18 CEMENTING POWER OF ROAD MATERIALS. 



Considering only the crystalline rocks and excluding clays and 

 gravels, Table IV, given at the close of the report, reveals a decided 

 tendency toward high-binding rocks in certain sections of the country 

 and to exceedingly low ones in others. The amount of data so far 

 collected does not as yet justify a definite conclusion being drawn on 

 this point, but it is highly significant that in one State, out of some 30 

 samples tested, not one had a higher value than 10, while in another 

 State, out of an equal number of samples, only 1 fell below that figure. 

 It is perhaps too soon to say that these results are not fortuitous, but 

 it is quite apparent that in those localities where good road materials 

 are abundant good roads will be found, and it is a fact that the samples 

 which are sent to the laboratory from the two States noted for having 

 the best roads and greatest mileage represent almost invariably high- 

 binding materials. It is evident that the possession of good road 

 materials will stimulate their use, whereas the discouraging results of 

 failure in less-favored communities will keep the people shut in by 

 mud and ruts for much longer periods. This point of geographical 

 distribution, which perhaps has never been brought out before these 

 investigations were instituted, is sufficient to justify and encourage all 

 scientific stud}' of road materials. Undoubtedly what is needed is 

 more data, much more indeed than can be supplied b} T one laboratory, 

 however complete its equipment. State laboratories under the direction 

 of or in collaboration with the State highway commissioners would soon 

 accumulate data which would make possible road-material maps giving 

 all the plrysical data in as accurate a manner as possible. Before, how- 

 ever, such cooperation can be of the slightest value, the methods of 

 tasting must be standardized so that all results may be comparable. To 

 this end the writers in 1903 urged the American society*- for testing 

 materials to appoint a committee to consider the whole subject and 

 report on standard methods. This committee has been appointed and 

 is at work with every prospect of arriving at a successful conclusion. 



One great obstacle to the growth of road -material testing is the cost 

 of the machines. An important problem which is engaging the atten- 

 tion not only of this laboratoiy but also that of the Maryland geological 

 survey is the simplification of the various tests, and more particularly 

 of the various machines necessary, so that the cost of equipment of a 

 road-material laboratory shall be brought within the means of all. 



