Petroleum bitumen: properties, grades and applications

Petroleum bitumen is a solid or viscous carbonaceous product obtained from the processing of petroleum and its heavy residues. It is one of the oldest and at the same time most in-demand industrial materials: it is used for road construction, waterproofing, roofing materials and as a component of anti-corrosion compositions. In terms of consumption volumes in the road sector, bitumen has no alternatives, and in terms of its combination of properties it remains the reference binder for asphalt concrete mixtures.

Chemical Nature and Composition

From a chemical point of view, bitumen is a complex multicomponent system consisting of high-molecular-weight hydrocarbons and their hetero-derivatives containing oxygen, sulfur and nitrogen. Three main groups of components are distinguished in bitumen: oils, resins and asphaltenes. Oils impart mobility and elasticity, resins provide plasticity and adhesion, and asphaltenes form the structural framework that determines hardness and heat resistance. The ratio of these groups, as well as the presence of paraffinic hydrocarbons, determines the performance properties of the final product. The elemental composition of bitumen includes carbon (80–85%), hydrogen (10–12%), sulfur (up to 5–7%), oxygen and nitrogen.

Classification and Grades

Petroleum bitumens are divided into several groups by application, each regulated by a separate standard. Viscous road bitumens conforming to GOST 22245 are intended for the construction and repair of road and airfield pavements. Depending on the depth of needle penetration at 25 °C, they are produced in grades BND 200/300, BND 130/200, BND 90/130, BND 60/90, BND 40/60, as well as BN 200/300, BN 130/200, BN 90/130 and BN 60/90. The index "D" in the marking indicates road bitumen, and the numerical values reflect the penetration range. BND grades possess improved performance characteristics and are intended for more critical road structures.

Construction bitumens according to GOST 6617 are used for waterproofing, roofing and various construction purposes. They are produced in grades BN 50/50, BN 70/30 and BN 90/10, where the numerical values correspond to penetration and softening point. Roofing bitumens according to GOST 9548 are intended for impregnation and for producing the covering layers of roofing materials; their marking, for example BNK 40/180 or BNK 90/30, reflects the application area — from impregnation to the covering layer.

Production Technology

The main industrial method for producing bitumen is the oxidation of heavy petroleum residues — vacuum residues, deasphalting asphalts and selective refining extracts. The oxidation process is carried out at a temperature of 200–250 °C by bubbling air through the feedstock layer. During the reaction, molecules enlarge, the content of asphaltenes and resins increases, which leads to an increase in viscosity and softening point of the product. Compounding is also used — mixing oxidised and non-oxidised residues to obtain bitumen with specified properties.

Bitumen quality is assessed by a set of indicators: needle penetration depth, softening point by ring and ball, ductility, brittleness temperature, flash point, and mass change after heating. These characteristics determine the behaviour of the binder at high and low temperatures, its resistance to ageing and the durability of the road pavement.

Applications

Road construction remains the largest consumer of bitumen. Viscous road bitumens are used as a binder for preparing asphalt concrete mixtures used in the construction of upper and lower pavement layers, as well as for surface treatment and base strengthening. Construction bitumens find application for waterproofing foundations, basements and underground structures, for the production of rolled roofing materials, mastics and sealants. Roofing bitumens are used for impregnating the base and creating the covering layer of roofing felt and other built-up materials. In addition, bitumen is used in the paint and coatings industry for producing anti-corrosion coatings, in electrical engineering as an insulating material, and as a component of drilling fluids and in other special areas.

Safety and Storage

Bitumens are classified as combustible substances with a flash point above 220 °C and an autoignition temperature of at least 368 °C. By the degree of impact on the human body, they are classified as low-hazard substances (hazard class 4). When working with molten bitumen, there is a risk of thermal burns, so personal protective equipment must be used, and premises must be equipped with supply and exhaust ventilation. Bitumen storage is carried out in closed containers or specialised bitumen storage facilities with heating that prevents the product from solidifying. During transportation, bitumen is moved in a hot state in thermal tankers or in solid form in paper bags and in bulk.