TKST 



TortJHNKSS. 



33 



The maximum and minimum results obtained t'rom (lie tests of the 

 cementing value of the various materials received in this laboratory 

 are given in the following table, and in Table A of the Appendix are 

 found the results obtained on each sample. 



T \ lil.K 111. -O ni, utiutj ruin,-* <>f i-niitl-liuililiiit/ ruck*. 



TEST FOB TOUGHNESS." 



This test is made on 25 mm X 25 mm (0.98 inch) rock cylinders 

 with an impact machine especially designed for the purpose (fig. 8). 

 Instead of a flat-end plunger resting on the test piece as in the cemen- 

 tation test, a plunger with the lower and bearing surface of spherical 

 shape, having a radius of 1 cm (0.4 inch) is used. It can be seen that 

 the blow as delivered through a spherical-end plunger approximates 

 as nearly as practicable the blows of traffic. Besides this, it has the 

 further advantage of not requiring great exactness in getting the two 

 bearing surfaces of the test piece parallel, as the entire load is applied 

 at one point on the upper surface. The test piece is adjusted so that 

 the center of its upper surface is tangent to the spherical end of the 

 plunger, and the plunger is pressed firmly upon the test piece by two 

 spiral springs which surround the plunger guide rods. The test piece 

 is held to the base of the machine by a device which prevent- it> 

 rebounding when a blow is struck by the hammer. The hammer 

 weighs 2 kg and is raised by a sprocket chain and released automatic- 

 ally by a concentric electro-magnet. The test consists of a 1 cm 

 fall of the hammer for the first blow, and an increased fall of 1 cm 

 for each succeeding blow until failure of the test piece occurs. The 



a This test was designed by the writer while in charge of the laboratory of the 

 Massachusetts Highway ( 'on i mission, but was never put in operation. It has been 

 very much modified in the Washington laboratory. 



6090 No. 7903 3 



