Knowing where stress fractures are may lead to greater use of composite concrete. Source: University of LeedsResearchers from the University of Leeds have developed a new way to measure the strength of concrete using a light-refracting coating designed to give a better understanding of where the material could fracture.

The epoxy coating has the ability to split light waves in different directions in relation to the amount of stress and then reflect it back to a photonic camera. The camera then takes a picture showing where potential stress levels are and where likely cracks or fractures will occur.

The coating is not new but it is the first time it has been used to measure shear stress of concrete and assess the material's propensity to fracture.

“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 Antony, researcher from the School of Chemical and Process Engineering at Russell Group UK University. "The photonic method we developed can directly measure shear strain, even on opaque materials. Until now, photonic and optical methods of measurement have only been associated with transparent materials."

The rise in composite concretes, which are used extensively in the construction industry, prompted the team to look for new ways to study concrete’s strength. Traditionally, concrete is made from cement, gravel and sand, but in recent decades numerous waste products, such as plastic pellets, have been used to reduce the levels of natural materials and to recycle waste products.

This type of concrete has shown to have superior qualities to traditional concrete but few studies have been made to ensure the material can handle loads without fracturing.

The new method for measuring toughness of composite concrete could lead to more use of the building material because of the ability to know where fractures might form.

"We believe this new photonic or optical approach to fracture testing could be applied not only to develop sustainable manufacturing using materials that would otherwise be discarded as waste, but also in other diverse engineering designs including mechanical, civil, materials, electronics and chemical engineering applications,” Antony says.