5
TESTS OF METALS AND OTHER MATERIALS, 1900.
ones. The spliced bars had covering straps on each side, secured by means of bolts or rivets.
The effects of overstraining loads on wrought-iron bars were determined^ These tests had reference to phenomena accompanying the exaltation of the elastic limit by overstraining loads, followed by an interval of rest. The examination included different grades of puddled iron, and overstraining loads of different magnitude were employed, followed by intervals of rest of long and short duration.
In addition to the exaltation of the elastic limit to be expected in tests of _ this kind, in further confirmation of this well-established feature it appeared from the results that the effects of these lower overstraining loads—i. e., where the elastic limit is but slightly exceeded—could be traced in the subsequent behavior of the metal up.to loads nearly approaching, if not indeed coincident with, the ultimate tensile strength of the material.
Among other tests of a miscellaneous order are a number of bronze specimens, copper cylinders for pressure gauges in the determination of powder pressures in guns, cartridge cloth, paper, and a series of tests on a number of kinds of bricks submitted by the engineer commissioner of the District of Columbia.
In continuation of the tests of preceding reports there are results on concretes of arsenal manufacture 1 and 2 years old; also of some cement and concretes submitted by Mr. H. A." Carson, chief engineer of the Boston transit commission, and by Messrs. William Wirt Clarke & Son, Baltimore, Md.
An inquiry into the properties of cements has furnished some important information. The inquiry has been directed toward features which are regarded as possessing fundamental value in the physics of this class of material.
Beginning with the chemical analyses of the cements the tests have proceeded with observations on the fineness of grinding, specific gravity determinations on the ground material before and after hydration, and in the cake; determinations of the water held in hydrated material and carbon dioxide present; the rate of setting as'influenced by the quantity of water used in gauging; the temperature acquired by large cubes of neat cement while setting, which it is shown may exceed the boiling point of water; tests on retarded sets, or when the cement has been held in the mortar bed different intervals before being allowed to set and indurate undisturbed, and also tests bearing on the so-called ‘ ‘ second set ” of cement.
A special lot of cement in which there was no sulphate of lime—the usual “ restrainer ” for controlling the rate of setting—was supplied through the courtesy of the Bonneville Portland Cement Company, and its behavior has been ascertained in conjunction with cement of the same manufacture in which the usual commercial mixture was represented.
A large number of tests have been made on Portland, slag, and natural cements which set in air at different temperatures. The facilities of a cold-storage warehouse were utilized for exposing one group of specimens to a temperature of about 0° F., another group to a temperature in the vicinity of 39° F., while a third group remained in the open air during the period of setting. The several groups were each exposed to their respective temperatures immediately after guaging.