16 THE TESTING OF KOAD MATERIALS. 



Observations were taken over :^,<M)0 miles of road. The traffic was 

 classified and rated as follows: 



(1) Kach horse hauling a public vehicle or a cart loaded with prod- 

 uce or merchandise, 1. 



(*2) Each horse hauling an empty cart or a private carriage, ^. 



(3) Each horse, cow, or ox unharnessed, and each saddle horse, j. 



(4) Kach small animal (sheep or goat), -gV 



A record of traffic was made every thirteenth day throughout the 

 year, and an average taken to determine the amount. The general 

 average over all the roads in IS!);] was 17<>J> units of travel. To 

 repair the roads there had been required an average of 4i> cubic yards 

 per mile and per 100 units of travel. The detailed accounts of this 

 work are published in the official report of the minister of public- 

 works of France," and offer a mass of data which, when combined 

 with the results of laboratory tests, should be of great service in 

 determining the value of the latter. The results of these elaborate 

 service* tests show, in general, a decided agreement with the results of 

 the laboratory tests which were conducted at the same time. Since 

 the investigation described laboratory tests have been the basis of 

 selection of road materials in France. 



In Portugal some attempt has been made to determine on a large 

 scale the wear of roads and its relation to laboratory tests. A census 

 of the traffic was kept at the tollgates and the wear was determined 

 by making observations of the thickness of the roadbed whenever 

 excavations had to be made. The results of these observations have 

 not yet been published, but in a ministerial report it is stated that the 

 laboratory tests indicated very clearly the best materials for use. 



HISTORICAL REVIEW OF ROAD-MATERIAL TESTS. 



It is only comparatively of recent years that tests of materials of 

 construction have been carried on in a systematic way and the history 

 of road material testing is of Mill more recent date. Doubtless the 

 ancient Roman engineer satisfied himself of the suitability of his mate- 

 rials to the end in view, but this was probably done in a very general 

 way. 01- snme record- would have come down to us of the methods 

 employed. Many of the earlier wiiters on macadam road building 

 noted the >uper'mrity of wear in certain varieties of rock, and reference 

 is often made to the desirability of hard and tough rock. As early as 

 the middle of the last century compre>-ion te-N were made on rocks in 



the endeavor to determine, their road- build ing <pialit\. The systematic 



testing of road materials may he said, however, to have been begun 

 during the decade opening with I s7n. in France, where it has been 



Campau, A. P. Rockwell, Roads unl Pavements in France. 



