CEMENT INVESTIGATIONS IN ARIZONA. 
375 
ing render possible a reduction in size of cement grains at a cost 
which is small when compared with the great increase in the value of 
jithe resulting material. Where the freight charges are high, as is the 
ase at the locations under consideration, it is especially important 
to take advantage of this improvement, and there is no doubt that if 
the specifications call for a fineness such that only 1 per cent is to be 
left on a 100-mesh screen, the manufacturers will respond to the 
requirements. Engineering specifications have ordinarily allowed a 
residue of 5 per cent on a 50-mesh screen, although manufacturers 
have for some years permitted a residue of only 1 or 2 per cent on a 
50-mesh screen. 
CRUSHING TESTS. 
In order to obtain the crushing strength of the various cements and 
concrete considered, two 1-inch cubes of each were broken. The 
results given are the averages of the crushing strength of the two 
cubes. The cubes were allowed to remain thirty days in water and 
then thirty days in the air. 
Crushing tests of l-inch rubes. 
Character of mixture. 
Water. 
Average 
crushing 
strength. 
Standard C< >lton cement 
Colton cement. 1 part, and ordinary testing sand, 3 parts _ 
Col ton cement, 1 part, and marble sand, 2 parts 
Per cent. 
IS 
8 
8 
Tons. 
3.25 
1.75 
2.38 
Crushing tests were also made of 0-inch cubes of concrete after 
these had been immersed for thirty days in water. The portions of 
the mixture and the breaking strain in tons are given in the follow- 
ing table. In the mixture the proportions are given by volume and 
not by weight. 
Crushing tests of 6-inch cubes. 
Character of mixture. 
Colton cement, 1 part; ordinary sand, 3 parts; pebbles from gravel, 6 parts. 
Colton cement, 1 part: sand, 3 parts; crushed marble, 6 parts 
Colton cement. 1 part; sand. 2 parts; crushed marble, 5 parts 
Breaking 
strength. 
Tons. 
38 
30 
20 
It is believed that concretes of approximately equal value can be 
obtained by using cements in the following proportions, measured by 
volume: 
Portland cement, 1; sand. 3; broken stone, 7. 
Sand cement, 1; sand, 2; broken stone, 6, 
