CONCRETE (from Latin concretas, tthat which is grown togethe0), an artificial stone, a composition of hydraulic cement, sand and broken stone, used for a long time for sub marine foundations, and since 1890 more and more in place of building stone. In place of hydraulic cement pure lime was originally used and the name concrete applied only to this com pound, °beton)) being the proper term for the composition based on hydraulic cement until it became the only method. The mixture of sand and cement is termed the matrix, and the broken stone or other addition is styled aggre gate and is composed usually of local crushed stone, but may be slag, coke, broken bricks, gravel or pebbles. The ideal aggregate is broken, sharply angular and irregular stone, as this material mixes better with the matrix than rounded pebbles, minute particles of gravel or the more spongy brick shell or coke, although broken stone or gravel may be used advanta geously in connection with pebbles, even in such small proportion as three to five. Broken lime stone is considered especially efficacious as an aggregate, possibly because of an affinity be tween the molecules of carbonate of lime in it and the matrix. The proportions of the various parts approximate 1 part of cement, 3 parts of sand and 4 to 6 parts of aggregate, but no fixed norm is to be followed, the true rule being that the cernent paste is to be thoroughly incorpo rated with sand coating each particle and that the matrix thus formed shall fill all interstices in the aggregate. In the process of mixture there are two extreme methods of watering, one very wet and the other scarcely more than moist. The spraying is followed by a mixture by shovel or by mixing machines. These ma chines are of two types: continuous, a trough or cylinder with a revolving screw shaft which works until the mixture is complete; and inter mittent, a box being rotated slowly. The con crete may either be made into blocks, one layer of comparatively small depth being made at a time. By the newer method it is applied to its place on the building or foundation in the soft state and allowed to harden there. The world is indebted to Germany for the revivifi cation of the concrete industry. They diffused a wider laiowledge of the artificial manufacture of cement from lime and clay (see PoirmAND CEmEbrr), and demonstrated that the degree of expansion and contraction of structural steel and concrete under changes of temperature were the same. The United States was very prompt to make use of this development, which has so greatly altered building construction throughout the civilized world. While the large use of concrete is a comparatively modern de velopment, it was employed in ancient times and in some of the most renowned works of history. The factitious stones employed by the Babylonians and the early Egyptians, as well as among the Greeks and Romans and at the present day in Barbary and among the nations of Malabar, were all a species of beton. Pliny mentions that the columns which adorn the peristyle of the Egyptian labyrinth were of this material, and the great length of time it has existed (over 3,600 years) shows the durabil ity of this mode of construction. Puzzonlana,
a volcanic earth, formed the basis for an ex cellent natural hydraulic cement used by the Romans. The aggregate consists of broken stone and was poured in wooden molds. In Rome the pyramid of Ninus is formed of a single block, as was also the square stone that formed the tomb of Porsena, which was 30 feet wide by 5 feet high. The Romans made free use of this material in constructing their walls, aqueducts, piers and roads, many por tions of which exist at the present day. The mole which shelters the harbor of Algiers is so much exposed to the effect of winds that breaches were continually 'being made in it by the force of the sea, 'and to such an extent that in former times the Moors were compelled to employ a large number of workmen constantly repairing it, at an annual expenditure of over $60,000. Between 1833 and 1840 the French rebuilt this with concrete, or beton as it was then called, this being among the earliest of modern successful use of artificial cement-made stone. The action of the sea is so tempestuous here that the engineers calculated that stone blocks would have to be of about 350 cubic feet bo remain in place. The impracticability of quarrying and transporting such enormous blocks of stone led to the employment of arti ficial stone or beton. Two kinds of blocks were manufactured: the first in the water, in the place they were intended to occupy, and the second on shore, to be afterward thrown into the sea. In the process of reconstruction, these blocks were used as follows: Those of the first kind, made in lined caissons, formed an outer sea line; on these blocks molds were placed filled with beton, and after these second blocks had set, they were launched into the sea, form ing a line in front of the first; the intervening space was then filled up with blocks of natural stone. Behind this embanlanent thus formed, the ground was dredged to a depth of over six feet, and the whole of this space filled up with a continuous mass of beton. The entire work was performed in five years, at a cost of less than $420,000, notwithstanding that the mole, at the time of the occupation of Algiers by the Frernch army in 1830, was irr a state of complete dilapidation, in spite of the extensive repairs which had been annually executed upon it by the Moors during a period of two centuries. Marine works of the above character present numerous advantages over constructions in which natural stone is employed, of which the following are some of the most prominent: (1) immediate stability, while ordinary pierre perdue is never secure; (2) incomparably greater fa cility in transportation, which is always expen sive and troublesome when blocks of stone are to be quarried exceeding 100 cubic feet; (3) a cbnsiderable reduction in the sectional area of the pier, and consequent economy of cost; and (4) that the system can be applied in every locality, now that our advanced knowledge of the subject of hydraulic mortars enables us to manufacture beton in any place where it may be needed. See CONCRETE BRIDGES ; CONCRETE CONSTRUCTION ; PORTLAND CEMENT.