Testing the Brick

The test is comparatively easy to make, and is a valuable check upon the rattler test (§ 740).

Impact and Abrasion Test.

This test is made by rolling or tumbling the brick, with or without pieces of iron, in a foundry rattler or revolving cast-iron barrel. This test is often called the rattler test. It is the crucial test of a paving brick and greatly exceeds in importance all the other tests combined. It is pre eminently the test that will show whether a brick will prove sat isfactory in service, and which of two or more samples will be the more enduring in the pavement. This test imitates more closely than any other the impact due to the horse's hoofs and shoes, and to the bumping of the vehicle wheels, and also the abrasion due to the slipping of the horse's feet and the sliding of the wheels. The tumbling, rolling, and sliding of the brick and iron over each other rapidly wear off the brick, and closely represents the treatment a brick will receive in the pavement. The result is jointly de pendent upon the toughness of the brick—its ability to resist shock,—and its hardness—its ability to resist abrasion.

To make this test of any scientific value in determining either the probable behavior of the material in the pavement or the rela tive merits of different brick, it is necessary to have some standard method of conducting the experiments. Unless some standard is established, this method can be employed only to select the best of a number of samples tested under exactly the same conditions. Several methods of standardizing this test have been proposed.

The first attempt to standardize the rattler test was made by the author.* Brick that had seen service in a pavement and pieces of well known natural stones used for paving purposes, together with small pieces of scrap cast-iron, were rolled in a rattler.

By this method any new paving brick could be compared with an absolute standard by securing samples of the natural stones used, and testing the brick and the stone under similar conditions. Shortly after being proposed, this method was quite widely adopted; but did not give satisfactory results, chiefly because the original experiments were made with a rattler having wooden staves, while subsequent tests were made with rattlers having staves. The method was objectionable on account of the trouble and expense of preparing the test pieces of natural stone.

Later the author made a series of tests using 2-inch cubes of brick and stone with foundry " stars" in a rattler having metal sides; but it was found that the results varied so greatly with the form, size and speed of the rattler as to make them of no great value.

Orton's Method. From 1895 to 1897, Prof. Edward Orton, Jr., of the Ohio State University, under the auspices of the Na tional Brick Manufacturers' Association,* conducted a very exten sive series of experiments upon the effect (1) of varying the form, size, and speed of the rattler; (2) of varying the quantity of brick in the rattler; (3) of successive periods of rattling; (4) with and without miscellaneous pieces of cast iron; and (5) with and without blocks of natural stone. Based upon these experiments a series of recommendations were made to the National Brick Manufacturers' Association which were adopted in 1897t as the standard method of making the impact and abrasion test of paving brick, and which were largely used for two or three years. This test was aban doned because of its failure to sufficiently discriminate the good and the poor paving brick, and also because of the great variation of duplicate tests. The distinguishing characteristic of this method was that only brick were placed in the rattling chamber.

In this method bricks or blocks equal to 15 per cent of the volume of the rattling chamber were placed in the standard rattler (see paragraphs 1 and 2, § 745) and revolved at the rate of 30 revolutions per minute for 1 hour. Under these conditions the loss of good paving brick varied from 15 to 25 per cent.

Talbot's Method. From 1895 to 1899 experiments were conducted at the University of Illinois under the direction of Prof. A. N. Talbot to determine the best composition of the abrasive material.* From these experiments the conclusion was drawn that the best results were obtained by the use of a mixed charge of two sizes of cast-iron blocks the distinguishing characteristic of this method of conducting the abrasion and impact test is the use of a charge of abrasive material composed of two sizes of moder ately heavy cast-iron blocks. The large blocks give chiefly impact and the small ones principally abrasion. The relative amount of these two forms of wear may be varied by varying the proportion of the two sizes. This method has been employed by a number of experimenters, and it has been shown conclusively that it is superior to that in which brick alone was used in the rattler for the following reasons : (1) it more nearly represents the condition of service in the pavement, (2) it gives more uniform results, and (3) it is more sensitive in differentiating hard and soft brick.