Currently, oil continues to be one of the main natural resources used in the world as a primary energy source (representing more than 30% of total energy consumption). The largest proven oil reserves are in Venezuela (17.5%), Saudi Arabia (17.2%), Canada (9.8%), Iran (9.0%), Iraq (8.4%), and Russia (6.2%) [1], among others. As a result of the depletion of light and medium crudes, heavy oil and natural asphalts (NAs) have become an important source of raw materials to meet the growing demand for fuels and petrochemical products [2,3,4,5]. On the other hand, the existence of large quantities of NA mines worldwide and NA’s relatively low price make it an alternative material of wide industrial use [6,7]. NAs could produce bitumen of various standards by compounding it with residues of heavy oil, reducing the duration of the process of bitumen production and energy consumption [8,9]. Furthermore, in the last decade, NAs have received great attention, as they can be used to modify binders and asphalt mixtures due to their high compatibility with conventional asphalts [10]. With these natural materials, the cost of modification could be lower compared with polymers, and the latter tends to separate from the asphalt binder, generating stability problems [11].

NA could be subdivided into soluble and pyrobitumens (a natural hydrocarbon substance, solid, and different from bitumen because it is infusible and insoluble). Some natural bitumens are paraffin or petroleum wax (solid but soft, white or colorless wax, derived from petroleum, composed of saturated hydrocarbons, and used mainly to produce candles, polishes, cosmetics, and electrical insulators), pitch (has certain mineral contents), and asphaltites such as: (i) gilsonite or uintaite (solid black organic material, originating from the solidification of petroleum; carbon residue in the range of 10–20% by weight); (ii) grahamite or anthraxolite (similar to gilsonite, it is a bitumen-impregnated rock, which is the result of metamorphic changes in gilsonite; it differs by its high fixed carbon value—35 to 55%—and higher melting point); and iii) glance pitch or manjak (similar to gilsonite, but has higher specific gravity and carbon percentage—20 to 30%) [17,18]. Differences in the quality of NAs depend mainly on their depositional sources (differences in chemical and mineralogical compositions) [4]. If the NA reaches the ground surface, it forms bituminous springs, and if it remains underground, it will gradually solidify and oxidize, forming a solid and hard substance that is mineral asphalt (e.g., asphaltites) [7].

From the natural materials listed above, asphaltites are the most used material in pavements. These are usually heavy (4–18° API) [19,20], blackish, hard, exhibit high softening points [21], and are recognized as asphalt hardening materials due to their high asphaltene content [14,22,23]. The melting point of asphaltites is in the range of 200 to 315 °C [24]. Asphaltite is a rock of petroleum origin, formed from a liquid or semi-liquid asphaltic material present at depth, which is deposited in crevices, veins, cracks, and voids transported by pressure, gravity, and/or temperature during tectonic movements [25,26,27,28]. Afterward, the material solidifies and alters mainly due to the loss of light fractions and exposure to biodegradation processes, oxidation, water washing, and other chemical reactions that can cause an increase in molecular weight and a decrease in the atomic H/C ratio [24,29,30]. These materials are used in the production of paints and varnishes, road construction, automobile tire production, electrical insulation, and ink production. In the past, they were used as natural pitches for lining containers, floors, and walls, and, in general, as a moisture insulator. After some refining operations, synthetic gas [31], liquid fuel, ammonia, and sulfur can be obtained. In addition, they can be used in power plants for energy production [26,32,33]. They can also be used for heating in residential sectors because of their high calorific value [26,34], as fuel in industrial plants [35], and as an additive in sand molds used by the foundry industry [36]. As a result of the presence of carbon in its structure, it is a suitable adsorbent for a wide variety of contaminants [32]. In the world, some valuable materials such as vanadium, nickel, and uranium can be produced from asphaltite ashes [37]. They are characterized by high heteroatom and metal content [3]. They contain some valuable crude metals, such as Mo, Ni, and V, and some radioactive metals, such as U and Th [38,39]. They are also a potential source of hydrocarbons [40] and could be precursors of high-tech carbon materials such as carbon fibers [41].

Within the asphaltites, gilsonite is perhaps the most studied in pavements. It was discovered in the early 1860s, and in 1888, Samuel H. Gilson and an associate established the first company to extract and market it on a commercial scale [42,43]. It is a natural fossil resource, similar to petroleum-derived asphalt with high asphaltene content [44,45,46,47,48,49]. It has a higher content of nitrogen than oxygen in its structure, giving it special properties of surface wetting and resistance to oxidation by free radicals [22]. It is a black, brittle material that can be crushed to powder [50]. It is a high-purity natural material with zero penetration at 25 °C, a softening point between 129 °C and 204 °C, and specific gravity at 25 °C of 1.04 to 1.06 [51]. Gilsonite is known for its ease of use, good affinity with asphalt, and low cost [16,43,51,52,53,54]. World gilsonite reserves are about 100 million tons and are found in countries such as the USA, Canada, Iran, Iraq, Russia, Venezuela, China, Australia, Mexico, and the Philippines [32,48,55]. The annual world consumption of gilsonite is more than 90 Mt, and the percentage of use in road paving is between 60 and 70% [47,48]. According to [56,57], the stiffness of gilsonite is about 50 times higher than that of conventional asphalt at room temperature. It has carbon content (above 80%) and a low H/C ratio, indicating a high degree of molecular condensation. It contains a large number of N, O, and S elements, which exist in polar functional groups [28] such as hydroxyl and a carboxyl group, which enhance the bonding of the aggregate and binder [57]. The physical and chemical properties of gilsonite range from a combination of refinery bitumen and carbon [32]. Another name given to gilsonites in some studies is rock asphalt—RA (extracted from mines or quarries depending on the type of deposit). The long coexistence time (millions of years) with nature gives them high stability and compatibility with asphalt binders. They are formed after billions of years of accumulation and changes under the combined action of heat, pressure, oxidation, catalysts, and bacteria [58,59,60,61,62]. They show economic and environmental benefits [63,64] and are mainly composed of coarse-grained sandstone completely impregnated with bitumen (10 to 35 wt% of the rock weight) [51]. Chemically, it is mainly composed of asphaltenes and other chemical compounds such as hydrogen, nitrogen, and oxygen. The asphaltene in asphalt rock, due to its polar functional groups, has anti-stripping, anti-oxidation, high adhesion, and temperature resistance properties [65]. Some asphaltene rock deposits can be found in Iran, Xinjiang, Qingchuan, Sichuan (China), and Buton Island (southeast Sulawesi, Indonesia). The latter are known locally as ASBUTON, and the deposits are estimated at 677 million tons with an average asphalt rock percentage between 13% and 20% [66].

Another widely used and studied NA pavement is Trinidad Lake (TLA), which is located on the island of Trinidad in the West Indies. It is perhaps the most well-known source of lake asphalt (47 ha, 87 m deep and contains approximately 10 million tons of asphalt; [67]). Finely divided minerals are dispersed throughout the bitumen [4]. The extracted TLA, when refined, presents soluble bitumen (53–55%), mineral matter (36–37%) and others (9–10%) [51,67]. The bitumen consists of maltenes (63%–66%) and asphaltenes (33%–37%). TLA minerals are composed of particles of various grades, as follows: Pass 200 (0.08 mm): 89.8%; Pass sieve 100 (0.17 mm): 8.0%; Pass sieve 80 (0.20 mm): 2.2% [68]. It is a material with a high softening point, high content of asphaltic matrix and resins, and a more gel-like structure [69]. According to [70], the mineral matter (named by them as ash) could improve the performance and high-temperature resistance of asphalt because of its small size, large surface area, and rough surface. It is widely used as waterproofing material in bridge decks or overlaps [71,72,73]. Due to the existence of mineral matter, high asphaltene content, and similar chemical composition with petroleum, TLA has good thermo-chemical stability, good oxidation and water resistance, good adhesiveness, as well as good compatibility with asphalt [58,74,75,76]. In towns near Trinidad Lake in Trinidad and Tobago, they use it as a source of tourism [77].

Another type of natural asphaltic material is tar sand (also known as oil sand and bituminous sand). It is a sand deposit that is impregnated with a dense, viscous petroleum-like material called bitumen [78]. In situ, oil sand deposits are predominantly quartz sand surrounded by a fine thin film of water and fine aggregates with bitumen that fill the pore spaces between the sand grains. Inorganic materials in the oil sand composition constitute approximately 80% by weight, and bitumen and water constitute approximately 15 and 5%, respectively [79]. The composition and mineral content may vary with location and geologic condition [80]. Bitumen-impregnated sandstone deposits occur in a variety of stratigraphic and climatic environments [4].