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Some Novres ON THE STRENGTH OF CONCRETE BUILDING 
Buiocks. 
By H. H. Scorrerp. 
The concrete building block industry is rapidly assuming an important 
position and-is now established on a firm basis among the other industries 
supplying building materials. 
Reinforced concrete is now very largely used and seems to be the 
best form of concrete used for floors, beams and columns, but the concrete 
block seems to be the form of concrete most adaptable for use in the 
walls of residences and other buildings. 
The industry has grown so rapidly in the past few years that stand- 
ard specifications for their manufacture and use have been adopted by 
the National Association of Cement Users and by many cities of the 
United States. The need for proper specifications was brought about 
mainly on account of the large number of inferior blocks placed on the 
market by irresponsible manufacturers. The causes for this are various, 
such as: a desire for higher profits brought about by using inferior in- 
gredients; ignorance as to the best methods of using the materials at 
hand, careless workmanship and improper treatment as to storage, ete. 
The specification for crushing strength as called for by most specifi- 
cations is so high that it can be filled only by the best methods and the 
best material, and although it is many times more than a block will ever 
be called upon to stand in actual use in a wall, yet it insures a block 
which is strong, dense and thereby water-proof, with elean-cut, smooth 
edges, and a block which will endure for ages. 
The following are some items which enter into the making of good 
concrete blocks: 
In the selection of a cement, a maker has two alternatives. Ile must 
either use a first-class, standard brand of known excellence, or he may 
use the competitive brands on the market, thereby getting lower prices. In 
the latter case, he should have each shipment sampled and tested by a re- 
liable testing laboratory. 
An unsound cement may not show up till the block is in the wall or 
for years after, but it is practically inevitable that the block will finally 
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