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TESTS ON BITUMEN Bituminous Material: British Standards: “ Bitumens are naturally occurring hydrocarbons, and the residues obtained from the distillation of petroleum.” American Standards: According to American Standards, Bitumens are the same as that defined under BS, the only addition is that they must be soluble in Carbon Disulphide (CS2). Bituminous Materials Bitumen Tar Petroleum Native asphalt What is Tar? asphalt TAR: “Tar is a viscous liquid obtained when natural organic materials such as wood and coal are carbonized or destructively distilled in the absence of air.” ASPHALT: “When the bitumen contains some inert material or minerals, it is called asphalt.” Why to Perform Tests? To gather as much data as possible, which may be helpful in the construction of Pavements. Material properties can be analyzed by performing various tests on specified samples of the material. Although there is a general agreement as to their significance, it is impractical to attempt and discuss all tests and their variations. In the following, tests will be placed on factors relating to why they are carried out. Tests Consistency Flash & Fire Specific Composition Point Gravity Penetration Viscosity Softening Ductility Float Point Solubility Ash Loss on Water Distillation Content Heating Content 1. CONSISTENCY TESTS DEFINITION: Consistency is defined as: “The resistance of a material to flow.” Since this property changes as the temperature varies, it must be realized that there is no single method of test that can readily evaluate all bituminous binders for consistency over such a wide range. PENETRATION TEST AASHTO Designation: T49-80 ASTM Designation : D5-73 BS Designation : 2000-49 PURPOSE: To determine the penetration grade of bitumen, to be used for road construction. It gives the choice to select the grade of bitumen according to the climatic conditions of the area where the road is to be constructed. DESCRIPTION OF TERM: Consistency of a bituminous material expressed as "the distance in 1/10 th of mm that a standard needle vertically penetrates a sample under standard conditions of load, time and temperature." STANDARD TEST CONDITIONS: Temperature : 25C Load : 100 grams Time : 05 seconds PROCEDURE: Temperature raised up to 100C i.e. above its softening point. Sample is cooled to a temperature of 5C. Place the sample in the Penetrometer. Standard needle is approximately 50 mm (2 in.) in length and 1.00 to 1.02 mm (0.039 to 0.040 in.) in diameter. The needle tapered at an angle of 8.7 to 9.7. At least three penetrations are carried out, then the nearest whole value unit the average of the three penetrations, whose values do not differ maximum by 8, gives the penetration value of the bitumen. For penetration values greater than 200, three different needles should be used. PENETRATION GRADE REPEATABILITY 0-80 4% 80-225 5% 225-above 7% SIGNIFICANCE OF THE TEST: Used to measure the consistency of semi-solid asphalt bitumen so that they can be classified into standard grades. Penetration values lower than 20 have been associated with bad cracking of road surfacing, while cracking rarely occurs when the penetration exceeds 30. Surfacing containing penetration-grade bitumen, must be premixed & laid hot. The higher penetrations are preferred for use in “colder” climates. VISCOSITY TEST AASHTO Designation: T54-61 ASTM Designation : D1665-61 DEFINITION: The viscosity of a liquid is: "The property that retards flow so that when a force is applied to a liquid; the slower the movement of the liquid, the higher the viscosity; in this sense viscosity is the “pure” measure of consistency." “Resistance to flow” MEASUREMENT OF VISCOSITY: Almost 58 instruments are used for measuring “VISCOSITY”. They may be divided into main three groups, based on the following principles of operations. 1- The flow of a body through a liquid. 2- The flow of a liquid through a tube. 3- The rotation of 1 of 2 co-axial cylinders when the space between them is filled with a liquid. Most bitumen binder specifications for road works are based on the results obtained with industrial viscometers that utilize the second principle. The most common test, which is performed in BRITIAN, is the STANDARD TAR VISCOMETER (S.T.V). PROCEDURE: Time is measured, in seconds, for a fixed quantity of the binder liquid (50 ml) to flow from a cup through a standard orifice under an initial standard head and at a known test temperature. The temperature ranges from 25-100C and is generally so selected that the specific viscosity is no more than 45 dynes sec./cm2. The orifice having size of 10mm is used for important physical characteristic of road. SAYBOLT FUROL VISCOMETER: AASHTO Designation: T72 ASTM Designation : D88, D244 Saybolt viscometer is used to measure viscosity of American grades of cutback bitumen. It utilizes a much smaller orifice than the STV. Because of this, high temperatures are required and it is usual to conduct the test in an oil bath. SIGNIFICANCE OF THE TEST: If a binder of very low viscosity is used & pre-mixed with the aggregates, it may flow off the stone while en route from the mixing plant to the site. Conversely, if the viscosity is too high, the mixture may be unworkable by the time it reaches the site. In case of handling, mixing & spraying, the lower the binder viscosity, the better it would be. In case of the low-viscosity binders, there is less chance of pipes blocked, mixing and application temperature can be kept lower, aggregates are more easily coated. SOFTENING POINT TEST DEFINITION: “It is the temperature at which the substance attains particular degree of softening under specified test conditions.” RING & BALL TEST AASHTO Designation: T53-81 BS Designation : 2000-58 PROCEDURE: This method is extensively used to evaluate the consistency of bituminous binders. A steel ball of 3/8 in. , weighing (3.50.03) gms, is placed upon a disk of sample contained within a horizontal, shouldered, metal ring of specified dimensions. The whole assembly is heated in either ethylene glycol (B.P 193-204C) or water bath at a uniform rate (50.5C per min). Temperature is raised until the test sample is soft enough and allows the ball to fall through a distance of 2.5 cm. Temperature at this point is read to the nearest 0.5C and called “SOFTENING POINT”. SOFTENING POINT REPEATABILITY Below 30C 2C 30-80C 1C 80C -above 2C SIGNIFICANCE OF THE TEST: Softening point is not a melting point; bituminous binders do not melt but instead gradually change from semi-solids to liquids when heated. It is useful in the classification of certain asphalts and tars and is indicative of the tendency of the material to flow at elevated temperatures encountered in service. When two bitumens have same penetration grade (value), the one with the higher softening point is normally less susceptible to temperature changes. Practical significance of the test is limited. Therefore specifications of many bituminous binders for particular purposes are often written without softening point requirements. DUCTILITY TEST DEFINITION : DUCTILE MATERIAL: “A ductile material is the one that elongates when held in tension.” DUCTILITY: It is defined as: “The distance in centimeters that a standard semi-solid will elongate before breaking.” SIGNIFICANCE OF THE TEST: The property is desirable in road bitumen in order to overcome the movements induced in the surfacing by traffic and temperature stresses. The ductility test is actually the measure of the internal cohesion of bitumen. Bitumens possessing high ductility are normally cementations and adhere well to aggregates. Thus bitumen with 100 cm ductility might well be considered a better road-surfacing constituent than with 10 cm ductility, but a binder with a 80-cm ductility is not necessarily better than a 60 cm one. Bitumens possessing high ductility are highly susceptible to temperature changes, while low ones are not. The lack of ductility does not necessarily indicate the poor quality; indeed, bitumen of low susceptibility and low ductility are highly desirable as crack- fillers in roadways. The harder grades of bitumen are less ductile than the softer ones. Ductility test is probably the most controversial of the many empirical tests found in the asphaltic bitumen literature. AASHTO Designation: T 51-81 ASTM Designation : D113-79 PROCEDURE: The distance to which it will elongate before breaking, when two ends of a briquette are pulled apart at a specified temperature (25C) and speed (50mm per min 5%) is measured. Minimum cross-section of the briquette before testing is 1 cm2. FLOAT TEST AASHTO Designation: T 50-81 ASTM Designation : D139-77 PURPOSE & SIGNIFICANCE: For a certain range of consistency of the bitumen materials, orifice viscometer test or penetration test cannot be used to define consistency of the material. Float Test measures the material of this group. PROCEDURE: Sample is completely melted at the lowest possible temperature that will bring it to sufficiently pouring condition. A float made of aluminum or aluminum alloy (weighing 37.90-38.10 gms) and a brass collar (weighing 9.60-10.00 gms) is filled with the specimen material to be tested. Test specimen is cooled to room temperature for 15-60 min at 5C and screwed in to the float. The float assembly is then placed in a water bath at 50C and the time required in seconds, for water to force its way through the bitumen plug is noted, as the float test value. Higher the float test value, stiffer is the material. COMPARISION BETWEEN TESTS: Bitumen A 25 A 35 A 45 A 65 A 90 A 200 grade Penetration 20-30 30-40 40-50 60-70 80-100 175-225 value,1/100cm Min. ductility 5 10 12 15 15 15 value, cm Softening 55-70 55-70 45-60 45-60 35-50 30-45 point, C 2. FLASH & FIRE POINT PURPOSE & SIGNIFICANCE: Bituminous materials leave out volatiles at high temperatures. The quantity of volatile materials depends upon their grades. These volatiles catch fire causing a flash. This condition is very hazardous and it is therefore essential to qualify this temperature for each bitumen grade, so that paving engineers may restrict the mixing and application temperatures. Flash and Fire Point tests are primarily safety tests, flash point being the more important since it indicates the maximum temperature up to which the binder can be safely heated. Flash Point of most penetration-grade bitumen lies in the range of 246-316 C. FLASH POINT: „„The temperature at which the vapors given off from the binder first burn with a brief flash of blue flame‟‟ FIRE POINT: „„The temperature at which the vapors continue to burn for a period of at least 5 seconds‟‟ CLEVELAND OPEN CUP AASHTO Designation: T 48-81 ASTM Designation : D 92-78 PROCEDURE: The test cup is filled with the sample to the filling line, at a temperature not exceeding 100-180C above softening point. The temperature of the sample is increased rapidly at first and then at slow rate as the flash point is approached. At specified intervals, a small test flame is passed across the cup. The lowest temperature at which application of the test flame causes the vapors above the surface of the sample to ignite is taken as the flash point. To find the fire point, the test is continued until the application of the test flame causes the sample surface to ignite and burn for at least 5 sec. 3. SPECIFIC GRAVITY TEST DEFINITION: Specific gravity is defined as: “The ratio of the weight of a given volume of material at a given temperature to that of an equal volume of water at the same temperature”. PURPOSE & SIGNIFICANCE: Density of a bitumen binder is a fundamental property frequently used as an aid in classifying the binders for use in paving jobs. In most applications, the bitumen content, when used with aggregate, is converted into volume basis. Principle use is the establishment of relationship between binder weight and volume for transporting and filling purposes. Specifications for binders in road surfacing are normally expressed as percentages by weight whereas they are usually shipped and measured in volume. Also, useful in determining the percentage of voids in mechanically designed mixtures of bitumen‟s and mineral aggregate. Also, useful in bituminous mix design. MEASUREMENT BY PYCNOMETER AASHTO Designation: T 74-70 ASTM Designation : D 369-67 PROCEDURE: Weigh the empty pycnometer (W1). Weigh the pycnometer and sample (W3 ). Weigh the pycnometer again, filled with water (W2 ). Fill the pycnometer with sample, mix it thoroughly with water and weigh it again (W4 ). Finally by using the formula, find out the specific gravity: Gs = ______ W3-W1______ (W2-W1) - (W4-W3) Test temperature is usually 15.5 C. It varies from 0.97 to 1.02. 4. COMPOSITION TESTS As it is clear from the table, most binder specifications include criteria regarding composition. A number of tests have been devised to determine the proportions of the specific fractions and components of the bituminous binders. DISTILLATION TEST AASHTO Designation: T78-80 ASTM Designation : D402-76 PURPOSE: It is used to find out the quantity and quality of volatile constituents. The amount of non-volatile residues present in road tars, cutback bitumen and binder emulsions. In emulsions, the volatile component is of course water. PROCEDURE: Two Hundred milliliters of the sample is distilled in a 500 mL flask at a controlled rate to a temperature of 360C. Then determine the volume of distillate removed at prescribed standard temperatures. SIGNIFICANCE OF TEST: The distillation tests are amongst the most valuable of the highway tests for bituminous binders. The test enable a close check to be kept on the quality of the binders used on road schemes. Results also provide very useful information not only on the type of volatiles in the binders, but also on the rate at which these volatiles will be lost under field conditions. If, for instance, a given cutback is found to speed its volatiles too slow on a given road scheme, then under similar conditions a cutback with higher boiling range volatiles, as determined by the distillation test, can be expected to cure even more slowly. WATER CONTENT TEST AASHTO Designation : T55-78 ASTM Designation : D95-70 PROCEDURE: The moisture content of a binder is automatically determined when a distillation test is carried out. Some time it is desirable to determine the moisture content alone, without carrying out a complete distillation procedure. In such instances the moisture content may be determined directly by mixing a specified amount of binder with a predetermined amount of petroleum spirit (for bitumen) with which it is immiscible & distilled in a flask or still which is attached to a glass water-cooled reflux condenser & graduated receiver. Distillation is continued until the volume of water in the receiver is constant. This volume is then measured and expressed as a %age by weight of the original material. SIGNIFICANCE OF TEST: Bituminous binders should only contain extremely low moisture contents if they are to be heated beyond 100 C. If significant quantities of water are present & this temperature is exceeded, foaming of the binder will occur. LOSS-ON-HEATING TEST AASHTO Designation : T47-82 ASTM Designation : D6-80 BS Designation : 2000-45 PROCEDURE: A 50gram sample of bitumen is placed in a small container. It is left for 5 hours in a revolving-shelf oven. The temperature of oven is maintained at 165 C. At the end of the heating period, the sample is cooled to room temperature & weighed. The loss in weight of the sample is then determined and expressed as a %age of the original weight. The penetration test is often carried out on the residue of the loss-on-heating test. The result obtained is expressed as a %age of the penetration of the bitumen before heating. SIGNIFICANCE OF TEST: Specifications for penetration-grade asphalt bitumen may require that the max loss of weight on heating & the max. drop in penetration should not exceed particular values. In practice, the losses in weight & penetration values are almost within the specifications requirements. This loss on heating is essentially an accelerated volatilization test. The test is of use only as a general indication of volatile content under the specified conditions of test. If the consistency of the residue is compared with that of the original, the amount of hardening resulting from this amount & manner of volatilization is all that is indicated. ASH CONTENT TEST AASHTO Designation : T59-82 ASTM Designation : D244-79 DEFINITION: “It is the % age by weight of inorganic residue left after ignition of the sample.” PROCEDURE: Place a 2-5 sample of residue in a weighed porcelain or platinum crucible and weigh the sample to the nearest 0.1g. Slow burn off the combustible matter and finally ignite the residue until the ash is free of carbonaceous matter. Cool the crucible and content in a desiccators and weigh, reporting the result as % age of ash. SIGNIFICANCE OF TEST: This test is carried out on both penetration-grade & cutback bitumen. In refinery bitumen, the test ensures that undesirable amounts of mineral matter are not present. This is particularly important for surface dressing materials. The presence of ash in bitumen is not necessarily harmful in itself, as it is evidenced by the use of lake asphalt in road surfacing either on its own or in blended mixtures. In such instances, the ash test is most useful in determining the composition of the binder. SOLUBILITY TEST AASHTO Designation: T44-81 ASTM Designation : D2042-76 PROCEDURE: Differ solvents are used in determining the %age of the binder present in bitumen or tar. In the case of bitumen, the accepted solvent is carbon disulphide (cs2). A specified quantity of binder, usually about 2gms, is dissolved in a given quantity of solvent. Filter the solution through a fine porosity filter. Then the residue retained is determined and the %age of soluble material is calculated. SIGNIFICANCE OF TEST: A solubility requirement of 99.5% in CS2 is found in all British specification for refinery bitumen.
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