Volcanic Ash Mix?
Apparently, the 'secret' ingredient in Roman concrete (like in the coliseum) was volcanic ash. Anyone tried a volcanic ash mix?
The recipe for Roman concrete was described around 30 B.C. by Marcus Vitruvius Pollio, an engineer for Octavian, who became Emperor Augustus. The not-so-secret ingredient is volcanic ash, which Romans combined with lime to form mortar. They packed this mortar and rock chunks into wooden molds immersed in seawater. Rather than battle the marine elements, Romans harnessed saltwater and made it an integral part of the concrete.
probably no shortage of volcanic ash and seawater in Hawaii, amirite?