21-Bituminous Materials The bituminous materials are hydrocarbons, which are combinations of hydrogen and carbon. The heavier combinations of these hydrocarbons include paving materials.The bituminous materials include asphalt and tars, varying from liquids to solids in consistency according to the heating grade. Asphalts produced from the refining of petroleum or may occur in nature in a pure state or associated with varying quantities of mineral matter.
3DefinitionsBitumen : Bitumen is hydrocarbon material of either natural or pyrogenous origin, gaseous, liquid, semisolid or solid, which is completely soluble in carbon disulfide (ASTM).the greatest part of bitumen produced from petroleum.Asphalt : Asphalt is a black to dark brown cementitious material, semisolid to solid consisting principally of bitumen that gradually liquefy when heated.
4Tar: Tar is a black or dark brown bituminous material, which obtain as a condense in the destructive distillation of organic materials such as bituminous coal, petroleum and wood. Tar is principally bitumen of liquid to semisolid in consistency.
5Sources of Bituminous Materials Some of bituminous binders used in paving purposes occur naturally, but most of them are products from the manufacture of gas, liquid fuels and lubricants, or coal gas and coke. The principal sources of these materials are as follows:Native asphalt: Native asphalt come from Trinidad island off the northeast coast of Venezuela, Bremudez, Maracaibo and Cuba. This asphalt is softened with viscous petroleum fluxes.Rock asphalt: Rock asphalt is natural deposits of limestone or sandstone impregnated with bituminous material.Petroleum asphalt materials : In recent years asphalt is obtained from the refining of petroleum.
6Asphalt Classification 1-Asphalt Cement : Asphalt cement is semisolid hydrocarbons remaining after lubricating oils as well as fuel oils have been removed from petroleum. The consistencies of asphalt cements are given according to its penetration, the distance that a standard needle penetrates a sample under known conditions of loading, time and temperature. There are five asphalt cements varying in consistency from a semi-liquid to a solid at room temperature.
7The asphalt cement is classified according to its penetration as ( ), ( ), (85-100), (60-70) and (40-50). The most commonly used asphalt in highways at present is AC and AC The selection of asphalt cement grade to be used for the pavement construction depends upon the following three factors:1.Type of construction;2.Degree of temperature of exposure;3.Traffic volume.
82-Slow Curing Liquid Asphalt’s or Road Oils (SC) Road oils or slow curing liquid asphalt’s are liquid petroleum products that harden or set very slowly. Road oils may range from a liquid road oil to a very viscous material.Slow curing asphalts may be produced by :-as a product remaining after distillation ;-combining asphalt cement AC with gas oil fluxes.Slow curing asphalts are more fluid than asphalt cements AC , but are more viscous than the very high grades of lubricating oils. They ranging from light liquid SC-70 to semisolid SC-3000 consistencies.
93-Cut-Back Asphalt’sCutback asphalts are asphalt cements fluxed or cut back to greater fluidity by mixing with distillates of the kerosenea-Medium-curing liquid asphalt’s (MC)Medium curing asphalt’s are produced by dissolving a relatively soft asphalt cement ( ) or (85-100) in a kerosene solvent. These solvents evaporate slowly when exposed to heat or air. This type of asphalt is workable at relatively low temperatures.Medium curing asphalts range from light liquid MC-70 to almost semi solid MC Fluidity of the various grades is controlled by the amount of solvent, MC-70 may contain as much as 40% solvent (Vol.-%), and MC-3000 as much as 18%.
10b-Rapid-curing liquid asphalt’s (RC) Rapid curing asphalts are produced by dissolving asphalt cement, generally AC , in a gasoline. These types of solvents are more volatile than kerosene and diesel oil, and since the distillation evaporate more rapidly than kerosene.Rapid curing asphalt’s range from RC-70 to RC-3000 consistencies. The higher the number, the higher is the quantity of asphalt cement.
114-Emulsified Asphalt’s Asphalt emulsion is a mixture in which minute globules of asphalt are dispersed in water by means of an emulsifier. The emulsifying agent, such as soap of fatty and resinous acids, helps in the mixing of the two materials, resulting in a liquid end product. Emulsified asphalt’s can be mixed with damp or wet aggregates without heating, thus leading to reduction in energy requirements and air pollution. Figure 45 appears a flow diagram for manufacture of asphalt emulsion.
13Asphalt emulsions are divided into three categories: anionic, cationic and nonionic. The anionic and cationic classes refer to electrical charges surrounding the asphalt particles.Asphalt emulsions are classified as rapid setting (RS), medium setting (MS) and slow setting (SS),with one or more subheads under each to designate the viscosity of the emulsion or the penetration of the suspended asphalt. These products having fast medium and slow breaking times. They are suitable for a variety of purposes. Asphalt cement is approximately 55 to 70% by weight. Generally, asphalt cement of penetration is the basis for all emulsified asphalts.
145-Road TarsTars are a by-products obtained by the destructive distillation of coal. The American society for testing materials makes the following designations to produce the road tars;-gas-haus coal tar: produced in gashause retort in the manufacture of gas from bitumen coal.-Coke-oven tar: produced in the manufacture of coke from bituminous coal.-Water-gas tar: produced in the manufacture of carbonated water-gas by cracking oil vapors at high temperatures.
15The AASHO classify road tars into 14 grades, from RT-1 to RT-12 and RTCB-5 and RTCB-6. RT-1 is a light oil suitable for application at normal temperatures. As the number of designation is larger, the tar is more viscous. RTCB-5 and RTCB-6 are tars cut backs with a quick evaporating solvents for application at low temperature and quick setting.
16-Testing of Bituminous Materials Tests on bituminous materials may be divided into the following groups:1-Consistency Testsa.Saybolt furol viscosity test;b.Engler's viscosity test;c. Float test;d.Penetration test;e. Softening point test.2-Ductility test3-Solubility test (bitumen content)4-Distillation test5-Special tests for asphalt emulsions
171-Consistency TestsThe consistency of the bituminous material ranges from a very liquid, to a semisolid and relatively solid materials.Brief descriptions of consistency tests are as follows:a.Saybolt furol viscosity test:This test is the present control of consistency for liquid asphalt’s (RC ,MC,SC), and emulsified asphalt’s.The saybolt viscometer is a special cylindrical vessel approximately 1.2 in. in diameter and 5 in. height, enclosed in an oil bath. The standard outlet tube is closed with cork stopper. The viscosity is defined as the time in seconds required for 60 ml of the oil to flow by gravity from the filled cylinder at a specified temperature. Standard temperatures used (AASHO specifications) are 77, 122, 140, 180 and 210F.
18b.Engler's viscosity test: The engler viscosity test is the control for the consistency of liquid products, RT-1 to RT-6 and RTCB-5 and RTCB-6.Engler viscometer is a shallow cylindrical vessel of about 4 in. in diameter equipped with a slightly tapered outlet tube about 0.11 in. in diameter and 0.8 in. long.The viscometer is calibrated at a temperature of 25 C (77 F) by filling it with water and measuring the time in seconds needed for the passage of 50 cm3 under gravity. Bituminous materials are tested in a like manner at a specified temperature.Engler specific viscosity, a dimensionless number, is the ratio of time required for 50 ml of bituminous material to flow through the tube at the time for the same volume of the water to flow through it at specified temperature. The engler viscosity increases at the material becomes stiffer.
19c.Float testThe float test is performed on the heavier tars, RT-7 to RT-12,.The test specimen is a small tapered plug of bitumen about 0.9 in. long, the diameter is about 0.4 in. at the top tapered to a diameter of 0.5 in. at the bottom. This plug is molded into a brass collar, which is threaded to fit into the bottom of a small aluminum dish .The testing materials is powered into the brass collar and after fitting it in the aluminum dish is allowed to float in ice-water for 15 minutes at a temperature of 5 C, then the assembly is placed in a water bath kept at the specified test temperature until the water breaks through the plug and into the dish.The consistency of the material by this test is the time in seconds, measured from the placing of the assembly in the bath until the water breaks through. This time is shorter for soft materials.
20d-Penetration testThe penetration test is made to determine the consistency of asphalt cement, the residues after distillation of medium- and rapid-curing asphalt oils and emulsions. Under specified conditions of loading, temperature and time, a standard needle penetrates vertically into the sample .The test is normally conducted at a temperature of 25 C (77 F) by loading the needle for 5 seconds with a weight of 100 gm.Asphalt cement are classified, by means of penetration limits, into grades on the basis of hardness as 40-50, 60-70, , and The asphalt cement means that the penetration ranges from 8.5 mm to 10 mm.
22e.Softening point test (Ring and Ball) The softening point test determines the temperature susceptibility of asphalt’s.The test specimen is molded in a brass ring 5/8 in. diameter and 1/4 in. thick. the ring is filled with a melted sample of the materials to be tested and is suspended in a glass beaker with its base 1.0 in. above the bottom of the beaker. The beaker is filled with water at 5 C(41 F), after the water temperature is maintained at the same level for 15 minutes, a solid steel ball 3/8 in. in diameter is placed on the center of the upper surface of the bitumen in the ring .The water is then heated at the rate of 5 C per minute. The temperature at which the steel ball after passing through the sample touches the bottom of the beaker, gives the softening point of the material.
232-Ductility TestDuctility of a material is its property to elongate when subjected to tension, before breaking. The bituminous materials must have some specified ductility, so that the pavement surface will distort rather than crack and fail by fatigue under the effects of repeated loads.The materials which be tested are original material for asphalt cement and the residue after distillation for liquid and semiliquid asphalts. The tested material is heated and poured into a brass mold which produces a specimen with a thickness of about 0.4 in. and total length of about 3.0 in. This specimen is pulled horizontally at designated speed in a special machine. The test is conducted under water of controlled temperature. The used test temperature is 77 F(25 C), and the usual test speed is 5 cm per minute.
24Mineral Aggregate for Bituminous Pavements Asphalt pavements contain between 90 to 95% by weight mineral aggregates, or between 80 to 85% by volume. The most common materials are crushed stone, gravels, slag, sand and mineral filler.The choice of an aggregate for bituminous construction depends upon the aggregates available, their cost, and the type of construction, which may be a low-cost surface treatment or a high-type of bituminous concrete.
25-Properties of Mineral Aggregates: 1.Particle shapeThe workability and the compactive effort which required to produce a given density, and also the stability influenced by the particle shape of the mineral aggregate. The classification according to the shape of particles is as follows:a.angular;b.subangular;c.subraunded;d.raunded.The angularity of the particles depends on their sharpness..
262.Particle strengthBase course aggregate must have enough strength and toughness to resist repeated loads without breakdown. Aggregates degraded or broken as a result of loads imposed upon them, during construction or later by the traffic action. Degradation of the aggregates led to increasing the surface area to the point where insufficient bituminous material is present for proper coating. The aggregate which be used should have a greater crushing resistance to prevent excessive gradation. Los Angeles abrasion test is used to determine the aggregate crushing resistance
273.Surface textureThe surface texture is the degree of roughness of particles. It is important for mixture stability. A rough surface makes it quite difficult to displace one particle relative to another, and thus lead to increasing the stability of the mixture. the surface texture can be classified as:a.very rough;b . rough;c .smooth;d. polished.
284-.GradationThe stability and workability of asphaltic mixture mainly influenced by the aggregate gradation. The aggregates may be classified on the basis of gradation as:a.dense gradedThis materials include appropriate amounts of all sizes from coarse to fine, and also fillers, which passing sieve No.200. They used in hot-mix and other dense-graded types.b.open graded :The open graded materials may have an incomplete grading, or may differ from dense graded materials in that they contain much less material passing No.200 sieve. Drain asphalt is an example for open graded materials.
29c.one size materials :These materials are essentially one size, they are generally used in macadam base courses, surface treatments and seal coats.Logically, the best method of attaining high stability in a bituminous mixture would be to use the densest aggregate gradation possible. But this concept is does not provide sufficient space for the bitumen necessary for durability of the mixture. One of the best curves known for the maximum density is Fuller's curve.The equation for Fuller's maximum density curve is:P = 100 d/Dwhere P: total percentage passingd: size of sieve opening consideredD: largest size in gradation
305. PorosityThe porosity of an aggregate is generally reflected by its percentage absorption, when immersed in water. A certain degree of porosity is required in an aggregate since it permits the bituminous material to penetrate into the aggregate. Highly porous aggregates is a disadvantage because its low unit weight and also needs more bituminous material to fill the surface voids. Blast-furnace slag is an example of such a material.
31Mineral Aggregate Tests There are some tests to determine the different characteristic of mineral aggregates, which be used for highway purposes, as example:Los Angeles TestThis test is used to evaluate the a abrasion due to traffic action (AASHO -96). The stone is placed in a metal drum 28 in. diameter and 20 in. long with a charge of steel balls 1/8 in. in diameter, and the drum is rotated 500 times at about 32 rpm. The inside of the drum is equipped with an angle iron, which run longitudinally. After the end of the test the stone is shaken over a 12 mesh sieve. Percentage of passing to the total charge is the los Angeles abrasion value, often called "percent wear".