Mat 28, 1915] 



SCIENCE 



799 



continuity of the policy. The territory is going 

 through practically the same experience that every 

 state in the Union has been through in its road 

 work. 



Service Tests on Various Classes of Pavements: 



H. W. Durham. 



A solid unyielding foundation is a necessity for 

 all road construotion, but type and details are 

 purely a local question. Much unnecessary eon- 

 fusion is caused in road discussion by inability to 

 discriminate between cause and effect and by lay- 

 ing more importance on details of specifications 

 than on the result they obtain. 



The only true test is that of service under con- 

 ditions of actual use. Final selection must be 

 made among a limited number of types and suit a 

 limited number of conditions. Carrying inter- 

 mediate operations in the problem of selecting 

 road types to extremes of refinement is unnecessary 

 in that the conditions to be satisfied are few, and 

 the final selection must be from among these 



Service Tests of Stone BlocJc Pavements in Brook- 

 lyn: H. H. Schmidt. 



About five years ago studies were begun of the 

 various granite pavements in the borough of 

 Brooklyn, with a view tO' determining, if possible, 

 the causes which created the objectionable fea- 

 tures. Observation showed that certain granite 

 blocks polished under traffic, so that they became 

 extremely slippery; some wore down rapidly at 

 the edges, causing the top of the block to become 

 turtle-backed, which made the pavement extremely 

 rough; some blocks were found which disinte- 

 grated under traffic, and still others were extremely 

 rough and not well-shaped, owing to the fact that 

 they were made from a granite which had im- 

 proper cleavage planes. We learned from the 

 service tests of the stones actually subjected to 

 traffic, that the mineralogical composition of the 

 granite, the presence or absence of certain miner- 

 als, and the proportions in which they occur, as 

 well as the size of the crystals, all had a direct 

 bearing on its value for paving purposes. 



After a conclusion had been reached as to the most 

 desirable granite, a study of the size, dressing and 

 filler was taken up. With the use of a concrete 

 base, the extreme depth of the block was unneces- 

 sary, and the depth was therefore reduced from 

 i eight to five inches. With modern granite block it 

 is possible to obtain joints averaging from a 

 quarter to three eighths of an inch. The blocks are 

 laid so close together that a considerable area of 



the blocks touch one another, thus giving stability 

 to the pavement, even without the joint filler. It 

 is unnecessary with the modern granite block pave- 

 ment to use paving gravel, and the modern practise 

 favors the use of a mixture of tar or asphalt with 

 hot sand, poured into the joints. 

 Wood Block Pavements : W. P. Taylor. 

 The Value of the Absorption Test on Wood BlocTcs: 



George W. Tillson. 



When municipal engineers were considering the 

 advisability of laying treated wood block pave- 

 ments some twelve or fourteen years ago, it was 

 uncertain as to just what should be the require- 

 ments of the specifications. It was felt that it 

 was necessary to prevent the blocks from decay 

 and also to treat them so that they would be stable 

 under all climatic conditions; that is, they should 

 not absorb so much water as to swell and cause 

 the pavement to bulge, during a wet spell, nor 

 should they shrink too much in dry, hot weather, 

 so that they would become loose. 



After careful consideration, it was decided to 

 require an absorption test of the blocks. The test 

 provided that after being dried in a kiln at a tem- 

 perature of 100° F. for 24 hours, the blocks should 

 not gain in weight more than 3 per cent, during 

 immersion. Pavements were laid under this speci- 

 fication in 1903 and 1904, and on one street with a 

 preservative that did not contain any resin, but 

 was a specially prepared oil. The blocks obtained 

 did, however, conform to the requirements as to 

 weight and absorption. These pavements have 

 been in use 10 and 11 years, without any expan- 

 sion joint, and have required almost no attention 

 on account of the instability of the blocks. In cer- 

 tain cases where pavements were laid not under the 

 supervision of the city, so that the absorption test 

 was not applied, the pavements did expand to a 

 very considerable extent. 



The city of New York is the only municipality 

 of which the writer knows where the absorption 

 test is required, and it is also the only city, in his 

 knowledge, where an expansion joint is not used. 

 The writer firmly believes that with a heavy oil 

 treatment of 20 pounds and a specification requir- 

 ing an absorption test, as given above, satisfactory 

 results can be obtained without an expansion joint. 

 Sand Cushion vs. Mortar Bed for Wood BlocTc 



Pavements: Theodoe 8. Oxholm. 



In this country it has been the custom for 

 many years to lay wood block pavement on a con- 

 crete base with a cushion of sand or a bed of mor- 

 tar between the base and the blocks. A sand 

 cushion is intended primarily to smooth out the 



