Cracked concrete bridge with glowing gel, symbolizing Alkali-Silica Reaction (ASR).

Concrete's Silent Killer: How ASR Cracks Our Foundations and What We Can Do About It

Jordan Keane in Tech & Innovation December 2025 • 4 min read.

"Discover the science behind Alkali-Silica Reaction (ASR), the hidden threat causing concrete structures to crumble, and the innovative solutions researchers are exploring to combat it."

Across the globe, countless concrete structures are silently battling a destructive force: Alkali-Silica Reaction (ASR). This chemical process, often called 'concrete cancer,' leads to cracking and weakening of our bridges, buildings, and roadways. While seemingly solid, concrete is vulnerable to internal reactions that compromise its integrity, resulting in costly repairs and safety concerns.

The root of the problem lies within the concrete itself. ASR occurs when certain types of silica found in the aggregate (the sand and gravel mixed with cement) react with alkaline hydroxides in the concrete. This reaction forms a gel-like substance that expands, creating internal pressure that eventually cracks the concrete from within. Despite extensive research, fully understanding the complex mechanisms of ASR and developing effective preventative measures remain a challenge.

Now, researchers are making headway by focusing on characterizing the structure of ASR products at a microscopic level. By identifying the unique 'fingerprint' of these reaction products, scientists hope to better understand how ASR develops and spreads, leading to more targeted and effective solutions for protecting our infrastructure.

What Exactly Makes Concrete Crack? Unpacking the Science of ASR

Cracked concrete bridge with glowing gel, symbolizing Alkali-Silica Reaction (ASR).

To fully grasp the threat of ASR, it's essential to understand the process. Concrete is a composite material, primarily made of cement, water, and aggregate. Cement acts as a binder, holding the aggregate together. However, certain forms of silica within the aggregate are reactive when exposed to the highly alkaline environment created by the cement hydration process.

This reaction produces an alkali-silica gel that absorbs water and expands. The expansion generates internal stresses within the concrete, leading to cracking. The cracking not only weakens the structure but also allows water and other harmful substances to penetrate, accelerating further degradation. The challenge is that this process often occurs slowly over many years, making early detection difficult.

The Key Ingredients for ASR: Reactive silica in the aggregate, high-alkali cement, and sufficient moisture.
The Reaction: Silica + Alkaline Hydroxides → Alkali-Silica Gel (expands with moisture)
The Damage: Internal stress, cracking, reduced structural integrity, increased vulnerability to further degradation.

Traditional methods for analyzing ASR relied on identifying the chemical composition of the reaction products using techniques like Energy-Dispersive X-ray Spectroscopy (EDS) in a Scanning Electron Microscope (SEM). While EDS can easily reveal the elements present, determining the actual structure of the ASR product has proven difficult due to the extremely small volumes formed within the concrete. This structural information is crucial for a deeper understanding of the reaction mechanism and for developing targeted mitigation strategies.

Looking Ahead: A Future for Concrete Structures

The ongoing research into ASR, particularly the focus on characterizing the structure of the reaction products, offers hope for the future of concrete infrastructure. By understanding the fundamental mechanisms of ASR, engineers can develop more effective preventative measures, repair strategies, and design durable concrete structures that can withstand the test of time. Further exploration using advanced techniques like Raman microscopy will undoubtedly play a key role in safeguarding our built environment.

About this Article -

This article was crafted using a human-AI hybrid and collaborative approach. AI assisted our team with initial drafting, research insights, identifying key questions, and image generation. Our human editors guided topic selection, defined the angle, structured the content, ensured factual accuracy and relevance, refined the tone, and conducted thorough editing to deliver helpful, high-quality information.See our About page for more information.

This article is based on research published under:

DOI-LINK: 10.1016/j.cemconres.2017.08.014, Alternate LINK

Title: Raman Microscopy Of Alkali-Silica Reaction (Asr) Products Formed In Concrete

Subject: General Materials Science

Journal: Cement and Concrete Research

Publisher: Elsevier BV

Authors: Andreas Leemann

Published: 2017-12-01

Everything You Need To Know

What exactly is Alkali-Silica Reaction (ASR), and why is it a concern for concrete structures?

Alkali-Silica Reaction (ASR) is a chemical process that occurs within concrete when reactive forms of silica in the aggregate react with alkaline hydroxides from the cement. This reaction produces a gel-like substance that expands, creating internal pressure leading to cracking and weakening of concrete structures like bridges, buildings, and roadways. It's concerning because it compromises the integrity of infrastructure, leading to costly repairs and potential safety hazards. Fully understanding ASR is a challenge, and continued research is vital to developing effective preventative measures to protect concrete infrastructure.

What are the key ingredients that cause Alkali-Silica Reaction (ASR) to occur in concrete?

The key ingredients for Alkali-Silica Reaction (ASR) are reactive silica in the aggregate, high-alkali cement, and sufficient moisture. The reactive silica, when combined with alkaline hydroxides from the cement, forms an alkali-silica gel that expands in the presence of moisture. This expansion causes internal stress, cracking, and ultimately reduces the structural integrity of the concrete. Addressing one or more of these elements is crucial in preventing ASR. For example, using non-reactive aggregates or low-alkali cement can mitigate the risk.

How do researchers identify the 'fingerprint' of Alkali-Silica Reaction (ASR) products, and why is this important?

Researchers are characterizing the structure of Alkali-Silica Reaction (ASR) products at a microscopic level to identify their unique 'fingerprint'. Traditional methods like Energy-Dispersive X-ray Spectroscopy (EDS) in a Scanning Electron Microscope (SEM) are used to identify the elemental composition. Identifying the structural fingerprint is crucial for a deeper understanding of how ASR develops and spreads. This knowledge enables scientists to develop more targeted and effective solutions for protecting concrete infrastructure. Techniques such as Raman microscopy are further being explored to gain better insights.

What are the traditional methods for analyzing Alkali-Silica Reaction (ASR) and what are their limitations?

Traditional methods for analyzing Alkali-Silica Reaction (ASR) rely on identifying the chemical composition of the reaction products, often using techniques like Energy-Dispersive X-ray Spectroscopy (EDS) in a Scanning Electron Microscope (SEM). While EDS can easily reveal the elements present, determining the actual structure of the ASR product has proven difficult due to the extremely small volumes formed within the concrete. This limitation makes it challenging to fully understand the reaction mechanism and develop targeted mitigation strategies. Advanced techniques like Raman microscopy offer promise in overcoming these limitations by providing more detailed structural information.

What future solutions are being explored to combat Alkali-Silica Reaction (ASR) and ensure the longevity of concrete structures?

Ongoing research focuses on characterizing the structure of Alkali-Silica Reaction (ASR) products to understand the fundamental mechanisms. This understanding allows engineers to develop more effective preventative measures, repair strategies, and design durable concrete structures. Future solutions include using advanced techniques like Raman microscopy, to explore the composition, as well as developing innovative materials and construction practices that minimize the risk of ASR. By understanding the process, more durable concrete structures can be designed that can withstand the test of time.