The primary purpose of the I-79/I-70 South Junction Interchange Improvement Project in South Strabane Township, Washington County, Pennsylvania was to eliminate a severely curved ramp connecting I-79 Northbound to I-70 Westbound by replacing it with a large nine-span fly-over bridge and new ramp system. The existing curved ramp had been the site of numerous accidents over the past 50 years. Two other smaller bridge structures were replaced as part of this project as well.
Consistent with the project objective to improve safety, an innovative box culvert re-design alternative to the “as designed” rehabilitation of the two mainline bridges carrying I-70 over the ramp to I-79 south, eliminated the requirement for mainline crossovers on a curve during reconstruction. This innovative alternative solution not only enhanced construction efficiency, it improved traffic flow and safety during construction and simplified future planed mainline reconstruction of I-70.
Innovative design and construction solutions were complemented by use of slag cement at a 50% replacement level in both self-consolidating concrete (SCC) and mass concrete mixtures. Self-consolidating concrete was used for drilled shafts, while mass concrete was defined as any concrete element with a minimum dimension of 6 feet or greater including drilled shafts and pier caps. The 50% slag cement mass concrete mixture aided in meeting the thermal control plan for mass concrete placements and allowed discontinuing temperature monitoring of mass concrete elements earlier than expected. The 50% SCC mixture provided specified flow, penetration, segregation resistance, visual stability index, strength, permeability, and freeze-thaw durability performance requirements.
Project credits: Pennsylvania Department of Transportation, Owner; HDR Engineering, Project Engineer; Mackin Engineering, Engineer (Culvert Redesign); Golden Triangle Construction, Contractor; Golden Triangle Construction, Concrete; Essroc Italcementi Group, Slag Cement.