58 DEPARTMENT BULLETIN 1216, U. S. DEPT. OF AGRICULTURE 
(1) 1:2: 3Vi=94 : 2 times 95 : SV> times 110. 
=94:190:385 proportion by weight. 
=1:2.02:4.10=1:6.12. 
190 
(2) Percentage of sand in base mixture aggregate — , . X 100=33 
Percentage of sand in new mixture=60 
(3) 60—33=27. 
27 times 0.05=1.35. 
6.12—1.35=4.77, therefore the new proportion by weight is 1 : 4.77. 
(4) since 60 per cent of the total aggregate is to be fine aggregate, 
1:4.77=1:2.86:1.91 
(5) 1 : 2.86: 1.91=94 pounds: 269 pounds : 180 pounds. 
Dividing by the unit weights of materials. 
94 : ~95~ ' 110 =1 CUDic foot: 2.83 cubic feet : 1.64 cubic feet. 
Or if unscreened gravel is to be used, determine the unit weight of the 
gravel. Assume for this case 115 pounds per cubic foot. 
Then 1 : 4.77=94 pounds to 449 pounds. 
Dividing by unit weights, 
94 449 
ttt : tte— 1 cubic foot: 3.90 cubic feet. 
94 115 
This method applies to either screened or unscreened mixtures of sand and 
gravel in which the specific gravities of the fine and coarse aggregate are 
approximately equal, and to percentages of fine aggregate greater than 33 ^ 
Recommended practice in the use of unscreened gravel : 
1. The fine aggregate portion must pass the user's specification for fine 
aggregate. 
2. The coarse aggregate portion must pass the user's specification for coarse 
aggregate. 
3. Unscreened gravel should not be used unless in the opinion of the engineer 
in charge, the amount of sand in the aggregate will not vary more than 10 
per cent. 
4. Unscreened gravel should only be used from stock piles containing the 
largest practicable amount of material. 38 
39. METHODS OF TESTS FOR WIRE ROPE (GUARDRAIL) 
1. The report of the physical test of wire rope shall include the following in- 
formation : Diameter of the rope, diameter of the wire, number of strands and 
wires, length of lay of strands and wires, cross-sectional area in square inches, 
breaking load in pounds, and a note as to whether the failure was in the body 
of the rope or at the socket. 
DEFINITIONS 
2. (a) The "lay of the rope" is the length expressed in inches for each com- 
plete turn of a strand around the axis of the rope measured along the axis. 
(&) The "lay of the strand" is the length expressed in inches for each com- 
plete turn of a wire around the axis of the strand measured along the axis, 
(c) The diameter of a wire rope is the diameter of a circle inclosing it. 
3. The cross-sectional area of the rope shall be determined as follows : Meas- 
ure the diameter of the component wires of a strand and obtain the mean 
diameter. The area calculated from the mean diameter of the wire multiplied 
by the number of wires in each strand and by the number of strands gives the 
aggregate area of the wires in the rope. 
4. The test specimen for the tension test shall be free from bends and not less 
than 4 feet in length. Before cutting the test pieces from the coil of rope the 
ends must be " served " or wound about with wire for a length of about 1 inch 
to prevent the strands from unlaying. 
37 The method can be applied to mixtures of materials of different specific gravities, 
such as sand and crushed limestone, by reducing the proportions to relations by absolute 
volume and making the adjustment upon that hasis. 
38 For a theoretical discussion of the method of proportioning see Bulletin No. 60, 
Engineering Experiment Station, Iowa State College (6) and also a paper by R. W. 
Crum, Proceedings American Society for Testing Materials, 1922 (7). 
