22 Feb Sick Concrete: The Bane Of Every Engineer’s Existence
Concrete is used more than any other manmade material in the world. We use it to build roads, set foundations, construct walls and floors, and rely on it heavily in civil construction; it is a favorite when it comes to channel lining and reinforcing retaining walls. Unfortunately, concrete structures can begin to disintegrate after around 30 years in a condition referred to as “sick concrete.”
Where The Problem Begins
When lining water channels, engineers often reinforce their concrete with steel frameworks. This provides support while also offering the benefits of each material: concrete is hard and strong under compression (which is why roller-compacted concrete is used), but weak when stretched under tension. Steel, on the other hand, is flexible and strong under tension. It’s one of the reasons reinforced concrete lasts as long as it does, and why it has been so favored in past decades.
However, even the strongest materials have their weaknesses. It isn’t uncommon for concrete to crack, allowing water and moisture to get inside; if the rebar used internally is not specially treated, corrosion will begin to occur as chlorides and oxygen turn to rust. Steel rebars swell and expand as rust is formed, creating tensile stresses within the structure. This stress leads to further cracking, spalling, and potential failure in civil construction projects. Concrete contractors and engineers refer to this phenomena as sick concrete; if you’ve ever seen it, you know that the name is apt.
Healing Sick Concrete
Sick concrete originates from two types of corrosion.
- Chloride-induced: Wastewater and acid mine drainage frequently contain more chloride than normal water.
- Carbonation-induced: Exposure to air, saltwater, and mist can cause the calcium in the concrete to turn into calcium carbonate.
The main way to avoid sick concrete is to apply epoxy coatings to the steel before it becomes embedded in concrete. Since corrosion can seriously affect the lifespan of a concrete structure, it’s better to be safe than sorry; many roller-compacted concrete (RCC) strucures built decades ago are now beginning to show the devastating impact corrosion can have on structural integrity. The risk of huge failures where the reinforcing steel suddenly buckles is too great, especially when it comes to buildings that people live and work in.