ditryek] CEMENT INVESTIGATIONS IN ARIZONA. 373 
SAND CEMENT. 
Sand cement is a term applied to a mixture of cement and sand 
ground together in a dry state to an impalpable powder. As a rule 
Portland cement and quartz sand are the materials thus used. This 
mixture is then used with ordinary sand and gravel, as in the cus- 
tomary practice. The proportion of pure cement is thus considerably 
reduced, but the strength and durability of the concrete has been 
found to be nearly as great as that made with the undiluted cement. 
The explanation offered for the remarkably good results obtained 
with sand cement when used with ordinary coarse sand is that the 
voids in the coarse sand are nearly filled with the finely ground sand. 
The grains are thus bonded together and to the coarse sand by the 
uniformly diffused particles of the fine cement. The amount of voids 
in the ordinary sand, in other words, is greatly reduced by the fine 
sand, fulfilling the requirement for a strong mortar that must be of 
dense character, the grains being of such graduated size and so 
well mingled as to afford the maximum contact of the surfaces of the 
particles. 
In sand-cement mortar the grains of sand are extremely minute, 
the mixture being so fine that only 5 per cent residue is left on a 
screen of 200 meshes to the linear inch or 40,000 meshes to the square 
inch. The great density thus obtained contributes to the imperme- 
ability to water and increases the compressive strength and load- 
bearing capacity, thus rendering the mass of value for constructing 
foundations, dams, and sea walls. 
In the tests made in this investigation a rock known as pearlite, an 
acidic lava or rhyolite from the Buttes dam site, was used, and also 
samples of quartzite from the San Carlos dam site. These were chosen 
because of the abundance of these rocks at the localities named and 
their superior hardness. The Portland cement used was that manu- 
factured at Colton, Cal., this being made nearest to the place where 
it will be used and being sold at a lower price than other Portland 
cement in the local market. All of the tests were made with the 
same sample of cement, portions of this being taken for the several 
mixtures with cruahed pearlite and quartzite. The sand used with 
the foreign cement in making sand cement was clean beach sand from 
dunes along the coast. 
TESTS OF SAND CEMENTS. 
Results of the tests of the sand cements and comparisons with other 
mixtures are given in the following table. In each case the crushed 
pearlite was mixed with an equal weight of cement, and the mixture 
was ground in a mortar until it all passed through a screen having 200 
meshes to the linear inch. The same method was pursued with the 
quai'tzite from San Carlos, thus making sand cements composed of 
equal parts of Portland cement and pulverized rock ground to an 
exceedingly fine condition. 
