design characteristics of the bridge (i.e., structural design factors). Construction techniques also contribute to volume change and/or to degree of restraint of concrete mass. Factors associated with mix design/material and construction procedures have been the subject of a significant number of research studies over the past several decades. Structural design factors, however, have not been the subject of much research in the past and they were the main thrust of this research study. Using 2-D and 3-D linear and nonlinear finite element models many design factors such as girder stiffness, deck thickness, girder spacing, relative stiffness of deck to girder, amount of reinforcements, etc., were studied. The research study also included a comprehensive review of the existing literature as well as survey of 24 bridges in the state of New Jersey. Results of each research task are presented and discussed in detail. Furthermore, based on analytical results and literature review, the effect of various factors are quantified and specific recommendations for possible consideration in design are made. These are classified under the three major categories: 1) material and mix design; 2) construction practice and ambient condition factors; and 3) structural design. A simple Windows application program to more accurately estimate deck stresses during design is also developed under this study. Future research needs are also identified.