10 CEMENTING POWER OF ROAD MATERIALS. 



mer head is brought into the cone of the adjusting rod the hammer 

 is exactty centered and brought free of the guide rods (D). As the 

 cross head (/) continues to rise, the bolts supporting the hammer, 

 which are tapered at an angle of about 45, are thrust open by the 

 sloping head of the adjusting cone rod (P), releasing the hammer, 

 which falls on a flat-end plunger (B] of 1 kg weight, which is pressed 

 upon the briquette ( 0) by two light spiral springs surrounding the 

 guide rods (F). This plunger (B] is bolted to a crosshead (G). A 

 small lever (</), holding a brass pencil (!} at its free end, is connected 

 with the side of the crosshead by a link motion arranged so that it 

 gives a vertical movement to the pencil five times as great as the move- 

 ment of the crosshead. The pencil is pressed against a drum (A), 

 and its movement is recorded on a slip of silicated paper fastened 

 thereon. The drum is moved automatically through a small angle at 

 each stroke of the hammer. In this way a record is obtained of the 

 movement of the crosshead during and after each blow of the hammer. 

 To the crosshead ( G] is fastened a steel rod (7?), which passes up through 

 the crosshead (/) and through a piece of metal securely attached to 

 the cone rod (P). At this junction a vernier scale is graduated, by 

 means of which the height of blow of the hammer can be accurately 



r 



QB Blowe, 



FIG. 5. Diagram showing point of failure in cementation test. 



set to 0.1 mm, and by lowering the cone rod until it rests on the ham- 

 mer cone (Z) the height of the briquette can also be measured to 0.1 mm. 



The standard fall of the hammer for a test is 1 cm (0.39 inch) and 

 this blow is repeated until the bond of cementation of the material is 

 destroyed. The blow producing failure is easily ascertained, for when 

 the hammer falls on the plunger, if the material beneath it can with- 

 stand the blow it recovers; if not, the plunger stays at the point to 

 which it is driven, and in either case the behavior of the test piece is 

 recorded on the drum. The automatic record thus obtained from each 

 briquette is filed for future reference. A copy of one of these records 

 is shown in figure 5. The number of blows required to destroy the 

 bond of cementation or resilience, as described above, is noted, and 

 the average obtained upon five briquettes is given as the cementing 

 value. 



The problem of holding the test piece rigidly under the intervening 

 plunger so that it would not be subjected to lateral movements and 

 transverse strains is one which has given much difficulty. Until 

 recently, a small brass plate with a beveled hole slightly larger than 

 the diameter of the briquette was used, but it was found that the test 

 piece was often seriously abraded by the side thrust developed. Later 



