240 



RETAINING WALLS. 



CHAP. V. 



that there should be more than enough cement paste to fill the voids in the sand, and more than 

 enough mortar to fill the voids in the stone. With voids in sand and stone varying from 40 to 45 

 per cent, the quantities of the ingredients are closely given by Fuller's rule, where 



c = number of parts of cement; 



5 = number of parts of sand ; 



g = number of parts of gravel or stone. 



Then - - = p = number of barrels of Portland cement required for one cu. yd. concrete. 



\ s 

 - 



= number of cu. yd. sand required for one cu. yd. concrete. 



- --- - - - = number of cu. yd. gravel or stone required for one cu. yd. concrete. 



FIG. 12. CONTENTS OF CONCRETE RETAINING WALLS, ILLINOIS CENTRAL RAILROAD. 



The materials for one cu. yd. of I : 2 : 4 concrete will then be: Portland cement 1.57 barrels, 

 sand 0.44 cu. yd., gravel or stone 0.88 cu. yd. 



The proportions for plain walls commonly vary from r : 2| : 5 to I : 3 : 6, while the pro- 

 portions for reinforced walls vary from i : 2 : 4 to I : 2| : 5. 



Mixing and Placing Concrete. For mixing concrete a batch mixer in which the materials 

 can be definitely proportioned and thoroughly mixed is to be preferred. In cold weather the 

 concrete materials should be heated by the addition of boiling water to the mixer. To prevent 

 scalding the cement the sand, aggregate and hot water should first be placed in the mixer and, 

 after giving it several turns to remove the frost, the cement should be added and the mixing 

 completed. 



The author uses the following specifications for placing concrete in cold or freezing weather. 

 "When the temperature of the air during the time of mixing and placing is below 40 Fah. the 

 water used in mixing the concrete shall be heated to such a temperature, that the temperature 

 of the concrete when deposited in the forms shall not be less than 60 Fah. Care shall be used 

 not to scald the cement." 



Where the wall is in a cut and the materials can be delivered on the bank, the mixer may be 

 installed on the bank above and the concrete wheeled or chuted to place. Concrete should not 

 be chuted in freezing weather. In building the West Alameda Avenue Subway retaining walls, 



