New Mexico Route 50 (NM 50) serves Glorieta, N.Mex., to the west and Pecos, N.Mex., to the east. The nearly 100-year-old crossing over Glorieta Creek exhibited severe deterioration and needed to be replaced. However, the closure of the bridge would force residents living east of the bridge to detour 18 miles to get to Santa Fe, N.Mex. In addition, the National Park Service had concerns that construction would disturb local flora and fauna and wanted to maintain the bridge’s historic setting. An all–precast concrete structure helped the New Mexico Department of Transportation (NMDOT) to limit the closure time for residents and minimize the site impact. “Given its ability to be quickly prefabricated off site and stored until needed, precast concrete was the best solution,” recalls Richard C. Castillo, president and CEO of Castillo Prestress. “Speed was of the essence to minimize the economic impact on the community as well as the inconvenience,” he adds.
The bridge is within the Pecos National Historical Park where the Battle of Glorieta Pass occurred during the U.S. Civil War. An adjacent historic well, witness trees, building, and stone wall from the Civil War era had to be protected during construction. Using a low-profile cross section reduced the visual impact of the bridge, and the aesthetic enhancements made in the design helped build community support for the project.
Construction activity was reduced to a narrow right-of-way, and the road closure was limited to seven weeks. “Precast concrete was selected to speed construction, minimize on-site formwork, and minimize the disruption to the historic and environmentally sensitive site,” says Kimberly Coleman, PE, project engineer for NMDOT. “In addition, we needed a durable structure to withstand deicing chemicals and snowplows through the winters.” Given its historic setting and environmental sensitivity, the bridge’s surroundings had to be protected during construction. “The witness trees that date back to the Civil War on each side of the road were preserved,” Coleman says.
To limit the impact of construction, a 60 ft right-of-way was allocated for construction. Given the restricted access, crane swings, piece weight, and crane lifting capacity were all evaluated during design to ensure everything could be placed from one location. All demolition equipment for removal of the old bridge operated on the west side of the creek, opposite from the historic structures. The 1923 bridge was cut apart and lifted out from above to protect the environmentally sensitive stream below and the wetlands downstream. Existing abutments were left in place to preserve the flow characteristics of the creek, to preserve the existing aesthetics of the site, and to protect the new substructure. The project used accelerated bridge construction (ABC) methods such as all precast concrete bridge elements, which included abutment caps, wing walls, slab beams, and approach slabs. With no staging area, all precast concrete components were delivered on a just-in-time schedule. This arrangement was critical because haulers had to drive in reverse for the last mile approaching the site since there was no room to turn around.
“This project honed our skills for future ABC projects” says Castillo. “The bridge was completed on time due to the combined efforts of the project team, and collectively we developed design and constructability details that will enhance our ability to offer fast-track construction projects to the community.”
To achieve the project’s durability goals, tight quality control in the precast concrete manufacturing plant was critical, and a high-strength, low-permeability concrete mixture design was specified. Additional durability measures used to extend the life of the structure included the use of stainless steel reinforcement, which resists corrosion, and the use of ultra-high-performance concrete (UHPC) in the joints to further resist the deterioration of the deck.
The all–precast concrete bridge required precise fabrication to ensure proper reinforcement and embed placement, piece dimensions, and installation tolerances. As a result of this project, NMDOT has revisited some quality assurance and quality control procedures to facilitate smoother assembly in the future. Similarly, Castillo Prestress is exploring the use of slender UHPC structural elements, which can bring further advantages to a project such as minimizing construction-site footprints, greater durability, longer spans, smaller bridge profiles, lower owner costs, and less economic impact on nearby communities.
The unique engineering and construction challenges did not deter the project team. The result is a durable bridge with a projected long service life that was built quickly and cleanly. Precast concrete was key to preserving the historic and environmentally sensitive project site. Because the abutment and superstructure elements were fully precast concrete, no formwork was required within the creek, construction vibration and traffic were minimized, and concrete pours were limited to the UHPC connections.
Harsh winter weather in the area means this bridge will be repeatedly subject to deicing chemicals and snowplows. The low-permeability concrete mixture design coupled with controlled curing produced a quality finish that will limit infiltration of harmful salts and increase the durability and longevity of the bridge. Precast concrete was also key to achieving the tight construction schedule with the limited road closure window. Because the labor-intensive and time-consuming formwork and long concrete cure times required for traditional construction were eliminated, the road was reopened with one day to spare.