cause the cement to set. In some cases, the
sand-cement bedding course is sprinkled just before the brick are laid
but in warm weather the setting would take place before the brick
could be rolled if that were done. In cool weather the setting is
sufficiently slow to permit rolling before the bedding course hardens.

The filler is applied to the surface after the rolling. If the
bituminous type of filler is employed, the hot filler is poured onto
the surface and worked into the joints by means of squeegees, with
comparatively little material left on the surface. In some instances
cone-shaped pouring pots are employed and the material is poured
directly into the joints.

The cement grout filler is applied in the same general manner as the
bituminous filler. The grout, consisting of equal parts of sand and
cement, is mixed to a thin consistency and poured onto the surface and
is then worked into the joints with squeegees. Two or more
applications are usually required to effect a complete filling of the
joints. The surface should be covered with sand and be kept moist
until the cement grout has set.

CHAPTER X

BITUMINOUS ROAD MATERIALS AND THEIR USE

Tars and asphaltic materials of various kinds are widely used for road
construction and maintenance, especially for road surfaces subjected
to motor traffic. Materials of this character that are employed in
highway work possess varying degrees of adhesiveness, and while they
may be semi-solid or viscous liquids at air temperature, they melt on
the application of heat and can be made sufficiently fluid to mix with
the mineral aggregates that may be used in the road surface. Upon
cooling, the bituminous materials return to the previous state and
impart a certain amount of plasticity to the mixture, at the same time
serving as a binding or cementing agent, which is sufficiently stable
for many classes of road construction.

=Classes of Bituminous Materials.=--Bituminous materials may be
classified, according to the source from which they are obtained, as
coal tars, water gas tars, native or natural asphalts and oil or
petroleum asphalts.

=Coal Tar.=--Coal tar is obtained as a by-product in the manufacture
of illuminating gas from coal. It is also obtained in the manufacture
of coke from coal. The tar thus obtained is manufactured into products
that are used for dust layers on gravel or macadam roads, binders for
macadam and gravel surfaces, fillers for brick, w