PAVING BRICK TKSTS. 23 



10 to 17 gave good results on roads where travel \\a> light, while those 

 below 10 were found to be too soft. 



Compression tests are also carried on at the laboratory for Icslin-^ 

 materials at Lisbon, which is equipped with three compression 

 machines. Tests can be made on 10 cm. Tern, and i> cm cnbe>. a- 

 desired but the smaller cubes, which are crushed both dry and wet. 

 are generally used for testing road materials. No coefficient ha> been 

 worked out for this test. The number of kilograms per square centi- 

 meter required to destroy a test piece is used for comparison. All 

 samples are sent to the laboratory by the directing engineer of the 

 district from which they come. The results of these laboratory te-N 

 have been found to be in agreement with the limited observations 

 made on the actual wear of roads. 



HISTORY OF PAVING BRICK TESTS. 



An account of the work of the National Brick Manufacturers' A>-< > 

 ciation in establishing a standard rattler test, and of the critical and 

 confirmatory studies of other investigators arising therefrom, would 

 give a fairly complete history of the development of paving brick 

 tests. 



Formerly reliance was placed entirely on the decisions of the street 

 inspector, who rejected individual bricks that were defective in form 

 or hardness. The necessity for such work has not disappeared, even 

 with the development of the present perfected tests. Many engineers 

 have used for some time the cross breaking and crushing tests, or else 

 the absorption test as an index of internal structure, but gradually 

 specific tests and standards of quality have been reached through 

 experience. 



The rattler test has been used for some years. In 1895 the National 

 Brick Manufacturers' Association appointed a commission on paving 

 brick tests. The first report a of work, issued in 1897, included the 

 results of the following studies: The rattler test by Edward Orton: 

 the absorption test by H. G. Wheeler; the cross-breaking test and 

 additional studies of the rattler test by F. F. Harrington, and specifi- 

 cations for the cross- breaking test by J. B. Johnson. As a conse- 

 quence of these reports the rattler test was chosen as the m<t 

 significant and reliable, and the size and speed of the rattler and 

 the duration of the test were specified in accordance with the prex-nt 

 standard, although no abrasive shot were then used in the rattler. 

 The absorption test was condemned because it did not indicate the 

 the relative value of different brands of paving brick. It was 

 admitted, however, that there existed in the case of any given brick 

 a particular per cent of absorption which indicated whether the brick 

 had been properly burned. The fact was also brought out that an 



o Report of the Commission appointed to Investigate the Subject of Paving Brick 

 Tests. T. A. Randall & Co., Indianapolis. 



