Bridges constructed with adjacent precast prestressed concrete box beams have been in service for many years and provide an economical solution for short and medium span bridges. A recurring problem is cracking in the longitudinal grouted joints between adjacent beams, resulting in reflective cracks forming in the asphalt wearing surface or concrete deck. The cracking appears to be initiated by stresses caused by temperature gradients, live loads, transverse post-tensioning, or a combination. Once the cracking has occurred, chloride-laden water can penetrate the cracks and cause corrosion of the reinforcement and prestressing strand.

 

NCHRP Synthesis 39: Adjacent Precast Concrete Box Beam Bridges: Connection Details reported a wide variety of practices used by state highway agencies for the connection details between adjacent box beams. These practices include partial depth or full depth grouted keyways, keyways grouted before or after transverse post-tensioning, prepackaged or non-prepackaged grout materials, post-tensioned or non-tensioned transverse ties, a wide range of applied transverse post-tensioning forces, and cast-in-place concrete decks or no decks. A few states reported that their methods had reduced the longitudinal cracking, whereas others had not been successful using similar methods. Research to evaluate those practices at the design and construction phases can lead to connection details that prevent cracking and leakage at the joints and extend the service life of the adjacent box beam bridges.

The objective of this research was to develop guidelines for the design and construction of connection details for adjacent precast concrete box beam bridges to eliminate cracking and leakage in the longitudinal joints between adjacent boxes. The research will produce proposed design and construction specifications with commentary in the format of the AASHTO LRFD Bridge Specifications.

 

STATUS:  A decision was made to discontinue work on the project beyond Phase I. The remaining work will be conducted in 2018 under NCHRP Project 12-95A.