A treatise on concrete, plain and reinforced : materials, construction, and design of concrete and reinforced concrete; 2nd ed. . PieceHead of Testing Machine Fig. 17a.—Bali-Bearing Block for Testing Machine. {See p. 78) of sand or dirt, which would prevent a good bearing. The load shouldbe applied at the rate of 600 lb. per min. The average of the results ofthe test pieces from each sample should be taken as the test of the pieces which do not break within | in. of the center, or are other-wise manifestly faulty, should be excluded in determining average Streng
A treatise on concrete, plain and reinforced : materials, construction, and design of concrete and reinforced concrete; 2nd ed. . PieceHead of Testing Machine Fig. 17a.—Bali-Bearing Block for Testing Machine. {See p. 78) of sand or dirt, which would prevent a good bearing. The load shouldbe applied at the rate of 600 lb. per min. The average of the results ofthe test pieces from each sample should be taken as the test of the pieces which do not break within | in. of the center, or are other-wise manifestly faulty, should be excluded in determining average Strength. 57. The tests may be made with any machineprovided with means for so applying the load that the line of pres-sure is along the axis of the test piece. A ball-bearing block for thispurpose is shown in Fig. 17a. Some appliance should be provided to STANDARD CEMENT TESTS 78g,. j^ aqtn jaqqnj eiqixajj \ \ nooo qooid-tf-}- 7Sb A TREATISE OX CONCRETE facilitate placing the axis of the test piece exactly in line with the centerof the ball-bearing. 58. The test piece should be placed in the testing machine, with apiece of heavy blotting paper on each of the crushing faces, which shouldbe those that were in contact with the mould. Constancy of Volume. 59. Significance. The object is to detectthose qualities which tend to destroy the strength and durability of acement. Under normal conditions these defects will in some casesdevelop quickly, and in other cases may not develop for a considerabletime. Since the detection of these destructive qualities before using thecement in construction is essential, tests are made not only under nor-mal conditions but under artificial conditions created to hasten the devel-opment of these defects. Tests may, therefore, be divided into tw^oclasses: (i) Normal tests, made in either air or w^ater maintained, asnearly as practicable,
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