314 MASONRY 



that the materials will be of such various sizes that all voids will 

 be filled. When a concrete is made of cement, sand, and stone, 

 and the stone is of such a size that it will pass through a 3-in. 

 ring, but will not pass through a 2^-in. ring, the concrete is 

 weaker and requires more cement than one made with stone 

 graded from 3 in. down. When the stone is graded in size, 

 the smaller-sized stones fill the voids between the larger stones, 

 and thus reduce the amount of cement required. The grading 

 of the stone also makes the concrete stronger. Some engineers 

 specify that the stone must pass through a ring 2 in. in diameter, 

 more engineers specify a 2^-in. ring, and even a 3-in. ring is 

 not uncommon. For very thin walls, and for small work, 

 such as concrete blocks, it is necessary, of course, that the 

 size of broken stones shall not be too large to place them in 

 the mold. It can, however, be stated as a general proposi- 

 tion that the larger the stones, the stronger will be the concrete. 



Usual Proportions of Concrete. For reinforced concrete and 

 more important concrete work, such as piers and dams, a 

 1-2-4 mixture is generally used. In columns, even a richer 

 mixture is sometimes required. For less important work, 

 a 1-2-6 mixture is commonly used; and for rubble concrete, 

 even a 1-4-8 mixture is sometimes employed. 



Methods of Measuring Concrete Ingredients. Cement is 

 bought by the barrel, but it is usually shipped by the bag. 

 Four bags of Portland cement make a barrel. Natural cement 

 comes in the same-sized bags, or in larger bags making 3 bg. 

 to a barrel. An ordinary box car holds from 400 to 600 bg. 

 The purchaser is charged with the bags by the manufacturer, 

 unless they are of paper, but he gets a rebate for those he 

 returns. A barrel of Portland cement weighs 375 lb.; a barrel 

 of natural cement, 300 lb. 



Cement is usually measured by the barrel the way it comes 

 from the manufacturer, or as 4 bg. to the barrel, while broken 

 stone and sand are measured loose in a barrel. Portland cement, 

 after it is taken out of its original packing 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, it is customary to measure it by the barrel compact. 

 A cement barrel contains about 3.6 cu. ft. 



