In an international collaboration, researchers from the College of Engineering and Computer Science at Florida Atlantic University, the Metallurgical Institute in Kryvyi Rih, Ukraine, and Ariel University in Israel, have joined forces to explore how corrosion of reinforced concrete affects the design of structures exposed to harsh environments. A major challenge they tackled was understanding the relationship between corrosion rates and structural stress, along with how long these structures can endure under corrosive conditions.
Reinforced concrete structures are designed to handle mechanical loads but can face significant challenges when exposed to corrosive environments. Corrosion of steel reinforcement bars (rebar) weakens the material by reducing its cross-sectional area, which increases stress and may lead to cracks or failure.
Advertisement
Reinforced concrete, made stronger by embedding rebar, combines the tensile strength of steel with the compressive strength of concrete. This makes it more durable than regular concrete. However, corrosion is a global issue, causing annual losses of between US$1.8trillion and US$2.5trillion, with some countries – including the USA, the UK and Germany – experiencing losses of up to three per cent of GDP.
The study focused on optimising the design of reinforced concrete elements, such as beams and columns, which are susceptible to corrosion in aggressive environments. The aim was to minimise initial costs, including both concrete and steel reinforcement, while optimising the performance and durability of reinforced concrete elements to ensure their strength and reliability in corrosive environments.
Advertisement
For the first time, the team applied Dolinsky’s corrosion model to investigate how corrosion affects rebar in these structures. Dolinsky’s model predicts the impact of corrosion on materials, particularly steel reinforcement in concrete, by linking the stress on steel to its corrosion rate. The model shows how stress can either accelerate or slow the corrosion process.
The study’s results demonstrated that the most efficient design for reinforced concrete beams uses the smallest possible amount of material while still ensuring the structure remains strong and functional. This means that the beam’s dimensions and the amount of rebar are minimised to keep costs down without compromising performance.
Advertisement
The findings showed that the beam’s ability to bend didn’t have an impact on the design’s optimisation process. This suggests that, even under the most stressful conditions, the structure can still be designed efficiently.
The results also revealed that the initial size of the rebar used in the beam is influenced by the expected level of corrosion over time. The more corrosion anticipated, the larger the rebar may need to be to maintain the beam’s integrity and performance throughout its lifespan.
‘It has been called “the great destroyer” and “the evil”. The Pentagon refers to it as “the pervasive menace”. It destroys cars, fells bridges, sinks ships, sparks house fires and nearly brought down the Statue of Liberty. Rust costs America more than US$400billion per year – more than all other natural disasters combined,’ said Isaac E Elishakoff, distinguished research professor in FAU’s Department of Ocean and Mechanical Engineering, quoting from the book Rust: The Longest War by journalist Jonathan Waldman. ‘Our model assumes that corrosion affects the rebar evenly on all sides. It shows how stress, like tension or pulling forces, speeds up the corrosion process – the higher the stress, the faster the corrosion. What’s innovative about this work is applying Dolinsky’s model directly to the steel reinforcement, treating it as a round rod. This approach helps us predict how corrosion will impact the structural elements over time, leading to smarter design choices that improve the structure’s long-term durability in corrosive environments.’
Advertisement
One of the most important things about this method is that it can be applied to a wide range of reinforced concrete elements, regardless of their shape, and in different types of mechanical load conditions.
‘This model not only helps us track the progression of corrosion but also allows us to predict how the initial construction costs of the structure may increase over time as corrosion worsens. Depending on the level of load and the severity of corrosion, these costs can rise substantially, impacting both maintenance expenses and overall structural durability,’ said Elishakoff. ‘This approach helps engineers better understand and optimise how reinforced concrete structures behave when exposed to corrosion, allowing for more durable and cost-effective designs.’
Advertisement
The researchers also looked at how difficult it is to monitor the condition of reinforced concrete structures over time, especially when corrosion reduces their strength and increases deformation, which affects the safety of these structures. As the global market for reinforcement is expected to reach US$246.3billion by 2028, preventing corrosion in these materials becomes even more important.
The collapse of the Champlain Towers South building in Surfside in 2021 killed 98 people and drew significant attention to the dangers of corrosion in reinforced concrete structures. One major issue in the collapse was the corrosion of the rebar in the concrete, particularly in the underground parking garage. The building had been exposed to the harsh coastal environment, with saltwater from the nearby ocean accelerating the corrosion process. As the rebar corroded, it expanded, causing cracks in the concrete, weakening the structure.
‘Corrosion of steel reinforcement in concrete structures, especially in aggressive environments like coastal areas, can have devastating consequences if not properly addressed,’ said Stella Batalama, dean of the FAU College of Engineering and Computer Science. ‘The Surfside condo collapse is a tragic example of how the corrosion of rebar, combined with insufficient maintenance and delayed inspections, can weaken a structure to the point of failure.’
The research has been published in Mechanics Research Communications.