CONCRETE, a mixture of hydraulic or other mortar with gravel or shingle, which, on hardening, forms an artificial conglomerate. The best C. is made by well mixing hydraulic mortar (see CEMENT) with sand and sufficient water for complete hydration, and then adding the shingle or screened ballast, and mixing them well together. An inferior C. may be made by laying the shingle into the foundation or other place where the C. is required, and then pouring mortar upon it, to fill the interstices between the pebbles.
The principal use of C. is to form a basis of artificial stone for buildings that rest upon loose or damp subsoils. Such a basis, if well made, forms a solid foundation-slab upon which the weight of the whole structure is equally distributed. It also resists the capillary ascent of moisture from the soil, which -would otherwise take place through brick-work or porous stone. A very extensive and important application of C. in this manner has been made iu the lower part of Pimlico and Thames batik. An extensive district that, only a few years since, was a pestiferous marsh, is now covered with high class houses, and forms one of the fashionable quarters of the w. end of London. The
houses, and, in fact, the streets altogether, may be said to rest upon 'a substratum of artificial rock formed of C., which, besides giving stability to the buildings, shuts out the exhalations from the soil, and prevents the ascent of the moisture so abundant below.
C. is occasionally used for building walls by ramming it into molds, giving it the form desired. A very beautiful application of C. for making mosaic floors is common in Italy. A stratum of cement is laid, and the surface carefully leveled; then pebbles of variegated colors are sifted over it; before it is quite hardened, these are beaten down, so as to be imbedded in the cement, and form the top layer. When the C. has coin pletely hardened, the rounded surfaces of the pebbles are ground down by maans of a large slab of stone, which, together with sharp sand, is rubbed over the surface until it is quite smooth; and thus a variegated pavement is formed by the flattened surfaces of the colored pebbles and the cement between them.