Asphaltic Cement

Residuum. California petroleum, in asphalt paving literature often called asphalt oil, is an excellent solvent of asphalt, and in recent years has been much used as a fluxing material.

Maltha. This is a liquid bitumen which is often, but somewhat improperly, called liquid asphalt. In several respects it resembles asphalt-petroleum residuum; but in other particulars it is quite different. It is unsuitable for use as a fluxing agent fcr asphalt, since a considerable part of it, by some authorities * esti mated at as high as 20 to 25 per cent, is itself asphalt and has no fluxing effect upon the asphalt to which it is added.

Mixing the Asphalt and the Flux.

The refined asphalt is brought to a temperature of about 300° F., and, to produce rapidly a uniform mixture, the flux also is heated to about the same tem perature. The proper amount of the residuum to secure an asphal tic cement of the desired consistency (a 613) is then added to the asphalt. the exact amount depending upon the consistency of the asphalt and the character and the fluidity of the flux. Trinidad asphalt, for example, requires about 17 or 18 per cent of pat affin petroleum residuum. After adding the flux, the mixture is agitated for several hours with a current of air until it is quite homogeneous This agitation must be done with great thoroughness to insure a uniform cement, and must be continued whenever the material is in a melted condition, as a certain amount of separation takes place when the melted cement stands at rest. The resulting mixture is known as asphaltic cement; and if the mixing has been well done and the proper amount of suitable flux has been used, the cement is ready for use in the pavement.

Testing the Asphaltic Cement.

To determine the suita bility of the asphaltic cement for use in a pavement, it is necessary to test its chemical and physical properties. The chemical test consists in the determination of the per cent (1) of bitumen. (2) of foreign or non-bituminous organic matter, and (3) of inorganic matter; and the physical tests consist in determining (1) the con sistency or the softness of the cement and its susceptibility to changes of temperature and to changes with age, (2) the stability of the cement at high temperatures, (3) the effect of water and of dilute ammonia upon the cement, (4) its adhesiveness, and (5) its cohesiveness.

Chemical Composition. The per cent of bitumen may be determined in various ways, hut is most easily done as follows: * "The asphalt is spread in a thin layer in a suitable dish (a nickel or an iron one will do), and kept at a temperature of 225° F. until it practically stops losing weight. The greater part, and in some cases all, of the water and some light oils are expelled in this way. From 2 to 10 grams (depending upon its richness in bitumen) of this substance is weighed in a large test tube (8 inches. long by 1 inch diameter), the tare of which has been previously ascertained. The tube containing the substance is then filled to within 14 inches of the top with carbon bisulphide and allowed to stand for a few minutes. Then the tube is tightly corked with a good sound cork, and is shaken vigorously until no asphalt can be seen adhering to the bottom. Care should be taken while shaking to keep one finger on the cork to prevent its being blown out. The tube should then be put away in an upright position and not be disturbed in the slightest way for two days, after which the carbon bisulphide is de canted off into a small bottle. As much of the solvent should be poured off as is possible before losing any of the residue. The tube is again filled and shaken as before, and put away for two more days. After the liquid has been carefully decanted the second time, the tube with the residue is dried first at a low temperature and then at 225° F. After cooling the tube is weighed. As there is always a small portion of the residue poured off in the solution with the bitu men, this solution must be evaporated and the bitumen burned off in a platinum dish, and the weight of the residue added to that in the tube." During the year ending June 30,1897, the per cent of bitumen in the asphaltic cement used in Washington, D. C., by the two paving companies doing work there was as follows, respectively: average 10.6 and 10.5, maximum 12.6 and 12.7. and minimum 9.2 and 9.0.