Ten years ago, Dr Guillermo Riveros was at home when his son came to see him with a – deep – cut in his hand trying to open a tin can. It was Sunday and there was no possibility to go to the doctor for stitches.
To hold him off until the next morning, Riveros pinched the area around the cut to relieve the wound and placed pieces of white duct tape over the entire cut. During the next day’s visit to the doctor, Riveros learned that his method had successfully avoided the need for stitches and sparked an idea that will likely save the US Army Corps of Engineers (USACE) millions. dollars in operating and maintenance costs at its locks and dams.
Using an innovative approach to solving the repetitive problem of fatigue-induced cracks in lock miter gates, Riveros, a civil research engineer in the Information Technology Laboratory at the Engineering Research and Development Center of the The US Army (ERDC), has discovered and developed methods and materials that not only reduce time and cost, but offer a solution to extend the life of gates by decades.
Riveros’ research, which was funded by USACE’s Navigation Research Program, uses fiber-reinforced polymers (FRPs), such as fabric-like materials enriched with carbon fiber or basalt, to repair fatigue-induced cracks. This method, combined with other current repair methods, can extend the life of hydraulic steel structures by about 20 years.
“You have a door that is 70 years old and cracking everywhere, and you stop the cracking; now they can wait 90 years before they have to replace it,” he said.
This method of using FRP to repair fatigue cracks was first tested in July 2015, when Riveros’ team joined others from USACE’s Nashville District as part of the dewatering and scheduled repairs at Old Hickory Lock in Tennessee. While other routine maintenance work was carried out around the lock, the ERDC team placed FRP on more than 20 cracks located at the gate, using application processes first tested in a laboratory environment.
“At Old Hickory, we took a little longer and used a little more material than we do now, but we wanted to get it right the first time; we wanted to make sure it worked,” he said. “The Nashville District team also did a great job. After applying the material, they turned it over, ground it down, and painted it, just like any other repair, giving it an extra layer of protection and the best chance of hit.
And the results?
In 2019, four years after its first application, divers equipped with an acoustic camera were sent to inspect the areas repaired with FRP and found the areas to be in perfect condition. No change. No damage.
“During the inspection, we looked at the durability of the fibers in the harsh environment around our doors,” Riveros said. “River waters aren’t the pure, crystal clear waters you find in the lab. They have a lot of chemicals brought in by runoff from regional farms, sediment, and sometimes doors and repaired areas are hit by logs. .
“We knew how these fibers would perform in perfect conditions, but we just didn’t know how well they would hold up in river conditions,” he said. “After seeing with our own eyes that there was no change, that they were still perfect, we were super happy.”
Traditional methods of repairing fatigue cracks vary depending on the size of the cracks, but generally fall into three areas: drilling a hole at the top of the crack to prevent it from spreading, digging and welding the crack, while the other, and more extensive repair route, digs and welds the crack, then places large metal plates on either side of the door to reinforce the cross section of the door.
Since 95% of all cracks that form on valves are fatigue – or shear – cracks caused by the torque created during the operation of a valve, Riveros said current repair methods do not much to deal with the cyclical forces that create the cracks and don’t. extend the life of gates.
“All of our doors have shear stresses no matter what, due to operations. The solutions most used are ultimately ineffective for the problem that appears most often,” he said, adding that traditional or current repairs do not reset the life of the valve. “Whatever problems led to the crack, they don’t go away; they are still there. With the exception of using the metal plates, you are not reinforcing the cross section of the gate. The crack will start again, often very soon after the crack is repaired.
Unlike heavy metal plates, FRP can be easily handled by those carrying out the repairs and, like the plates, the material reinforces the cross section of the door.
“The problem with the plates is that they are heavy, which puts more weight on the structure than it was not designed to support, which can also cause issues that we are not yet aware of,” Riveros said. “These materials are so light. Their strength to weight ratio is very high and adds relatively no weight to the structure, while giving enormous stiffness to the cross section.
Regarding the difference between using carbon fiber FRP and materials using basalt, Riveros said the choice comes down to what is readily available, noting that the current supply of materials and expertise are available to meet current and future demand. One difference between the two types of material is that carbon fiber FRP requires a layer of fiberglass, due to the risk of corrosion with carbon. Since basalt is a volcanic rock and does not have the same corrosion problem, it does not require a layer of fiberglass in its application.
The installation process isn’t just about applying the hardware, it’s all about education. Riveros said his team provides the know-how, teaches lock operators, technicians and engineers how to apply the material and then is there to offer technical assistance while district crews carry out repairs.
“We go to the District offices. We take a day to teach the lock operators a course, let them learn how to do the repairs, and then they will know how to do it,” he said. “If they need help, they call.”
With seven projects completed and more underway, Riveros said interest in the process continues to grow. “More and more people want information and want to use it,” he said. “More and more Districts are interested.”