High-Early Strength Concrete with Polypropylene Fibers as Cost-Effective Alternative for Field-Cast Connections of Precast Elements in Accelerated Bridge Construction

Accelerated bridge construction (ABC) technologies are being adopted by state departments of transportation. ABC requires that bridge precast concrete components be effectively connected to one another in the field. Currently there is a trend of using ultra-high performance concrete (UHPC) to connect precast bridge deck panels or girders in 15-cm (6-in.)-wide closure pours between the precast elements. As an alternative, the Idaho Transportation Department (ITD) is proposing to place high-early strength (HES) concrete with polypropylene fibers in 25-cm (10-in.) closure pours, with standard reinforcing bars at the top and headed bars at the bottom. The advantages of this alternative material are the reduction in costs and construction time. An experimental research project was carried out to determine the effectiveness of the alternative material and connection detail. The experimental work consisted of standard test specimens and specimens with headed bars. Among the six closure pour concrete mixes considered, the mix containing HES concrete, $0.89\mathrm{kg}/{\mathrm{m}}^3$ ($1.5\mathrm{lb}/{\mathrm{yd}}^3$) of fiber, and shrinkage-reducing admixture performed the best. It had the largest compressive strength, the largest tensile strength, the lowest shrinkage, and the largest bond strength. Headed bar tensile strength tests with the optimum mix resulted in bar stress of 67% of the steel specified yield strength. Flexural testing of beams composed of two precast segments with the optimum mix in the 25-cm (10-in.) closure resulted in ultimate moment capacity of about $55\mathrm{kN}·\mathrm{m}/\mathrm{m}$ ($147\mathrm{kip}\text{-}\mathrm{in.}/\mathrm{ft}$).