Concrete is a material used in building construction, consisting of a hard, chemically inert particulate substance, known as an aggregate (usually made from different types of sand and gravel), that is bonded together by cement and water.
Concrete has been used in construction for over 2,000 years, perhaps first by the Romans in their aqueducts and roadways.
The Romans used a primitive mix for their concrete. Mortar consisted of small gravel and coarse sand mixed together with hot lime and water. To reduce shrinkage, they used horse hair, much like we use polypropylene fibers today. They even unintentionally entrained the air in the mix by adding animal blood. That process created small air bubbles in concrete, making the mix more durable.
The Romans' use of concrete was extensive -- they built some 5,300 miles of roads (compare this to 4,200 miles of interstate highways in the United States).
While Roman roads ceased carrying chariot traffic long ago, one road in Bellefontaine, Ohio, has put in over 100 years of service and still provides a route for cars and trucks to travel.
Closer to home, a section of concrete pavement in Spokane is thought to be "circa 1910-ish" and, by the way aggregate was deposited in the mix, some experts think it was poured by horse and buggy.
Today, concrete is finding more inventive uses including residential construction and works of art.
Some homes in hurricane-ravaged Florida are being replaced by concrete dwellings because of their high wind resistance.
In Malibu, Calif., a fire several years ago decimated an entire hillside of homes, except for one house: it was made of concrete.
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