2-4 BULLETIN 373, U. S. DEPARTMENT OF AGRICULTURE. 
subgrade. a 6-inch concrete foundation, and suitable curbs, niay be 
estimated by substituting in the formula : 
Cost per square yard = 1.90 L + .213 C + .138 S + .157 A — .010 B. 
The cost as estimated from this formula should usually be increased 
by about 10 per cent to allow for wear on tools and machinery and 
to guard against unforeseen contingencies. If it is desired to use a 
different thickness of foundation, it is safe to assume that each inch 
subtracted or added to the thickness of the foundation will make a 
corresponding difference of from S to 12 cents in the cost per square 
yard. 
MAINTENANCE OF BRICK PAVEMENTS. 
If brick pavements are properly constructed at the start, the work 
of maintaining them is very slight. Under the closest inspection, 
however, some inferior material is likely to become incorporated 
either in the foundation or hi the surface, and it is therefore very 
important that a brick pavement be very carefully watched for the 
first few years of its life to see that no unevenness develops either 
because of defective brick having been used in the surface or because 
of insufficient support from the foundation at any point. T\ Tienever 
any unevenness develops, it should be immediately rectified. Other- 
wise the pavement will become irregularly worn in the vicinity of the 
defects, and expensive repairs will eventually be necessary. 
Not infrequently weak spots develop in broken stone or gravel 
foundations, owing to surface water finding its way through joints 
in the pavement which have not been properly filled with grout. 
Careful observation of the joints should therefore constitute a part 
of the early maintenance work, and any defective joints discovered 
should be immediately remedied. TThere the foundation is con- 
structed of concrete, however, slight defects in the joints seldom 
result in any very serious damage. 
If care is exercised to correct all defects which appear within the 
first few years of the life of a well-constructed brick pavement, the 
work of maintaining the pavement proper should thereafter, except 
for cleaning, be almost negligible for a considerable period. The 
shoulders and drainage structures, of course, need occasional atten- 
tion, just as in the case of any other pavement, but if they are 
properly constructed at the start repairs will usually be very slight. 
The life of a well-constructed brick pavement can not be estimated 
with any great degree of exactness, first, because the traffic condi- 
tions are constantly changing, and. second, because no brick pave- 
ment which has been constructed in accordance with the best modern 
practice has yet worn out. Such measurements as have been made 
