Portland cement is also incredibly brittle (and thus short-lasting) compared to the natural lime-based concrete used pre 19th century. Here's a great explanati

Portland cement is also incredibly brittle (and thus short-lasting) compared to the natural lime-based concrete used pre 19th century. Here's a great explanation of the differences: http://limes.us/about-saint-astier-nhl/what-is-natural-hydraulic-lime/ http://limes.us/about-saint-astier-nhl/what-is-natural-hydra...