7G BULLET!?^ 724, U. S. DEPAKOOVIENT OP AGRICULTURE, 



iisuall}'^ employed in operating it is about 80. The hdurly output of 

 the hirger size should average about 18 cubic yards of concrete and 

 of the smaller size about 12.5 cubic yards. Assuming the cost of 

 labor at 20 cents per hour and malring a reasonable allowance for 

 depreciation of equipment and supervision, the cost of mixing and 

 placing the concrete may usually be estimated at from 60 to 80 cents 

 per cubic yard. 



NOTES ON SPECIFICATIONS. 



The following notes on specifications are given as typifying what 

 is believed to be the best practice so far developed in connection with 

 the various features of highway improvement that have been dis- 

 cussed in the preceding pages. These notes are given with a view to 

 making the information contained in the text readily applicable to 

 contract work. In order to. avoid repetition the notes on materials 

 are separated from those on the methods of construction. 



MATERIALS. 



Cement. — The cement for use in this work shall meet the requirements of 

 the standard specifications for Portland cement of the American Society for 

 Testing Materials, adopted in 1904 and revised in 1916, serial designation 

 C9-17. 



Provisions are made in these specifications for testing and storing the cement. 

 Under certain conditions, if the cement meets the 7-day tests satisfactorily, it 

 need not be held until the results of the 28-day tests are available. 



Fine aggregates: Sand. (See Bulletin 555, p. 19.) 



Stone or gravel screenings. (See Bulletin 555, p. 10.) 



Coarse aggregates: Broken stone or gravel. (See Bulletin 555, p. 9.) 



Broken slag. (See Bulletin 555, p. 15.) 



Cushion or bedding: Sand. (See Bulletin 555, p. 21.) 



Granulated slag. (See Bulletin 555, p. 15.) 



Grouting sand. (See Bulletin 555, p. 20.) 



Water. — The water used in the mixing of concrete or grout shall be free 

 from oil, acid, alkali, or vegetable matter, and fairly free from clay or silt. 



Cobblestones. — Cobble paving shall be constructed of bank or river cobbles, 

 sound in all respects and fairly symmetrical in shape. No stone shall be 

 used which is less than 6 inches or more than 10 inches in its longest dimension 

 or which does not have one lesser dimension at right angles to the length of 

 at least 4 inches. If preferred by the contractor, quarried stones which, in the 

 judgment of the engineer, are equal to the colibles above specified, may be sub- 

 stituted for the cobbles, provided that the limiting dimensions of the individual 

 blocks of quarried stone shall be the same as those specified for cobbles. 



CLAY FARM DRAIN TILE. 



NOT EXCEEDING 12-INCH DIAMETER. 

 [Copied largely from A. S. T. M. Standard Spociflcations C4-16.] 



The tile shall be made from shale, fire clay, or surface clay by such method 



of manufacture as will insure excellence of product and unifoi'mity in quality. 



The presence in the tile of visible grains or masses of caustic lime, iron 



