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The Pamphlet Collection of Sir Robert Stout: Volume 73

Testing Cement

Testing Cement.

The usual tests adopted by Engineers when using cement in very large quantities, and upon important works are:

(1.)The Specific Gravity.—A properly clinkered and new cement should not be less than 3.1 after drying for 15 minutes in a dessicator. Any cement that shows this result may be accepted as a thoroughly well-burnt cement—whatever other faults it may possess. If the specific gravity is as low as 2.9 it shows either very light and imperfect burning, or old and deteriorated cement, or perhaps adulteration, and should certainly be looked upon with suspicion. Dr. Schumann's apparatus is very useful for this purpose. The result may readily be ascertained by noting the displacement of a carefully weighed quantity of cement in turpentine contained in a graduated tube; or by using a specific gravity bottle with water. In the latter case after adding the cement the whole must be well shaken for three or four minutes to prevent the cement setting.
(2.)The weight per striked bushel.—The minimum is usually specified at 110lbs. This is a very imperfect method, since the slightest variation in the manner of filling is liable to make a difference of several pounds—more or less—in the result.page 10
(3.)To ascertain that the cement has a right [unclear: composition] complete chemical analysis is necessary. This determines the [unclear: p] portion of the several ingredients. The principal [unclear: constituents,] before stated, are lime, silica and alumina (generally in [unclear: combination] iron). The hydraulic properties are due to the silica and [unclear: alumina] iron. The highest standard of quality is probably attained [unclear: wit] parts Ca O 2 Si O2, and 1 Al2 O3 (with Fe2 O3). Le [unclear: Chateli] equation is:— mathematical equation

The maximum quantity of lime permissible is still a [unclear: debati] question, Some German manufacturers fix the standard at 65 [unclear: percent].—a few English makers as high as 64 per cent.—but it is [unclear: ag] by all authorities that a greater proportion than 62 per [unclear: cent.] courting a dangerous compound.