PORTLAND CEMENT CONCRETE PAVEMENTS. 
Table I. — Granulometric analysis of quartz sand. 1 
Size of grains. 
Grams. 
Per cent. 
Retained on — 
0.0 
74.0 
124.5 
266.0 
460.0 
624.0 
930.5 
1, 139. 5 
1, 159. 5 
1, 198. 5 
51.5 
0.0 
5.9 
, 10.0 
21.2 
36.7 
49.8 
74.3 
91.1 
92.7 
No. 200 screen 
96.5 
3.5 
100.0 
1 Total weight of sample, 1,250 grams; weight of sample after washing, 1,208 grams. 
Experience has shown that when first-class sand is used very good 
results are obtained by using a proportion of 1 part of cement to 1J or 
If parts of sand and making the proportion of coarse aggregate such 
that the resulting concrete will contain slightly more mortar than is 
sufficient to fill all voids. If a well-graded gravel is used as coarse 
aggregate, the proportion should be about 1 : 1J : 3, while in most cases 
where broken stone is used as coarse aggregate it will be found desir- 
able to make the proportion about 1 : 1 J : 3, and in some cases, where 
the particles of stone are of uniform size, even a still greater propor- 
tion of mortar will be required, but this should be effected by de- 
creasing the amount of coarse aggregate and not by further increas- 
ing the amount of sand. 
Since the bottom course of a two-course pavement is not subjected 
to the wearing action of traffic, it would appear that the rules for 
proportioning the materials for this course might be considerably 
modified. On the other hand, using different proportions in the top 
and bottom courses undoubtedly results in the concrete of the tAvo 
courses having different coefficients of expansion and different moduli 
of elasticity, and these differences might tend to cause a separation 
of the two courses. The fact that such separations sometimes occur 
strengthens this theoretical objection. 
CONSTRUCTION. 
There are two general types of concrete pavement, known as the 
one course and the two course. These designations are due to 
the fact that the former consists of one course of concrete, all of 
which is mixed in the same proportion and composed of the same 
kind of materials, while the latter consists of two courses of concrete, 
usually mixed in different proportions and containing different kinds 
of aggregate. Plate X, figure 1, shows a typical cross section for a 
