performance evaluation of high modulus asphalt mixtures for long life asphalt pavements

1、Performance evaluation of high modulus asphalt mixtures for long life asphalt pavementsHyun Jong Lee a,1, Jung Hun Lee a,2, Hee Mun Park b,*a Department of Civil and Environmental Engineering, Sejong University, Seoul, R

2、epublic of Korea b Highway Research Department, Korea Institute of Construction Technology, 2311, Daehwa-Dong, Ilsan-Gu, Goyang-Si, Gyeonggi-Do 411-712, Republic of KoreaReceived 22 December 2005; received in revised for

3、m 18 January 2006; accepted 26 January 2006 Available online 18 April 2006AbstractThis paper describes the results of laboratory and full scale performance tests for a high modulus asphalt binder (HMAB) and mixes (HMAM)

4、developed in this study for long life asphalt pavements. Various binder tests were first conducted on the HMAB and test results showed that the stiffness of the HMAB was significantly increased compared to the convention

5、al binder without changing the low temperature properties of the binder. Laboratory tests for the mixes included dynamic modulus, moisture susceptibility, wheel track- ing and fatigue tests. Dynamic modulus test results

6、showed that the modulus of the HMAM was 50% higher than those of the conventional mix at the high temperatures. The results of performance test indicated that the resistances of the HMAM against moisture, rutting, and fa

7、tigue damage were better than those of the conventional mix. It was also found from the full scale test sections that the tensile strain values at the bottom of the asphalt layer for the HMAM sections were lower than tho

8、se of the conventional mix sections although the asphalt layer thicknesses of the HMAM sections were thinner than those of the conventional sections. All the tensile strain values measured from the HMAM sections were wit

9、hin the fatigue endurance limit of 70 microstrain which is the fatigue criterion of a long life asphalt pavement. Similar to the wheel tracking test results, the rut depth occurred in the thick HMAM test section was two

10、times smaller than the con- ventional pavement section. ? 2006 Elsevier Ltd. All rights reserved.Keywords: High modulus asphalt binder; High modulus asphalt mix; Long life asphalt pavement; Dynamic modulus1. Introduction

11、Asphalt pavements in Korea have been usually designed for 20-year life expectancies. That is, if an asphalt pave- ment has a serious structural failure after the 20-year of service period, the pavement should be reconstr

12、ucted to gain its original structural capacity. However, due to the significantly increasing traffic volume and insufficient bud-get, most of old pavements in Korea have been partly reha- bilitated using a 5 cm thick ove

13、rlay instead of reconstruction. In general, the performance period of a newly constructed pavement is longer than 10 years before a major rehabilitation like an overlay after milling. How- ever, after the first rehabilit

14、ation, the performance period of the pavement is getting shorter because the pavement keeps losing the structural capacity mainly due to the cumulative damage occurred in the asphalt layer. Thus, if the existing pavement

15、 has serious fatigue cracking and deformation, an overlay to extend its life might be ineffec- tive from structural and economical point of view. To overcome those problems mentioned above, the con- cept of a long life p

16、avement proposed by Nunn et al. [1] has0950-0618/$ - see front matter ? 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.conbuildmat.2006.01.003* Corresponding author. Tel.: +82 31 9100 323; fax: +82 31 9100 161. E-

17、mail addresses: hlee@sejong.ac.kr (H.J. Lee), ugg97@korea.com(J.H. Lee), hpark@kict.re.kr (H.M. Park). 1 Tel.: +82 2 3408 3812; fax: +82 2 3408 3332. 2 Tel.: +82 2 2205 3812; fax: +82 2 3408 3332.www.elsevier.com/locate/

18、conbuildmatConstruction and Building Materials 21 (2007) 1079–1087Construction and BuildingMATERIALSminimize the cracking potential due to the brittleness, a 4% of styrene–butadiene–styrene (SBS) polymer was added to the

19、 mixed binder. The use of the polymer could be helpful to increase the cracking and rutting resistance of the bin- der. An additive that can create the chemical bonding between asphalt and polymer was also used to preven

20、t the phase separation of the asphalt and polymer. Since the design life of long life asphalt pavements is at least more than 40 years, there always exists a possibility that the high modulus base mix is exposed to moist

21、ure. There- fore, a liquid type of anti stripping agent has been added to binder to minimize the moisture induced damage.3. Laboratory testingTo evaluate the performance of the HMAM, various laboratory tests were perform

22、ed. Before the performance tests of the HMAM, binder tests were first conducted on the HMAB and compared with the conventional unmodi- fied and SBS modified binders. The laboratory tests for the HMAM include the dynamic

23、modulus, moisture susceptibility, wheel tracking, and indirect tensile fatigue tests.3.1. Asphalt binder testVarious binder tests were conducted on the conventional (PG 64-22), SBS modified (PG 76-22), and the HMAB to ev

24、aluate the physical and mechanical properties of the binders. The important tests results are presented in Table 1. The typical properties of French hard grade asphalts are also included in this table for a comparison pu

25、rpose. As shown in this table, the penetration value of the HMAB is lower than 30 dmm at 25 ?C. The dynamic modulus of the HMAB is three times larger than those of the conven- tional and polymer modified asphalt binders.

26、 However, the HMAB shows a slightly smaller dynamic modulus than those of the French hard grade asphalt binder. The Fraass temperature of the HMAB is ?8 ?C, whereas PG 64-22 binder is ?11 ?C indicating that the resistanc

27、e to low tem- perature cracking decreases as the binder stiffness increases. Overall, the HMAB properties such as penetration, soften-ing point, and Fraass temperature are satisfactory com- pared to the French hard grade

28、 asphalt ones.3.2. Materials and sample fabricationTo produce asphalt concrete specimens, two types of asphalt binders, the conventional unmodified and HMAB were used. The conventional asphalt binder has a penetra- tion

29、grade of 60–70 (PG 64-22), and the HMAB has a pen- etration grade of 20–30. The physical and mechanical properties of these two binders were given in Table 1. Only a single aggregate gradation was selected as shown in Fi

30、g. 2. As can be seen in this figure, a typical dense grada- tion with a nominal maximum aggregate size of 25 mm was used. This is the typical aggregate gradation most widely used in many locations throughout Korea. Combi

31、ning the two asphalt binders and a single aggre- gate gradation described above, two different types of asphalt mixtures, conventional mix and HMAM, were pro- duced for the laboratory testing. The optimum asphalt con- te

32、nts were determined according to the Marshall mix design method. The optimum asphalt contents for the two mixes at the 5% of air void were 4.5% for the conven- tional asphalt mix and 4.7% for the HMAM, respectively. This

33、 laboratory formula was later modified to obtain job site formula for the test sections of the full scale perfor- mance testing. All the materials used in the laboratory tests are the same as the materials used in the te

34、st sections. The asphalt contents extracted from the test sections were 4.5% for conventional mix and 4.8% for HMAM, respectively. The tests specimens used in the dynamic modulus tests were directly obtained from the cor

35、es taken from the test sections. The geometry of the specimens for the dynamic modulus tests are 150 mm in diameter and 50 mm in height. The samples to be used in the moisture susceptibility tests were compacted using a

36、Marshall compactor, whereas a Superpave gyratory compactor was used for the compac- tion of the samples to be used in the indirect tensile fatigue tests. The specimens for the moisture susceptibility testsTable 1 Compari

37、son of asphalt binder propertiesProperty PG 64-22 PMA HMAB French hard grade asphalt35/50a 10/20bPenetration, 25 ?C (dmm) 70 63 28 35/50 10/20Softening point (?C) 48 100.3 89 62 –70Fraass temperature (?C) ?11 ?18 ?8 +3 t

38、o ? 8Ga, 15 ?C (MPa) 7.1 7 21 34.5 40–90a 35–50 dmm of penetration. b 10–20 dmm of penetration.0204060801000.01 0.1 1 10 100Sieve Size (mm)Percent Passing (%)SpecificationTargetCombinedFig. 2. Aggregate gradation.H.J. Le