Which structural problem plagued Roman concrete fortifications exposed to seawater, starting ~2000 years ago?

💡 Explanation

When Roman concrete was exposed to seawater, sulfate attack occurred because sulfates reacted with the tricalcium aluminate hydrate in the cement, forming ettringite which is highly expansive. Therefore sulfate attack weakened the binder, rather than expansion, rebar corrosion or freeze-thaw, which involve dissimilar mechanisms under alternate conditions.

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