1 6.2 Asphalt concrete properties T RANSPORTATION S YSTEM E NGINEERING 1, 61360

2 The properties of asphalt materials pertinent to pavement construction can be classified into four main categories: 1.Consistency 2.Aging and temperature sustainability 3.Rate of curing 4.Resistance to water action T RANSPORTATION S YSTEM E NGINEERING 1, 61360

3 1.Consistency: It is usually considered under two conditions: A)Variation of consistency with temperature » The consistency changes as the temperature varies. » The change in consistency may differ considerably even for the same amount of temperature change. » This property of asphalt materials is known as temperature susceptibility. » The temperature susceptibility of a given asphalt depends on the crude oil from which the asphalt is obtained T RANSPORTATION S YSTEM E NGINEERING 1, 61360

4 1.Consistency: B)Consistency at a specified temperature » The consistency of an asphalt material will vary from solid to liquid depending on the temperature of the material. » Whenever the consistency of an asphalt material is given, the associated temperature also should be given. T RANSPORTATION S YSTEM E NGINEERING 1, 61360

5 2.Aging and temperature sustainability ‒This natural deterioration of the asphalt material is known as weathering. ‒When asphaltic materials are exposed to environmental elements, natural deterioration gradually takes place The materials eventually loose their plasticity and become brittle. ‒This change is caused primarily by chemical and physical reactions that take place in the material. T RANSPORTATION S YSTEM E NGINEERING 1, 61360

6 3.Rate of Curing ‒Curing is defined as the process through which an asphalt material increases its consistency as it loses solvent by evaporation ‒Rate of Curing of Cutbacks The rate of curing of any cutback asphalt material depends on the distillate used in the cutting-back process T RANSPORTATION S YSTEM E NGINEERING 1, The rate of curing indicates the time that should elapse before a cutback will attain a consistency and simultaneously the binder to perform satisfactorily

7 4.Resistance to Water Action ‒The asphalt must sustain its ability to adhere to the aggregates even in the presence of water ‒If this bond between the asphalt and the aggregates is lost, the asphalt will strip from the aggregates, resulting in the deterioration of the pavement. ‒In hot-mix, hot-laid asphalt concrete (aggregates are thoroughly dried before mixing), stripping does not occur. ‒When water is added to a hot-mix, cold-laid asphalt concrete, anti-strip additives are added to improve the asphalt’s ability to adhere to the aggregates. T RANSPORTATION S YSTEM E NGINEERING 1, 61360

8 Several tests are conducted on asphalt materials to determine both their consistency and quality to ascertain whether they meet the prescribed specifications T RANSPORTATION S YSTEM E NGINEERING 1, These specifications are given by AASHTO and ASTM such as those listed in Tables 18.1 and 18.2.

11 The tests which will be studied are: 1.Consistency Tests a.Saybolt Furol Viscosity Test b.Kinematic Viscosity Test 2.Penetration Test 3.Ring-and-Ball Softening Point Test 4.Rheological Tests 5.Specific Gravity Test 6.Ductility Test 7.Flash-Point Test T RANSPORTATION S YSTEM E NGINEERING 1, Asphalt materials in the liquid state Asphalt materials in the semisolid and solid states May be used for blown asphalt

12 It is defined as the time in seconds for exactly 60 ml of the asphalt material to flow through the orifice at a specific temperature. The principal part of the equipment is the standard viscometer tube, which is 5in long and about 1in in diameter. – Small opening of specified shape and dimensions is at the bottom of the tube T RANSPORTATION S YSTEM E NGINEERING 1, 61360

13 The tube is filled with the material to be tested. The bath is heated to a specified temperature. Immediately upon reaching the prescribed temperature, the stopper is removed, – Time in seconds for exactly 60 ml of the asphalt material to flow through the orifice is recorded. This time is the Saybolt Furol viscosity in seconds. The asphalt materials are tested at 25 ○ C (77 ○ F), 50 ○ C (122 ○ F), and 60 ○ C (140 ○ F).

14 It is defined as the absolute (dynamic) viscosity divided by the density. T RANSPORTATION S YSTEM E NGINEERING 1, The test uses a capillary viscometer tube to measure the time it takes the asphalt sample to flow at a specified temperature between timing marks on the tube. Its unit is Centistokes 1 cSt = 1 mm 2 ·s −1 = 10 −6 m 2 ·s −1

15 There are: – Zeitfuch’s cross-arm viscometer – Asphalt Institute vacuum viscometer – Cannon Manning vacuum viscometer The viscometer tube is placed in a thermostatically controlled constant-temperature bath A sample of the material to be tested is preheated and poured into the large side of the viscometer tube until the filling line level is reached. The temperature of the bath then is brought to 135C (275F), T RANSPORTATION S YSTEM E NGINEERING 1, 61360

16 Flow then is induced by applying a slight pressure to the large opening or a partial vacuum to the efflux (small) opening of the viscometer tube The time it takes for the material to flow between two timing marks is recorded The kinematic viscosity of the material in units of centistokes is obtained by multiplying the time in seconds by a calibration factor for the viscometer used. The factor for each viscometer usually is provided by the manufacturer T RANSPORTATION S YSTEM E NGINEERING 1, 61360

17 It measures the consistency of a material in terms of the distance a standard needle sinks into that material under a prescribed loading and time. More fundamental tests are being substituted for this test, – It still may be included to ensure the exclusion of materials with very low penetration values at 25C (77F)

18 A sample is placed in a container which in turn is placed in a temperature-controlled water bath. The sample is then brought to the 25C (77F) Standard needle (loaded to a total weight of 100 g) is left to penetrate the sample of asphalt for the prescribed time of exactly 5 seconds. T RANSPORTATION S YSTEM E NGINEERING 1, The penetration is given as the distance in units of 0.1 mm. Example: needle penetrates a distance of 20 mm, the penetration is 200

19 It is used to measure the sensitivity of blown asphalt to temperature changes – by determining the temperature at which the material will be adequately softened to allow a standard ball to sink through it. T RANSPORTATION S YSTEM E NGINEERING 1, 61360

20 The equipment consists of: – A small brass ring of 5⁄8in inside diameter and 1⁄4in high – Steel ball 3⁄8in in diameter – Water or glycerin bath A sample of the bituminous material is placed in the brass ring which is cooled and immersed in the water or glycerin bath – It is maintained at a temperature of 5C (41F). T RANSPORTATION S YSTEM E NGINEERING 1, 61360

21 The temperature of the bath then is increased gradually, – causing the asphalt to soften and – permitting the ball to sink to the bottom of the bath. The temperature ( ○ F) at which the asphalt material touches the bottom of the bath is recorded as the softening point. T RANSPORTATION S YSTEM E NGINEERING 1, 61360

22 Superpave Systems These tests measure the relation between deformations, stresses, and their derivatives Example of these tests: – Dynamic Shear Test » It is used to determine the dynamic (oscillatory, تذبذبي ) shear modulus and phase angle of a sample of asphalt binder when tested in an oscillatory mode – Bending Creep Test » Indirect loading techniques are used in this test to determine the tensile creep compliance of hot-mix asphalt under different loading times and tensile strength T RANSPORTATION S YSTEM E NGINEERING 1, 61360

23 Specific gravity G b is defined as the ratio of the weight of a given volume of the material to the weight of the same volume of water. The specific gravity of asphalt materials is used mainly to: – determine the weight of a given volume of material to determine the amount of voids in compacted mixes – correct volumes measured at high temperatures. The specific gravity of bituminous materials changes with temperature – Temperature at which the test is conducted should be indicated. T RANSPORTATION S YSTEM E NGINEERING 1, 61360

24 The test normally is conducted with a pycnometer. T RANSPORTATION S YSTEM E NGINEERING 1, The dry weight (W1) of the pycnometer and stopper is obtained. Weight (W2) of pycnometer filled with distilled water is determined. Weight (W3) of pycnometer filled with material at the specified temperature is determined.

25 If the asphalt material cannot flow easily: – a small sample of the material is heated to facilitate flow – then poured into the pycnometer – then left to cool to the specified temperature Weight (W4) of pycnometer and material then is obtained. Water is poured into the pycnometer to completely fill it → W5 T RANSPORTATION S YSTEM E NGINEERING 1, 61360

26 Ductility is the distance in centimeters a standard sample of asphalt material will stretch before breaking when tested on standard ductility test equipment at 25C (77F). T RANSPORTATION S YSTEM E NGINEERING 1, 61360

27 The result of this test indicates the extent to which the material can be deformed without breaking. – The exact value of ductility is not as important as the existence or nonexistence of the property in the material. It is used for semisolid or solid materials which: – Firstly are heated gently to facilitate flow – Then poured into a standard mold to form a briquette of at least 1 cm 2 in cross section – Then it is cooled to 25C (77F) in a water bath – Then the sample is placed in the ductility machine and extended at a specified rate of speed » until the thread of material joining the two ends breaks T RANSPORTATION S YSTEM E NGINEERING 1, 61360

28 The distance (in centimeters) moved by the machine is the ductility of the material. T RANSPORTATION S YSTEM E NGINEERING 1, 61360

29 The flash point is the temperature at which asphalt vapor will ignite instantaneously in the presence of an open flame. – The flash point normally is lower than the temperature at which the material will burn – It gives an indication of the temperature limit at which extreme care should be taken, particularly when heating is done over open flames in open containers. T RANSPORTATION S YSTEM E NGINEERING 1, 61360

30 The test can be conducted by using: T RANSPORTATION S YSTEM E NGINEERING 1, – Tagliabue open-cup apparatus » It is more suitable for materials with relatively low flash points, such as cutback asphalts – Cleveland open-cup apparatus » It is more suitable for materials with higher flash points

31 It is conducted by partly filling the cup with the asphalt material and gradually increasing its temperature. A small open flame is passed over the surface. The increase in temperature will cause evaporation of volatile materials When a sufficient quantity of volatile materials is present, an instantaneous flash occurs when the open flame is passed over the surface. T RANSPORTATION S YSTEM E NGINEERING 1, The minimum temperature at which this occurs is the flash point.