Concrete

Ancient Roman concrete lasts 2,000 years by healing itself. In 2023 MIT found the lime specks in it were deliberate, not careless. When water enters a crack, the lime dissolves into calcium that reacts with CO2, sealing it as Calcium carbonate.

In 2011, France had to destroy an armored vehicle in a Libyan city. Their fix: a 300 kg concrete bomb — a casing of concrete, not explosives. No blast, no shrapnel; the GPS-guided block smashed the vehicle on impact. The USA had used the trick in Iraqi no-fly zones since the 1990s.