DRAINAGE METHODS FOR COUNTY ROADS. 67 
under even the most favorable circumstances, while 8 inches is suffi- 
cient for the worst conditions, except in the case of stone curbs where 
the stone used is not of very good quality. In the latter case a thick- 
ness of as much as 12 inches has been employed. 
STEEL HEINFOKCEMENT. 
In a few instances concrete foundations have been reinforced with 
steel in order to secure the required strength with less depth. But, 
in general, the use of steel reinforcement has been confined to anchor 
rods for tying flange curbs on to the foundation. For this purpose 
one-half -inch rods spaced about 18 inches apart should be sufficient. 
The rods should extend about 1 foot back into the foundation and 
should be bent so as to project up into the curb near its inner face. 
MATEEIALS. 
The materials composing Portland-cement concrete are: (1) Port- 
land cement, (2) sand, (3) gravel, crushed stone, or crushed slag, 
and (4) water. To secure high-grade concrete it is necessary that 
each of the constituent materials shall possess certain definite qual- 
ities. Inferiority in the quality of a single constituent may easily 
be responsible for complete failure of the concrete in which it is 
used, and can not be overcome by the relative excellence of the other 
constituents. While the cement and sand are the two materials 
most frequently responsible for failures, the coarse aggregate usually 
composes the bulk of the concrete, and if it is defective a correspond- 
ing weakness necessarily must be apparent in the concrete. 
In selecting materials for concrete availability is, of course, a 
very important consideration, but preference for local materials 
should be exercised only in so far as it can be controlled by such 
requirements regarding the quality of the materials as are known 
to have produced satisfactory results. Wherever any doubt exists 
as to the suitability of some particular material proposed for use in 
the concrete it should be subjected to such tests as will determine 
the points in question before its use is permitted. The following 
brief discussions of the different concrete materials should serve at 
least as a partial guide in making proper selections. 
Cement. — Portland cement is manufactured in nearly every section 
of the country, and most plants are equipped to turn out a satisfac- 
tory product. But the facts that poor cement sometimes may be 
produced by the most carefuly operated plants, and that good cement 
is damaged easily by age or exposure make it advisable to subject 
the cement to very careful investigation before it is used. Suitable 
specifications for Portland cement have been isued by the United 
States Bureau of Standards in their Circular No. 33 and by the 
