Yes, we (Italy) often use as well flying ashes added in the concrete mix, to reduce permeability and, besides, it acts in the wet mix as a sort of lubricant and

Yes, we (Italy) often use as well flying ashes added in the concrete mix, to reduce permeability and, besides, it acts in the wet mix as a sort of lubricant and makes the pumping of the concrete much easier. BTW Pozzolanic is way stronger (in the long run), "pure" Portland based concrete is much faster in setting, but then hits a ceiling, so where there is no particular need for fast setting (massive foundations and similar) Pozzolanic is (was) preferred (and also costed a little less). What is called Pozzolanic cement here is anyway now essentially Portland cement 65-70% and flying ashes 30-35%, while "pure" Portland is between 90 and 95% Portland clinker and the remaining is limestone. JFYI: https://news.ycombinator.com/item?id=29377799 https://news.ycombinator.com/item?id=29377799