PROJECTS IN CONCRETE CONSTRUCTION 143 



6) Test a small quantity of sand for clay by putting 



about 4" or 6" in a fruit jar, adding water and 

 shaking until clay is in solution. Set aside and 

 let clay settle on top of the sand. Determine the 

 per cent of clay present. 



7) What per cent of clay is allowable in average con- 



crete work? 



8) Examine available gravel or broken stone. See if it 



is free from clay, organic matter or soft particles. 



9) Can you scratch the stone with your thumb nail? 



10) What would the effect be to use soft stone in making 



concrete? 



11) Is the coating of fine dust ordinarily found on lime- 



stone detrimental in making concrete? 



12) Examine some bank-run sand and gravel as in Nos. 



5 and 8. 



13) Why is it poor practice to use ordinary bank-run 



material for making concrete? 



14) Suppose it is required that a piece of concrete work 



be made of bank-run material that has 50 per cent 

 as much sand as gravel, and that it is to be equi- 

 valent in strength to a 1 : 2 : 4 mixture where the 

 sand and gravel are graded. How much would 

 be required for each sack of cement? 



c) Problems: 



Assume a 1 : 2 : 4 mixture and determine the amount of 

 materials needed; also cost: 



1) To make a circular tank 6' 0" inside diameter at the 

 top and 5' 4" diameter at the bottom, and 2' 0" 

 deep, The wall of the tank to be 4" thick at the 



