Concrete

__**Concrete.**__ Concrete is a manufactured mixture of cement and water, with aggregates of sand and stones, which hardens rapidly by chemical combination to a stonelike, water-and-fire-resisting solid of great compressive but low tensile strength. Concrete was employed in ancient Egypt (check this short article) and was highly developed by the ancient Romans, whose concrete made with volcanic-ash cement (pozzolana) permitted a great expansion of architectural methods, particularly the development of domes and vaults (often reinforced by brick ribbing) to cover large areas, of foundations, and of structures such as bridges and sewerage systems where water-proofing was essential. Reinforced concrete was developed to add the tensile strength of steel to the compressive strength of mass concrete. It was invented (1849) by Joseph Monier, who received a patent in 1867. He exhibited his invention at the Paris Exposition of 1867. Besides his pots and tubs Joseph Monier promoted reinforced concrete for use in railway ties, pipes, floors, arches, and bridges. The metal is embedded by being set as a mesh into the forms before pouring, and in the hardened material the two act uniformly. The steel reinforcement is employed to take full advantage of the plastic, or sculptural, character of concrete. It can be joined or bent to unify supporting members with the floors and the coverings they carry. Concrete is often used in hardscape construction. For instance, concrete may be used to form the flooring of a patio, or concrete footings may be used to support a wooden deck.

The concrete-shell construction permits the erection of vast vaults and domes with a concrete and steel content so reduced that the thickness is comparatively less than that of an eggshell.



The precast-concrete construction, employs bricks, slabs, and supports made under optimal factory conditions to increase waterproofing and solidity, to decrease time and cost in erection, and to reduce expansion and contractions.



Finally, the prestressed concrete provides bearing members into which reinforcement is set under tension to produce a live force to resist a particular load. Since the member acts like a spring, it can carry a greater load than an unstressed member of the same size.