Other natural rock asphalts

All the other natural asphalts in rock formation can be found at a depth ranging from 3 to 1000 m. The typical asphalt content of these deposits range from 5% to 20%. Because of this low asphalt content and the costly and time-consuming purifying procedure, the exploitation of these natural asphalts turns out to be unprofitable. As a result, their extensive usage in both highway engineering and other industrial applications is limited. 

The only exception seems to be the rock asphalt of Buton Island (south of Sulawesi Island) in Indonesia. In this island, the rock asphalt forms hills and mountains. This porous rock contains hard natural asphalt (penetration of 5-10 dmm) at 15%-30% and soft limestone with fossilised shell impurities. The extraction is very simple and cheap, because of low local labour cost thus, it is used locally for the production of bituminous mixtures. 

Natural rock asphalt in larger deposits can be found in the Jordan Valley, Dead Sea banks, France, Switzerland, Antilles, Venezuela and Cuba. 

Tar is a product of fractional distillation of primary tar produced by carbonation of natural organic matters, such as coal or wood. When the primary tar is derived from coal, the product is called pitch tar. Similarly, when it is derived from wood, it is called wood tar. The pitch tar is further mixed with oil distillates, to produce the processed tar, commonly known as tar. The tar differs in chemical composition and odour to bitumen. Tars consist of variable mixtures of phenols, polycyclic aromatic hydrocarbons (PAHs) and heterocyclic compounds, and their odour is characteristically more aromatic than the odour of the asphalt. 

The classification of the tars is carried out mainly in reference to the equiviscous temperature (EVT). According to BS 76 (1974), there are eight different tar types, from 30 C to 58°C EVT. EVT is the temperature in which 50 ml of tar has a flow time of 50 s when passing through the 10 mm hole of the tar viscometer. As a consequence, the higher the EVT, the more viscous the tar is. Tar with 50°C-58°C EVT is suitable for dense bituminous mixtures in heavy traffic volume sites, whereas tar with 30°C-38°C EVT is used in open graded bituminous mixtures for low traffic volume sites. Tar with 34°C-46°C EVT is usually used for surface dressings. 

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Apart from Trinidad and Venezuela asphalt, all other natural asphalt sources were used only occasionally in pavement construction. Today, only a few of the abovementioned deposits are currently exploited (mainly deposits of Albania, Romania and Kazakhstan). The reason is the high cost of recovering the asphalt from the rock. 

Bitumens Another important class of oil-based products is bitumens. Bitumen is a generic term defined by ASTM as a class of black or dark-colored (solid, semisolid, or viscous) cementitious substances, natural or manufactured. Bitumens are composed principally of high-molecular-mass hydrocarbons of which asphalt, tars, pitches, and asphaltite are typical. Commercially these are produced from the destructive distillation of coal, crude oils, and other organic matter. Asphalt occurs naturally either in rock or a lake. In the United States the terms bitumen and asphalt are interchangeable, whereas in the United Kingdom asphalt is reserved for the naturally occvuring product and bitumen is the residue from crude oil distillation. It is important to note that the compatibility of various classes of bitumen with other raw materials can vary widely. This can lead, for example, to marked differences in chemical and solvent resistance of the end product. 

Ci uuc oil—complex, naturally occurring fluid mixture of petroleum hydrocarbons, yellow to black in color, and also containing small amounts of oxygen, nitrogen, and sulfur derivatives and other impurities. Crude oil was formed by the action of bacteria, heat, and pressure on ancient plant and animal remains, and is usually found in layers of porous rock such as limestone or sandstone, capped by an impervious layer of shale or clay that traps the oil (see reservoir). Crude oil varies in appearance and hydrocarbon composition depending on the locality where it occurs, some crudes being predominately naphthenic, some paraffinic, and others asphaltic. Crude is refined to yield petroleum products. See distillation, hydrocarbon, sour crude, sweet crude, asphalt, naphthene, paraffin. 

Figure 1 illustrates the different phases available for organic chemicals in the environment. These may include the original HWM, as well as water, air, soil, and other organic chemicals present in liquid or solid phases. As previously mentioned, the HWM may be recycled-asphalt pavement or shredded tires. Both the HWM and soil can be very complex. HWM may consist of different polymers, rocks and mineral fragments, and various HOPs. Soils consist of different types and amounts of natural organic matter, black carbon, and minerals. As discussed below, carbonaceous materials typically have the greatest affinity for HOPs. 

Asphalt (Natural) A natural mineral pitch, tar or bitumen composed principally of hydrocarbons a natural bituminous rock that is dark colored, comparatively hard and nonvolatile. Does not include asphalt, bitumen, tar or other substances, derived from petroleum processing. 

Bituminous materials are dark brown or black, semi-solid or liquid, thermoplastic mixtures of hydrocarbons derived from natural or synthetic processes in which hydrocarbon mixtures have lost their volatile components leaving a denser residue. Natural bitumens come from exposed and weathered petroleum and rock deposits. Synthetic bitumens come from the residue remaining after the distillation of petroleum, coal tar, and other organic materials like wood and peat. The complexity of the high molecular weight hydrocarbon oils and resins bitumens contain make complete chemical characterization impossible. The terms bitumen, tar (8007-45-2), pitch (61789-60-4), and asphalt (8052-42-4) apply to any of these substances, although pitch and tar also describe the sticky resins that exude from various trees. 

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