Jan Lamprecht: Military Fortifications: Have Concrete mixer, will travel! – The Romans invented Concrete!
(008274.77-E001840.93NAVRLOSUC20V)
You can read the article here: http://historyreviewed.com/index.php/2017/12/27/jan-lamprecht-military-fortifications-have-concrete-mixer-will-travel-the-romans-invented-concrete/