VITRIFIED BRICK AS MATERIAL FOR COUNTRY ROADS. 23 
by the engineer, and the materials composing it shall conform to the 
following requirements : 
Cement. — The cement shall be of some standard brand, and shall 
conform to the United States Government specifications for Portland 
cement, as contained in Circular 33 of the Bureau of Standards. 
Cement shall be delivered in sacks of 94 pounds net weight, and each 
sack shall be considered as having a volume of 1 cubic foot. All 
sacks which contain lumps or the contents of which have been dam- 
aged by exposure to the weather or other cause shall be rejected. 
Sand. — The sand shall consist of dry clean quartz grains, and shall 
not contain more, than 5 per cent of clay, loam, or other foreign mate- 
rials. The grains shall be well graded and of such size that all will 
pass a ^-inch mesh screen and not more than 20 per cent will pass a 
No. 50 sieve. 
Coarse aggregate. — The coarse aggregate may consist of either 
broken stone or gravel. Stone shall be hard and tough, and shall be 
broken in such manner that all will be retained on a ^-inch mesh 
screen and will pass a H-inch mesh screen. Xot more than 75 per 
cent of the stone shall pass a f-inch mesh screen, and not more than 
75 per cent shall be retained on such a screen. 
Gravel shall consist of hard, sound particles of stone, thoroughly 
clean, and shall conform in size to the above specifications for broken 
stone. 
Placing. — The concrete shall be deposited in place immediately 
after it is mixed and shall be thoroughly compacted as fast as it is 
placed. The top surface shall be smoothed by troweling with spades 
or by some other means approved by the engineer, and when com- 
pleted shall conform to the proposed surface of the finished pavement 
at the required depth below it. 
Time of setting. — The concrete shall be carefully protected from 
the weather and all other disturbing influences, and kept moist by 
sprinkling for at least 36 hours after it is placed in the foundation. 
This period may be increased at the discretion of the engineer. Any 
damage resulting to the foundation before the wearing surface has 
been laid, no matter what the cause of such damage may be, shall be 
repaired by the contractor at his own expense. 
Sand cushion. — After the foundation has been constructed and 
permitted to set as above provided, a layer of sand shall be uniformly 
spread over the foundation to such depth that when " struck off" 
and compacted its thickness shall be 2 inches. The sand composing 
this layer shall be dry when spread and shall conform in all respects 
to the requirements given above for the sand to be used in concrete. 
The cushion shall be struck off with a suitable template which con- 
forms to the cross section of the finished pavement, and shall be 
thoroughly compacted by rolling with a hand roller weighing not less 
