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Some Notes on the Strength of Concrete Building 



Blocks. 



By H. II. Scofielu. 



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, etc. 



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 clean-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. He 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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