Roman concrete can heal its own cracks

A closer look

While your modern driveway cracks after three mildly harsh winters, Roman seawalls have spent 2,000 years getting battered by oceans and actually getting stronger. Scientists recently figured out why: Roman builders aggressively mixed quicklime with highly reactive volcanic ash. Whenever micro-cracks form and water seeps in, a chemical reaction occurs that physically grows new minerals, literally letting the concrete heal its own wounds.