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Concrete

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Concrete is a composite material composed mainly of water, aggregate, and cement, and is the most widely used man-made material (measured by tonnage). Often, additives and reinforcements are included in the mixture to achieve the desired physical properties of the finished material. When these ingredients are mixed together, they form a fluid mass that is easily molded into shape. Over time, the cement forms a hard matrix which binds the rest of the ingredients together into a durable stone-like material with many uses. Concrete is widely used for making architectural structures, foundations, brick/block walls, pavements, bridges/overpasses, highways, runways, parking structures, dams, pools/reservoirs, pipes, footings for gates, fences and poles and even boats. Concrete is used in large quantities almost everywhere mankind has a need for infrastructure. Famous concrete structures include the Hoover Dam, the Panama Canal and the Roman Pantheon.

Concrete has an enormous carbon footprint. A major component of concrete is Portland cement - the source of the “glue” that holds most modern concrete together - which similarly exerts environmental and social effects. Its manufacture releases carbon from burning fuel, needed to heat a mix of limestone and clays to 1,450 degrees Celsius (2,642 degrees Fahrenheit) – and from the heated limestone (calcium carbonate) itself. The cement industry is one of the three primary producers of carbon dioxide, a major greenhouse gas (the other two being the energy production and transportation industries). As of 2001, the production of Portland cement contributed 7% to global anthropogenic CO2 emissions, largely due to the sintering of limestone and clay at 1,500 °C (2,730 °F).

ROMAN CONCRETE

The earliest large-scale users of concrete technology were the ancient Romans, and concrete was widely used in the Roman Empire. The Colosseum in Rome was built largely of concrete, and the concrete dome of the Pantheon is the world's largest unreinforced concrete dome. After the Roman Empire collapsed, use of concrete became rare until the technology was re-pioneered in the mid-18th century.

According to the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), a 2,000-year-old breakwater in the Mediterranean Sea was produced using a fraction of the energy required to create modern concrete – and it’s more durable too. The Romans perfected a mixture that used much less lime and cemented at 1,652˚F or lower, which means it required less energy to make. In an environment of escalating carbon emissions, this ancient concrete recipe could dramatically slash the building industry’s overall emissions if adopted today. The Romans mixed lime and volcanic rock for regular concrete structures, while underwater structures were made with lime and volcanic ash that formed a mortar. When this mix connected with seawater, a hot chemical reaction occurred that cemented the lime and ash mixture. The secret ingredient is aluminum-rich pozzolan ash, a material in abundance in oil-producing Saudi Arabia. Pozzolan could replace 40 percent of the world’s demand for Portland cement, and there are sources of pozzolan all over the world.

CONCRETE RECYCLING

Concrete recycling is a common method of disposing of concrete structures. Concrete, which must be free of trash, wood, paper and other such materials, is collected from demolition sites and put through a crushing machine, often along with asphalt, bricks and rocks.

Concrete Dome: Inside the Pantheon dome, looking straight up. The concrete for the coffered dome was laid on molds, probably mounted on temporary scaffolding. As of December 2014, the Roman Pantheon was the largest unreinforced solid concrete dome built in 118-128 AD. ©2008 Matthias Kabel