Engineered Aggregates Could Improve Self-healing Concrete

Brief 

Researchers at the University of Southern California have developed a computational model to determine the ideal shapes and sizes of engineered aggregates for self-healing concrete while minimizing the volume fraction of the healing agent. Self-healing concrete with engineered aggregates could be a cost-effective alternative to bacteria- or microcapsule-based self-healing concrete.

Insight

Concrete is the second-most used material in the world after water, favored for its high compressive strength, which allows it to support heavy loads.

But concrete also has low tensile strength, meaning it’s easily pulled apart—or cracked–under stress. Changes in temperature or humidity can also make concrete crack. Since it’s difficult to create concrete that doesn’t crack, some are trying instead to create concrete that is self-healing.

USC Viterbi School of Engineering researchers created a new method for developing self-healing concrete that replaces the natural aggregates (pieces of rock) in concrete with engineered aggregates that contain healing agents within them.

Unlike other methods pursued over the past two decades, their method prioritizes keeping costs low and maintaining other properties of concrete, particularly strength and production method.

The researchers, which include Associate Professor of Civil and Environmental Engineering Bora Gencturk and Ph.D. candidate Xiaoying Pan, identified the prevailing methods of self-healing concrete such as adding bacteria, which is activated by chemical reactions resulting from a crack to heal the space.

This could also include placing microcapsules containing healing agents inside the concrete, which are activated once the concrete is stressed. These methods, Pan said, are prohibitively expensive, making them impractical in real-world applications.

“Normally the price of concrete is around $150 per cubic meter,” she said, “But using bacteria-infused self-healing concrete, that price can increase to $6,000 per cubic meter.” It is not just the cost that is off-putting, she said, but there were other drawbacks, such as the higher-level expertise and technical knowledge required to mix the concrete appropriately that might slow and complicate the construction processes.