242 PLAIN CONCRETE 



for a 1-2-4 mixture, 380 Ib. per sq. in. for a 1-2-5 mixture, 

 and 285 Ib. per sq. in. for a 1-3-5 mixture, while a 1-3-6 

 mixture gave a result of 226 Ib. per sq. in. 



The values given in the accompanying table are recom- 

 mended as ultimate values by W. Purves Taylor, engineer 

 in charge of the municipal testing laboratory of Philadelphia. 

 The figures represent values obtained from six hundred 

 experiments made on concrete properly mixed with good 

 Portland cement. It will be noticed that the values given 

 for shear are considerably lower than those just given. The 

 results obtained depend to a large extent on the method of 

 testing. Some engineers prefer the lower values. 



MIXING AND WORKING OF CONCRETE 



CONCRETE MIXTURES 



Methods of Measuring Ingredients. After deciding what 

 proportions of ingredients will be used for the concrete, the 

 engineer must be able to calculate the exact quantity of 

 each material that he must order. An ordinary box car 

 holds from 400 to 600 bags of cement. The purchaser is 

 charged for the bags by the manufacturer, unless they are 

 of paper, but he gets a rebate for those which are returned. 



Cement is usually measured by the barrel just as it comes 

 from the manufacturer, or as 4 bags to the barrel, while 

 broken stone and sand are measured loose in a barrel. Port- 

 land cement, after it is taken out of its original package and 

 stirred up, fills a larger volume than when packed. It is 

 therefore necessary to state just how the cement is to be 

 measured; and, as said before, the custom is to measure 

 it by the barrel, compact. A cement barrel contains about 

 3.8 cu. ft. 



Fuller's Rule for Quantities. A practical rule has been 

 devised by W. B. Fuller whereby, after the proportions of 

 ingredients have been fixed, the quantity of material for a 

 certain work may be obtained. It is called Fuller's rule for 

 quantities, and may be expressed in mathematical symbols 

 as follows: 



