PORTLAND CEMENT CONCRETE PAVEMENTS. 6 
4. They can be maintained at comparatively small cost until re- 
newals become necessary. 
5. They may be made to serve as an excellent base for some other 
type of surface when resurfacing becomes desirable. 
6. They present a pleasing appearance. 
The principal disadvantages are: 
1. They are somewhat noisy under horse traffic. 
2. There is no method of constructing necessary joints in the pave- 
ments which will entirely prevent excessive wear in their vicinity. 
Furthermore, joints do not altogether eliminate cracking, and wher- 
ever a crack develops it must be given frequent attention in order to 
prevent rapid deterioration of the pavement. 
3. They can not be as readily and effectively repaired as many other 
types of pavements. 
MATERIALS AND CONSTRUCTION. 
It is especially desirable that concrete for road pavements should 
possess, in as great degree as practicable, (1) hardness, in order to 
resist the abrasive action of traffic; (2) toughness, in order to resist 
the disintegrating action of horses' hoofs and other shocks; and (3) 
homogeneity, in order that the surface may wear uniformly. 
The character of the constituent materials and the proportions in 
which they are mixed both have a marked influence on the degree in 
which these qualities are possessed by the concrete. In selecting the 
materials and determining the proportion in which they are to be 
mixed, the prospect of securing the desired qualities in the resulting 
concrete should be given primary consideration. The methods of 
mixing, depositing, and curing the concrete are also important fac- 
tors in securing satisfactory results and. will be discussed in their 
proper places. 
MATERIALS. 
No hard and fast rules can be laid down which would fit all cases 
in the selection of concrete materials, as availability is necessarily a 
very important factor. Satisfactory cement can usually be obtained, 
and none should be used in constructing pavements which does not 
meet all the requirements for a high-grade Portland cement. The 
cost of importing the sand and coarse aggregate from any consider- 
able distance is usually prohibitive, and if there are any local mate- 
rials which are or can be made suitable for aggregates they should 
be given first consideration. But if the local materials are not such 
as to meet substantially the requirements outlined in the following 
paragraphs, it would be very doubtful economy to use them. 
