Urban infrastructure projects have unique challenges relative to greenfield construction. Working in tight areas, accommodating legacy structures, and designing for high traffic are common constraints in big city contracts. Concrete construction firms must meet sophisticated stakeholder demands with simple design and execution plans to meet their mandates.
The Metropolitan Transportation Authority (MTA) of Greater New York City knows all this. The MTA is North America’s largest transit network. It maintains a large vehicle fleet and an aging infrastructure. Bridge repair, railway maintenance, and rehabilitation projects are priorities for MTA authorities to ensure safety and reliability for the thousands of riders who use the system every day.
PAV Replacement Using Cor-Tuf UHPC
The MTA is in the middle of the PAV Replacement Project, which uses Cor-Tuf Ultra High-Performance Concrete (UHPC) to address design and constructability complexities.
The PAV is essential to mass transit in upper Manhattan, carrying four Metro-North Railroad tracks and linking regional commuters to New York City. On a typical weekday, approximately 220,000 riders take the PAV to and from Grand Central Terminal and the Harlem-125th Street Station.
Built in 1893, the 1.25-mile, 5-track primary structure is a prime example of critical legacy infrastructure issues. It has extensive structural fatigue, which increases annual maintenance costs.
The MTA is repairing or replacing portions of the raised rail system between East 115th Street and East 132nd Street. The transit authority is seeking a more resilient, long-term structural solution to keep the public safe and provide reliable Metro-North train service in the long term.
Bidders were requested to use materials that meet cost, durability, and sustainability goals. In particular, the MTA wanted lower proportions of steel, with longer design life and lower long-term maintenance demands.
The MTA awarded a $382 million Design-Build contract in 2022. Significant portions of the project are already complete, and closeout is expected in 2027. PAV rehabilitation work includes initial short-term reinforcement, removal of old bridge and track sections, new structural improvements (such as piles, columns, and decks), and upgrades to train power and communication systems.
Ultimately, Cor-Tuf UHPC was selected as the plinth material for multiple sections on the project.
Project Design and Execution
The bridge work requires new plinths to serve as horizontal structural members, elevating the railway tracks above the deck. Plinths are typically made of concrete with steel reinforcement, but the Engineer of Record wanted to find a material that could meet multiple design and construction constraints of the project.
The design had to utilize materials that accommodate high-traffic loading, have an extended design life, are sustainable, and have low electrical conductivity, with straightforward constructability in a dense urban setting.
Cor-Tuf UHPC was selected for the plinth sections of the project because it has exceptional compressive, tensile, and flexural strength without the need for rebar. Its durability extends the design life with less weather degradation, resulting in lower maintenance needs and costs.
Cor-Tuf UHPC also eliminated the concern of stray electrical currents from the railway based on testing results for electrical resistivity. As measured using ASTM C1876, electrical resistivity, or conductivity, is a material property that depends upon the pore volume, structure, and composition, in addition to moisture and temperature considerations. Railway activity will be safer and less prone to failures because of the electrical properties of the plinths.
Another key factor for selecting Cor-Tuf UHPC is its contractor-friendly installation approach. Working on an elevated railway in uptown Manhattan requires precision for mobilization and clean pours. Contractors don’t have the luxury of large mixing yards or extended street closures. They need to get in and get the job done with familiar means and methods.
When it was time to install Cor-Tuf UHPC on the PAV, a local Ready-Mix partner mixed it, delivered it to the job site via a Ready-Mix truck, and pumped it on site. Conventional concrete strategies were used, including local aggregate for the mix and standard skid loaders to distribute the material. The crew efficiently poured multiple decks without needing special equipment or unique installation techniques.
Cor-Tuf UHPC for Infrastructure Renewal
Public infrastructure will continue to need replacements and repairs. The PAV project demonstrates the benefits of UHPC for engineering design, project execution, and long-term maintenance outcomes. Contractors and project authorities are taking note of material that makes sense.
Your sand, your cement, our Cor-Tuf UHPC.
