Bitumen in road construction
Bitumen in road construction Bitumen in road construction means black adhesives used in road construction, which include bitumen and tar materials. The main property of bitumen is that it sticks the stone grains together and turns them into a single body. Bitumen is a black body made of a large number of hydrocarbons.
Pure bitumen is solid or semi-solid at ambient temperature and is liquefied by heat. Bitumen dissolves in mineral oils and solvents such as carbon sulfide, carbon tetrachloride and ethylene trichloride. Tar, which is black but brown in color, is obtained by distilling gases from heating coal, wood, and schist rocks. This substance is called raw tar and is obtained by refining that tar. Tar is produced in very small quantities in Iran and its use in road construction works is not common in the country. Types of bitumen There are two main types of bitumen used in road construction. If it is obtained from a mine, it is called natural or mineral bitumen, and if it is obtained from the refining of crude oil, it is called petroleum bitumen or refinery. Petroleum bitumen should be used in road construction. If the use of mineral bitumen is in the desired projects, the mixing ratio of petroleum or mineral bitumen should be specified in the private technical specifications.
Petroleum bitumens Bitumens obtained from crude oil refining are divided as follows according to the type and conditions of its use in road construction and other industrial uses.
Pure bitumen Bitumens that are obtained directly from the refinery vacuum in the distillation tower or briefly exposed to the aeration process are called pure bitumens. These bitumens should be homogeneous and free of water and should not foam at 176 degrees Celsius. Pure bitumen deforms into a thick, watery liquid due to pressure and heat, and is elastic and springy at low temperatures.
Soluble bitumen Soluble bitumen, or back bitumen, is obtained by dissolving pure bitumen in solvents or petroleum oils. The type and quality of soluble bitumen depends on the quality of the original pure bitumen, the type and amount of solvent. The higher the amount of petroleum solvents in the bitumen solution, the greater its fluidity. Usually, the percentage of solvent used in soluble bitumens varies from 20 to 50%. Soluble bitumen is used in road construction for surface coatings, infiltration, surface asphalt, cold factory asphalt or on-site mix. Soluble bitumens are divided into the following three groups according to the setting speed and the type of solvent.
Instant soluble bitumens If gasoline is used to dissolve pure bitumen, dissolved bitumen is called quick-setting. Because the solvent in the bitumen evaporates shortly after the consumption of bitumen and the main bitumen remains. Quick bitumen is classified into four types in terms of RC-70, RC-250, RC-800, RC-3000.
Solution bitumen Slow bitumen is made by dissolving pure bitumen in kerosene, which is slower and longer than gasoline. Slab contraction joints should intersect at the openings for columns, and should intersect at the openings for columns, at a minimum of 30 to a maximum of 6,000 cm.
Delayed bitumen solution In addition to dissolving pure bitumen in refractory oils and petroleum solvents, such as diesel or black oil, retardant soluble bitumens can be obtained directly from the distillation of crude oil, such as pure bitumen, from which solvent oils have not yet been separated. It takes a long time for these bitumens to fully set after consumption. In fact, retarded bitumens do not evaporate under normal climatic conditions, but undergo molecular deformation that is relatively gradual and long.
Blown bitumen Pure bitumens are pressurized at 200 to 300 ° C to combine the hydrogen atoms in the bitumen molecules with oxygen in the air, resulting in polymerization reactions that produce heavier hydrocarbons with lower penetration and softer points than bitumen. Have an initial net.
Blowed bitumen is not widely used in road construction. These bitumens are used to fill cracks in concrete pavements and to fill joints in concrete surfaces. The elasticity of blown bitumens is usually increased by the use of special chemical additives, and this condition remains constant even at low temperatures where pure bitumen becomes brittle. This type of blown bitumen, which is somewhat similar to rubber, is used to cover the floor of water pipes.
Functional bitumens Functional classification for bitumen selection in road construction has been developed by SHRP. In this classification, which is based on recognizing the behavior of bitumen and its functional characteristics, with the characteristics of resistance to deformation, resistance to cracking due to cold, resistance to cracking due to fatigue, prediction of how hard bitumen in the asphalt plant When preparing the asphalt mixture, how the bitumen hardens over time and with the tests specified in the specifications, and the appropriate bitumen according to the temperature of the project site, traffic, loading speed and geographical location selected It becomes.
Bitumen type and traffic conditions Traffic conditions including the type and amount of heavy traffic, how to load (fast, slow or static loading) and the total number of equivalent axes of 80 kN and traffic are effective in choosing the type of bitumen in each project. In general, the heavier the traffic, the denser and more directed it is, and the steeper and more steep the slopes and the more exposed to the intense sun, the harder the bitumen is used.
Based on SHRP research, bitumen consumption is determined by the condition that the asphalt mixture is under rapid loading. In slow loading mode, such as traffic at intersections, toll booths, crossing steep and long slopes, and generally traffic was slow and controlled