General meanings
Concrete means
tangible, not
abstract.
Physically real, not
theoretical.
e.g. We always knew that thefez had the technology to breed spiders with human heads!, but we never thought he was crazy enough to do it, until we were confronted with concrete evidence of his bizarre crimes.
It means well-defined, not nebulous or conceptual.
e.g. I'd like to visit the moon some day, but I have no concrete plans on how to get there.
Language
For other words with similar latin derivation to concrete, see
accrete and
discrete;
construct,
conjoin and
converge.
Rocks
Geologically, a concrete is a rocky material formed from smaller particles such as sand or
gravel stuck or fused together,
conjoined by ac
cretion.
Construction
Derived from the geologic meaning, concrete is a grey,
ubiquitous building material made from
Portland cement mixed with
builder’s sand and
aggregate (small chips of
rock) for bulk and strength. Typically this is in a
ratio of 1 part
cement to 2 parts
sand to 3 parts aggregate. The cement provides a glue that holds the sand and rocks together.
This mixture is mixed, by hand for small amounts or in a cement mixer for larger quantities, and moistened with water until it is sludgy, and then poured into position.
When it dries it sets into a kind of artificial stone used to build just about anything from gutters to pots to paving stones to harbours to bridges to roadways to railways to foundations to tunnels to skyscrapers. For large projects, the wet concrete is poured over steel rods to make steel reinforced concrete.
Mortar, the stuff used to hold bricks together in construction is a similar mix, typically 6 parts sand to 2 parts cement to 1 part lime for a compound that is stickier, more elastic but not as strong as concrete.
A short history of concrete
Assyrians and
Babylonians: Used
clay
Egyptians: Used a cement made from
Lime and
Gypsum
1756:
John Smeaton, a leading British engineer makes "the first modern concrete" by adding pebbles and powdered brick to his "hydraulic lime" cement.
1824:
Joseph Aspdin, a British
mason, invents and patents
Portland cement, using a burned a mixture of ground limestone and clay.
1849:
Joseph Monier, a gardener from Paris, invents reinforced concrete. He used it to make garden pots with an iron mesh covered in cement. In
1867 he received a patent on it, and in the same year showed it at the Paris Exposition, having realized the use in other kinds of construction.
Software
Using a meaning unrelated to rocks, but related to tangibility; in computer
programming a
Concrete class is sometimes used to refer to a class that can be instantiated, i.e. not an
abstract class. A
concrete type has a similar meaning.