Basics of Concrete
is made up of five primary constituents:
- Fine Aggregate (FA)
- Coarse Aggregate (CA)
The water and cement form a paste, which binds the aggregate into a rock-like mass as the water and cement combine through a chemical reaction called hydration. The paste also includes entrapped air introduced by mechanical mixing and entrained air introduced by the addition of chemical admixtures. The paste constitutes between 25 and 40 percent of the volume. The aggregate makes up the remaining 60 to 75 percent. Air in concrete varies from about ½ to 2 percent in non-air-entrained concrete to about 4 to 8 percent entrained air in concrete containing air-entraining admixtures.
FA, sometimes called "sand", is composed of particles that pass the 4.75 mm (No.4) sieve. CA, or gravel, consists of particles retained on or above 4.75 mm (No.4) sieve. Well-graded aggregate, consisting of a wide range of FA and CA sizes, provides for efficient use of the water/cement paste. Since aggregate makes up most of the mix volume, it should consist of particles with adequate strength and resistance to exposure conditions.
Concrete is a construction material that consists, in its most common form, of Portland cement, aggregate (generally gravel and sand) and water.
Concrete solidifies and hardens after mixing and placement due to a chemical process known as hydration. The water reacts with the cement, which hardens, bonding the other components together and eventually creating a stone-like material.
Concrete is used more than any other man made material on the planet. It is used to make pavements, architectural structures, foundations, motorways/roads, overpasses, parking structures, brick/block walls and footings for gates, fences, and poles.
Concrete powers over a $35 billion industry which employs over two million workers in the United States alone. Over 55,000 miles of freeways and highways in America are made of this material. The People's Republic of China currently consumes approximately 40% of world cement production.