Repairing Steel Bridges with Cold Spray Additive Manufacturing

Across the United States, thousands of steel bridges are showing the impact of traffic loads and repeated exposure to weather, moisture, and deicing chemicals. As these structures age, corrosion remains one of the most common and costly forms of deterioration confronting bridge owners.

Traditional repairs often involve welding replacement steel, installing bolted cover plates, or, in severe cases, replacing entire structures. More recently, preservation strategies such as ultra-high-performance concrete encasements have demonstrated that extending the service life of existing bridges is often more practical and economical than replacement. However, many repairs remain labor-intensive, disruptive to traffic, and difficult to implement, highlighting the need for innovative repair technologies that are efficient and cost-effective.

Cold spray additive manufacturing (AM) offers a fundamentally different approach by rebuilding lost material directly at the location of deterioration. This additive repair approach could provide bridge owners with a new tool for extending the service life of aging steel infrastructure.

Researchers at the University of Massachusetts (UMass) Amherst, working with collaborators from the Massachusetts Institute of Technology (MIT), the Massachusetts Department of Transportation (MassDOT), and industry partners, have investigated whether cold spray can be adapted to address corrosion damage in steel bridges. That effort recently culminated in what’s believed to be the first field implementation of cold spray AM for the structural repair of a steel bridge.

What Is Cold Spray?

Cold spray is a solid-state AM process in which metallic powder particles are accelerated to supersonic velocities and bond to a surface through severe plastic deformation, forming a dense metallic deposit. Because the material remains in the solid state throughout deposition, cold spray avoids many of the heat-related effects associated with welding, including distortion, residual stresses, and undesirable changes to the underlying steel.

Over the past two decades, cold spray has gained widespread attention in aerospace, defense, and industrial maintenance for restoring damaged surfaces and rebuilding worn components. Its application to civil infrastructure, however, has remained largely unexplored due to the scale, accessibility, and structural demands of bridge systems. Determining whether cold spray could serve not only as a protective coating but also as a structural repair technology became the central focus of the research program.

Building the Scientific Foundation

The successful deployment of cold spray repair on a bridge represents the latest step in a broader bridge infrastructure research program at UMass Amherst. The program focuses on understanding, assessing, preserving, and extending the service life of aging transportation systems. Over the past decade, the UMass bridge program has addressed a range of challenges associated with bridge deterioration, structural performance, condition assessment, and rehabilitation. Working with transportation agencies, particularly the MassDOT, researchers have developed new approaches for bridge inspection, digital documentation, structural evaluation, load rating, and repair design.

A central focus of this effort has been corrosion damage in steel bridges. Particular attention has been given to steel girder ends, which are among the most common sites of deterioration encountered by inspectors. These areas are especially vulnerable because leaking or malfunctioning expansion joints above the bridge supports repeatedly allow water and deicing chemicals to infiltrate the girder ends, accelerating corrosion and section loss over time.

To better understand the structural consequences of this deterioration, the research team established an experimental program using naturally corroded bridge components removed from service and provided through a long-standing collaboration with the MassDOT. This program utilized full-scale steel girders recovered from actual bridges, preserving the complex corrosion patterns and damage mechanisms that developed over decades of field exposure.

The recovered girders were documented using high-resolution 3D scanning technologies, tested under realistic loading conditions, and analyzed using advanced numerical models — Fig. 1. The findings led to the development of new assessment methodologies and load-rating formulations that have since been incorporated into MassDOT practices and the Massachusetts Bridge Manual.

This progress prompted a natural evolution of the program from assessment toward rehabilitation and repair. Within this context, cold spray emerged as a particularly promising technology, offering the potential to restore lost steel directly at the site of deterioration.

Digital Inspection Meets AM

A key aspect of the project was integrating advanced digital inspection technologies into the repair process. Before repairs could be designed, the extent of corrosion damage needed to be accurately quantified.

The UMass team employed high-
resolution 3D scanning technologies with a newly developed, patented point-cloud processing algorithm that transforms scan data into detailed remaining-thickness maps of corroded bridge components. These maps provided a quantitative representation of material loss and enabled engineers to identify critical regions requiring repair.

Building on this work, the research team also developed convolutional neural network models capable of automatically identifying and quantifying corrosion damage directly from 3D scan data. Together, these tools established a framework for digital condition assessment, automated damage characterization, and repair planning.

The Great Barrington Demonstration

The opportunity to validate the technology under real-world conditions emerged through the long-standing partnership with the MassDOT. A bridge in Great Barrington, Mass., was selected as the site for the first field demonstration of cold spray additive repair on a steel bridge — Fig. 2. The structure contained localized corrosion damage representative of deterioration commonly observed in steel bridge systems throughout the northeastern United States.

Before repair, the deteriorated regions were documented using high-resolution 3D scanning technologies and analyzed using the digital assessment tools developed through the research program. A portable cold spray system was then transported directly to the bridge site and operated under field conditions. The research team deposited material onto the corroded region, rebuilding lost section thickness and restoring the damaged steel surface.

The demonstration represented a major milestone for both the research team and the broader cold spray community. More importantly, it moved the technology beyond controlled laboratory environments and into an operational transportation asset. The project required addressing many of the practical challenges encountered during real bridge repairs, including site access, equipment mobility, environmental conditions, and field implementation procedures.

The successful completion of the repair demonstrated that cold spray can function as a practical bridge preservation technology and provided a critical first step toward broader deployment on transportation infrastructure.

Lessons from the Field and Looking ahead

The most important lesson learned during the project was that successful infrastructure deployment requires much more than a functioning manufacturing process. The repair workflow involves inspection, condition assessment, digital documentation, repair design, deposition, quality assurance, and postrepair verification.

Moving an emerging technology from laboratory development to field implementation requires expertise spanning materials science, manufacturing, structural engineering, inspection, and asset management. Another important finding was the value of portability; unlike traditional manufacturing environments, bridge repairs must occur where the structure is located. Portable cold spray systems enable AM to be brought directly to infrastructure assets rather than requiring components to be transported to fabrication facilities.

The Great Barrington repair marks an important milestone, but it is only the beginning. Future efforts will focus on expanding repair applications, improving deposition efficiency, and developing standardized procedures that transportation agencies can adopt. Researchers are also exploring integrating robotics, automation, artificial intelligence, and digital twins into infrastructure repair workflows, as well as applying cold spray to other critical infrastructure systems.

Acknowledgments

This work was made possible through the collaboration of UMass Amherst, MIT, and MassDOT; industry partners; students; and technical staff.

SIMOS GERASIMIDIS (sgerasimidis@umass.edu) is an associate professor with the Department of Civil and Environmental Engineering, UMass Amherst, Amherst, Mass.