The U.S. Army Corps of Engineers (USACE) maintains 12,000 miles of inland waterways in the United States which contain 200+ inland navigation structures such as locks and dams. Approximately 565 million tons of cargo is moved along these waterways and through these structures annually. The majority of these structures were constructed in the 1930-1950 time period with a 50 year design life. Due to national budgetary constraints, these aging structures are not being replaced, but simply maintained. However, the rate of degradation due to corrosion and wear is exceeding the rate at which they can be maintained. The risk of a prolonged failure of components to these structures, which could have a devastating effect to commerce, is becoming more likely every year. For this reason, USACE has placed a high priority on developing novel materials to repair or replace aging infrastructure in order to extend the structures' working lifetime. Emphasis has been placed on cost reductions for both first costs and long term maintenance costs, reductions in labor to implement and maintain, as well as longer durability.
In 2014, USACE researchers and engineers, researchers from West Virginia University (WVU), and a private industry manufacturer, Composites Advantage, reverse engineered a timber wicket gate in order to develop a glass fiber reinforced polymer (FRP) composite wicket gate. The timber wicket gates, which are located at Peoria Lock and Dam on the Illinois Waterway and measuring 4 ft. by 16.5 ft., were manufactured in-house out of White Oak. The timber gates are prone to rot and have a working lifetime of only 10-15 years. By reverse engineering the timber wicket gates, the team was able to manufacture a composite gate using a vacuum assisted resin transfer molding (VARTM) technique. The composite gate uses all of the same steel hardware as well as maintains the same dimensions, weight, balance, and buoyancy as the timber gates. The new composite gates were two thirds the cost to manufacture as the timber gates and are expected to have at least a 50 year working life. The composite gates were installed in August, 2015 and have shown no signs of damage or deterioration upon inspection.
Around this same time period, USACE and WVU researchers developed a glass FRP composite contact block to replace carbon steel miter blocks on miter gates. The purpose of the miter blocks is to provide a tight seal as well as transfer the hydraulic load placed on the miter gates. These blocks experience an abrasive force upon opening and closing that most coatings cannot withstand. Therefore, a microscopic layer of corrosion forms just at the surface of the miter block and is abraded away during operation. This section loss over time causes a loss in hydraulic seal which causes a redistribution of loads and stresses in the gates. The glass FRP composite block was manufactured using a thermal press technique and was shown to be lighter weight and just as strong in compression as a steel block. The composite blocks were installed at Hiram Chittenden Locks in March, 2015 and the performance is being monitored. This lock has the highest amount of lockages per year than any other lock in the USACE inventory.
In 2015, PIANC established a working group, WG 191 – Composites for Hydraulic Structures, with representatives from both WVU and USACE. This international group is tasked with identifying where composite materials provide a benefit over conventional materials for hydraulic inland navigation structures and to develop a report identifying best practices of how to use composite materials, summarizing case studies with pros and cons, and to compile guidance documents to aid engineers when using composite materials in the demanding environments of hydraulic structures. This working group has allowed researchers to collaborate and exchange information with other agencies.
Through lessons learned from previous FRP projects and technology exchange meetings, USACE intends to develop and install FRP gates and valves for inland navigation structures. USACE has a sizeable inventory of miter, vertical lift, tainter (radial), and sector gates. These gates are larger and more complex in design than wicket gates. Due to their size and intended use, they will be subjected to much greater loading conditions and stresses. The large size of these types of gates will likely require them to be manufactured in large monolithic pieces using a VARTM process. Research and development will need to be conducted to limit the amount of pieces required to construct an entire FRP composite gate.
In addition, there will be some capability gaps that will need to be filled regarding monitoring, inspection, and repair of FRP composite gates. Structural health monitoring of inland navigation structures using strain gages and accelerometers has proven to be a valuable Operations and Maintenance (O&M) tool to monitor the functionality and integrity of these large structures. The VARTM manufacturing process allows for a new and innovative way to include sensors within the structure rather than adhered to it. When FRP composite materials are damaged, it may be difficult if not impossible to visualize the damage from the surface. Non-destructive testing (NDT) techniques such as a digital tap hammer, ultrasonics, thermography, x-ray, and shearography need to be explored in an attempt to not only discover possible damage areas such as delaminations and voids, but to also quantify the damage. If a damage area can be quantified as critical, then a repair of the structure will be necessary. Research will need to be conducted into which repair techniques such as step sanding and hot bonding are most appropriate to regain structural strength and integrity. The effort will ultimately result in guidance to allow USACE to confidently design and implement FRP composites in navigation structures.