New High-Tech Sensing Illuminates Concrete Stress Testing

The coating can create a candle-like “flame” to highlight shear stress distribution in a concrete beam.

Scientists at the University of Leeds (Leeds, United Kingdom) and the University of Qatar (Doha, Qatar) discovered a new way to measure the strength of modern concrete composites and the points when it could fracture.

Their approach involves applying a light-refracting coating, designed to display stress positions, to the surface of concrete beam samples. The epoxy coating is birefringent, which means it can split light waves in different directions in proportion to any stress.

The light reflects back to a photonic camera, and the camera takes a picture showing where the stress levels are most extreme—before cracks or fractures occur.

While the coating is not new, this project is the first time it has been used to measure shear strain on opaque materials rather than transparent materials. With the process, the researchers believe they can prove that concrete made from non-traditional ingredients—such as waste plastic products—can sustain service loads without fracturing.

“There are other methods to measure stress and strain levels in the engineering sector, but we do not believe any of them can measure shear strain directly with high precision, which is most relevant to assess the failure strength of materials,” says Joseph Anthony, a chemical and process engineering professor at Leeds. “The photonic method we developed can directly measure sheer strain, even on opaque materials. Until now, photonic and optical methods of measurement have only been associated with transparent materials.”

Funded by the Qatar National Research Fund, the research results using the new method compared favorably with conventional methods of stress testing—which have relied on combined experimental and numerical or analytical approaches.

Source: University of Leeds,