The Romans big concrete invention that I am aware of was waterproof concrete. The secret in the mix was supposedly volcanic ash. They could build piers and make it work underwater!
The incredible stuff about the aquaducts is they had to build them on a constant downslope from the mountains to bring water to the cities - around the freaking world they did this! I have no idea how they were able to calculate a constant decreasing elevation. Truly amazing. With the fall of Rome - this knowledge was lost for hundreds of years (Dark Ages).
http://www.franklin.ma.us/auto/schools/horace/grade6/corey/ss1/classnotes.htm
waterproof concrete
allowed Romans to build in and under water – piers, bridges – concrete allow Rome to build “Rome like” cities throughout empire –
“new Rome” had lots of jobs, higher standard of living; mixture water, lime and the new secret ingredient pozzolana ash from volcanoes
bonus concrete info from https://sites.google.com/a/brvgs.k12.va.us/roman-technology/concrete-ralph–;
At first, this cement was used as mortar to bind together bricks in foundations and city blocks. In time, the entire empire was stitched together with concrete infrastructure that supported its lifestyle - roads, aqueducts, dams, and many other practical structures. The Romans had a very organized system of construction based around the speed and efficiency that was made possible by using concrete instead of masonry as the Greeks did. Engineers standardized their methods of working with concrete to perfect them over time, and detailed planning work went into every project to ensure a high level of craftsmanship. The simpler method of pouring concrete into a wooden framework also decreased the need for skilled labor, making it economical and easier to implement across the vastness of the empire in comparison to the more laborious masonry construction.