In the light of what we know today about the undesirability of dry mixes, why were the early structures built with such mixes so successful?
The Concrete Primer published by the American Concrete Institute attributes this to the fact that the concrete was placed in thin layers, each of which was thoroughly rammed until water appeared on the surface. The ramming process eliminated voids and brought about a complete embedding of all the aggregate particles in the cement paste—an essential requirement for durable concrete. The method is impractical today because of higher labor costs and the use of reinforcing.