Concrete is omnipresent in every critical infrastructure system in the country because it is strong, inexpensive, and can be cast into almost any shape, including dams and bridges. After a certain time, as with most building materials, water infrastructure like dams start to deteriorate and need repair and retrofitting, so they can serve the public longer.
More than 91,000 dams are listed in the US Army Corps of Engineers’ (USACE) National Inventory of Dams (NID), which catalogues dams taller than 25 ft or reservoirs with a storage capacity of more than 50 acre-feet (1-acre surface area to 1-foot depth). NID classifies the downstream hazard potential as high, significant, or low. Currently, 76% of the 91,750 dams across the country built in the past 150 years are classified as high hazard potential, meaning that their failure could result in loss of life, as well as economic losses and environmental damages.
Ageing dams need sustainable modernization to ensure their resilience and continuous reliability into the next century and beyond. Different types of everyday environmental stressors – chemical action, corrosion, freezing and thawing – have been gradually deteriorating concrete dams across the US, and severe weather events, extreme temperatures, erosion, and rising water levels are adding more strain, exacerbating the ageing impacts, ultimately causing dams and levees to fail. Heavy rains caused the failure of the Oroville Dam in California in 2017, the Spenser Dam in Nebraska in 2019, and the Edenville and Stanford Dams in Michigan in 2020, all built early in the 20th century. Simply replacing old dams is not a viable option due to high costs and the enormous amount of work.
Seeking resilient, reliable solutions for ageing dams
In 2020, the Department of Homeland Security (DHS) Science and Technology Directorate (S&T) started a priority five-year research effort to find reliable science and technology solutions for ageing dams. S&T is collaborating with stakeholders from the infrastructure and emergency management communities – including USACE and its Engineer Research and Development Center (ERDC), the Federal Emergency Management Agency, the Cybersecurity and Infrastructure Security Agency, and the University of Kansas (KU) and Mississippi (UM) – to not only extend the life of dams and other concrete flood risk management infrastructure, but to do so in an environmentally responsible and sustainable way.
S&T chose to work on this effort because water poses very challenging and complex situations for concrete. What works for aging water infrastructure like dams and levees, most likely would work for dry-land concrete-based infrastructure like bridges and buildings. This initial use case could become the catalyst for an entire research agenda.
S&T is investing in and leading this five-year initiative because disaster or weather-related risks and threats to critical infrastructure continue to rise. This partnership will help better position the US by using innovative retrofitting technologies to create a new economy of more resilient concrete structures. Together, the partners are researching and developing innovative materials that can sense and detect potential stressors for better monitoring of overall conditions, reacting if necessary, and ultimately saving on maintenance costs.
Composite materials are advantageous to infrastructure operations
For this effort, the team is studying and working with fibre-reinforced polymers (FRPs), composite materials that typically consist of strong fibres (carbon or glass) embedded in a resin matrix. FRPs, which come in sheets, panels, structural shapes or monolithic structures, are very strong but lightweight and are not susceptible to corrosion unlike steel. These materials are stronger than steel in strength-to-weight ratio, meaning much less material is needed than steel for building repair.
Currently, an extensive amount of steel is used in dams and spillways, especially those with steel spillway gates. FRPs have additional advantages over conventional steel materials used in dam and spillway repair or construction: they are easier to install, impermeable to water, and their fibres can be adapted to include sensors that monitor concrete conditions in real-time.
Concrete dam deterioration includes most commonly cracking, but also corrosion of the spillway gates’ hydraulic steel structure, damaged concrete spillway, lack of monitoring capabilities in real-time, and more. Each of these issues could benefit from different types of FRP retrofits, however, such retrofit guidance is lacking. The good news is that after S&T completes this research initiative, guidance will be coming out.
Researching and developing the best FRPs and use cases
S&T’s goals for this project include researching how FRPs can help reinforce existing concrete dams to improve performance and extend their service life; surveying dams’ condition using drones to take photos and using deep learning to recognize the damage; and using sensors embedded in FRP fabric or laminates to monitor the condition of underlying concrete.
The S&T team has finished the first phase of four overall research phases. Researchers completed extensive literature reviews of FRPs for concrete repairs/retrofits, lab-tested selected FRPs in dry conditions to study bond performance to concrete surfaces, and designed a shear test to determine how FRP laminates perform when applied over a lift joint prone to sliding under hydraulic forces. So far, results show promising bonding performance, and the team will soon conduct lab testing under wet conditions as well.
The researchers were surprised by the lack of publicly available image sets of damage in concrete dams. Creating such a resource could lead to significantly more accurate damage detection via deep learning.
The research team is currently in the second research phase, which entails conducting a series of internal lab experiments on simulated components of concrete dams and creating virtual models that can be leveraged to use Artificial Intelligence (AI) for damage detection.
To improve and expedite surveying half-a-mile-wide dam structures, S&T is looking at AI. With a drone, surveyors can take thousands of photos, which then must be catalogued and analyzed, which is very time-consuming. Here, deep learning can make surveying more efficient by automating photo processing for damage detection, quantification and documentation.
The project team is also facilitating dam monitoring via self-sensing FRP laminates. Researchers will test two types of sensors embedded in the laminate – carbon fibres, already part of the laminate, and naturally possess electrical conductivity; and optical fibers, which will be added to the laminate. The sensors will collect baseline data whenever the FRP material strains from concrete deterioration.
Looking ahead to Phase Three, outdoor FRP field testing will take place at USACE dam structures in partnership with ERDC. In Phase Four, longer-term demonstration trials will test FRP repairs in tandem with an existing structure.
USACE has a huge stake in the outcomes of this FRP research and field testing as it operates and maintains more than 700 dams and related structures nationwide. Its role in this effort is twofold: physically demonstrate the FRPs on dams/levees and modernize the ways they improve the dams’ performance under future hazards (extreme floods or seismic events with diverse climate-induced variations). The effort developed and supported through S&T is in strong alignment and partnership with the USACE Civil Works research and development portfolio and will provide broad benefits that help to modernize our nation’s water resources infrastructure.
Environmental considerations
Remaining cognizant of the environmental implications of this initiative, the team knows that any time an innovation is introduced, an environmental assessment is conducted. If the FRP installation increases the carbon emissions budget, there could be tradeoffs. For example, if a dam doesn`t need frequent maintenance, this could offset production process emissions. Using FRPs to replace steel structural parts will help avoid painting, which could be hazardous to the environment. Additionally, by extending the life of existing dam/levee infrastructure, carbon emissions decrease because no new concrete material is used, and no material is wasted from the demolition of existing structures.
Right now, dams still need in-person visual inspections, but with the help of drones for photos, seismic data to determine how much geo stress the structures have been experiencing, and self-sensing FRPs could help monitor the dams from a distance.
What is next after the initiative is completed?
At the end of this initiative, the successfully tested products – FRP repairs, AI and self-sensing FRPs for damage detection – will be transitioned to the commercial sector. In cooperation with the American Society for Civil Engineers and the Association of Dam Safety Officials, USACE will update its industry guidance on dam/levee retrofits, so industry can easily deploy the FRPs for construction projects.
This research could potentially trigger innovations in how the U.S. designs and constructs roadways, bridges and other concrete structures. The chosen FRPs could make structures more resistant to deterioration, increasing their resilience to seismic activity and vibrations from increased road traffic.
Longer-term, S&T’s research agenda includes addressing saltwater infrastructure because it, too, may require a different research approach. S&T will also study self-healing concrete, which can self-repair internal damage like cracks without the need for external intervention. Fibre capsules filled with repair solution are added to the concrete mix; over time, the fibres/capsules break when cracks appear, and the liquid contained within spreads immediately to heal the crack.
As concrete infrastructure typically has a 50-year lifespan, these emerging technologies and the retrofitting work are the first of many important steps and opportunities to study disaster risks, strengthen critical infrastructure and prepare the workforce in a future economy that could lead to more equitable outcomes.
This article first appeared in International Water Power magazine.
