FOUNDATION - BRICK Each brick should have an adequate sup port from below, as otherwise the loaded wheels will force it down ward and make the surface uneven, a condition which conduces to the rapid destruction of the pavement by the impact of the wheels in passing over the depressions. There are several forms of foun dation in common use for brick pavements.
The best foundation is doubtless a bed of concrete laid as described in Art. 2, Chapter XII, pages 367-82. Fig. 130 is a section of a brick pavement having a concrete foundation. In recent years there has been a marked tendency to use concrete for the foundation of a brick pavement; although a brick pave ment should have adequate support, and although concrete when properly made makes an excellent foundation, it does not follow that every such pavement should be laid upon concrete,—at least upon a 6-inch layer, as is the common practice. Under certain conditions a layer of macadam may be cheaper and equally effec tive—see § 562, Art. 3, Chapter XII; and sometimes a layer of gravel of proper thickness, when laid as described in § 564, Art. 3, Chapter XII, is sufficient. In some localities the natural soil is so gravelly that it needs only to be leveled and rolled to make a rea sonably good foundation, particularly if the traffic is only mod erately heavy. Many cities, some of which have a considerable traffic, for example, Cleveland, Ohio, and Galesburg, Illinois, thus lay brick directly upon the native soil. Under certain condi tions 4-inch macadam roads have given fair service (see § 321), and a 4-inch course of brick has at least approximately as much sta bility as an equal thickness of broken stone.
However, it is poor policy to build an inadequate foundation for a brick pavement. The foundation for any block pavement, whether of brick, stone, or wood, should be substantial enough to keep the blocks in position so that the traffic will be received per pendicular to the face of the block, since then the surface of the pave ment will be smoother and the wear upon the blocks will be less. Brick pavements, being made of comparatively small blocks, are proportionally more injured by any derangement of the blocks, and consequently require a very carefully constructed foundation.
The best foundation for any particular work will depend upon the character of the soil and the availability of the various materials.
During the first ten or fifteen years after the introduction of brick pavements in the Middle West, the foundation consisted almost exclusively of a course of brick laid flatwise on a thin bed of gravel or cinders. Fig. 131 is a section of a brick pavement having a brick foundation. Such pavements are generally known as two-course brick pavements. The layer of cinders or gravel was leveled, and inferior paving brick were laid flatwise thereon; and then the joints of the bricks were swept full of sand. Brick foundations were formerly used very extensively, but recently have generally given place either to concrete, crushed stone, or gravel, and are used now only in a few localities which are remote from stone quarries and gravel pits in which brick are comparatively cheap. The chief defect in this form of founda tion was that the joints of the lower course were not fully filled, and consequently after the pavement was in service the sand of the cushion coat (the layer between the two courses of brick) would work into these joints and permit the bricks in the wearing course to settle. To cheapen the pavement, broken and chipped brick were used in the lower course, and the tendency was to place the larger face uppermost, thus making it nearly impossible to fill entirely the joints during the time of construction. This form of foundation was abandoned on account of its cost and in ferior quality.
The first brick pavement in this country, that at Charles ton, W. Va., was laid on a foundation of 1-inch tarred boards resting on a layer of 3 or 4 inches of sand, with a cushion of coat of 11 inches of sand between the bricks and the boards. This form, known as the Hale or the Charleston foundation, was not used to any consid erable extent, and has been entirely abandoned.