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Researchers at Florida International University have developed a spray-on concrete system that they believe could revolutionize how U.S. bridges are repaired.
According to an article in FIU News, engineers at the school have created a system that sprays Ultra-High Performance Concrete (UHPC) onto structures. This type of concrete has the potential to patch walls, fix pipes and restore drainage culverts – and it can make these structures stronger than they were originally.
According to information on the U.S. Department of Transportation website, UHPC is increasingly being used to build and repair America’s transportation infrastructure. Most of the time, these applications of UHPC involve pouring it into place. This UHPC would either be self-consolidating – filling its forms completely under its own weight – or thixotropic – a UHPC that is vibrated and struck off with a vibrating screed under initial placement.
Existing UHPC applications – such as girder end repairs and the restoration or protection of walls and columns – could be enhanced by the ability to spray UHPC directly into place. Emerging or future uses, including bridge deck soffit repairs and culvert rehabilitation or retrofitting, may also benefit from sprayable UHPC.
In these cases, spraying UHPC is often more economical than traditional pouring methods, primarily because it eliminates the need for formwork. Spray application also offers greater flexibility, allowing UHPC to be applied from any angle. This overcomes the limitations of gravity-based pouring, which can be hindered by structural obstructions like bridge decks.
“UHPC has historically been very expensive to use, mainly because most of those available [mixes] on the market have been commercial versions,” said Atorod Azizinamini, a professor of civil engineering and director of a U.S. Department of Transportation-funded research center at FIU. “Even a very thin layer of UHPC can drastically improve the strength of a structure and protect it from water.”
“We have developed an affordable type of UHPC, and a system that can spray it,” Azizinamini continued. “This could become a major tool in repairing or upgrading structurally deficient bridges quickly and efficiently.”
FIU’s UHPC mix comes in at around $500 per cubic yard, which is considerably cheaper than many comparable commercial versions of the product. The school’s application system deposits thin layers of concrete onto surfaces through a nozzle, like how spray paint is applied. These layers can be added, one upon another, in coats. Their light weight doesn’t significantly alter the mass of a structure.
The FIU team used their system and UHPC mix on a bridge in Virginia last year.
“The reason that we invited the FIU team here to Virginia is that we had a bridge abutment wall that had corrosion issues due to the deicing salt that is used here,” said Sam Fallaha, an engineer with the Virginia Department of Transportation. “We liked it because it is easy to apply a thin layer to vertical surface creating a durable solution for problems like these that occur in cold climates.”
The Virginia job was the first-ever application of its kind in the U.S. The Risk and Resilience Tech Hub is investing roughly $1 million into the FIU researchers’ system to commercialize the technology and help the university train more engineers and builders to use it.
"Anyone who has used a glue gun for an arts and crafts project knows how difficult it can be to keep the nozzle from getting clogged,” said Morgan Dickinson, a Ph.D. student in Azizinamini’s lab. “The same goes with our UHPC system. If you don’t know how to clean it, the concrete hardens, and you might have to throw parts away. Fortunately, we are seeing widespread interest in people who want to learn about our system and use it properly.”
Kia Hajifathalian, Vice President and Market General Manager at Baker Construction, told FIU News that he sees the FIU system as a practical way of bringing the benefits of UHPC to more buildings and bridges around the nation.
“This is not just research in a lab that will only have a couple of specific uses,” Hajifathalian said. “I think that FIU has figured out how to utilize UHPC in a way that can be used to repair buildings and bridges at scale.”
"The biggest nightmare of a concrete contractor is pouring concrete, testing it later and finding out that it is not as strong as you thought it would be because something unexpected happened,” he added. “Having that concrete in a pre-bagged system like FIU is doing, where you have quality control, is so important.”
The State of America’s Bridges
There are more than 623,000 bridges across the United States, according to the American Society of Civil Engineers (ASCE) 2025 Report Card for America’s Infrastructure.
The ASCE gave America’s bridges a C in that report card, citing the fact that 49.1% of the country’s bridges are in “fair” condition, 44.1% are in “good” condition, and 6.8% are in “poor” condition.
“Unfortunately, the nation continues to see the number of fair bridges surpassing those in good condition,” the ASCE wrote. “As bridges in fair condition continue to age – presenting the possibility of being further downgraded – they also exemplify an opportunity because they can be preserved at a lower cost than bridges in poor condition.”
Bridges received a significant amount of funding through the Infrastructure Investment and Jobs Act (IIJA), which included $27.5 billion for the Bridge Formula Program and $12.5 billion for the Bridge Investment Program.
“Despite this infusion of federal funding, bridge-related system rehabilitation needs are estimated at $191 billion,” the ASCE wrote. “Therefore, strategic asset management planning and routine maintenance are essential to keeping bridge conditions from further declining and avoiding costly repair or rehabilitation work. While the effects of extreme weather events pose threats to bridges, innovative techniques are improving their security and resilience.”
As we wait to see if innovations like FIU’s spray-on concrete system, or Allium’s stainless-steel-clad rebar truly revolutionize bridge construction and maintenance, it’s important that you know exactly where all reinforcements are within bridge decks and other concrete slabs before you attempt to cut or core that concrete.
Striking rebar, post tension cables or other support systems within concrete can lead to catastrophic structural failure that endangers you and your workers, and anyone else in the vicinity of your job site.
GPRS provides precision concrete scanning and imaging services designed to keep your concrete cutting and coring projects on time, on budget, and safe. Utilizing state-of-the-art ground penetrating radar (GPR) scanners and other, complementary technologies, we visualize where you can and can’t safely penetrate the slab, providing you with accurate, actionable information that helps you plan, build, and manage better.
Our SIM-certified Project Managers have achieved and maintain a 99.8%+ rate of accuracy when scanning concrete slabs for buried rebar, post tension cable, electrical conduit, and any other types of embedded obstructions that could compromise the safety and success of your project. We’re so confident in their abilities that we introduced the Green Box Guarantee, which states that when we place a Green Box within a concrete layout prior to you cutting or coring that slab, we guarantee that the area within will be free of any obstructions.
If we’re wrong, we agree to pay the cost of the damage.
From bridges to skyscrapers, GPRS Intelligently Visualizes The Built World® to keep your projects on time, on budget, and safe.
What can we help you visualize?
Frequently Asked Questions
How is GPR used to identify tendons vs. rebar in a post-tensioned slab?
In post-tensioned structures, we typically find one mat of support rebar near the base of the slab. This mat is generally consistently spaced and remains at a constant elevation.
Post-tension cables are generally found above this support mat and “draped” throughout the rest of the structure. The elevation of the cable is usually high near the beams and column lines and drapes lower through the span between beams and column lines. Knowledge of these structural differences allows us to accurately differentiate between components. Our Project Managers will leave you feeling confident in our findings and in your ability to drill or cut without issue.
What types of concrete scanning does GPRS provide?
GPRS provides two specific but different scanning services: elevated concrete slab scanning and concrete slab-on-grade locating. Elevated concrete slab scanning involves detecting embedded electrical conduits, rebar, post-tension cables, and more before core drilling a hole through the slab. Performing a concrete slab-on-grade locating service typically involves scanning a trench line for conduits before conducting saw cutting and trenching to install a sanitary pipe, water line, or something similar.
