DUST PREVENTION AND EOAD PRESERVATION. 
concrete the faces of such joints were washed with a 10 per cent 
solution of muriatic acid and then with water. 
Protection of concrete after laying. — As soon as practicable after 
laying the pavement it was covered with canvas and was so pro- 
tected until the concrete had set hard enough for it not to be injured 
by a man walking upon it. The canvas was then removed and the 
concrete was covered with a layer of loam or sand about 2 inches 
in depth. This was kept wet for a period of 8 days. The cov- 
ering was allowed to remain on the pavement for a period of 15 days, 
after which it was removed whenever it was convenient to do so. 
Typical mechanical analyses of all the coarse aggregates used are 
given in Table 4. 
Table 4. — Mechanical analyses of coarse aggregates used in all concrete experiments. 
Passing 2-inch, retained on lj-inch screen. 
Passing 14-inch, retained on 1^-inch screen 
Passing lj-inch, retained on 1-inch screen. 
Passing l-inch, retained on f-inch screen. . 
Passing f-inch, retained on J-inch screen. . 
Passing J-inch, retained on J-inch screen. . 
Passing J-inch screen 
Gravel. 
2.3 
10.8 
24.0 
25.8 
26.4 
Lime- 
stone. 
13.2 
34.2 
47.4 
5.2 
Trap. 
19.5 
40.6 
24.9 
8.4 
100.0 
Table 5. — Analyses of fluid residual petroleum used in oil-cement concrete for experiment 
No. 4. 
Specific gravity 25°/25° C 0. 933 
Viscosity, Engler, 50° C., 100 c. c. specific 27.8 
Per cent of loss at 163° C, 5 hours (20 grams) 2.67 
Float test of residue, 32* C. (time) V 35" 
Per cent of total bitumen insoluble in 8G° B . naphtha 2. 31 
Per cent of fixed carbon. „ 3. 01 
Per cent soluble in CS 2 (total bitumen) 99. 90 
Per cent of organic matter insoluble 08 
Per cent of inorganic matter insoluble 02 
Total : 100. 00 
Hydrated lime experiment. — Between stations 47 + 90 and 49 + 00 
hydrated lime was also added to the concrete. The proportioning 
of the mixture for this section of the experiment was as follows: 
Hydrated lime, 20 pounds; cement, 188 pounds; sand, 4 cubic feet; 
coarse aggregate, 7 J cubic feet; and oil, 10 pints. 
Experiment No. 5. — Cement concrete. 
Location: 
Station 33+60 to station 37+85, gravel aggregate. 
Station 37+85 to station 42+50 .. 
, ,. .. . „-, , , ,. An , ,,+ limestone aggregate. 
Station 44+61 to station 46+10] to& ° 
Station 46+10 to station 52+00, trap rock aggregate. 
• Total length: 1,339 feet. 
Total area: 3,013 square yards. 
