Piotrsko -- The helical screw tractors had hollow aluminum screws.
The Romans had a single source for their material.
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https://www.britannica.com › technology › pozzolanic-cement
pozzolanic cement | cement | Britannica
Pozzolanic cements are mixtures of portland cement and a pozzolanic material that may be either natural or artificial. The natural pozzolanas are mainly materials of volcanic origin but include some diatomaceous earths. Artificial materials include fly ash, burned clays, and shales. Pozzolanas are materials that,…
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IIRC Grand Coulee Dam used local pozzalana. The hot new amendment is flash graphene.