**Engineers have created a system that allows ultra-high performance concrete (UHPC) to be sprayed directly onto structures for quick fixes to walls and pipes.**
The team from Florida International University (FIU) believes its process could transform bridge repairs, which are typically complex and costly operations.
More than 40,000 bridges in the US are deemed structurally deficient, with as many as 221,000 in need of some form of repair, according to the American Road and Transportation Builders Association.
UHPC is many times stronger and more water-resistant than regular concrete, but its use in the US has been limited mainly due to high cost.
“UHPC has historically been very expensive to use, mainly because most of those available \[mixes\] on the market have been commercial versions. Even a very thin layer of UHPC can drastically improve the strength of a structure and protect it from water,” said Atorod Azizinamini, a professor of civil engineering at FIU.
“We have developed an affordable type of UHPC, and a system that can spray it. This could become a major tool in repairing or upgrading structurally deficient bridges quickly and efficiently.”
At around $500 per cubic yard, the team’s UHPC mix comes at a fraction of the cost of many comparable commercial versions. Since only a thin layer of it is needed, the overall costs should be reduced.
The system deposits thin layers of concrete onto surfaces through a nozzle, similar to the way spray paint is applied. These layers can be added, one upon another, in coats. Their light weight does not significantly alter the mass of a structure.
The researchers applied their system to a bridge in Virginia last year that had corrosion issues due to the use of de-icing salt. The project was the first time the system had been used in the US and was considered a success, but there are some drawbacks.
“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. 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,” said Morgan Dickinson, a PhD student in Azizinamini’s lab.
In February, Ecuadorian researchers [unveiled a cellular concrete](https://eandt.theiet.org/2025/02/05/cellular-concrete-offers-viable-environmental-alternative-earthquake-prone-areas-study) that is a sustainable and structurally resilient alternative to traditional concrete for earthquake-resistant buildings.