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BULLETIN 246, U. S. DEPARTMENT OF AGRICULTURE. 



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 : 



Table 1. — Ratio of thickness of cushions to width of roadway. 



Width of roadway 

 (feet). 



Thick- 

 ness of 

 cushion 

 (inches). 



20 or less . 

 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. 



