Yeah there was a theory discussed on HN a couple of years ago that superior qualities came from mixing in quicklime (CaO). I'm not sure if they've developed that and tested it against modern concretes. I guess it's hard to tell if they'll last 2000 years without waiting quite a while. (https://news.ycombinator.com/item?id=34280239)
I heard it was that they used seawater not freshwater.
And yes, we'll have to wait a while. Though probably not 2000 years - we only have to wait until our concrete starts failing, which might be a lot sooner than that.
