The New Student's Reference Work/Concrete
Concrete, a composition of broken rock, gravel, broken bricks, sand, etc., usually cemented into solid form by the use of hydraulic cement. The proportions of the various ingredients differ according to the use to which the artificial stone called concrete is to be put, but the principle to be kept in mind in the mixing is that there should be enough of the mortar to a little more than fill the space between the fragments of broken rock, etc. A typical concrete is made of one part of cement, three parts of sand and five parts of broken rock. The mixing is usually done dry, only enough water being used to lay the dust, but more water is added when the stuff is tamped into position. Where concrete has to be laid down under water, it is usually put in position in bags. It is used for the foundations of structures of all sorts, for piers, fortifications, sidewalks and, recently, to a great extent in monolithic buildings, that is, buildings that are virtually one stone. In such buildings, as well as in many foundations, many iron girders and rods are imbedded in the concrete to add to its strength, and this is called reinforced concrete. The great earthquake in California made apparent the superiority of this kind of construction. Concrete was used extensively by the Babylonians, Egyptians, Greek and Romans. Some of their buildings have stood over 3,600 years. See Cement.