How Do You Combat Alkali-Silica Reaction in Concrete?

Anthony Bentivegna, PhD, PE

Learn how alkali-silica reaction (ASR) poses a threat to infrastructure across North America.

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This post was originally published on September 10, 2019

Alkali-silica reaction (ASR) affects existing concrete infrastructure across the globe. Cases of ASR causing cracking and deterioration in concrete structures are popping up in airports, nuclear plants, dams and bridges. It’s important to be aware of the risks ASR poses to our infrastructure and how to control the alkali aggregate reaction.

What is the Alkali-Silica Reaction in concrete?

ASR is a chemical reaction that typically occurs when concrete is made using certain aggregates that are reactive with alkalis. These aggregates are commonly composed of amorphous silica. The reaction can lead to a host of other durability issues, including cracking, corrosion of reinforcing steel and tensile stresses in the concrete. Once the reaction has begun, ASR is extremely difficult to treat. So, what can be done about it?

Diagnose Your Problem

The first step is to confirm whether your concrete has experienced ASR. Concrete petrography, a science that utilizes microscopes to study the composition and properties of the materials that make up the concrete is the only way to confirm this. Petrographic examinations, conducted in our lab, identify features such as specific minerology, gel, staining and cracking that are associated with ASR.

In our laboratory, we can examine samples of your concrete to estimate the extent of future deterioration due to ASR. Some methods involve grinding, crushing and extracting alkalis from the concrete to determine if there’s remaining “fuel for the fire” to contribute to the reaction. Instrumenting the structure to monitor if the expansion and deterioration continues is also a useful tracking method. Overall, understanding how concrete expands and cracks is key to combating ASR.

How to Address the Problem

The key to slowing down ASR is to choke off the moisture source. Breathable coatings, waterproofing materials and cladding can be effective methods to prevent the ingress of moisture.

Sometimes, ASR may be too advanced to only restrict moisture ingress. Alkali-silica reaction structural repairs can be completed where concrete is strengthened using carbon fiber wraps or post tensioning to constrain the expansion. In the worst-case scenarios, structures may need to be torn down due to serviceability and structural safety concerns.

How We Can Help

As concrete infrastructure in North America continues to age and reach the end of its intended lifespan, ASR will continue to present a serious challenge to the life of existing structures. We’re uniquely positioned to implement techniques to properly diagnose the cause of deterioration, determine the prognosis, develop remediation strategies to slow the reaction and extend the life of structures with ASR.

For new construction, we can help you develop and determine concrete mixtures to mitigate the potential for ASR.

With the development of our new innovative concrete lab, you will have a central location for all your laboratory testing, materials and durability engineering and structural evaluation and repair. Reach out here.

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