OFFICE OF PUBLIC ROADS. 741 



placing sand and cement in the mixer and adding enough water to 

 form a thin mortar. Oil is then added alternately with the stone 

 until enough oil has been added to the batch, when the remainder of 

 the stone is added and the mixing continued until completion. The 

 types of oil best suited for oil-mixed concrete work are fluid residual 

 petroleums. 



Practical tests of oil-mixed concrete roadways are now in progress 

 at the following places : Meridian Place, Washington, D. C. ; Innis 

 Street at Elm Park Station, Staten Island, running east from Morn- 

 ing Star Road to John Street; and two bridge floor surfaces at 

 Ridgewood, N. J.^ Oil-mixed concrete has likewise been used with 

 good success in the construction of new vaults in the United States 

 Treasury. These vaults were water-proofed by oil-mixed concrete 

 mixed in the proportions of 1 part of cement, 2 parts of sand, and 4 

 parts of gravel, together with 10 per cent of oil. They have 

 remained dry under very trying conditions. 



These service and laboratory tests are exceedingly encouraging 

 and indicate the possibilities of a very wide future usefulness of oil- 

 mixed concrete in a great variety of construction. 



A public patent, which has aroused much interest throughout 

 the country, has been granted for mixing oil with Portland-cement 

 concrete and hydraulic cements giving an alkaline reaction, so that 

 anyone may use this process without the payment of royalties. 



INVESTIGATIONS OF ROCK, SLAG, AND CEMENT. 



The work carried on in the petrographic laboratory is essentially 

 a continuation and extension of that of last year. Quantitative 

 petrographic analyses, of 141 rock samples were made, while 115 

 samples were qualitatively analyzed and 102 specimens were exam- 

 ined chemically for the purpose of identification. 



Besides this ordinary routine work, the study of blast-furnace and 

 open-hearth slags and Portland-cement clinkers was continued to 

 determine the composition and physical properties of this class of 

 road material. Up to the present time, 121 slag samples have been 

 examined microscopically and 30 chemical analyses have been made. 

 A classification of this material has been perfected, based on mineral 

 and chemical composition, and this meets all practical requirements. 

 The cementing value and other physical tests have demonstrated 

 that the more basic slag varieties possess hydraulic properties similar 

 to Portland cement, and they would, therefore, appear well suited 

 for road binders as well as for certain kinds of concrete construction. 



During the past year 23 samples of Portland-cement clinkers from 

 various parts of the country have been examined microscopically 

 and chemically, and a series of physical tests have shown that these 

 clinkers may be ground with a large proportion of water-cooled 

 blast-furnace slag to yield mixtures but slightly inferior in tensile 

 strength to that of the neat cement. There is good reason to believe, 

 therefore, that a small addition of Portland cement to blast-furnace 

 slag screenings will greatly increase the cementing properties of the 

 latter and render them more effective as road binders. 



1 A complete description of these experiments Is published In Circular No. 94 of the 

 Office of Public Roads. 



