Fillers.—Fillers are solid asphalts or tars that are used for filling expansion joints in rigid pavements and for filling the spaces between the blocks in brick, wood block and stone block pavements.
Bitumen.—Bituminous materials are all soluble to a greater or lesser extent in carbon disulphide and the soluble portion is called bitumen. It is the bitumen that gives to the materials the cementing properties utilized in road construction. Mixtures of mineral aggregates and bituminous materials for various purposes are proportioned with bitumen as a basis. Therefore, less of an asphalt containing one hundred per cent bitumen will be used than of one containing less than one hundred per cent of bitumen.
Table 8
Properties of Asphaltic Road Materials
| Material | Specific Gravity | Consistency | Solubility in CS2, Per Cent | Solubility of Bitumen in CCl4, Per Cent | Solubility of Bitumen in 86° Naphtha, Per Cent | Fixed Carbon, Per Cent | Flash Point | Ductility |
| Mexican oil asphalts | 1.03-1.05 | As desired | 99.5-99.9 | 99.5-99.9 | 70-80 | 13-16 | 200°C. up | 60-100 |
| California oil asphalts | 1.02-1.04 | As desired | 99.9 | 99.9 | 75-80 | 10-12 | 200°C. up | 100+ |
| Texas oil asphalts | 1.01-1.03 | As desired | 99.9 | 99.9 | 75-80 | 12-14 | 200°C. up | 50-100 |
| Bermudez natural asphalt | 1.07 | 25 | 95 | 99+ | 68-70 | 13-14 | ... | ... |
| Trinidad natural asphalt | 1.40 | 7 | 56-57 | 100 | 64-65 | 10-11 | ... | ... |
| Bermudez asphalt cement | 1.04-1.06 | Up to 135 | 95-97 | 99.5 or more | 77-80 | 11-12 | 175-200 | 25-50 |
Specifications.—Some properties of bituminous materials can be varied in the process of manufacture, while others are inherent in the material and cannot be changed in the process of manufacture. Specifications must therefore be drawn with care to insure that the requirements can be met by satisfactory materials. But certain properties, such as specific gravity, may vary greatly among materials equally satisfactory for construction purposes. One should not be misled by apparent differences in the characteristics of materials, because these may simply be natural peculiarities which have no bearing on the usefulness of the material. There are given in Table 8 the properties of some of the commonly used bituminous materials and the properties that can be varied in the process of manufacture are indicated with an asterisk. A variation in these properties will usually result in some change of other properties, but generally not a great change.
Surfaces in which Bituminous Materials are Utilized
I. Surface Treatments
Attention has been directed to the rapid deterioration of water-bound macadam when subjected to passenger automobile traffic.
In water-bound macadam the stones are held in place by a weak cement composed of stone dust and water, and this cement is not sufficiently strong to hold the stones in place when they are subjected to the shear of automobile tires. In finishing the water-bound macadam surface, the spaces between the stones are filled with screening and in addition a layer about one-fourth inch thick is left on the surface.