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Left out is the reason we don't use the Roman mix today: it takes years for the concrete to set; Roman concrete is weaker for the first decade compared to modern cement mixes.

Moreover, back in Roman times, Roman concrete was not as strong back as it is today. As the article you linked points out, "Because both minerals take centuries to strengthen concrete, modern scientists are still working on recreating a modern version of Roman cement."

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Very good point. Most building projects actually use admixtures to get as rapid strength increase as possible, even if it means less strength increase long term, because the early strength determines when you can strip formwork and start building the next floor. Builders want concrete reaching ~18MPA in like <2 days.

imagine a world where new houses are cheaper and as it ages and surrounding develops houses become more desirable and stronger

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