In 1895 the National Brick Manufacturers Association appointed a commission to investigate the subject of paving brick tests and to recommend standard methods for their conduct. This commission was made up of representative men, and they had unusual facilities for their investigation. The work done marked a distinct advance in the testing of paving brick. The report of this commission* made in February, 1897, contains much valuable data on the subject of testing paving brick. The investigation of the rattler test was made by Prof. Edward Orton, Jr., of Ohio State University. His experiments were conducted upon Canton red granite repressed brick pavers, burned so as to have a high degree of uniformity. These brick were of as high quality as is gen erally available for paving purposes. A general summary of the results of Professor Orton's investigation of the rattler test may prove of interest in this discussion.
Tests were made with charges of foundry shot made up of small scraps which had been used in a foundry as an abrasive to clean rough castings. These pieces composing the foundry shot were small, aver aging less than one-half pound and in no case being more than one and one-half pounds. The resulting loss was small and, of course, was due almost wholly to abrasive action, the impact, effect being very slight. Cast-iron bricks weighing approximately seven pounds each were next used in the rattler. Charges of these cast-iron shot equivalent to 10, 15, 20 and 25 per cent of the volume of the rattler were tried, five paving brick being tested each time. The bricks subjected to this test sustained comparatively little loss by abrasion, the principal loss being by break ing and chipping. The effect of the impact with these heavy shot was very severe. Without trying another size of shot or attempting to blend the abrasive and impact effect by means of a mixture of sizes, the use of iron was abandoned, though Professor Orton felt that its cheap ness, its long life, and its uniformity at all parts of the country would make it particularly suited for a standard filling if its action as an abrasive were favorable.
Tests were then made using natural stone of the general size of pav ing brick. It was found that limestone, sandstone, and granite were
as variable in their losses as are brick, that the results obtained with the paving brick when tested with blocks of stone were exceedingly erratic, and that the accompanying expense and trouble themselves rendered this method unacceptable.
Tests were made with paving brick alone in the rattler, no other abrasive or filling material being used. After an elaborate set of tests made with a few of determining the best speed, size of charge, etc., Pro fessor Orton reported that with brick alone in a rattler of 28-in. diameter the volume of the charge of brick should be from 10 to 15% of the vol ume of the rattler, the test should be continued for at least 1500 revolu tions, that the speed should be between 24 and 36 revolutions per min ute, and that the length of the rattling chamber should not be less than 18 inches. These conditions were found to give the least variation in results, the most severe wear, and to be the most convenient.
The commission also had the advantage of the tests made by Mr. E. F. Harrington, of the testing department of the city of St. Louis, which were along the same lines and gave confirmatory evidence. Pro fessor Orton's report submitted specifications for the conducting of a standard rattler test and ,these were adopted by the commission almost without modification. These specifications are now known as the old National Brick Manufacturers Association test and sometimes as Orton's test. The making of a standard for the size and speed of rattler and for the charge was a great step in advance, but the peculiar feature of the test, the use of brick alone in the rattler, did not prove to be a fortunate arrangement, as it was soon shown that this test failed to discriminate to a sufficient degree between good and poor paving brick. This feature has since been eliminated, and a definite charge of cast iron shot is now used in the standard test. However, as its reproduction here may make it convenient for reference for some, the specifications adopted by the Paving Brick Commission of the National Brick Man ufacturers Association are here given.