The History of Concrete from University of Illinois Urbana-Champaign.
Hydraulic cement is a very useful material for patching water leaks in concrete since it can harden underwater.
I learned from the History of Concrete that in 1793, "John Smeaton found that the calcination of limestone containing clay gave a lime which hardened under water (hydraulic lime). He used hydraulic lime to rebuild Eddystone Lighthouse in Cornwall, England which he had been commissioned to build in 1756, but had to first invent a material that would not be affected by water."
