STEEL 



25 



Test pieces of steel wire used for reinforcement should bend 

 180 degrees around their own diameter without fracture. 



PROBLEMS 



1. A concrete as proportioned by mechanical analysis is a 1 : 2.1 : 4.9 

 mixture by weight. If both the sand and stone weigh 100 Ib. per cubic 

 foot, what are the corresponding proportions by volume considering 100 

 Ib. of cement as 1 cu. ft.? 



2. What would be the correct proportions by volume of the concrete of 

 Problem 1, if the sand weighed 95 Ib. per cubic foot and the stone 90 Ib. 

 per cubic foot? 



3. Consider a 1 : 2 : 4 concrete, and let a cubic yard be composed of 1.57 

 bbl. of cement, 0.44 cu. yd. of sand, and 0.88 cu. yd. of stone. The 

 cement costs $1.50 per barrel and the stone $1.20 per cubic yard. Two 

 sands are available, one at 500 and the other at $1.00 per cubic yard, 

 which give a corresponding compressive strength of concrete of 2000 and 

 2200 Ib. per square inch respectively. Which sand is the more economi- 

 cal if the concrete is to be used in members sustaining purely compressive 

 stresses? 



4. By carefully grading the materials in Problem 3 using the 500 sand, it 

 was found that practically a 1 : 3 : 6 mixture having 1.11 bbl. cement, 

 0.47 cu. yd. sand, and 0.94 cu. yd. stone, per cubic yard of concrete, 

 could be used to give the same strength that the $1.00 sand gave in 

 Problem 3. The added cost of labor for proportioning and mixing the 

 concrete, due to the use of graded materials, was 100 per cubic yard. 

 WTiat would be the saving on a piece of work involving 10,000 cu. yd. 

 of concrete? 



5. The sieve analysis of a bank gravel is as follows: 



Show by mechanical analysis curves how you would screen the gravel 

 into two sizes and combine to secure a concrete of greater density and 

 strength. 



