154 EXPERIMENTS IN ROAD SURFACING 



only one to compare with it, but the material of section 12 con- 

 tains absolutely no rotten stone, and the plot compares favora- 

 bly, thus far, with the macadamized road described in Bulle- 

 tin 30, which is surfaced with Salem trap rock. 



Plot number 13 seems to have worn most nearly like 

 numbers 4 and 5. The cross section is now flat, and the sur- 

 face needs a new coat of gravel. 



Section 14 has received just enough gravel to keep it from' 

 being much muddy in the spring, but it has worn flat and hol- 

 lowing. 



In section 15 a few of the large bottom layer stones have 

 worked to the surface, and produce the same unevenness that 

 has been noted in some other plots. 



The macadamized section of 125 feet in length described in 

 Bulletin 30, has been tested now for five years, and, with the 

 exception of some 12 feet at the easterly end, has stood up per- 

 fectly. This particular portion was purposely underlaid with 

 several inches of clay, with a clay subsoil underneath that, 

 and, during the first spring following its construction, heaved 

 and settled unevenly. It does not seem to have been aflected 

 much since, but it shows conclusively that extra care and 

 depth of surfacing material are necessary with a clay subsoil. 

 There is a marked difference, evident at first inspection, be- 

 tween the wearing qualities of a first-class macadamized sur- 

 face, say of Salem crushed stone, and of one made from sili- 

 cious, water-worn stones found in gravel banks. The case of 

 section 12, however, shows that the difference is more in the 

 quality of the rock used than in the shape of the pieces, the 

 water-rounded pieces having bonded together surprisingly 

 well, though, of course, the angular fragments would be pre- 

 ferred. 



WORK BY TOWN OFFICIALS 



A commendable practice prevails in some towns of gravel- 

 ing immediately after using the road machine in the early 

 spring, the gravel thus covering up and helping to smooth 

 over the inequalities due to the running of the machine. In 

 such cases a very successful practice consists in dumping a 

 load of gravel about once in eighteen to tvv^enty feet, and 

 spreading this not over five feet in width along the centre of 



