CONSTITUENTS LAND • Hued 85th Per Cent Per Cent Per Cent water 27.85 34.10 26.62 Inorganic matter 2538 25.46 27.57 Organic non-bituminous matter . 7-1i3 6.25 8.05 Bitumen 38.14 34.50 37.76 100.00 100.00 - 101.00 When the analyses are calculated to a basis of dry substances, the composition is: Inorganic matter 36.56 38.00 37.74 Organic matter not bitumen 40.07 9.64 10.68 Bitumen .. 52.87 52.36 51.58 100.00 100.00 100.00 The substances volatilized in 10 hours at 41)0°F 3.66 12.24 0.88 to 1.37 The substances soften at .... 191° F. 170° F. 300° to 250° F.
•' " flow at 200° F. 185° F. 210° to 328° F.
The characteristics of refined Trinidad asphaltum are as follows: The color is black, with a homogeneous appearance. At a tempera ture of about 70° F., it is very brittle, and breaks with a conchoidal fracture. It burns with a yellowish-white flame, and in burning emits an empyreumatic odor, and possesses little cemzntitious quality. To give it the required plasticity and tenacity, it is mixed while liquid with from 10 to 21 pounds of residuum oil to 100 pounds of asphaltum.
The product resulting from the combination is called asphalt paving-cement. Its consistency should be such that, at a temperature of from 70° to 80° F., it can be easily indented with the fingers, and on slight warming be drawn out in strings or threads.
Artificial Asphalt Pavements. The pavements made from Trini dad, Bermudez, California, and similar asphaltums, are composed of mechanical mixtures of asphaltic cement, sand, and stone-dust.
The sand should be equal in quality to that used for hydraulic cement mortar; it must be entirely free from clay, loam, and vegetable impurities; its grains should be angular and range from coarse to fine.
The stone-dust is used to aid in filling the voids in the sand and thus reduce the amount of cement. The amount used varies with the coarseness of the sand and the quality of the cement, and ranges from 5 to 15 per cent. (The voids in sand vary from .3 to .5 per cent.) As to the quality of the stone-dust, that from any durable stone is equally suitable. Limestone-dust was originally used, and has never
been entirely discarded.
The paving composition is prepared by heating the mixed sand and stone-dust and the asphalt cement separately to a temperature of about 300° F. The heated ingredients are measured into a pu„ -mill and thoroughly incorporated. When this is accomplished, the mix ture is ready for use. It is hauled to the street and spread with iron rakes to such depth as will give the required thickness when compacted (the finished thickness varies between 11 and 21 inches). The re duction of thickness by compression is generally about 40 per cent.
The mixture is sometimes laid in two layers. The first is called the binder or cushion-coat; it contains from 2 to 5 per cent more cement than the surface-coat; its thickness is usually k inch. The object of the binder course is to unite the surface mixture with the foundation, which it does through the larger percentage of cement that it contains, which, if put in the surface mixture, would render it too soft.
The paving composition is compressed by means of rollers and tamping irons, the latter being heated in a fire contained in an iron basket mounted on wheels. These irons are used for tamping such portions as are inaccessible to the roller—namely, gutters, around man file heads, etc.
Two rollers are sometimes employed; one, weighing 5 to 6 tons and of narrow tread, is used to give the first compression; and the other, weighing about 10 tons and of broad tread, is used for finishing. The amount of rolling varies; the average is about 1 hour per 1,000 square yards of surface. After the primary compression, natural hydraulic or any impalpable mineral matter is sprinkled over the sur face, to prevent the adhesion of the material to the roller and to give the surface a more pleasing appearance. When the asphalt is laid up to the curb, the surface of the portion forming the gutter is painted with a coat of hot cement.