Even the tiniest cracks on the surfaces of concrete structures can lead to big problems if they aren’t immediately repaired. Researchers have demonstrated a way to give concrete surfaces the ability to heal when small cracks appear, an advance that could allow bridges and other structures to last longer. Previous approaches have mostly focused on restoring strength to damaged concrete, but this one focuses on protecting the surface, where tiny cracks can allow water, chloride ion from deicing salt or seawater, and carbon dioxide to penetrate the structure, which can lead to harmful deterioration. A range of microcapsule-based, self-healing systems were developed in recent years, consisting of a “healing agent,” often a polymer paired with a catalyst, but there are limitations to this system such as the availability and cost of the catalyst. Since sunlight induces the key reaction in this new coating, it has the advantage of being “catalyst-free” and potentially inexpensive.