Table 68 {continued). 

 MECHANICAL PROPERTIES. 



(c) Concrete . 



91 



Co^fCRETE; Compressive strengths. Experimental values for various mixtures. Results compiled by Joint 

 Committee on Concrete and Reinforced Concrete. Final Report adopted by the Committee July i, 1916- 

 Data are based on tests of cylinders 203.2 mm (8 in.) diameter and 406.4 mm (16 in.) long at 28 days age. 

 American Standard Concrete Compressive Strengths. 



Aggregate. 



Granite, trap rock 



Gravel, hard limestone and 

 hard sandstone 



Soft limestone and soft 

 sandstone 



Cinders 



Units. 



kg/mm* 

 lb/in2 



kg/mm* 

 lb/in2 



kg/mm^ 

 Ib/in^ 

 kg/mm^ 

 lb/in2 



Mix. 



2-3 

 3300 



2.1 

 3000 



1-5 



2200 



0.6 



800 



2.0 



2 Soo 



1-3 



1800 



o-S 



700 



2200 



1.4 

 2000 



I . t 



1500 



0.4 



600 



1-3 



1800 



1600 



0.8 



1200 



0.4 



SOO 



i.o 

 1400 



0.9 

 1300 



0.7 

 1000 



0.3 



400 



Note. — Mix shows ratio of cement (Portland) to combined volume of fine and coarse aggregate (latter as 

 shown). 



Committee recommends certain fractions of tabular values as safe working stresses in reinforced concrete 

 design, which may be summarized as follows: 

 Bearing, 35 per cent of compressive strength; 



Compression, extreme fiber, 32.5 per cent of compressive strength; 



Vertical shearing stress 2 to 6 per cent of compressive strength, depending on reinforcing; 

 Bond stress, 4 and 5 per cent of compressive strencth, for plain and deformed bars, respectively. 

 Modulus of Elasticity to be assumed as follows: 



(See Joint Committee Report, Proc. A. S. T. M. v. XVII, 1917, p. 201.) 



Editor's Note. — The values shown in the table above are probably fair values for the compressive strengths 

 of concretes made with average commercial material, although higher results are usually obtauied in laboratory 

 tests of specimens with high grade aggregates. Observed values on 1:2:4 gravel concrete show moduli of 

 elasticity up to 3160 kg/mm^ or 4,500,000 lb/in- and compressive strengths to 4.2 kg/mm^ or 6000 \h/\vr 



Tensile strengths average 10 per cent of values shown from compressive strengths. 



Shearing strengths average from 75 to 125 per cent of the compressive strengths; the larger percentage 

 representing the shear of the leaner mixtures (for direct shear, Hatt gives 60 to So per cent of crushing strength) . 



Compressive strengths of natural cement concrete average from 30 to 40 per cent of that of Portland 

 cement concrete of the same proportioned mLx. 



Trans\xrse strength: modulus of rupture of i : 2§ : S concrete at i and 2 months equal to one sixth crushing 

 strength at same age (Hatt). 



Weight of granite, gravel and limestone, 1:2:4 concretes averages about 2.33 g/cm' or 14s lb/ft'; that of 

 cinder concrete of same mix is about 1.85 g/cm' or 115 lb/ft' 



Concrete, 1:2:4 Mix, Compressive Strengths at Various Ages. 



Experimental Values: one part cement, two parts Ohio River sand and four parts of coarse aggregate as 

 shown. Compressive tests made on 203.2 mm (8 in.) diameter cylinders, 406.4 mm (16 in.) long. (After Pitts- 

 burgh Testing Laboratory Results. See Rwy Age, vol. 64, Jan. 18, 1918, pp. 165-166.) 



Coarse aggregate. 



Gravel. . . . 

 Limestone, 

 Trap rock. 

 Granite . . . 

 Slag No. I 

 Slag No. 2 



Unit. 



kg/mm- 



lb/in2 



kg/mm'^ 



lb/in2 



kg/mm" 



lb/in2 



kg/mm^ 



lb/in= 



kg/mm- 



lb/in2 



kg/mm^ 



lb/in2 



Age. 



14 days. 



1-35 

 1921 

 1.24 

 1758 

 1-45 

 2063 

 1.49 

 2122 



1-75 

 2484 



1-37 



1941 



30 days. 



1. 61 

 2294 



1-53 

 2174 

 1.67 

 2386 

 1. 61 

 2292 

 2.16 



3075 

 1.78 



2525 



60 days. 



2.0(j 

 2925 

 2-35 

 3343 

 2.36 



3360 

 2.14 



3043 

 2.37 

 3365 

 2.06 

 2930 



I So days. 



2.67 

 3798 

 311 

 4426 



3-39 

 4S19 

 2.92 



4151 

 3-38 

 4803 

 2.64 



3753 



Note. — Maximum and minimum test results varied about 5 percent above or below average values shown above. 

 Smithsonian Tables, 



