Secret ingredient found to help ancient Roman concrete self-heal

Concrete is the most commonly used building material in the world, but it’s not impervious to damage. Weather and stress can lead to tiny cracks, which can grow into much larger cracks that eventually threaten the integrity of the entire structure. That can require expensive maintenance or replacement to prevent catastrophic failure.

In contrast, ancient Roman structures have stood the test of time for more than two millennia. To find out how, scientists have long examined samples of the material under microscopes to study the composition and uncover the ingredients that bestow such strength.