18 
lGEICULTUKE. 
and constructed of proper material. They not only furnish a means 
for the pavement to expand and contract with changes in tempera- 
ture, but they also eliminate to a large extent the disagreeable 
rumbling which has been so frequently associated with grout-filled 
brick pavements. 
The bituminous material of which the expansion cushions are made 
should be such as to remain firm in summer and not to become brittle 
in winter. It should also possess the quality of durability. In order 
to insure that any given material is suited for such a purpose, it is 
usually considered necessary to prescribe certain laboratory require- 
ments to which it must conform, and examples of these, which have 
been found to give good results, are contained in the section entitled 
"Typical specifications." (Cf. p. 22 et seq.) 
Expansion cushions should be provided for at the time the brick 
are laid, by placing a board of the required thickness on edge adjacent 
to each curb, as shown in figure 3. Small iron wedges, such as are 
shown in this figure, may be inserted between the curb and the board 
at the time the board is set. These wedges may be readily loosened 
and removed after the bricks have been laid and grouted, and may 
consequently be made to facilitate the removal of the board. 
The proper thickness for expansion cushions is a matter concerning 
which much difference of opinion exists among highway engineers. 
Some engineers advocate a minimum thickness of 1 inch, while others 
claim to have secured their best results by using expansion cushions 
having a minimum thickness as low as three-eighths inch for very 
narrow pavements. It is generally agreed that the thickness of the 
cushion should vary with the width of the pavement. The following 
suggestions for proportioning the cushion are offered as being fairly 
representative of the best practice : 
T^ble 1. — Ratio of thickness of cushions to width of roadway. 
Width of roadway 
(feet). 
Thick- 
ness of 
cushion 
(inches). 
20 or less 
1 
4 
1 
XI 
20 to 30 
30 to 40 
Over 40 
Plates III to VII, and Plate VIII, figure 1, show the various steps 
in the construction of a brick pavement. Plate VIII, figure 2, and 
Plate IX. figure 1, show the finished pavement as it should appear, 
and Plate IX, figure 2, shows the advantage possessed by grout-filled 
joints over joints filled with a soft material. 
