117. Testing Portland Cement

In all important engineering works it is customary to test every fifth or tenth cask of cement for its soundness, fineness and strength.

For use in building piers and footings for ordinary buildings, it will be sufficient if the superintendent sees that only brands bearing a good reputation are used and that none of the cement has commenced to set or crust in the casks. Any such cement should be rejected.

In places where great strength and durability is required of the mortar careful tests should be made of every lot of cement used, as one lot of cement may differ very much from another lot of the same brand.

118. Color

Some idea of the quality of the cement may be gained from its color, but it should be supplemented by further tests for strength and fineness, as a bad cement may be of good color. Good Portland cement, as received from the manufacturers, should be of a gray or bluish gray color.

A brown or earthy color indicates an excess of clay and shows that the cement is inferior - likely to shrink and disintegrate. A coarse,.

* William G. Hartranft, before the Master Builders' Exchange of Philadelphia.

bluish-gray powder is probably over-limed and likely to blow. An undue proportion of underburnt material is generally indicated by a yellowish shade.

Weight. - The weight of Portland cement is sometimes specified as one of the requirements to be fulfilled, but as it is never constant, and cannot be precisely determined, it is of very little service in determining the value of a cement.

The finer a cement is ground the more bulky it becomes, and, consequently, the less it weighs; a light-burned cement also weighs less than one that is harder burned, so that light weight may indicate either a desirable fine grinding or an objectionable underburning.

The weight of cement should be determined by sifting the cement into a measure with a fall of 3 feet and striking the top level with a straight-edge. The following values determined in this way give fair averages for ordinary cements:

Portland, English and German................

77

to

90

lbs.

per cubic foot.

Portland, fine ground French.................

69

"

"

Portland, American......................

95

"

"

Roman............................

54

"

"

Rosendale......................

49

to

56

"

"

A bushel contains practically 1 cubic feet, so that the weight per bushel can be easily computed from the above table, if desired.