BQ BULLETIN SOI, IT. S. DEPARTMENT OF AGRICULTURE. 
Keinforcement should consist of steel of medium hardness and for 
generalise should be in the form of bars or rods, as they are adaptable 
alike for Trails, columns, beams, and slabs. These bars may be of any- 
suitable shape, of which there are a great variety on the market. The 
plain, round or square bars are entirely satisfactory for all ordinary 
sizes. Many companies make a specialty of supplying steel for this 
use; the rods may be had cut to the proper length and bent to the 
exact shape desired. Usually it is best to use regular stock lengths 
and do the bending locally. A very simple bending machine for 
hand operation may be had for this work. Keinforcement for use in 
the slab may consist in whole or in part of woven-wire reinforcing 
not over 2 inches in diameter, and preferably should be of varying sizes, ranging 
from li inches down. It may consist of hard stone, such as trap rock, 
granite, limestone, and aggregates which are hard and do not decompose when 
subjected to severe heat. (The U. S. Bureau of Standards may supply re- 
ports, at a very small charge, on materials submitted.) The sand should 
be clean and free from loam, clay, or organic matter. The grains should be 
fairly coarse or a mixture of fine and coarse with the coarse grains predom- 
inating. The Portland cement should be of a good quality. While analytic 
tests have been fixed as a required standard (see U. S. Bureau of Standards 
Circular Xo. 33, United States Government Specification for Portland Cement 
1912; also Standard Test Specifications for Portland Cement recommended 
by the American Society for Testing Materials), it is usually a safe policy 
to use a brand of cement which has! been on the market and in satisfactory 
use for five years and is made by a reliable company. Water for mixing 
should be free from alkali or injurious salts! in damaging qualities. (See 
U. S. Bureau of Standards Bulletin Xo. 12: Action of the Salts in Alkali 
Water and Sea Water on Cement.) 
Slag from blast furnaces, if burned free from coal, may be used as the 
coarse aggregate for concrete. It makes a concrete which is light, fairly 
strong, and withstands fire well. However, there are but few localities where 
slag is available. 
Crushed terra cotta, 'tile, or brick are good substitutes for crushed stone 
for concrete, provided the clay material is hard-burned and used properly. 
After crushing, the dust should be screened out and the crushed brick should 
be wet thoroughly before mixing, for if the material is used dry it will absorb 
too rapidly the water used in mixing the concrete. Care should be exercised 
to see that brick used are hard and well-burned and that they are free from? 
mortar; otherwise the finished concrete will be unreliable in strength. 
Gravel should not be used for concrete work which may be subjected to 
fire, as such use has been found exceedingly dangerous. The use of quartz 
gravel in the reinforced concrete of a warehouse at Far Eockaway. X. Y., 
caused serious damage from a fire of comparatively short duration. A detailed 
report of this fire, written by Mr. Ira H. Woolson, may be had from the 
Xational Board of Fire Underwriters, Xew York City. A valuable test of 
gravel as compared with other stone for concrete has been made by the Bureau 
of Standards and the results have been recorded in an illuminating way by 
Mr. Walter A. Hull. (See Proceedings American Concrete Institute, Vol. 
XIY, 191S.) There is no objection to gravel, however, for concrete paving 
and for footings of the foundation, 
