Numerous methods have been proposed and tried for the construction of tar footwalks, differing from each other in the materials mixed with the tar to form the concrete, and in the manipulation of the process. Ashes mixed with sand and gravel are usually em ployed, and sometimes clinkers from an iron foundry. A somewhat successful pavement of this class has a small amount of Portland cement mixed with the ashes and sand used in forming the concrete before the addi tion of the tar.
Asphalt footway pavements are formed either of as phalt blocks or of a surface of sheet asphalt. Where blocks are used they are laid in the same manner as brick upon a foundation of sand or gravel. The blocks, or tiles as they are commonly called, are usu ally made flat, about 8 inches square and 2 to 2i inches thick. They are laid with their edges either at right angles to the street line or at an angle of 45° with the street line — usually at right angles, on account of greater ease in laying.
Sheet-asphalt footways are laid in the same manner as an asphalt street pavement, the pavement, however, being given a less thickness. In Washington, D. C., these pavements are made about 3 inches thick, and constructed upon a bituminous base. Material re
moved from street pavements in re-surfacing is used for forming the surface material of the footway.
In Europe rock asphalt is frequently used for foot ways. Asphalt mastic is commonly employed, mixed with sand or gravel to give a wearing surface. The in gredients are heated together and applied hot to a broken-stone or concrete foundation. In Europe hy draulic cement concrete is used for the base, as in the driveways., A layer of 3 or 4 inches of concrete is em ployed, with a surface layer of rock asphalt or asphalt mastic and sand, ' to I inch in thickness for ordinary work.