laboratory performance evaluation of warm mix asphalt ...docs.trb.org/prp/12-4542.pdf · 13...

Laboratory Performance Evaluation of Warm Mix Asphalt containing 1 High Percentages of RAP 2

3 4 5 Sheng Zhao 6 Department of Civil and Environmental Engineering 7 The University of Tennessee 8 Knoxville, TN 37996 9 Email: [email protected] 10 11 Baoshan Huang, Ph.D., P.E. (Corresponding Author) 12 Department of Civil and Environmental Engineering 13 The University of Tennessee 14 Knoxville, TN 37996 15 Email: [email protected] 16

17 Xiang Shu, Ph.D. 18 Department of Civil and Environmental Engineering 19 The University of Tennessee 20 Knoxville, TN 37996 21 Email: [email protected] 22

23 Xiaoyang Jia 24 School of Transportation Engineering 25 Tongji University 26 Shanghai, China 27 Email: [email protected] 28 29 Mark Woods 30 Manager - Bituminous Control, Pavement Evaluation 31 Materials and Tests Division 32 Tennessee Department of Transportation 33 Nashville, TN 37243 34 Email: [email protected] 35 36 37 Word Count: 38 Text: 3085 39 Figures: 14 (250 ea) 40 Tables: 4 (250 ea) 41 Total: 7540 42 43 44 45

TRB 2012 Annual Meeting Paper revised from original submittal.

Zhao, Huang, Shu, Jia, and Woods 2

ABSTRACT 1 2 This paper evaluated the rutting resistance, moisture susceptibility and fatigue resistance 3 of warm-mix asphalt (WMA) mixtures containing high percentages of reclaimed asphalt 4 pavement (RAP) through laboratory performance tests. The WMA mixtures were plant 5 produced with a commonly-used foaming technology in the U.S. RAP content ranged 6 from 0 up to 50%. Laboratory performance tests included asphalt pavement analyzer 7 (APA) rutting test, Hamburg wheel tracking test, tensile strength ratio (TSR) test, 8 Superpave indirect tension (IDT) tests and beam fatigue test. For comparison purposes, 9 HMA mixtures containing 0% and 30% RAP were also evaluated and compared to WMA. 10 The laboratory test results indicated that WMA with high percentage of RAP exhibited 11 higher rut resistance, better moisture damage resistance, and better fatigue performance. 12



INTRODUCTION 1 2 Background 3 4 5 The utilization of warm-mix asphalt (WMA) containing high percentages of recycled 6 asphalt pavement (RAP) has been a topic of intensive study for many years due to 7 economic and environmental benefits. However, there still remains a big challenge for 8 the State departments of transportation (DOTs) which is to use this new technology while 9 maintaining a high-quality well-performing pavement infrastructure. 10

RAP was originally added in hot-mix and, sometimes, cold-mix before WMA 11 technology was introduced in asphalt industry. Plenty of research was conducted to 12 characterize the performance of asphalt mixtures containing RAP. NCHRP Report 452, 13 “Recommended use of reclaimed asphalt pavement in the Superpave mix design method: 14 Technician's Manual” [1] showed how RAP could be used in Superpave System. 15 Performance tests were conducted on the mixtures containing different RAP contents (0%, 16 10%, 20% and 40%). A stiffening effect seemed to be likely to happen on high-RAP 17 mixtures, while the performance behaviors of mixtures containing less RAP was not 18 significantly different from virgin mixtures.[1]. By evaluating the influences of 19 engineering properties of crumb rubber mixtures containing RAP, Xiao and Amirkhanian 20 [2] found that the addition of RAP and rubber increases the resilient modulus values at 21 various temperatures, and furthermore, the addition of rubber helped a lot in increasing 22 fatigue resistance of HMA containing RAP. Shu and Huang [3] evaluated the fatigue 23 characteristics of hot-mix asphalt (HMA) mixtures with different RAP contents (0%, 24 10%, 20%, and 30%) using different testing methods, and indicated that inclusion of RAP 25 may result in shorter fatigue life based on both Superpave IDT and beam fatigue tests. Li, 26 et al [4] showed higher dynamic modulus could be found in mixtures with stiffer asphalt 27 binder and RAP source was a significant influence factor of dynamic modulus at high 28 temperatures only, not at low temperatures. No significant statistical relationship between 29 dynamic modulus and fracture energy was found in this study. Huh et al. [5] presented a 30 method in which a specially developed polymer-modifier was introduced that used 100 % 31 reclaimed asphalt pavement (RAP) without adding any virgin materials. 32

With the development of warm-mix technology, researchers began investigaing 33 the incorporation of RAP into WMA because of the urgency towards ‘green’ 34 technologies. Mogawer et al. [6] investigated the performance of WMA containing RAP 35 in which Advera and Sasobit were used as additives, and evaluated binder properties, 36 workability, and mixture durability. Results showed that Sasobit changed the 37 performance grade and decreased the viscosity of binders, while Advera had no effect on 38 the binder. All WMA mixtures improved workability and increased moisture 39 susceptibility. An anti-stripping agent was recommended to help with moisture problems. 40 Copeland et al. [7] conducted performance tests to evaluate a high RAP-HMA control 41 mix and a high RAP-WMA mix produced with foamed WMA technology. Results 42 indicated the high RAP-WMA mix is softer than the high RAP-HMA control mix based 43 on performance grade (PG) determination test and flow number test, while dynamic 44 modulus results indicated the high RAP-WMA mix is slightly softer than the high RAP-45 HMA control mix. Lee and Park [8] addressed that additives and aged binders played an 46



important role in determination of the binder properties by conducting a laboratory 1 investigation of performance properties of WMA binders containing aged binders. 2 Mallick [9] conducted a study using a base course mix with 75% RAP and 1.5% Sasobit 3 by weight of virgin binder as an additive mixed at 135˚C, showing Sasobit helped in 4 obtaining a uniform mix. Washington Department of Transportation [10] placed an 11-5 mile strip in June 2008 on I-90 west of George containing 20% RAP with 2% Sasobit by 6 weight of virgin binder and a PG76-28 binder. Clumps in warm-mix with RAP were 7 observed in this project. However, the clumps density and Hamburg wheel testing results 8 of WMA were equivalent to those of HMA mix, and dynamic modulus of the WMA was 9 even higher. 10 11 Objectives and Scope 12 13 The objective of the study is to evaluate the performance of WMA containing high 14 percentages of RAP through laboratory performance tests. The performance of WMA 15 includes rut resistance, moisture susceptibility, and fatigue performance. 16

The WMA mixtures employed in the study were produced in an asphalt plant with 17 a commonly-used foaming technology in the U.S. WMA mixtures contained up to 50% 18 RAP with control HMA containing up to 30% RAP (Table 1).The following laboratory 19 performance tests were employed for the evaluation: asphalt pavement analyzer (APA) 20 rutting test, Hamburg wheel tracking test, tensile strength ratio (TSR) test, Superpave 21 indirect tension (IDT) tests, and beam fatigue test. 22 23 24

TABLE 1 WMA and HMA evaluated in the study 25 Mix RAP content (%)

WMA

0 30 40 50

HMA 0 30

26 27 LABORATORY EXPERIMENTS 28

29 Materials 30 31 One asphalt binder, PG 64–22, was selected in the study. The virgin aggregates selected 32 in this study consisted of limestone with a nominal maximum size of 1.25”, No. 7 33 screenings and natural sand. Two types of RAP, with nominal maximum sizes of 3/4” 34 and 3/8”, were used in this study. Table 2 presents the gradations of both aggregates and 35 RAP. All the aggregate properties meet the specification of TDOT [11]. 36 37 38 39



TABLE 2 Aggregates Gradation 1 Sieve size Sieve size

(mm) BM-2 Rock(Limestone) No 7. No 10.

(soft) Natural

sand RAP-I RAP-II

1.25" 37.5 100 100 100 100 100 100 3/4" 19 81 100 100 100 100 100 3/8" 9.5 43 68 100 100 60 100 No.4 4.75 10 12 98 98 38 82 No.8 2.36 4 5 85 85 29 68 No.30 0.60 3 4 65 65 17 42 No.50 0.30 3 3 26 26 11 26

No.100 0.15 2.0 2.0 4.0 3.0 9.0 18.0 No.200 0.075 1.3 1.0 2.0 0.5 7.5 15.0

2 3 Mix Design 4 5 The Marshall mix design procedure was employed to design mixture. Materials meet the 6 gradation specification of TDOT and all the mixtures were adjusted to keep the similar 7 aggregate structures after RAP was added. Table 3 presents the different asphalt 8 contribution from RAP and virgin asphalt. The optimum asphalt content for each mix was 9 4.2%, namely asphalt from RAP together with the virgin asphalt was 4.2% by the weight 10 of the mix. Anti-strip additive was added in the mixture with a dosage of 0.3%, which is 11 determined based on TDOT construction experience. 12 13

TABLE 3 Composition of each mix 14 RAP

content Virgin Binder

RAP Binder

BM-2 Rock (Limestone) No 7 No 10 Natural

sand RAP-I RAP-II

0 4.2 0 38.32 19.16 14.37 23.95 0 0 30 2.686 1.51 33.53 14.37 0 19.16 9.979 20.275 40 2.445 1.76 33.53 0 0 23.95 29.938 10.138 50 1.887 2.31 33.53 0 0 14.37 29.938 20.274

15 Sample Preparation 16 17 HMA and WMA mixtures were collected at plant site and kept in Oven for 2 hours for 18 short-aging prior to compaction. Cylindrial WMA samples were fabricated on site with 19 the Superpave gyratory compactor (SGC) to avoid reheating and further loss of moisture. 20 HMA mixtures were shipped to the laboratory and cylindrical samples were compacted 21 with SGC. The beam samples for both WMA and HMA were fabricated in the laboratory 22 with a vibratory compactor. 7% was selected as the target air void to simulate a properly 23 designed and constructed mixture immediately after construction, while 4% was selected 24 for mixture after two or three years of traffic. The sample dimensions and the target air 25 voids are presented in Table 4. 26 27 28 29 30



1 2 3

TABLE 4 Laboratory percentage of material for each mix 4 Performance test Dimension Target air void

APA rutting test 150 mm in diameter, 75 mm in thickness 7± 0.5%

Hamburg wheel-track test 150 mm in diameter, 75 mm in thickness 7± 0.5%

Flow number test 100 mm in diameter, 150 mm in thickness 4± 0.5%

Superpave IDT test 150 mm in diameter, 50 mm in thickness 4± 0.5%

TSR test 150 mm in diameter, 50 mm in thickness 7± 0.5%

Beam fatigue test 38.1 cm in length, 5.08 cm in thickness, 6.35 cm in width

7± 0.5%

5 6 Performance Tests 7 8 Tests for rutting resistance 9 10 APA Rutting Test 11 The Asphalt Pavement Analyzer (APA) (Fig. 1) was tested at a temperature of 64 oC. Rut 12 depths at 8,000 cycles were recorded for comparison in this study. The APA rut test was 13 conducted in accordance with the AASHTO T340 procedures. 14 15

16 FIGURE 1 The APA test setup 17

18 Tests for Moisture Susceptibility 19 20 TSR test 21



The tensile strength ratio (TSR) test is widely used to determine the potential for moisture 1 damage and whether or not an anti-stripping additive is effective. TSR test procedures in 2 this study were based on ASTM D4867 and TSR value can be defined as follows: 3

100 tm

td

STSRS

⎛ ⎞= ⎜ ⎟

⎝ ⎠ 4

Where, 5 TSR = tensile strength ratio; 6 Stm = average tensile strength of the moisture-conditioned subset; 7 Std = average tensile strength of the dry subset. 8

Freeze-thaw conditioning cycle was selected to evaluate the effect of moisture in 9 this study. Samples were submerged and partially saturated with a 70kPa vacuum to 10 assure the volume of water is between 70% and 80% of the volume of air. After 11 saturation, samples were wrapped tightly with two layers of plastic film, sealed into a 12 leak-proof plastic bag, placed into a freezer at -18 oC for at least 16 h and eventually 13 immersed in a water bath at 60 oC for 24 h. 14 15 Hamburg Wheel-tracking test 16 The hamburg wheel tracking test was conducted using the latest version of APA in 17 accordance with the testing procedures specified in AASHTO T324. Samples were 18 submerged in the water bath controlled at 50 ±0.5 oC for a minimum of 30 min. The test 19 apparatus is the same (Fig. 2) with that of APA rutting test, except for a moving wheel 20 with 8” in diameter and 1.85” in width that reciprocates over the specimen during the test, 21 with the position varying sinusoidally over time. A data acquisition system records 22 rutting out to 20,000 wheel passes at 25 Hz and plots rut depth versus number of passes 23 for each sample automatically. 24 25 26

27

FIGURE 2 The Hamburg wheel-track test setup 28 29

30 31



Tests for Fatigue Behavior 1 2 Superpave IDT Tests 3 The Superpave IDT tests includes resilient modulus, creep and indirect tensile strength 4 tests, The tests were conducted following the procedures developed by Roque and Buttlar 5 [12,13]. Fig. 3 shows the test setup of the Superpave IDT tests. The tests were performed 6 at room temperature of 25 oC. 7

8 FIGURE 3 The Superpave IDT test setup 9

10 The term DCSEmin was proposed by Roque et al. to indicate the minimum 11

dissipated creep strain energy. With the use of two parameters obtained from creep test, 12 D1 and m, DCSEmin is expressed as follows [14]: 13

2.981

minm DDCSE

A×

= 14

Where, 15 A = a function of tensile strength and tensile stress in the asphalt pavement. 16 D1 and m = parameters obtained from creep test 17

According to Roque et al. [14], another term DCSEf, dissipated creep strain 18 energy threshold, can be determined with the stress-strain response obtained from indirect 19 tensile strength test, as shown in Fig. 4, where εf is the failure strain, MR is the resilient 20 modulus and St is the indirect tensile strength. With DCSEf, and DCSEmin, energy ratio 21 (ER) was expressed as follows [13]: 22

min

fDCSEER

DCSE= 23

The higher the value of DCSEf or ER, the better the fatigue resistance of asphalt mixtures. 24 25



1 FIGURE 4 The calculation of DCSEf 2

Beam Fatigue Test 3 The flexural beam fatigue test that allows four-point bending with free rotation and 4 horizontal translation is used to determine the fatigue life of beam specimens in a stress- 5 or strain-controlled mode.(Fig. 5). Following the procedures in AASHTO T321, a test 6 temperature of 7 oC, a strain level of 300 micro-strains, and a loading frequency of 10 Hz 7 were used to ensure a minimum of 10,000 load cycles for each specimen. 8

The stiffness versus load cycles plot is automatically recorded as test result, as 9 shown in Fig. 6. Traditionally, the number of cycles corresponding to 50% reduction in 10 initial stiffness (measured at the 50th cycle) is regarded as the fatigue life of a asphalt 11 mixture. Carpenter et al. [15-17] introduced the ratio of dissipated energy change (RDEC) 12 and the plateau value (PV) to evaluate the fatigue life. A typical RDEC versus load 13 cycles plot is shown in Fig. 7, where PV is obtained in zone II representing a period 14 where a constant percent of input energy is turned into damage. 15 16

17 FIGURE 5 Beam fatigue test apparatus 18

19



1 FIGURE 6 Typical load cycles versus flexural stiffness plot 2

3

4 FIGURE 7 Typical load cycles versus RDEC plot 5

6 7

RESULTS AND DISCUSSION 8 9 Rutting Resistance Test Results 10 11 Fig. 8 presents the rut depths from APA rutting test. As expected, the incorporation of 12 RAP into WMA and control HMA mixtures improved rutting resistance, which means 13 that both WMA and HMA containing higher percentages of RAP were more likely to 14 exhibit better rutting resistance. This phenomenon can be attributed to the stiffening 15 effect from aged asphalt binder in RAP. 16

WMA without RAP was not as good as virgin HMA in rutting resistance, which 17 might be attributed to the reduced oxidation of asphalt binder due to lowered mixing 18 temperatures. Rut depths of WMA containing RAP were significantly reduced from those 19 of WMA without RAP, while the change in rut depths of HMA was less than WMA, 20 which means effect of RAP in rutting resistance improvement on WMA seemed to be 21 more significant than that on HMA. 22



1 2

3 FIGURE 8 APA rutting test results 4

5 6 Moisture Susceptibility Test Results 7 8 Fig. 9 presents the TSR results. It can be seen that the TSR values of WMA containing 9 high percentages of RAP (30%, 40% and 50%) were more than or close to 0.8, much 10 higher than that of virgin WMA, which means adding RAP would significantly reduce 11 the moisture suceptibility of WMA. Same effect was also seen for RAP in HMA. HMA 12 containing 30% RAP had a higher TSR value than the HMA mixture without RAP. 13

It can also be seen that virgin HMA showed much better resistance to moisture 14 damage than virgin WMA and HMA containing 30% RAP had a higher TSR value than 15 that of WMA containing 30% RAP. Therefore, moisture suceptibility may still remain a 16 concern for WMA, especially WMA without RAP. 17 18

19

WMA 0%

HMA 0%

HMA 30%

WMA 30% WMA 40%

WMA 50%



0

0.2

0.4

0.6

0.8

1

HMAVirgin

HMA30%RAP

WMAVirgin

WMA30%RAP

WMA40%RAP

WMA50%RAP

Mix and RAP content

TSR

1 FIGURE 9 TSR results 2

3 Fig. 10 presents the results from Hamburg wheel-tracking test. Only WMA 4

without RAP had an inflection point of 665 while other mixtures evaluated in this study 5 did not experience inflection points. The results indicated that the incorporation of RAP 6 would significantly reduce the moisture susceptibility of WMA. Under saturated 7 condition, WMA containing 30% RAP exhibited the same rutting resistance with that of 8 HMA containing 30% RAP , and WMA containing 40% and 50% showed even better 9 rutting resistance, which indicated WMA containing high percentages of RAP (30%, 40% 10 and 50%) would exhibit a good resistance of moisture damage. 11

The improvement in moisture resistance caused by RAP might be due to the fact 12 that the aggregate of RAP have been covered and protected by aged asphalt binder. The 13 bond between aggregate and asphalt in RAP is stronger than that between aggregate and 14 virgin binder, making the mixture containing RAP less vulnerable to moisture damage. 15 16

17 FIGURE 10 Hamburg wheel-tracking test results 18

WMA 0%

HMA 0%HMA 30%

WMA 30%

WMA 50%

WMA 40%



1 2 Fatigue Test Results 3 4 Superpave IDT test results 5 Fig. 11 presents the test results of the dissipated creep strain energy threshold (DCSEf) 6 from the Superpave IDT tests. It can be seen that with the increase in RAP content, 7 DCSEf values slightly decreased, indicating that the fatigue life of asphalt mixture was 8 slightly lowered by adding RAP. However, the tendency was not significantly apparent. 9 Futher studies need to be conducted using the same testing method. 10

Figure 12 shows the test results of energy ratio. It can be seen that the energy ratio 11 values increased with the increase of RAP, which was not consistent with those obtained 12 from DCSEf method. Since both the dissipated energy accumulation and the energy 13 required to fracture the mixture are taken into account by energy ratio method, the energy 14 ratio method is more reasonable than DCSEf method in describing cracking resistance of 15 asphalt mixtures. More tests are needed to validate the energy ratio results. 16

17

0

0.5

1

1.5

2

2.5

3

3.5

4

HMAVirgin

HMA30%RAP

WMAVirgin

WMA30%RAP

WMA40%RAP

WMA50%RAP

Mix and RAP content

DC

SEf (

KJ/

m3 )

18 Figure 11 DCSEf results 19

20



0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

HMAVirgin

HMA30%RAP

WMAVirgin

WMA30%RAP

WMA40%RAP

WMA50%RAP

Mix and RAP content

Ene

rgy

Rat

io

1 Figure 12 Energy ratio results 2

3 Beam Fatigue Results 4 Figures 13 and 14 present the results from the beam fatigue test. It can be seen from 5 Figure 13 that HMA with higher percentages of RAP experienced less load cycles 6 compared to HMA virgin mix. On the contrary, WMA containing higher RAP contents 7 could be subjected to more load cycles. The results indicate that with the increase in RAP, 8 HMA would have a shorter fatigue life while WMA would have a longer fatigue life. It 9 can be seen from Figure 14 that HMA containing higher percentages of RAP showed 10 higher plateau values, which indicated that they were subjected to more damage that led 11 to shorter fatigue life. WMA incorporating more RAP, however, exhibited just the 12 opposite and showed lower plateau values, which would result in longer fatigue life. 13

The results from the plateau value method and the 50% modulus reduction 14 method are consistent with each other. It is widely accepted that the fatigue performance 15 of HMA with RAP might be compromised due to the aged binder in RAP. However, the 16 situation is complicated when it comes to WMA. The fatigue performance of WMA with 17 RAP would be subjected to the combined effect of soft virgin binder and stiffened RAP 18 binder. The effect of aged binder might be compromised by the existing soft virgin binder. 19 Therefore, WMA containing RAP might have a longer fatigue life than HMA containing 20 the same content of RAP. WMA containing higher percentages of RAP might perform 21 better when the interaction of the two binders is beneficial to the fatigue life of asphalt 22 mixtures. 23

24



0

20000

40000

60000

80000

100000

120000

140000

160000

HMA Virgin HMA 30%RAP WMA Virgin WMA 30%RAP WMA 40%RAP WMA 50%RAP

Mix and RAP content

Load

cycle

s to failure

1 Figure 13 Load cycles to failure from beam fatigue test 2

3 4

0

1

2

3

4

5

6

HMA Virgin HMA 30%RAP WMA Virgin WMA 30%RAP WMA 40%RAP WMA 50%RAP

Mix and RAP content

Plateau Va

lue(×1

06)

5 Figure 14 Plateau value from beam fatigue test 6

7 8 CONCLUSIONS 9 10 Multiple laboratory performance tests were conducted to evaluate the rutting resistance, 11 moisture suceptibility and fatigue resistance of WMA mixtures with high percentages of 12



RAP produced with a foaming technology. Based on the test results, conclusions can be 1 summarized as follows: 2

1. With the incorporation of RAP, the rut resistance of WMA was improved 3 significantly. The effect of RAP in rutting resistance improvement on WMA 4 seemed to be more significant than that of HMA. 5

2. Adding RAP significantly reduced the moisture susceptility of WMA. WMA with 6 high percentages (30% minimum) exhibits a good resistance to moisture damage. 7

3. Based on the DCSEf values obtained from the Superpave IDT tests, incorporation 8 of RAP slightly reduced the fatigue life of WMA mixtures. Whereas using energy 9 ratio values, addition of RAP would make WMA mixtures more resistant to 10 fracture, resulting in a longer fatigue life. Energy ratio results would be more 11 reliable because energy ratio concept is more reasonable than DCSEf in 12 characterizing cracking resistance of asphalt mixtures. 13

4. Based on the failure criterion of 50% reduction in stiffness and plateau value 14 failure criterion, the incorporation of RAP increased the fatigue life of WMA 15 while the fatigue resistance of HMA was reduced. 16

5. The results presented in this paper were only the preliminary findings of a more 17 complete study. Further studies would be needed before WMA containing high 18 percentages of RAP can be widely used. 19

20 21 ACKNOWLEDGEMENT 22 23 The authors would like to thank TDOT for providing funding for this project. Special 24 appreciations are to the Lojac Inc. for helping with field sampling and testing. The 25 authors would also like to thank Hao Wu, Jinsong Chen, Christopher Jon Kahner, Kris 26 Leatherman who helped with the field and laboratory tests. 27 28 29 REFERENCE 30 31 1. Mcdaniel, R and R.M. Anderson. NCHRP Report 452:Recommended use of 32

reclaimed asphalt pavement in the Superpave mix design method: Technician's 33 Manual, TRB, National Research Council, Washington, D.C., 2001 34

2. Xiao, F and S.N. Amirkhanian. Laboratory investigation of moisture damage in 35 rubberized asphalt mixtures containing reclaimed asphalt pavement. International 36 Journal of Pavement Engineering, Vol. 10 (5), 2009, pp. 319-328. 37

3. Shu, X and B. Huang. Laboratory evaluation of fatigue characteristics of recycled 38 asphalt mixture. Construction & building materials, Vol. 22(7), 2008, pp. 1323-1330. 39

4. Li, X, M.O. Marasteanu, R.C. Williams, T.R. Clyne. Effect of reclaimed asphalt 40 pavement (proportion and type) and binder grade on asphalt mixtures. 41 Transportation Research Record, No 2051, 2008, pp 90-97. 42

5. Huh, J.D. and J.Y.Park. A new technology of recycling 100% reclaimed asphalt 43 pavements. Journal of Testing and Evaluation. Vol. 37(5), 2009, pp 479-482. 44

6. Mogawer, W.S., A. J. Austerman. and R. Bonaquist. Evaluating effects of warm-mix 45 asphalt technology additive dosages on workability and durability of asphalt mixtures 46



containing recycled asphalt pavement. Presented at Transportation Research Board 1 88th Annual Meeting, 2009. 2

7. Copeland, A., J. D’Angelo, R. Dongre, S. Belagutti and G. Sholar. Transportation 3 Research Record: Journal of the Transportation Research Board, No. 2179, 2010, 4 pp.93-101. 5

8. Lee, S, S.N.Amirkhanian, N. Park and K.W.Kim. Characterization of warm mix 6 asphalt binders containing artificially long-term aged binders. Construction and 7 Building Materials. Vol. 23 (6), 2009, pp. 2371-2379. 8

9. Mallick, R.B., P.S. Kandhal, and R. L. Bradbury. Using warm-mix asphalt 9 technology to incorporate high percentage of reclaimed asphalt pavement material in 10 asphalt mixtures”, Transportation Research Record: Journal of the Transportation 11 Research Board, No. 2051, 2008, pp. 71-79. 12

10. Russell,M., J. Uhlmeyer., J. Weston., J. Foseburg., T. Moomaw. and J. Devol. 13 Evaluation of warm mix asphalt. WSDOT Research Report WA-RD 723.1, 2009. 14

11. TDOT. Standard specification for road and bridge construction. the Tennessee 15 Department of Transportation, Nashville, TN, March, 1995. 16

12. Roque, R., and W.G. Buttlar. The development of a measurement and analysis 17 system to accurately determine asphalt concrete properties using the indirect tensile 18 mode. J Assoc Asphalt Paving Technology. 61,1992, pp.304-322. 19

13. Roque, R., and W.G. Buttlar. Experimental development and evaluation of the new 20 SHRP measurement and analysis system for indirect tensile testing at low 21 temperature. Transportation Research Record: Journal of the Transportation 22 Research Board, No. 1454, 1994, pp.163-171. 23

14. Roque, R., B. Birgisson, B. Sangpetngam and Z. Zhang. Hot mix asphalt fracture 24 mechanics: a fundamental crack growth law for asphalt mixtures. J Assoc Asphalt 25 Paving Technology. 71, 2002, pp.816-827. 26

15. Carpenter, SH., K. Ghuzlan and S. Shen. Fatigue endurance limit for highway and 27 airport pavements. Transportation research record: Washington DC: National 28 Research Council, 1832, 2003, pp.131-138. 29

16. Ghuzlan, K. and SH. Carpenter. Energy-derived/damage-based failure criteria for 30 fatigue testing. Transportation research record: Washington DC: National Research 31 Council, 1723, 2000, pp.141-149. 32

17. Shen, S. and SH. Carpenter. Application of dissipated energy concept in fatigue 33 endurance limit testing. Transportation research record: Washington DC: National 34 Research Council, 1929, 2005, pp.165-173. 35


1

Responses to Review Comments

Laboratory Performance Evaluation of Warm Mix Asphalt containing High Percentages of RAP

Sheng Zhao, Baoshan Huang*, Xiang Shu, Xiaoyang Jia, and Mark Woods

*Corresponding Author Baoshan Huang, Ph.D., P.E. Department of Civil and Environmental Engineering The University of Tennessee Knoxville, TN 37996 Phone: (865)974-7713 Email: [email protected] REVIEWER 1: - Please explain the reason(s) for different targeted air voids. Response: The authors are thankful to the reviewer's comments. The following sentence was added on page 5 line 19: "7% was selected as the target air voids to simulate a properly designed and constructed mixture immediately after construction, while 4% was selected for mixture after two or three years of traffic". - Further explain the improvements due to adding RAP, particularly in moisture resistance. Response: The authors are thankful to the reviewer's comments. The following sentences were added on page 12: "The improvement in moisture resistance caused by RAP might be due to the fact that the aggregate of RAP have been covered and protected by aged asphalt binder. The bond between aggregate and asphalt in RAP is stronger than that between aggregate and virgin binder, making the mixture containing RAP less vulnerable to moisture damage”. REVIEWER 2: couple of typographical errors nigh instead of high on page 3 and the SGC acronym incorrectly stated as SGD on page 5 Response: The authors are thankful to the reviewer's comments. The paper was reviewed and the English expressions were revised.


2

This is a good paper to summarize multiple laboratory performance test results of WMA + RAP and highlights the complexity of WMA with higher percentages of RAP. WMA + high RAP warrants further investigation by the industry as a whole. Response: The authors are thankful to the reviewer's comments. REVIEWER 3: This paper provides some very good data. However, since the focus of the paper is laboratory performance evaluation, it would be desirable to tie the results with performance and then make conclusions. As it is, the paper just provides the results from several tests, and in some cases, the results are contradictory. What is the reader supposed to conclude? Essentially, it becomes a paper on comparison of test methods, rather than a paper on performance evaluation. Response: The authors are thankful to the reviewer's comments. As it shows in the paper, the results from several tests are provided as well as the conclusions based on these results. Regarding the contradictory conclusion made based on the results of energy ratio and DCSEf methods, the authors consider results from energy ratio to be more reasonable and the following sentences were added on Page 13:” Since both the dissipated energy accumulation and the energy required to fracture the mixture are taken into account by energy ratio method, the energy ratio method is more reasonable than DCSEf method in describing cracking resistance of asphalt mixtures”. In addition, the following sentence was added at the conclusion 3 on page 16:” Energy ratio results would be more reliable because energy ratio concept is more reasonable than DCSEf in characterizing cracking resistance of asphalt mixtures.” Secondly, I hope I have not missed it, it is essential to have some properties of the RAP - how old, how aged, any viscosity/other data on the extracted asphalt? Response: The authors are thankful to the reviewer's comments. The extracted asphalt was not evaluated in this study. It is true that some properties of the RAP might be helpful. The RAP, however, came from the same source, which makes it reasonable to evaluate the properties of mixtures containing different amounts of RAP. Lastly, this WMA was produced using "foaming" technology. It will be good to discuss what the implications of this foaming technology are and then discuss the findings in the light of those implications. Simply saying WMA (since WMA can be of many types) is, in my opinion, not correct, when we are discussing the various properties. Response: The authors are thankful to the reviewer's comments. It is good to discuss the types of WMA and compare their various properties. This paper focuses on various properties of


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mixtures based on different percentages of RAP, so comparisons among different WMA technologies are not covered in this study. REVIEWER 4: Pg 2, line 6 - Change "US." to "U.S." Pg 2, line 9 - Change "purpose" to "purposes" Pg 2, line 11 - Spelling - "laboratory" Response: The authors are thankful to the reviewer's comments. The paper was revised and the English errors were corrected. Pg 2, line 12 - "...better fatigue performance." - Yes, according to failure criterion, but not according to DCSEf values. Response: The authors are thankful to the reviewer's comments. It is true that the results of do not indicate a better fatigue performance of WMA when RAP is added. The results of energy ratio method that is more reliable and reasonable in characterizing cracking resistance of WMA show the addition of RAP is beneficial. In addition, the results of energy ratio are consistent with those of beam fatigue test. It can be obtained that, therefore, WMA with high percentage of RAP exhibited better fatigue performance. Pg 3, lines 16 and 17 vs. 24 - "(0, 10, 20 and 40)" vs. "(0%, 10%, 20% and 30%)" - Be consistent... Pg 3, line 20 - Add "rubber" after crumb and remove "on" Pg 3, line 34 - Change "warm asphalt mixture" to "WMA" Pg 3, line 45 - Change "nigh" to "high" Response: The authors are thankful to the reviewer's comments. The paper was revised and the English errors were corrected. Pg 4, line 8 - Why is "clumps" in this sentence? Response: The authors are thankful to the reviewer's comments. ‘Clumps’ is used here because clumps in warm-mix with RAP were reported in the original WSDOT research report. Pg 4, line 14 - Remove "with" Pg 4, line 17 - Change "was" to "were" Response: The authors are thankful to the reviewer's comments. The paper was revised and the English errors were corrected.


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Pg 4, line 19 - HMA mixtures only went up to 30% RAP Response: The authors are thankful to the reviewer's comments. The following expression was revised on page 4 as “WMA mixtures contained up to 50% RAP with control HMA containing up to 30% RAP”. Pg 4, line 34 - Add "of" before 3/4" Pg 4, line 35 - Add " after 3/8 (show as 3/8") Response: The authors are thankful to the reviewer's comments. The paper was reviewed and the English expressions were revised. Pg 5, Table 2 - Consider adding metric sieve values to Sieve Size column. Add "." after No in 3rd and 4th column headings. Response: The authors are thankful to the reviewer's comments. The metric sieve values were added to the Sieve Size column. Pg 5, line 7 - It surprises me that the Optimum AC was 4.2% (total) for ALL of the mixes. My guess is 4.2% was the Opt AC for the original virgin HMA design, and therefore 4.2% was used for the target on the other blends. No where in the paper are there actual FIELD volumetric results presented for any of the various mixtures. Comparing these results might add to your evaluation and comparison of the different mixtures and different tests. Response: The authors are thankful to the reviewer's comments. Yes, 4.2% was the Opt AC for the original HMA design and therefore used for the target on the other blends. Composition of each mix is shown in Table 3 on page 5. It is true that the field volumetric results would be helpful, this study, however, focuses on the laboratory performance evaluation of WMA containing high RAP contents, so the air void of specimen for each mix is the most important concern. Field volumetric might be covered in future study. Pg 5, line 9 - Anti-strip was added at 0.3%. Was this determined in the original virgin HMA design? If so, was the decision then made to use 0.3% in all of the blends? Or is 0.3% simply a TNDOT spec? Response: The authors are thankful to the reviewer's comments. 0.3% was used in all of the blends. It is a number determined based on TDOT construction experience. The following sentence was added on page 5 line 10:” which is determined based on TDOT construction experience”.


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Pg 5, line 15 - Were the samples taken from haul trucks prior to leaving the plant site? Response: The authors are thankful to the reviewer's comments. WMA samples were fabricated on site with SGC in a trailer. HMA was collected on site from haul trucks in the plant and shipped to the laboratory in University of Tennessee. Pg 5, line 17 - Spelling - "moisture" Pg 5, line 18 - Should "SGD" be "SGC"? Response: The authors are thankful to the reviewer's comments. The paper was reviewed and the English expressions were revised. Pg 5, lines 15-18 - Does this mean the WMA mix samples were not allowed to cool, since they were run at the QC lab at the plant site? Was any amount of short term aging done to the loose WMA mix prior to compacting, or were the loose mix samples just brought up to compaction temperature? Perhaps the loose WMA mix wasn't heated at all, it was just split down and compacted? Since the HMA samples were "shipped to the laboratory", I assume they cooled to room temperature and therefore were re-heated to allow them to be split down into test sample size and then heated more to bring the loose HMA mix up to compaction temperature? As a minimum, it would appear the WMA and HMA SGC specimens were compacted using DIFFERENT SGC's. Do the authors feel this could have induced differences in test results? If there were differences in how the WMA and HMA mix was handled - prior to compacting each in different SGC's - do the authors feel this induced differences in test results? Response: The authors are thankful to the reviewer's comments. WMA samples were not allowed to cool and were kept in the oven for 2 hours for short term aging prior to compacting. HMA were allowed to cool to room temperature and be re-heated once up to compaction temperature prior to compaction based on asphalt industry practice. It is true that the WMA and HMA specimens were compacted using different SGC, but the induced differences would be insignificant. Both the SGCs used in this study meet the Superpave requirements and the specimens were compacted based on height-control mode. The following sentence was added on page 5 line 17:” and kept in Oven for 2 hours for short-aging prior to compaction”. Pg 6, Table 4 - Were ALL test specimens produced within the "Target air void" ranges shown? Response: The authors are thankful to the reviewer's comments. Yes, all the rest specimens met the target air void requirements.


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Pg 7, lines 6-11 - Was just one freeze-thaw cycle performed, or were there multiple F/T cycles? Response: The authors are thankful to the reviewer's comments. Just one freeze-thaw cycle was performed. Pg 7, line 8 - "...between 55% and 80%..." I think the current recommendation is a saturation level range of 70-80%. Were these tests conducted before the change? Were the saturation levels consistent? Saturation level can significantly impact TSR results...that's why they changed the range. Response: The authors are thankful to the reviewer's comments. AASHTO 283 (2010 30th edition) was followed when freeze-thaw conditioning was conducted. The degree of saturation was controlled to be between 70 and 80 percent. We started the new recommendation one and half year ago. This is a written problem. The level range was corrected on page 7. Pg 8, line 13 - Should also explain what "m" is and what "D1" is. Also, add a blank line under line 13 - prior to starting new paragraph. Response: The authors are thankful to the reviewer's comments. The explanation of D1 and m was added on page 8. Pg 8, line 16 - Is there an extra space after epsilon? Pg 8, line 20 - Make the "f" in "DCSEf" subscript Pg 9, Figure 4, subtitle - Make the "f" in "DCSEf" subscript Pg 9, line 4 - Spelling - "flexural" Pg 10, line 10 - Change "Tests" to "Test" Response: The authors are thankful to the reviewer's comments. The paper was reviewed and the English expressions were revised. Pg 10, lines 15-16 - What about the properties and influence of the RAP aggregate? Response: The authors are thankful to the reviewer's comments. The aggregate structures were similar for all the mixtures in this study. So the influence of the RAP aggregate should be insignificant compared with that of the aged binder. The following sentence was added on page 5 line 7:” and all the mixtures were adjusted to keep the similar aggregate structures after RAP was added”.


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Pg 10, line 22 - Add a period at the end of the sentence. Response: The authors are thankful to the reviewer's comments. The problem mentioned was corrected. Pg 12, Figure 9 - It can also help to closely examine/compare the actual tensile strength results (dry and wet). That information would be helpful in addition to this figure. Response: The authors are thankful to the reviewer's comments. The performance testing on field cores was not included in this study. We would, however, take into account adding performance tests on field cores in future study. Pg 12, line 4 - "Figure" is used here. At other spots in the paper, "Fig." is used. Use "Figure" or "Fig." consistently throughout. Pg 12, line 5 - Change "a" to "an" Pg 12, line 11 - Sentence appears to not be completed Pg 12, line 17 - Change "Tests" to "Test" Pg 13, line 1 - Change "tests" to "test" Pg 13, line 3 - Remove "of" Response: The authors are thankful to the reviewer's comments. The paper was revised and the English errors were corrected. Pg 15, Conclusions - Since conclusions 3 and 4 are contradictory, what do the authors plan to do for the rest of their work to determine which is right and which is wrong? Response: The authors are thankful to the reviewer's comments. As it shows in the paper, the results from several tests are provided as well as the conclusions based on these results. Regarding the contradictory conclusion made based on the results of energy ratio and DCSEf methods, the authors consider results from energy ratio to be more reasonable and the following sentences were added on Page 13:” Since both the dissipated energy accumulation and the energy required to fracture the mixture are taken into account by energy ratio method, the energy ratio method is more reasonable than DCSEf method in describing cracking resistance of asphalt mixtures”. In addition, the following sentence was added at the conclusion 3 on page 16:” Energy ratio results would be more reliable because energy ratio concept is more reasonable than DCSEf in characterizing cracking resistance of asphalt mixtures.”


laboratory performance evaluation of warm mix asphalt ...docs.trb.org/prp/12-4542.pdf · 13...

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