Sand Bedding Course.—The sand bedding course has been referred to as a sand cushion, but as a matter of experience the cushion effect is slight, although sometimes pavements have become uneven because the brick have pushed down into the sand after the pavement was used for a time. The sand for the bedding course should preferably be fine grained, all particles passing the eight mesh sieve, but ordinary concrete sand is satisfactory. The sand need not be clean, as a comparatively large percentage of silt or clay does not impair the usefulness of the material.
Fig. 19.—Cross Sections for Brick Highways
Sand Mortar Bedding Course.—In order to eliminate the tendency for the straight sand bedding course to shift because of the impact of traffic on the brick, a lean cement mortar is sometimes employed rather than the straight sand. Sand and cement in the ratio of one part cement to four or five parts of sand are mixed dry, and after the brick have been rolled, is moistened to furnish water to hydrate the cement. The sand employed is ordinary clean concrete sand.
Green Concrete Bedding Course.—In the monolithic type of brick road construction, the brick are laid directly on the green concrete base before the concrete has taken a set and the irregularities of the brick are taken up by rolling them until bedded in concrete.
Fillers for Brick Surfaces
The spaces between the brick are filled with some material that will prevent the brick from being displaced and prevent water getting to the bedding course. A suitable filler must adhere to the brick and fill completely the spaces between them. It must withstand traffic so as to remain intact in the joints and when in place it must be rigid enough to prevent displacement of the brick.
Cement Grout Filler.—One of the most commonly used fillers for brick pavements consists of a grout composed of Portland cement and fine sand. When properly mixed and applied the grout filler meets all requirements for a filler except that it is non-elastic and some means must be adopted for caring for pavement expansion.
Bituminous Fillers.—Asphaltic materials and tars are widely used as fillers for brick pavements. Such fillers are of high melting point and consequently solid at ordinary temperature. They are poured into the joints hot and when they cool are firm enough to comply with the requirements for a filler. In addition, they have enough ductility to accommodate the expansion of the pavement due to temperature changes.
Mastic Fillers.—Mastic consists of a mixture of about equal volumes of fine sand and a solid bituminous material. The mixture is prepared at high temperature and is worked into the joints between the brick while hot. When cool it resembles the straight bituminous filler except that the mastic is somewhat more resistant to wear than the straight bituminous filler.