Hammering Road-Beds to Make Them Even 



A one -man -operated machine imparts more 

 than a thousand hammer shocks a minute 



MAXY concrete road foundations fail 

 because they are made of a porous 

 mortar or of a mortar in which the 

 materials are not properly mixed and bound 

 together. In 

 the first case, 

 water enters 

 the porous 

 mortar, freez- 

 es, and cracks 

 the entire sur- 

 face; in the 

 second case, 

 the surface 

 wears uneven- 

 ly because 

 there are 

 many patches 

 of improperly 

 bound stone 

 in some places 

 and areas of 

 pure mortar 

 in others. To 

 overcome 

 these difficul- 

 ties, concrete 

 road foundations are now hammered into 

 place as if b\' a thousand hammers to form a 



MOTORaCLE MOTOR 



A concrete roadway being nammered into unifcrmity 

 after the mechanically mixed base has been deposited 



.-■i/'-iZli-'/ ' ■ ■ ' 



BY VIBWVT10S3 



A motorcycle motor with an unbal- 

 anced fly-wheel supplies the vibration 



road-bed which is of exceptional density 

 and uniformity. 



An entirely new method is employed in 

 laying the hammered concrete roadway. 



After the con- 

 crete base has 

 been mixed 

 mechanically 

 and deposited 

 in place a lay- 

 er of screened 

 hard clean 

 stone is 

 spread. On 

 top of this is 

 laid a series of 

 narrow slat- 

 ted platforms. 

 These plat- 

 forms are 

 shaken by a 

 \" i b r a t o r , 

 which con- 

 sists of a 

 motorcycle 

 motor with an 

 unbalanced 

 fly'wheel. The metal frame on which the 

 flywheel is mounted is pushed back and 

 forth by one man. As the unbalanced fly- 

 wheel revolves it causes the entire frame- 

 work to vibrate violently, imparting from 

 one thousand to twelve hundred shocks 

 each minute to the wood platforms. 

 These shocks, aided by the weight of the 

 vibrator and the operator, force the hard 

 stones down into the concrete and at the 

 same time drive all air bubbles, cavities and 

 surplus mortar out of the concrete base. 

 The grout or fluid concrete is forced to 

 the surface. It is later swept off to expose 

 the top layer of rock, upon which the final 

 wearing surface of a special grade of coal tar 

 is applied. The tar serves to keep the 

 moisture in the concrete so that it will not 

 dr>' out too rapidly and provides a pro- 

 tective coat so that the road may be thrown 

 open to traffic in a few days instead of a 

 few weeks. It also provides a wearing 

 surface which will last several years; after 

 which the dense concrete may be used as 

 the surface or some other top dressing 

 applied. The top dressing of tar is only 

 one-quarter-inch thick and wears evenly. 



