Material Selection for the Joint between Adjacent Box Beams

Bridges constructed with adjacent precast concrete box beams have been in service for many years. A recurring problem with this type of bridge is cracking in the longitudinal joints between adjacent beams. Many research results have indicated that efficient joint material should have small or zero shrinkage at an early age and achieve sufficient bond strength at the interface between the joint and the box beam. As the first part of a comprehensive study, two phases of material properties tests were conducted to select the best material for the joint between adjacent box beams to resist cracking. During Phase I work, four potential joint materials were tested and evaluated based on shrinkage, flexural tensile strength, and normal bond strength. During Phase II work, time-dependent material testing was conducted on the materials selected from Phase I to characterize the nonlinear changes in bond, compressive, and tensile strength with time. In addition, three-dimensional (3D) finite-element models (FEMs) were developed to calculate the early-age joint stress distribution and evaluate the structural performance of a Type IV joint grouted with epoxy grout and a Type V joint filled with shrinkage-compensated concrete. A finite-element modeling approach that is capable of simulating early-age joint behavior was illustrated, and models were developed for beam-joint-beam structures that were 1.2 m (4 ft) long. The analytical results indicated that a Type V joint filled with shrinkage-compensated concrete is expected to better resist joint cracking than a Type IV joint filled with epoxy. Although the FEM results indicated that a Type V joint filled with shrinkage-compensated concrete still induces tensile stress near the exterior of the interface, placing reinforcement near the edge will provide sufficient capacity to resist debonding at the interface during the early-age period when initial cracking has been found to occur.