1919] RUKAL ENGINEERING. 789 



affect the results very little, although for purposes of uniformity it is recom- 

 mended that all specimens be dried out prior to testing. Very accurately 

 prepared bearing surfaces are essential if reliable results are to be expected. 

 The effect of vibrations of the plunger and secondary blows produced by the 

 rebound of the hammer during the progress of the test are apparently 

 negligible." 



Tests of concrete road ag-gregates, J. P. Nash {Amer. Soc. Testing Materials 

 Proc, 17 (1917), pp. 894-421, figs. 12). — In studies of the causes of deterioration 

 of concrete in roads, tests wei'e conducted on concrete, using various coarse 

 aggregates, including wear and tension tests. The conclusions drawn from 

 these tests are as follows : 



"Uniformity of wear is obtained when the mortar and the coarse aggregate 

 wear equally, such as when crushed limestone or limestone gravel is used in a 

 1:2:4 mix. The coarse aggregate should be limited in size to about 1.5 in. 

 When hard, tough stone is used, the size should be limited to about 1 in. and 

 the cement content increased. It is questionable if a richer mix than a 

 1:2:4 is an economical one to use with crushed limestone of the ordinary 

 hardness. Crushed slag when hard and uniform should be satisfactory as a 

 concrete road aggregate from the standpoint of wear. In a 1:2:4 concrete, 

 a gravel composed of very hard stones such as flint, or quartz, does not wear 

 uniformly. The action of the cubical shot on the test specimens is a trifle more 

 severe than the traffic on the road. It can not be said that either the crushed 

 stone or gravel tested is superior as an aggregate to produce concrete having 

 a higher tensile strength." 



A new consistency tester for viscous liquid bituminous materials, P. Hub- 

 bard and F. P. Pkitchaed {Amer. Soc. Testing Materials Proc, 11 {1917), pp. 

 603-626, figs. 8). — In attempting to devise a convenient laboratory instrument 

 for determining consistency at normal temperatures, the authors followed the 

 general principle of the Lunge and Hutchinson tar testers with a view to im- 

 provement in certain important details. After numerous trials an instrument 

 was obtained made of aluminum and weighted with lead shot. 



The instrument is 3 in. long and weighs exactly 2.8 gms. It consists of two 

 aluminum rods of different diameters one of which is hollow, a thin aluminiun 

 disk 1.25 in. in diameter, and a tapered bottom weight. The larger rod is about 

 one-half the length of the smaller which passes through it and screws into the 

 bottom weight. The aluminum disk is riveted transversely to the rods where 

 they join about midway of the length of tlie instrument thus forming a balanced 

 plummet. 



A special bitumen container is used with this instrument. It consists of a 

 cylindrical flanged copper cup 2 in. in diameter and 3.75 in. deep, which is 

 placed in a water-bath fitted with a stirrer passing through the flange of the 

 cup. The flange is also provided with a small hole for the insertion of a 

 thermometer in the bath. 



Before making a test, the bituminous material which fills the inner com- 

 partment of the water-bath is brought to a temperature of exactly 25° C, 

 which must be maintained in the bath throughout the test. The surrounding 

 atmosphere should also be as close to 25° as possible. The test is made by 

 allowing the instrument to sink of its own weight in the bituminous material 

 from the upper edge of a lower scale marking on the small rod to that of an 

 upper marking, and noting the time required. 



This instrument was found to have a wide range of usefulness, as shown 

 by numerous tabulated test results. At normal temperatures it may be used for 

 all bituminous materials outside of the range of the Engler viscosimeter and 

 the usual penetration machine. When used in connection with a representative 



