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Laboratory performance comparison of the elastomer-modified asphalt mixtures
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Building and Environment 43 (2008) 1270–1277 www.elsevier.com/locate/buildenv
Laboratory performance comparison of the elastomer-modified asphalt mixtures Halit O¨zena,, Atakan Aksoyb, Su¨reyya Tayfurc, Fazıl C - elikb a
Department of Civil Engineering, Yıldız Technical University, Istanbul, Turkey Department of Civil Engineering, Karadeniz Technical University, Trabzon, Turkey c ISFALT Asphalt Company, Istanbul, Turkey
b
Received 2 May 2006; received in revised form 23 February 2007; accepted 10 March 2007
Abstract In this study, permanent deformation test results on the cylindrical samples produced with the Marshall compaction were compared with the wheel-tracking test results. Three different elastomeric polymer modifiers (OL, EL, and SB) were used. Repeated creep and LCPC wheel-tracking tests were realized at different loading conditions and temperatures. Repeated creep tests at 40 1C temperature do not correlate well with the LCPC wheel-tracking test results at high temperature (60 1C). Performance level of the elastomeric-modified asphalt mixtures can be different for same mixtures at different performance approaches. The evaluation of the dynamic creep test showed that the test can be used as an indicator of potential rutting, but the results in these cases should be confirmed with other more reliable tests. Also it is thought that gradation changing is more effectual than compaction effort types in view of evaluating efficiency of rutting test methods. r 2007 Elsevier Ltd. All rights reserved. Keywords: Asphalt mixture; Polymer; Elastomer; Repeated creep; LCPC wheel-tracking test
1. Introduction On the majority of the world’s roads and airports, conventional penetration grades of bitumen perform perfectly satisfactorily as the binder for asphalt mixes. However, the ‘‘working environment’’ of our roads is becoming more complex and severe, year on year, and includes factors such as: increased traffic densities, increased loads, increased axle pressures, shortage of good quality aggregates, and the effects of high and low ambient temperatures. The increasing punishment being given to our pavements is taking its toll and the most common manifestations of pavement distress include: permanent deformation, fatigue cracking, stripping, fretting, and reflective cracking [1]. Properties of the asphalt materials depend on the nature of the crude oil and on the refinery processes employed. These asphalts do not necessarily conform to the end specifications of pavement and industrial grade asphalts. Corresponding author.
0360-1323/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.buildenv.2007.03.010
Also there is a continuing trend towards higher tire pressures. Asphalt pavements have experienced accelerated deterioration. In recent years, more interests are concern in the use of polymer modifiers for asphalt cements. For a polymer to be effective in road applications, it should blend with the bitumen and improve its resistance (to rutting, abrasion, cracking, fatigue, stripping, bleeding, aging, etc.) at medium and high temperatures without making the modified bitumen too viscous at mixing temperatures or too brittle at low temperatures. In other words, it must improve the overall performance of the pavement. Many polymers have been used in the modification process but thermoplastic elastomers are enjoying wide acceptance as road bitumen modifiers, whereas polyolefins are used mostly for the preparation of waterproofing membranes, however, many other polymers are available and suggested [2]. Polymers, which are long-chain molecules of very highmolecular weight, used by the binder industry are classified based on different criteria. One method classifies polymers into two general categories—elastomers and plastomers.
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The mechanism of resistance to deformation is the basic difference between these two categories. The load-deformation behavior of elastomers is similar to that of a rubber band such as increasing tensile strength with increased elongation, which may reach 1300% of the original length, and ability to recover to the initial state after removal of load. Plastomers, on the other hand, exhibit high early strength but are less flexible and more prone to fracture under high strains than elastomers [3]. When a load is applied to the surface of an asphalt pavement it deforms, but because the asphalt is a viscoelastic material, when the load is removed the vast majority of the deformation recovers. However, there is a minute amount of irrecoverable viscous deformation which remains in the asphalt and which results in a very small permanent residual strain. Accumulation of millions of these small strains due to axle loading results in the surface rutting familiar on heavily trafficked pavements. Laboratory tests that attempt to measure the stability, i.e. the resistance to permanent deformation of an asphalt mix, are: the Marshall test, static and dynamic creep tests, wheel-tracking tests, and laboratory test track tests [1]. Although, generally, wheel-tracking tests appear to be well correlated with rutting in the field, there are at present no quantified relationships to link wheel-tracking test results to rutting in the field under variable traffic loading and environmental conditions. For this reason, wheeltracking tests cannot as yet be used to provide a quantitative estimate of rutting in the field. The test does, however, provide a reliable estimate of the rutting potential and, hence, can be used to rank mixes according to rut potential. Wheel-tracking tests are particularly recommended for the evaluation of rutting performance of stone-skeleton mixes, or mixes that include modified binders. Experience has shown that these mix types cannot be properly evaluated by means of conventional tests such as the unconfined uniaxial static or dynamic creep tests [4]. LCPC wheel-tracking test and repeated creep test gave similar results for selected SMA mixtures. In terms of rutting tests, it was thought that repeated creep tests may be a good indicator of SMA mixtures or else stony skeleton mixes [5]. The purpose of this research was to make a comparison between the LCPC wheel-tracking test results and traditional tests and to present an approach for preventing or minimizing rutting problem in context with the performance tests for the continuous gradation. Conventional and three elastomer-modified asphalt mixtures were evaluated with different temperatures and loading conditions. 2. Experimental methods 2.1. Materials used and specimen manufacture Used materials and experimental procedures in this study were following. Aggregate combination, asphalt cement, and three different additives were used. Aggregate
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was sampled from Omerli-Orkisan rock quarry in Turkey. Some properties of the used aggregate are given in Tables 1 and 2. 60–70 penetration asphalt cement produced from I˙zmit Oil Refinery (TUPRAS) was used. Standard laboratory test results for asphalt cement are incorporated in Table 3. A typical heavy traffic gradation for hot-mix asphalts (HMA), designated as wearing coarse (type II) in the Turkish specifications, was selected. The used gradation and specification limits are presented in Table 4 and Fig. 1. Stony skeleton mixtures were used in an earlier research for comparing LCPC wheel-tracking test and repeated creep test results. The gradation curve is also illustrated in Fig. 1 [5]. Three different modifiers were selected. All the modifiers were elastomeric polymers (OL, EL, and SB). Defining modification process of the modifiers was applied carefully. OL is a very cohesive product. This additive sticks aggregate particles very well and the produced thicker asphalt film is durable. The pre-added asphalt cement could be stored in conventional units that were already in situ. Additive was blended into asphalt cement at 170 1C at a ratio of the 5% of bitumen content.
Table 1 Some physical properties of the crushed aggregate Properties
Test method
Value
L.A. abrasion (%) Soundness in NaSO4 (%) Flakiness (%) Stripping resistance (%)
ASTM C-131 ASTM C-88 BS 182 (part 105) ASTM D-1664
26 1.53 28 55–65
Table 2 Specific gravities of aggregates (g/cm3) Properties
Coarse
Fine
Specific gravity—dry (g/cm3) Specific gravity—sat. (g/cm3) Specific gravity—apparent (g/cm3) Water absorption (%)
2.693 2.707 2.732 0.531
2.671 2.697 2.743 0.986
Filler
2.787
Table 3 The results of tests performed on asphalt cement (AC 60–70) Test
Method
Unit
Value
Specific gravity (25 1C) Flash point (Cleveland) Penetration (25 1C) Ductility (25 1C) Heating loss-163 1C Heating loss penetration/ original penetration Ductility after heating loss Softening point
ASTM ASTM ASTM ASTM
ASTM D-5
g/cm3 1C 0.1 mm cm % %
1.024 300 64 100+ 0.05 57.8
ASTM D-113 ASTM D-36
cm 1C
51.5+ 55
D-70 D-92 D-5 D-113
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Table 4 Gradation in this study and gradation limits Sieve size (mm)
Percentage passing (%)
Lower
Upper
SMA [5]
19.00 12.50 9.50 4.75 2.00 0.43 0.18 0.08
100 90.3 77.7 46.5 29.2 13.3 9.4 6.7
100 83 70 40 25 10 6 4
100 100 90 55 38 20 15 10
100 100 72.5 30 21.5 15 11.5 10
2.2. Repeated creep tests
100 used gradation
90 Percentage Passing, %
longer pavement service life: the rutting life increased by a factor of at least 10 [1]. SB additive was mixed to the 60–70 penetration asphalt cement 5% by weight of bitumen in this research. It is added to bitumen between 3% and 7% by weight of bitumen. Mixing was realized with high-speed stirrer. Marshall mix design procedure was applied with 50 blows on each side of cylindrical samples (ASTM D1559) and the optimum asphalt contents of HMA mixture were determined (Wa ¼ 4.41%). Some properties of the Marshall specimens for conventional and modified mixtures for repeated creep tests are presented in Table 5.
lower values
80
upper values
70
SMA gradation [5]
60 50 40 30 20 10 0 0.01
0.10
1.00
10.00
100.00
Sieve Size, mm Fig. 1. Gradation curve of used aggregate and limits.
EL product is a reactive elastomeric terpolymer. It is added to the asphalt cement between 1.5% and 3%. Asphalt cement reaches generally lower penetration value and higher softening point with the modification. Asphalt cement was heated. Additive was mixed to the binder at 180 1C temperature with a speed of 5 g/s. Additive ratio was selected as 1.5% of bitumen content. Modified binder was mixed at Marshall mixer during 6 h with a speed of 80 rpm. SB product is a styrene–butadiene–styrene block copolymer. When SBS is added to hot bitumen, it absorbs some of the maltene components from the bitumen which extends (softens) the polymer and causes it to swell. The absorption of the maltenes by the polymer is affected by several factors which include: the nature of the bitumen, polymer type, polymer morphology, temperature, and dispersion of the polymer (efficiency of mixer/mixing process). The uptake of the maltenes generally amounts to some 6–9 times the weight of the polymer forming the ‘‘polymer-rich phase’’. The blend of bitumen and SBS is not always homogenous and on cooling a two-phase system will become apparent. The second phase, composed of asphaltenes and the balance of the maltenes, is termed the ‘‘asphaltene-rich phase’’. In laboratory simulation tests asphalt mixes made with bitumen/SBS binders lead to
Strength of the bituminous mixtures to the plastic deformation may be determined with the repeated creep test. Test equipment is the same as the static creep test but repeated load is applied differently. Efficiencies of some selected chemical modifiers are especially evaluated with the repeated creep test, also rutting investigation of asphalt mixtures are done. Experiments were realized at 5, 25, and 40 1C test temperatures during 1000 ms pulse period. Samples were exposed to 780 N (100 kPa) starting load. Average 1100 N (138 kPa) was loaded duration of test. Loads and permanent deformations were saved at least 20 h. Figs. 2–4 show the repeated creep curves. Repeated creep tests on all of the mixtures demonstrated that the addition of modifiers enhanced the permanent deformation resistance at moderate temperature (25 1C) but different relations are concern at low (5 1C) and high (40 1C) temperatures. Repeated creep tests at 40 1C temperature do not correlate well with the LCPC wheeltracking test results at high temperature (60 1C). Relative performance of modified mixtures at different temperatures can be different. 2.3. LCPC wheel-tracking tests Rutting test was verified with the LCPC method. This test has been used in France for over 20 years to successfully prevent rutting in HMA pavements. In recent years, the test has been used in the United States. This test is capable of simultaneously testing two HMA slabs. Slab dimensions are typically 180 mm wide, 500 mm long, and 20–100 mm thick. Research indicates good correlation between LCPC test results and actual field performance [6,7]. Samples were prepared at 500 mm length, 180 mm width, 100 mm height. Test temperature was 60 1C. Samples were kept at least 12 h at this temperature. Each tire was applied 5000 N load. Tire pressure was 0.6 MPa (87 psi). Samples must be compacted as a determined degree of compacting. Test briquettes were compacted at 98% field compacting scale. Before the temperature was reached at 60 1C, precompacting (1000 cycles) was made. Pre-conditioning
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Table 5 Some properties of the Marshall samples and test parameter definition Percent add. (%)
Height (mm)
Weight in weather (g)
Weight in water (g)
Volume (cm3)
Mix density (g/cm3)
Test
Temperature (1C)
Conventional (NR) mixtures 6 4.41 7 4.41 8 4.41 9 4.41 11 4.41 13 4.41
0.0 0.0 0.0 0.0 0.0 0.0
63.2 63.1 62.6 63.2 61.8 61.9
1197.9 1185.7 1195.0 1199.5 1192.1 1193.3
702.9 694.5 700.7 703.7 706.7 707.5
495.0 491.2 494.3 495.8 485.4 485.8
2.420 2.414 2.418 2.419 2.456 2.456
Repeated creep test
25 25 5 5 40 40
OL mixtures 7 8 11 13 17 18
4.41 4.41 4.41 4.41 4.41 4.41
5.0 5.0 5.0 5.0 5.0 5.0
62.3 62.8 62.4 62.5 62.0 62.8
1194.2 1199.3 1192.1 1194.0 1193.6 1197.9
705.5 707.5 704.9 706.4 707.4 709.8
488.7 491.8 487.2 487.6 486.2 488.1
2.444 2.439 2.447 2.449 2.455 2.454
Repeated creep test
5 5 25 25 40 40
EL mixtures 4 5 10 17 21 22
4.41 4.41 4.41 4.41 4.41 4.41
1.5 1.5 1.5 1.5 1.5 1.5
62.9 62.1 62.7 62.4 63.1 61.7
1199.0 1198.8 1193.9 1198.6 1197.8 1195.7
705.5 705.1 701.0 707.4 705.5 705.2
493.5 493.7 492.9 491.2 492.3 490.5
2.430 2.428 2.422 2.440 2.433 2.438
Repeated creep test
5 5 25 40 25 40
SB mixtures 6 7 12 13 14 15
4.41 4.41 4.41 4.41 4.41 4.41
3.0 3.0 3.0 3.0 3.0 3.0
62.3 61.6 61.8 61.8 62.3 62.1
1201.5 1195.9 1201.3 1200.0 1200.5 1199.0
709.5 708.1 711.7 713.3 707.8 711.2
492.0 487.8 489.6 486.7 492.7 487.8
2.442 2.452 2.454 2.466 2.437 2.458
Repeated creep test
25 25 40 40 5 5
1000
10000
Sample no.
Asphalt cement (Wa) (%)
4000
7000 NR
NR OL
3500
OL
6000
EL
EL SB Permanent deformation
Permanent deformation
3000 2500 2000 1500 1000
SB
5000 4000 3000 2000 1000
500
0
0 1
10
100
1000
10000
100000
Log loading time (seconds)
1
10
100
100000
Log loading time (seconds)
Fig. 2. Number of cycles versus permanent deformation (5 1C).
Fig. 3. Number of cycles versus permanent deformation (25 1C).
temperature was regulated and values were saved. After the values were saved rutting was calculated. Two identical samples were used for each alternative.
LCPC rutting test results for conventional and modified mixtures are shown in Fig. 5. Conventional mixtures show the highest permanent deformation in this test.
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1274 12000
12.00 NR
Permanent Deformation 10-6 in/in
OL 10000
EL
Permanent deformation
SB 8000
6000
4000
10.00 NR
8.00
AP SE
6.00
PE 4.00
BE SB
2.00 0.00 0
2000
10000
20000 40000 30000 Number of Load Cycles
50000
Fig. 6. LCPC wheel-tracking test results [5].
0 1
10
100
1000
10000
100000
Log loading time (seconds)
12000 Permanent Deformation 10-6 in/in
Fig. 4. Number of cycles versus permanent deformation (40 1C).
6 NR OL 5
EL
Permanent deformation
SB 4
3
10000 NR
8000
AP SE
6000
PE 4000
BE SB
2000 0 1
10
100
1000
10000
100000
Number of Load Cycles
2
Fig. 7. Number of cycles versus permanent deformation (25 1C) [5].
1
0 0
10000
20000
30000
40000
50000
Number of load cycles Fig. 5. LCPC wheel-tracking test results.
3. Evaluation In this research performance known mixtures were used. Permanent deformation problem was evaluated with repeated creep tests and LCPC wheel-tracking tests. Many identical samples were prepared with great care and specific gravities were observed. It is known from the literature that repeated creep test for cylindrically compacted and laboratory-prepared samples and wheel-tracking tests for slabs may be used for evaluating rutting developing. The misleading or controversial results are also concern in literature and researches are going on.
Permanent Deformation 10-6 in/in
18000 16000 14000 NR
12000
AP
10000
SE 8000
PE
6000
BE
4000
SB
2000 0 1
10
100
1000
10000
100000
Number of Load Cycles Fig. 8. Number of cycles versus permanent deformation (40 1C) [5].
From an earlier study rutting problem was evaluated with the same tests for stony skeleton (SMA) mixtures. Harmonious results were obtained from this investigation.
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Rutting curves are given in Figs. 6–8. More performance developing was obtained from various polymer-modified mixtures (NR-conventional mixtures, AP–SE–PE–BE–SB polymer-modified mixtures). Identical samples were prepared with great care because of angularity effects of used rock combination [5]. Although different polymer modifiers were used such as elastomeric or plastomeric polymers, drainage inhibitors, mostly higher-performance levels were observed in all tests [5]. Repeated creep tests on Marshall samples may be used for explaining permanent deformation [8]. Repeated creep curves and wheel-tracking test results are given in Figs. 2–4. Repeated creep tests on all of the mixtures demonstrated that the addition of modifiers enhanced the permanent deformation resistance at moderate temperature (25 1C) but different relations are concern at low (5 1C) and high (40 1C) temperatures. Repeated creep tests at 40 1C temperature do not correlate well with the LCPC wheel-tracking test results at high temperature (60 1C). Relative performance of modified mixtures at different temperatures can be different. It was understood that this difference may stem from the gradation changing. For the laboratory mixes, it was the intention to assess most HMA mix types currently used in South Africa. These included both stone-skeleton mixes (stone-mastic asphalt and semi-open asphalt with bitumen-rubber binder) and sand-skeleton mixes (gap- and continuously graded asphalt). Porous asphalt was not included. The Transportek wheel-tracking test gave reasonable results, and is recommended for all high reliability projects. The test is appropriate for all mix types, including mixes containing modified binders and stone-skeleton mixes. For stone-skeleton mixes, the test must be performed at the refusal air void content otherwise the mix could deform excessively, which is not expected if the mix is well compacted in the field provided that it is designed correctly. Because the dynamic creep does not correctly determine the rutting resistance of all mixes, and the performance ratings do not agree with the the Transportek wheel-tracking test, the dynamic creep test is not recommended for assessing the rutting potential of HMA other than sand-skeleton mixes manufactured with unmodified binders, unless evaluated in conjunction with other rutting tests. The evaluation of the dynamic creep test showed that the test can be used as an indicator of potential rutting, but the results in these cases should be confirmed with other more reliable tests [4]. Although, generally, wheel-tracking tests appear to be well correlated with rutting in the field, there are at present no quantified relationships to link wheel-tracking test results to rutting in the field under variable traffic loading and environmental conditions. For this reason, wheeltracking tests cannot as yet be used to provide a quantitative estimate of rutting in the field. The test does, however, provide a reliable estimate of the rutting potential and, hence, can be used to rank mixes according to rut potential. Wheel-tracking tests are particularly recom-
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mended for the evaluation of rutting performance of stone-skeleton mixes, or mixes that include modified binders. Experience has shown that these mix types cannot be properly evaluated by means of conventional tests such as the unconfined uniaxial static or dynamic creep tests [4]. The usual testing methods (Marshall test, wheel-tracking test, repeated load uniaxial test) are inadequate for the characterization of the resistance to the permanent deformation of asphalt. This is not to say that these tests would be unsuitable for other applications, for example, in a mixture design procedure within given composition limits. However, reliable comparisons of the deformation behavior of various sorts of mixtures are not possible on the basis of these tests [9]. By evaluating asphalt mixes and pavements from a functional point of view, the possibility to develop better products that better stand up to demands of today and tomorrow will increase. To be able to use demands on functional properties there is however a necessity for functional methods of measurement that fulfill demands on good relevance, high flexibility, and low cost. The first step in the development of functional methods of measurement is to have for certainty samples with a good affinity to real conditions on the road. A study made in Sweden has proven that the traditional Marshall method is not suitable in this regard. The unsuitability of the Marshall method of compaction has also been proven by several other investigators in other countries. A study for alternatives has emphasized the importance of a kneading ingredient in the compaction effort, which is in accordance with methods like rolling wheel and gyratory compactor. The same study showed that a sample compacted in the laboratory, at the same degree of compaction, usually gets better mechanical properties (indirect tensile stiffness modulus, dynamic creep test, and indirect tensile test) than a sample compacted in the field and that the difference between laboratory and field is not the same for different types of mixes [10]. The dynamic creep test is an interesting alternative to the wheel-tracking test for measuring the sensibility for permanent deformations, but there is some doubt about the ability of the traditional method to be able to work as a functional method of measurement and to distinguish between different types of mixes. Enlarging the sample to a diameter of 150 mm while the platen is kept at normal size, i.e. 100 mm, accomplishes a limited lateral pressure, which gives more justice to mixes, which get their stability not so much by forces of cohesion but much more so by the inner friction of the aggregate. Trials have shown a much better coefficient of correlation (0.91) with the wheel-tracking test for the modified model (diameter of sample 150 mm and diameter of platen 100 mm) than for the traditional model (0.36) with the same diameter for sample and platen [10]. In this research 100 mm diameter Marshall samples were tested in dynamic creep test and controversial results were obtained from these two tests. Unlike this the same
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diameter was used in earlier study but logical trends were obtained for SMA mixtures [5]. The failure of the Marshall test to describe rutting resistance of asphalt mixes is demonstrated where the Marshall stability is plotted versus the rut depth at 50,000 wheels passes as determined in a laboratory test track experiment. Several conventional and polymer-modified binders were used in the experiments. From these results it is clear that no relation exists between the Marshall stability and rutting under actual wheel loading in the LTT. The Marshall test should therefore not be considered relevant to characterize the resistance of mixes with polymer-modified binders. Fortunately, this fact has nowadays been recognized by authorities who aim to implement rational performance-based specifications in the SHRP in the USA and in Europe in CEN specifications [11]. It is well recognized from the literature that the aggregate interlocking greatly occurred in the coarse aggregate. The image evaluation of aggregate morphological characteristic demonstrated that a stable aggregate skeleton resulted in more internal resistance. Traditional tests such as Marshall stability and the indirect tensile strength are considered to be inadequate to measure the internal resistance in HMA [12]. If asphalt mixes are regarded and judged from their functional abilities there is a demand for functional methods of measurement, methods that are not in existence today concerning all the parameters that are essential for the good behavior of the asphalt pavement. To be able to use demands on functional properties, there is however a necessity for functional methods of measurement that fulfill demands on good relevance, high flexibility, and low cost. The discussions about this subject started in Sweden in the late eighties. After a period of time it was clear, which should have been selfevident, that functional methods of measurement demand samples that have a good affinity with real conditions on the road. There were at this time a lot of people that had come to the conclusion that the Marshall method of compaction was not a suitable method in this regard. Because of this the first step in the development of functional methods of measurement was to study alternatives to use instead of the Marshall method. The unsuitability of the Marshall method of compaction has since then been proven by several other investigators in other countries [13,14]. 4. Conclusions A study has been conducted to understand permanent deformation properties of the asphalt mixtures containing elastomeric polymer modifiers (OL, EL, SB). An evaluation between the rutting potential of the cylindrical samples produced with the Marshall compaction and wheeltracking test results was done. Repeated creep tests on all of the mixtures demonstrated that the addition of modifiers enhanced the permanent deformation resistance at moderate temperature (25 1C) but different relations are concern at low (5 1C) and high (40 1C)
temperatures. Repeated creep tests at 40 1C temperature do not correlate well with the LCPC wheel-tracking test results at high temperature (60 1C). Relative performance of modified mixtures at different temperatures can be different. In this research performance known mixtures were tested. Obtained data were compared with the earlier research [5]. Unlike this research continuous gradation was offered and the result was that repeated creep test and wheel-tracking test did not give parallel result. The evaluation of the dynamic creep test showed that the test can be used as an indicator of potential rutting, but the results in these cases should be confirmed with other more reliable tests. Also it is thought that gradation changing is more important than compacting efforting types in view of evaluating efficiency of rutting test methods. Acknowledgments ISFALT Asphalt and Dogus- Construction Companies are gratefully acknowledged for their laboratory capabilities. The authors are also indebted to Mr. T. Erol and Mr. N. Bugan for assistance in laboratories. References [1] Robertus C, Mulder EA, Koole RC. SBS modified bitumen for heavy duty asphalt pavements. Second international conference on roads and airfield pavement technology. Singapore; September 1995. [2] Bonemazzi F, Braga V, Corrieri R, Giavarini C, Sartori F. Characteristics of polymers and polymer-modified binders. Transportation Research Record 1535. Washington, DC: Transportation Research Board; 1996. p. 36–47. [3] Mostafa AE, Gerardo WF, Imad LA. Quantitative effect of elastomeric modification on binder performance at intermediate and high temperatures. Journal of Materials in Civil Engineering 2003;15(1):32–40. [4] Visser AT, Long F, Verhaeghe A, Taute A. Provisional validation of the new South African hot-mix asphalt design method (mix design1:7–6). Ninth international conference on asphalt pavements. Copenhagen, Denmark; August 2002, p. 36–47. [5] Tayfur S, Ozen H, Aksoy A. Investigation of rutting performance of asphalt mixtures containing polymer modifiers, Construction and Building Materials 2006;21:328–37. [6] Aschenbrener T. Comparison of results obtained from the French rutting tester with pavements of known field performance. Colorado Department of Transportation, Report no: CDOT-DTD-R-92-11; October 1992. [7] Corte JF, Brosscaud Y, Simonceli JP, Caroff G. Investigation of rutting of asphalt surface layers: influence of binder and axle load configurations,.Transportation Research Board, 1436; 1994. [8] Brown SF. Practical test procedures for mechanical properties of bituminous materials. Proceedings of the Institution of Civil Engineers, Transport 1995;111:289–97. [9] Jansen Venneboer J, Van der Heide JPJ, Molenaar AAA. Asphalt constructions for heavy duty pavements and road widenings in the Netherlands, Eurasphalt & Eurobitume Congress; 1996. [10] Ulmgren N. Functional testing of asphalt mixes for permanent deformation by dynamic creep test modification of method and Round Robin Test, Eurasphalt & Eurobitume Congress; 1996. [11] Valkering CP, Lancon DJL, Hilster ED, Stoker DA. Rutting resistance of asphalt mixes containing non-conventional and polymer-modifed binders. AAPT Conference. Albuquerque, USA; 19/21 February 1990.
ARTICLE IN PRESS H. O¨zen et al. / Building and Environment 43 (2008) 1270–1277 [12] Chen J-S, Liao M-C. Evaluation of internal resistance in hot mix asphalt concrete. Construction and Building Materials 2002;16: 313–9. [13] Conuegra A. A comparative evaluation of laboratory compaction devices based on their ability to produce mixtures with engineering
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properties similar to those produced in the field. 68th TRB-meeting. Washington DC; January 1989. [14] Caltabiano MA, Waters TJ. The effect of sample compaction on the mix characteristics. 8th AAPA international asphalt conference. Sydney, Australia; 1991.
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Laboratory performance comparison of the elastomer-modified asphalt mixtures Halit O¨zena,, Atakan Aksoyb, Su¨reyya Tayfurc, Fazıl C - elikb a
Department of Civil Engineering, Yıldız Technical University, Istanbul, Turkey Department of Civil Engineering, Karadeniz Technical University, Trabzon, Turkey c ISFALT Asphalt Company, Istanbul, Turkey
b
Received 2 May 2006; received in revised form 23 February 2007; accepted 10 March 2007
Abstract In this study, permanent deformation test results on the cylindrical samples produced with the Marshall compaction were compared with the wheel-tracking test results. Three different elastomeric polymer modifiers (OL, EL, and SB) were used. Repeated creep and LCPC wheel-tracking tests were realized at different loading conditions and temperatures. Repeated creep tests at 40 1C temperature do not correlate well with the LCPC wheel-tracking test results at high temperature (60 1C). Performance level of the elastomeric-modified asphalt mixtures can be different for same mixtures at different performance approaches. The evaluation of the dynamic creep test showed that the test can be used as an indicator of potential rutting, but the results in these cases should be confirmed with other more reliable tests. Also it is thought that gradation changing is more effectual than compaction effort types in view of evaluating efficiency of rutting test methods. r 2007 Elsevier Ltd. All rights reserved. Keywords: Asphalt mixture; Polymer; Elastomer; Repeated creep; LCPC wheel-tracking test
1. Introduction On the majority of the world’s roads and airports, conventional penetration grades of bitumen perform perfectly satisfactorily as the binder for asphalt mixes. However, the ‘‘working environment’’ of our roads is becoming more complex and severe, year on year, and includes factors such as: increased traffic densities, increased loads, increased axle pressures, shortage of good quality aggregates, and the effects of high and low ambient temperatures. The increasing punishment being given to our pavements is taking its toll and the most common manifestations of pavement distress include: permanent deformation, fatigue cracking, stripping, fretting, and reflective cracking [1]. Properties of the asphalt materials depend on the nature of the crude oil and on the refinery processes employed. These asphalts do not necessarily conform to the end specifications of pavement and industrial grade asphalts. Corresponding author.
0360-1323/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.buildenv.2007.03.010
Also there is a continuing trend towards higher tire pressures. Asphalt pavements have experienced accelerated deterioration. In recent years, more interests are concern in the use of polymer modifiers for asphalt cements. For a polymer to be effective in road applications, it should blend with the bitumen and improve its resistance (to rutting, abrasion, cracking, fatigue, stripping, bleeding, aging, etc.) at medium and high temperatures without making the modified bitumen too viscous at mixing temperatures or too brittle at low temperatures. In other words, it must improve the overall performance of the pavement. Many polymers have been used in the modification process but thermoplastic elastomers are enjoying wide acceptance as road bitumen modifiers, whereas polyolefins are used mostly for the preparation of waterproofing membranes, however, many other polymers are available and suggested [2]. Polymers, which are long-chain molecules of very highmolecular weight, used by the binder industry are classified based on different criteria. One method classifies polymers into two general categories—elastomers and plastomers.
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The mechanism of resistance to deformation is the basic difference between these two categories. The load-deformation behavior of elastomers is similar to that of a rubber band such as increasing tensile strength with increased elongation, which may reach 1300% of the original length, and ability to recover to the initial state after removal of load. Plastomers, on the other hand, exhibit high early strength but are less flexible and more prone to fracture under high strains than elastomers [3]. When a load is applied to the surface of an asphalt pavement it deforms, but because the asphalt is a viscoelastic material, when the load is removed the vast majority of the deformation recovers. However, there is a minute amount of irrecoverable viscous deformation which remains in the asphalt and which results in a very small permanent residual strain. Accumulation of millions of these small strains due to axle loading results in the surface rutting familiar on heavily trafficked pavements. Laboratory tests that attempt to measure the stability, i.e. the resistance to permanent deformation of an asphalt mix, are: the Marshall test, static and dynamic creep tests, wheel-tracking tests, and laboratory test track tests [1]. Although, generally, wheel-tracking tests appear to be well correlated with rutting in the field, there are at present no quantified relationships to link wheel-tracking test results to rutting in the field under variable traffic loading and environmental conditions. For this reason, wheeltracking tests cannot as yet be used to provide a quantitative estimate of rutting in the field. The test does, however, provide a reliable estimate of the rutting potential and, hence, can be used to rank mixes according to rut potential. Wheel-tracking tests are particularly recommended for the evaluation of rutting performance of stone-skeleton mixes, or mixes that include modified binders. Experience has shown that these mix types cannot be properly evaluated by means of conventional tests such as the unconfined uniaxial static or dynamic creep tests [4]. LCPC wheel-tracking test and repeated creep test gave similar results for selected SMA mixtures. In terms of rutting tests, it was thought that repeated creep tests may be a good indicator of SMA mixtures or else stony skeleton mixes [5]. The purpose of this research was to make a comparison between the LCPC wheel-tracking test results and traditional tests and to present an approach for preventing or minimizing rutting problem in context with the performance tests for the continuous gradation. Conventional and three elastomer-modified asphalt mixtures were evaluated with different temperatures and loading conditions. 2. Experimental methods 2.1. Materials used and specimen manufacture Used materials and experimental procedures in this study were following. Aggregate combination, asphalt cement, and three different additives were used. Aggregate
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was sampled from Omerli-Orkisan rock quarry in Turkey. Some properties of the used aggregate are given in Tables 1 and 2. 60–70 penetration asphalt cement produced from I˙zmit Oil Refinery (TUPRAS) was used. Standard laboratory test results for asphalt cement are incorporated in Table 3. A typical heavy traffic gradation for hot-mix asphalts (HMA), designated as wearing coarse (type II) in the Turkish specifications, was selected. The used gradation and specification limits are presented in Table 4 and Fig. 1. Stony skeleton mixtures were used in an earlier research for comparing LCPC wheel-tracking test and repeated creep test results. The gradation curve is also illustrated in Fig. 1 [5]. Three different modifiers were selected. All the modifiers were elastomeric polymers (OL, EL, and SB). Defining modification process of the modifiers was applied carefully. OL is a very cohesive product. This additive sticks aggregate particles very well and the produced thicker asphalt film is durable. The pre-added asphalt cement could be stored in conventional units that were already in situ. Additive was blended into asphalt cement at 170 1C at a ratio of the 5% of bitumen content.
Table 1 Some physical properties of the crushed aggregate Properties
Test method
Value
L.A. abrasion (%) Soundness in NaSO4 (%) Flakiness (%) Stripping resistance (%)
ASTM C-131 ASTM C-88 BS 182 (part 105) ASTM D-1664
26 1.53 28 55–65
Table 2 Specific gravities of aggregates (g/cm3) Properties
Coarse
Fine
Specific gravity—dry (g/cm3) Specific gravity—sat. (g/cm3) Specific gravity—apparent (g/cm3) Water absorption (%)
2.693 2.707 2.732 0.531
2.671 2.697 2.743 0.986
Filler
2.787
Table 3 The results of tests performed on asphalt cement (AC 60–70) Test
Method
Unit
Value
Specific gravity (25 1C) Flash point (Cleveland) Penetration (25 1C) Ductility (25 1C) Heating loss-163 1C Heating loss penetration/ original penetration Ductility after heating loss Softening point
ASTM ASTM ASTM ASTM
ASTM D-5
g/cm3 1C 0.1 mm cm % %
1.024 300 64 100+ 0.05 57.8
ASTM D-113 ASTM D-36
cm 1C
51.5+ 55
D-70 D-92 D-5 D-113
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Table 4 Gradation in this study and gradation limits Sieve size (mm)
Percentage passing (%)
Lower
Upper
SMA [5]
19.00 12.50 9.50 4.75 2.00 0.43 0.18 0.08
100 90.3 77.7 46.5 29.2 13.3 9.4 6.7
100 83 70 40 25 10 6 4
100 100 90 55 38 20 15 10
100 100 72.5 30 21.5 15 11.5 10
2.2. Repeated creep tests
100 used gradation
90 Percentage Passing, %
longer pavement service life: the rutting life increased by a factor of at least 10 [1]. SB additive was mixed to the 60–70 penetration asphalt cement 5% by weight of bitumen in this research. It is added to bitumen between 3% and 7% by weight of bitumen. Mixing was realized with high-speed stirrer. Marshall mix design procedure was applied with 50 blows on each side of cylindrical samples (ASTM D1559) and the optimum asphalt contents of HMA mixture were determined (Wa ¼ 4.41%). Some properties of the Marshall specimens for conventional and modified mixtures for repeated creep tests are presented in Table 5.
lower values
80
upper values
70
SMA gradation [5]
60 50 40 30 20 10 0 0.01
0.10
1.00
10.00
100.00
Sieve Size, mm Fig. 1. Gradation curve of used aggregate and limits.
EL product is a reactive elastomeric terpolymer. It is added to the asphalt cement between 1.5% and 3%. Asphalt cement reaches generally lower penetration value and higher softening point with the modification. Asphalt cement was heated. Additive was mixed to the binder at 180 1C temperature with a speed of 5 g/s. Additive ratio was selected as 1.5% of bitumen content. Modified binder was mixed at Marshall mixer during 6 h with a speed of 80 rpm. SB product is a styrene–butadiene–styrene block copolymer. When SBS is added to hot bitumen, it absorbs some of the maltene components from the bitumen which extends (softens) the polymer and causes it to swell. The absorption of the maltenes by the polymer is affected by several factors which include: the nature of the bitumen, polymer type, polymer morphology, temperature, and dispersion of the polymer (efficiency of mixer/mixing process). The uptake of the maltenes generally amounts to some 6–9 times the weight of the polymer forming the ‘‘polymer-rich phase’’. The blend of bitumen and SBS is not always homogenous and on cooling a two-phase system will become apparent. The second phase, composed of asphaltenes and the balance of the maltenes, is termed the ‘‘asphaltene-rich phase’’. In laboratory simulation tests asphalt mixes made with bitumen/SBS binders lead to
Strength of the bituminous mixtures to the plastic deformation may be determined with the repeated creep test. Test equipment is the same as the static creep test but repeated load is applied differently. Efficiencies of some selected chemical modifiers are especially evaluated with the repeated creep test, also rutting investigation of asphalt mixtures are done. Experiments were realized at 5, 25, and 40 1C test temperatures during 1000 ms pulse period. Samples were exposed to 780 N (100 kPa) starting load. Average 1100 N (138 kPa) was loaded duration of test. Loads and permanent deformations were saved at least 20 h. Figs. 2–4 show the repeated creep curves. Repeated creep tests on all of the mixtures demonstrated that the addition of modifiers enhanced the permanent deformation resistance at moderate temperature (25 1C) but different relations are concern at low (5 1C) and high (40 1C) temperatures. Repeated creep tests at 40 1C temperature do not correlate well with the LCPC wheeltracking test results at high temperature (60 1C). Relative performance of modified mixtures at different temperatures can be different. 2.3. LCPC wheel-tracking tests Rutting test was verified with the LCPC method. This test has been used in France for over 20 years to successfully prevent rutting in HMA pavements. In recent years, the test has been used in the United States. This test is capable of simultaneously testing two HMA slabs. Slab dimensions are typically 180 mm wide, 500 mm long, and 20–100 mm thick. Research indicates good correlation between LCPC test results and actual field performance [6,7]. Samples were prepared at 500 mm length, 180 mm width, 100 mm height. Test temperature was 60 1C. Samples were kept at least 12 h at this temperature. Each tire was applied 5000 N load. Tire pressure was 0.6 MPa (87 psi). Samples must be compacted as a determined degree of compacting. Test briquettes were compacted at 98% field compacting scale. Before the temperature was reached at 60 1C, precompacting (1000 cycles) was made. Pre-conditioning
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Table 5 Some properties of the Marshall samples and test parameter definition Percent add. (%)
Height (mm)
Weight in weather (g)
Weight in water (g)
Volume (cm3)
Mix density (g/cm3)
Test
Temperature (1C)
Conventional (NR) mixtures 6 4.41 7 4.41 8 4.41 9 4.41 11 4.41 13 4.41
0.0 0.0 0.0 0.0 0.0 0.0
63.2 63.1 62.6 63.2 61.8 61.9
1197.9 1185.7 1195.0 1199.5 1192.1 1193.3
702.9 694.5 700.7 703.7 706.7 707.5
495.0 491.2 494.3 495.8 485.4 485.8
2.420 2.414 2.418 2.419 2.456 2.456
Repeated creep test
25 25 5 5 40 40
OL mixtures 7 8 11 13 17 18
4.41 4.41 4.41 4.41 4.41 4.41
5.0 5.0 5.0 5.0 5.0 5.0
62.3 62.8 62.4 62.5 62.0 62.8
1194.2 1199.3 1192.1 1194.0 1193.6 1197.9
705.5 707.5 704.9 706.4 707.4 709.8
488.7 491.8 487.2 487.6 486.2 488.1
2.444 2.439 2.447 2.449 2.455 2.454
Repeated creep test
5 5 25 25 40 40
EL mixtures 4 5 10 17 21 22
4.41 4.41 4.41 4.41 4.41 4.41
1.5 1.5 1.5 1.5 1.5 1.5
62.9 62.1 62.7 62.4 63.1 61.7
1199.0 1198.8 1193.9 1198.6 1197.8 1195.7
705.5 705.1 701.0 707.4 705.5 705.2
493.5 493.7 492.9 491.2 492.3 490.5
2.430 2.428 2.422 2.440 2.433 2.438
Repeated creep test
5 5 25 40 25 40
SB mixtures 6 7 12 13 14 15
4.41 4.41 4.41 4.41 4.41 4.41
3.0 3.0 3.0 3.0 3.0 3.0
62.3 61.6 61.8 61.8 62.3 62.1
1201.5 1195.9 1201.3 1200.0 1200.5 1199.0
709.5 708.1 711.7 713.3 707.8 711.2
492.0 487.8 489.6 486.7 492.7 487.8
2.442 2.452 2.454 2.466 2.437 2.458
Repeated creep test
25 25 40 40 5 5
1000
10000
Sample no.
Asphalt cement (Wa) (%)
4000
7000 NR
NR OL
3500
OL
6000
EL
EL SB Permanent deformation
Permanent deformation
3000 2500 2000 1500 1000
SB
5000 4000 3000 2000 1000
500
0
0 1
10
100
1000
10000
100000
Log loading time (seconds)
1
10
100
100000
Log loading time (seconds)
Fig. 2. Number of cycles versus permanent deformation (5 1C).
Fig. 3. Number of cycles versus permanent deformation (25 1C).
temperature was regulated and values were saved. After the values were saved rutting was calculated. Two identical samples were used for each alternative.
LCPC rutting test results for conventional and modified mixtures are shown in Fig. 5. Conventional mixtures show the highest permanent deformation in this test.
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1274 12000
12.00 NR
Permanent Deformation 10-6 in/in
OL 10000
EL
Permanent deformation
SB 8000
6000
4000
10.00 NR
8.00
AP SE
6.00
PE 4.00
BE SB
2.00 0.00 0
2000
10000
20000 40000 30000 Number of Load Cycles
50000
Fig. 6. LCPC wheel-tracking test results [5].
0 1
10
100
1000
10000
100000
Log loading time (seconds)
12000 Permanent Deformation 10-6 in/in
Fig. 4. Number of cycles versus permanent deformation (40 1C).
6 NR OL 5
EL
Permanent deformation
SB 4
3
10000 NR
8000
AP SE
6000
PE 4000
BE SB
2000 0 1
10
100
1000
10000
100000
Number of Load Cycles
2
Fig. 7. Number of cycles versus permanent deformation (25 1C) [5].
1
0 0
10000
20000
30000
40000
50000
Number of load cycles Fig. 5. LCPC wheel-tracking test results.
3. Evaluation In this research performance known mixtures were used. Permanent deformation problem was evaluated with repeated creep tests and LCPC wheel-tracking tests. Many identical samples were prepared with great care and specific gravities were observed. It is known from the literature that repeated creep test for cylindrically compacted and laboratory-prepared samples and wheel-tracking tests for slabs may be used for evaluating rutting developing. The misleading or controversial results are also concern in literature and researches are going on.
Permanent Deformation 10-6 in/in
18000 16000 14000 NR
12000
AP
10000
SE 8000
PE
6000
BE
4000
SB
2000 0 1
10
100
1000
10000
100000
Number of Load Cycles Fig. 8. Number of cycles versus permanent deformation (40 1C) [5].
From an earlier study rutting problem was evaluated with the same tests for stony skeleton (SMA) mixtures. Harmonious results were obtained from this investigation.
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Rutting curves are given in Figs. 6–8. More performance developing was obtained from various polymer-modified mixtures (NR-conventional mixtures, AP–SE–PE–BE–SB polymer-modified mixtures). Identical samples were prepared with great care because of angularity effects of used rock combination [5]. Although different polymer modifiers were used such as elastomeric or plastomeric polymers, drainage inhibitors, mostly higher-performance levels were observed in all tests [5]. Repeated creep tests on Marshall samples may be used for explaining permanent deformation [8]. Repeated creep curves and wheel-tracking test results are given in Figs. 2–4. Repeated creep tests on all of the mixtures demonstrated that the addition of modifiers enhanced the permanent deformation resistance at moderate temperature (25 1C) but different relations are concern at low (5 1C) and high (40 1C) temperatures. Repeated creep tests at 40 1C temperature do not correlate well with the LCPC wheel-tracking test results at high temperature (60 1C). Relative performance of modified mixtures at different temperatures can be different. It was understood that this difference may stem from the gradation changing. For the laboratory mixes, it was the intention to assess most HMA mix types currently used in South Africa. These included both stone-skeleton mixes (stone-mastic asphalt and semi-open asphalt with bitumen-rubber binder) and sand-skeleton mixes (gap- and continuously graded asphalt). Porous asphalt was not included. The Transportek wheel-tracking test gave reasonable results, and is recommended for all high reliability projects. The test is appropriate for all mix types, including mixes containing modified binders and stone-skeleton mixes. For stone-skeleton mixes, the test must be performed at the refusal air void content otherwise the mix could deform excessively, which is not expected if the mix is well compacted in the field provided that it is designed correctly. Because the dynamic creep does not correctly determine the rutting resistance of all mixes, and the performance ratings do not agree with the the Transportek wheel-tracking test, the dynamic creep test is not recommended for assessing the rutting potential of HMA other than sand-skeleton mixes manufactured with unmodified binders, unless evaluated in conjunction with other rutting tests. The evaluation of the dynamic creep test showed that the test can be used as an indicator of potential rutting, but the results in these cases should be confirmed with other more reliable tests [4]. Although, generally, wheel-tracking tests appear to be well correlated with rutting in the field, there are at present no quantified relationships to link wheel-tracking test results to rutting in the field under variable traffic loading and environmental conditions. For this reason, wheeltracking tests cannot as yet be used to provide a quantitative estimate of rutting in the field. The test does, however, provide a reliable estimate of the rutting potential and, hence, can be used to rank mixes according to rut potential. Wheel-tracking tests are particularly recom-
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mended for the evaluation of rutting performance of stone-skeleton mixes, or mixes that include modified binders. Experience has shown that these mix types cannot be properly evaluated by means of conventional tests such as the unconfined uniaxial static or dynamic creep tests [4]. The usual testing methods (Marshall test, wheel-tracking test, repeated load uniaxial test) are inadequate for the characterization of the resistance to the permanent deformation of asphalt. This is not to say that these tests would be unsuitable for other applications, for example, in a mixture design procedure within given composition limits. However, reliable comparisons of the deformation behavior of various sorts of mixtures are not possible on the basis of these tests [9]. By evaluating asphalt mixes and pavements from a functional point of view, the possibility to develop better products that better stand up to demands of today and tomorrow will increase. To be able to use demands on functional properties there is however a necessity for functional methods of measurement that fulfill demands on good relevance, high flexibility, and low cost. The first step in the development of functional methods of measurement is to have for certainty samples with a good affinity to real conditions on the road. A study made in Sweden has proven that the traditional Marshall method is not suitable in this regard. The unsuitability of the Marshall method of compaction has also been proven by several other investigators in other countries. A study for alternatives has emphasized the importance of a kneading ingredient in the compaction effort, which is in accordance with methods like rolling wheel and gyratory compactor. The same study showed that a sample compacted in the laboratory, at the same degree of compaction, usually gets better mechanical properties (indirect tensile stiffness modulus, dynamic creep test, and indirect tensile test) than a sample compacted in the field and that the difference between laboratory and field is not the same for different types of mixes [10]. The dynamic creep test is an interesting alternative to the wheel-tracking test for measuring the sensibility for permanent deformations, but there is some doubt about the ability of the traditional method to be able to work as a functional method of measurement and to distinguish between different types of mixes. Enlarging the sample to a diameter of 150 mm while the platen is kept at normal size, i.e. 100 mm, accomplishes a limited lateral pressure, which gives more justice to mixes, which get their stability not so much by forces of cohesion but much more so by the inner friction of the aggregate. Trials have shown a much better coefficient of correlation (0.91) with the wheel-tracking test for the modified model (diameter of sample 150 mm and diameter of platen 100 mm) than for the traditional model (0.36) with the same diameter for sample and platen [10]. In this research 100 mm diameter Marshall samples were tested in dynamic creep test and controversial results were obtained from these two tests. Unlike this the same
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diameter was used in earlier study but logical trends were obtained for SMA mixtures [5]. The failure of the Marshall test to describe rutting resistance of asphalt mixes is demonstrated where the Marshall stability is plotted versus the rut depth at 50,000 wheels passes as determined in a laboratory test track experiment. Several conventional and polymer-modified binders were used in the experiments. From these results it is clear that no relation exists between the Marshall stability and rutting under actual wheel loading in the LTT. The Marshall test should therefore not be considered relevant to characterize the resistance of mixes with polymer-modified binders. Fortunately, this fact has nowadays been recognized by authorities who aim to implement rational performance-based specifications in the SHRP in the USA and in Europe in CEN specifications [11]. It is well recognized from the literature that the aggregate interlocking greatly occurred in the coarse aggregate. The image evaluation of aggregate morphological characteristic demonstrated that a stable aggregate skeleton resulted in more internal resistance. Traditional tests such as Marshall stability and the indirect tensile strength are considered to be inadequate to measure the internal resistance in HMA [12]. If asphalt mixes are regarded and judged from their functional abilities there is a demand for functional methods of measurement, methods that are not in existence today concerning all the parameters that are essential for the good behavior of the asphalt pavement. To be able to use demands on functional properties, there is however a necessity for functional methods of measurement that fulfill demands on good relevance, high flexibility, and low cost. The discussions about this subject started in Sweden in the late eighties. After a period of time it was clear, which should have been selfevident, that functional methods of measurement demand samples that have a good affinity with real conditions on the road. There were at this time a lot of people that had come to the conclusion that the Marshall method of compaction was not a suitable method in this regard. Because of this the first step in the development of functional methods of measurement was to study alternatives to use instead of the Marshall method. The unsuitability of the Marshall method of compaction has since then been proven by several other investigators in other countries [13,14]. 4. Conclusions A study has been conducted to understand permanent deformation properties of the asphalt mixtures containing elastomeric polymer modifiers (OL, EL, SB). An evaluation between the rutting potential of the cylindrical samples produced with the Marshall compaction and wheeltracking test results was done. Repeated creep tests on all of the mixtures demonstrated that the addition of modifiers enhanced the permanent deformation resistance at moderate temperature (25 1C) but different relations are concern at low (5 1C) and high (40 1C)
temperatures. Repeated creep tests at 40 1C temperature do not correlate well with the LCPC wheel-tracking test results at high temperature (60 1C). Relative performance of modified mixtures at different temperatures can be different. In this research performance known mixtures were tested. Obtained data were compared with the earlier research [5]. Unlike this research continuous gradation was offered and the result was that repeated creep test and wheel-tracking test did not give parallel result. The evaluation of the dynamic creep test showed that the test can be used as an indicator of potential rutting, but the results in these cases should be confirmed with other more reliable tests. Also it is thought that gradation changing is more important than compacting efforting types in view of evaluating efficiency of rutting test methods. Acknowledgments ISFALT Asphalt and Dogus- Construction Companies are gratefully acknowledged for their laboratory capabilities. The authors are also indebted to Mr. T. Erol and Mr. N. Bugan for assistance in laboratories. References [1] Robertus C, Mulder EA, Koole RC. SBS modified bitumen for heavy duty asphalt pavements. Second international conference on roads and airfield pavement technology. Singapore; September 1995. [2] Bonemazzi F, Braga V, Corrieri R, Giavarini C, Sartori F. Characteristics of polymers and polymer-modified binders. Transportation Research Record 1535. Washington, DC: Transportation Research Board; 1996. p. 36–47. [3] Mostafa AE, Gerardo WF, Imad LA. Quantitative effect of elastomeric modification on binder performance at intermediate and high temperatures. Journal of Materials in Civil Engineering 2003;15(1):32–40. [4] Visser AT, Long F, Verhaeghe A, Taute A. Provisional validation of the new South African hot-mix asphalt design method (mix design1:7–6). Ninth international conference on asphalt pavements. Copenhagen, Denmark; August 2002, p. 36–47. [5] Tayfur S, Ozen H, Aksoy A. Investigation of rutting performance of asphalt mixtures containing polymer modifiers, Construction and Building Materials 2006;21:328–37. [6] Aschenbrener T. Comparison of results obtained from the French rutting tester with pavements of known field performance. Colorado Department of Transportation, Report no: CDOT-DTD-R-92-11; October 1992. [7] Corte JF, Brosscaud Y, Simonceli JP, Caroff G. Investigation of rutting of asphalt surface layers: influence of binder and axle load configurations,.Transportation Research Board, 1436; 1994. [8] Brown SF. Practical test procedures for mechanical properties of bituminous materials. Proceedings of the Institution of Civil Engineers, Transport 1995;111:289–97. [9] Jansen Venneboer J, Van der Heide JPJ, Molenaar AAA. Asphalt constructions for heavy duty pavements and road widenings in the Netherlands, Eurasphalt & Eurobitume Congress; 1996. [10] Ulmgren N. Functional testing of asphalt mixes for permanent deformation by dynamic creep test modification of method and Round Robin Test, Eurasphalt & Eurobitume Congress; 1996. [11] Valkering CP, Lancon DJL, Hilster ED, Stoker DA. Rutting resistance of asphalt mixes containing non-conventional and polymer-modifed binders. AAPT Conference. Albuquerque, USA; 19/21 February 1990.
ARTICLE IN PRESS H. O¨zen et al. / Building and Environment 43 (2008) 1270–1277 [12] Chen J-S, Liao M-C. Evaluation of internal resistance in hot mix asphalt concrete. Construction and Building Materials 2002;16: 313–9. [13] Conuegra A. A comparative evaluation of laboratory compaction devices based on their ability to produce mixtures with engineering
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properties similar to those produced in the field. 68th TRB-meeting. Washington DC; January 1989. [14] Caltabiano MA, Waters TJ. The effect of sample compaction on the mix characteristics. 8th AAPA international asphalt conference. Sydney, Australia; 1991.