Roman Concrete
Roman Concrete
Roman concrete is a Special mix of hydraulic-setting cement and an aggregate. The cement however also incorporates white clumps of lime clasts and pozzolanic ash.
The composition varied, depending on what was available. It included rock fragments, ceramic tile, rubble, and lime clasts. Tuff was also readily available. Gypsum and quicklime were also used as binders,
The use of lime clasts of Quicklime were used to create the ‘self-healing’ property. If the concrete cracked, and water seeped through, the water would react with the lime clasts, forming a calcium solution. This can then flow through the cracks, and crystalise again. This ‘heals’ the cracks, and prevents them from spreading.
Another technique used was by mixing ash, seawater, and quicklime. This creates a tobermorite, which helps resist fracturing in the rock. As seawater moves through the cracks in the cement, it reacts with phillipsite in the volcanic rock, forming aluminous tobermorite crystals. Some describe this as the ‘The most durable building material in human history’.
Under a microscope
This sample shows ancient Roman maritime concrete taken from Pozzuoli Bay near Naples. The sample's diameter is 9cm, and it shows parts of lava, pumice clasts, and relict lime clasts, used to help 'heal' the concrete when it cracks.
Roman concrete also has a smaller carbon footprint, unlike regular concrete, which requires fossil fuels to burn limestone and clays (7% of global CO2 emissions a year). Roman Concrete requires temperatures of 2/3rds of needed for Roman concrete, saving fuels, and reducing its carbon footprint.