Ten years ago, Dr. Guillermo Riveros was at home when his son came to him with a cut – a deep one – on his hand from trying to open a can. It was Sunday, and there was not an opportunity to go to the doctor for stitches.
To hold him over until the next morning, Riveros pinched the area around the cut to take stress off the wound and placed pieces of white tape going across the cut. At the next day’s visit to the doctor, Riveros learned his method was successful in avoiding the need for stitches and sparked an idea that will likely save the U.S. Army Corps of Engineers (USACE) millions in operational and maintenance costs at its locks and dams.
Using an innovative approach to address the repetitive problem of cracks brought about by fatigue found in lock miter gates, Riveros, a research civil engineer with the U.S. Army Engineer Research and Development Center’s (ERDC) Information Technology Laboratory, 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 has been funded by USACE’s Navigation Research Program, uses fiber-reinforced polymers (FRP) such as cloth-like materials fortified with carbon fiber or basalt, to repair fatigue-induced cracks. This method, in combination with other current repair methods, can extend the life of hydraulic steel structures by an estimated 20 years.
“You have a gate that is 70 years old and is cracking all over the place, and you stop the cracking; now they can they go 90 years before they have to replace it,” he said.
This method of using FRP to repair fatigue cracks was first put to the test in July 2015, when Riveros’ team joined others from USACE’s Nashville District in the scheduled dewatering and repairs at Old Hickory Lock in Tennessee. While other, routine maintenance was being done 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 more time and used a little bit more material than we do now, but we wanted to do it right the first time; we wanted to make sure it worked,” he said. “The Nashville District team did a great job too. After we applied the material, they went back, grinded it and painted, just like with any other repairs, giving it an additional layer of protection and the best chance of success.”
And the results?
In 2019, four years after it was first applied, divers with an acoustic camera were sent down to inspect the areas repaired with FRP and found the areas in perfect condition. No change. No damage.
“During the inspection, we were looking at the durability of the fibers under the harsh environment around our gates,” Riveros said. “The waters in the rivers are not the pure, crystally waters you find in the lab. They have a lot of chemicals brought in by runoff from regional farms, sediments, and sometimes the gates and repaired areas get hit by logs.
“We knew how these fibers would perform under perfect conditions, but we just didn’t know how well they would endure under river conditions,” he said. “After we saw with our own eyes that there was not any change, that they were still perfect, we were super happy.”
Traditional repair methods for fatigue cracks vary based on the size of the cracks, but generally fall in three areas: drilling a hole at the top of the crack to stop it from spreading, gouging and welding the crack, while the other, and most extensive repair route, is gouging and welding the crack and then placing large metal plates on either side of the gate to strengthen the gate’s cross section.
Given that 95 percent of all cracks that form on the gates are fatigue cracks – or shear -- brought about by the torque created during a gate’s operation, Riveros said current repair methods do little to address the cyclic forces that create the cracks and do not extend the life of the gates.
“All our gates have shear stresses no matter what, because of operations. The solutions most used are ultimately ineffective to the problem that appears most often,” he said, adding the traditional or current repairs do not reset the gate’s fatigue life back to zero. “Whatever issues led to the crack are not going away; they are still there. Except for the use of the metal plates, you are not strengthening the gate’s cross section. The crack will start again, often very shortly after the crack is repaired.”
As opposed to heavy metal plates, FRP can be easily handled by those making the repairs, and, like the plates, the material does strengthen the gate’s cross section.
“The problem with the plates is that they are heavy, putting more weight on the structure that it was not designed to carry, which may also cause issues we are not yet aware of,” Riveros said. “These materials are so lightweight. Their strength-to-weight ratio is very high and adds relatively no weight to the structure at all, while giving tremendous stiffness to the cross section.”
As for the difference in using carbon fiber FRP and material using basalt, Riveros said the choice comes down to what is readily available, noting the current supply of materials and expertise are available to meet current and future demand. One difference between the two types of materials is that carbon fiber FRP does require a layer of glass fiber, due to the corrosion risk with carbon. Since basalt is a volcanic rock, and does not carry the same corrosion issue, it does not require a glass fiber layer in its application.
The installation process is not all about applying the material, it’s about education. Riveros said his team provides the know-how, teaching lock operators, technicians and engineers how to apply the material and is then there to offer technical assistance as the District’s teams make the repairs.
“We go to the District offices. We take one day to teach a class to the lock operators, let them learn how to do the repairs, and then they know how to do it,” he said. “If they need help, they call.”
With seven projects completed and others in the works, Riveros said interest in the process continues to grow. “More and more people are wanting information and wanting to use it,” he said. “More and more Districts are interested.”