Concrete is a composite construction material composed primarily of aggregate, cement and water. There are many formulations that have varied properties. The aggregate is generally a coarse gravel or crushed rocks such as limestone, or granite, along with a fine aggregate such as sand. The cement, commonly Portland cement, and other cementitious materials such as fly ash and slag cement, serve as a binder for the aggregate. Various chemical admixtures are also added to achieve varied properties. Water is then mixed with this dry composite which enables it to be shaped (typically poured) and then solidified and hardened into rock-hard strength through a chemical process known as hydration. The water reacts with the cement which bonds the other components together, eventually creating a robust stone-like material. Concrete has relatively high compressive strength, but much lower tensile strength. For this reason is usually reinforced with materials that are strong in tension (often steel). Concrete can be damaged by many processes, such as the freezing of trapped water.

Concrete is widely used for making architectural structures, foundations, brick/block walls, pavements, bridges/overpasses, motorways/roads, runways, parking structures, dams, pools/reservoirs, pipes, footings for gates, fences and poles and even boats. Famous concrete structures include the Burj Khalifa (world's tallest building), the Hoover Dam, the Panama Canal and the Roman Pantheon.

Concrete technology was known by the Ancient Romans and was widely used within the Roman Empire. After the Empire passed, use of concrete became scarce until the technology was re-pioneered in the mid-18th century.

The environmental impact of concrete is a complex mixture of not entirely negative effects; while concrete is a major contributor to greenhouse gas emissions, recycling of concrete is increasingly common in structures that have reached the end of their life. Structures made of concrete can have a long service life. As concrete has a high thermal mass and very low permeability, it can make for energy efficient housing.

Adjective

concrete (comparative more concrete, superlative most concrete)

1. Particular, perceivable, real.

   Fuzzy videotapes and distorted sound recordings are not concrete evidence that bigfoot exists.

   • 2011 December 16, Denis Campbell, “Hospital staff 'lack skills to cope with dementia patients'”, Guardian:

     Professor Peter Crome, chair of the audit's steering group, said the report "provides further concrete evidence that the care of patients with dementia in hospital is in need of a radical shake-up". While a few hospitals had risen to the challenge of improving patients' experiences, many have not, he said. The report recommends that all staff receive basic dementia awareness training, and staffing levels should be maintained to help such patients.

2. Not abstract.

   Once arrested, I realized that handcuffs are concrete, even if my concept of what is legal wasn’t.

3. Made of concrete building material.

   The office building had concrete flower boxes out front.

Synonyms

• (perceivable): tangible
• (not abstract): tangible

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