REINFORCED CONCRETE 89 



composed of hard, clean, vitreous clinker, free from sulphides, 

 unburned coal, or ashes. 



371. Water. The water shall be clean, free from oils, acids, 

 strong alkalies, or vegetable matter. 



372. Metal Reinforcement. The reinforcement shall pref- 

 erably consist of structural steel conforming to the specifica- 

 tions adopted by the Association of American Steel Manufacturers, 

 1910. (See Part V, Pars. 192 to 201.) 



In general round bars are preferable to square bars. Deformed 

 bars of hard steel and cold-twisted bars may be used in special 

 cases. 



For the prevention of shrinkage cracks, leakage cracks, and as 

 reinforcement for temperature stresses, or for minor details, 

 the bars used need not be tested. All other bars shall be 

 tested. 



373. Proportions. The proportion of the materials in the 

 concrete and the percentage of the reinforcement shall be specif- 

 ically stated in the contract. 



The aggregates used in the concrete shall be carefully selected, 

 of uniform quality and proportioned so as to secure as nearly 

 as possible a maximum density. 



In ordinary work the proportions may be selected according 

 to judgment based upon experience; but in important work, 

 or where waterproofing is required, the correct proportions for 

 maximum density shall be determined in each case by experiments. 



374. Unit of Measure. The unit of measure shall be the 

 barrel, which shall be taken as containing 3.8 cu. ft. and shall 

 contain 376 Ib. of cement net. A bag of cement shall contain 

 94 Ib. of cement net. 



375. Normal Concrete. For reinforced concrete work " nor- 

 mal concrete " shall be composed of 1 part Portland cement and 

 6 parts of aggregate, approximately 2 parts of fine and approx- 

 imately 4 parts of coarse aggregates, which shall be measured 

 separately capable of developing an average compressive 

 strength of 2000 Ib. per sq.in. in 28 days, when tested in cylin- 

 ders 8 in. in diameter and 16 in. long, under laboratory con- 

 ditions of manufacture and storage, using the same consistency 

 as is used in the field. 



376. Other Concretes. The strength and suitability of 

 concretes, other than normal concrete, for reinforced concrete 



