262 



STRENGTH OF MATERIALS 



Arsenal.* The table shows the variation of the modulus of elasticity 

 for different stresses. Leliigh Portland cement was used and the 

 cubes were set in air. 



212. Concrete building blocks. During the past few years great 

 progress has been made in the manufacture and use of concrete 

 building blocks. In comparison with stone these have the adva: 

 of cheapness, ease of manipulation, and beauty of the finished 

 product. A type of concrete building block is shown in Fig. 158, and 

 illustrates the general characteristics of such blocks. 



Few tests have been made on concrete blocks, and but liulr is 

 known as to their durability. The following table is a report i a 

 series of tests made at the University of Michigan.! Tin- Mocks were 

 first tested in flexure, and then an uninjured portion of the block 

 was tested in compression. Blocks 3,4, 5, and (> \\ere from the same 

 mixture, and were composed of one part cement, two parts sand, and 

 three parts broken stone. They were all tested after four months. 



TESTS OF < <\ KI.TI. r,Ul.l>l\<; m.oCKS 



Problem 177. A concrete building block 24 in. in length ami having an eff< 

 -rrtion of 8 in. x 10 in. minus 4 in. x 10 in. is tested by being support 

 both ends and loaded in the middle. The load at failure is found to be 6000 Ib. 

 Find the- maximum fiber stress, the height of the block bt-ini: 1<> in. 



* Watertoion Arsenal Report, 1903. 



t Concrete, February. 



