Why Roman concrete still stands strong while modern version decays | Science | The Guardian

Their structures are still standing more than 1,500 years after the last centurion snuffed it: now the Romans’ secret of durable marine concrete has finally been cracked.The Roman recipe – a mix of volcanic ash, lime (calcium oxide), seawater and lumps of volcanic rock – held together piers, breakwaters and harbours. Moreover, in contrast to modern materials, the ancient water-based structures became stronger over time.Scientists say this is the result of seawater reacting with the volcanic material in the cement and creating new minerals that reinforced the concrete.

Source: Why Roman concrete still stands strong while modern version decays | Science | The Guardian