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Investigation into hot-mix asphalt moisture-induced damage under tropical climatic conditions
Construction and Building Materials 50 (2014) 567–576
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Investigation into hot-mix asphalt moisture-induced damage under tropical climatic conditions Juraidah Ahmad a, Nur Izzi Md. Yusoff b,⇑, Mohd Rosli Hainin c, Mohd Yusof Abd Rahman a, Mustaque Hossain d a
Institute for Infrastructure Engineering and Sustainable Management (IIESM), Faculty of Civil Engineering, Universiti Teknologi MARA, Selangor, Malaysia Dept. of Civil & Structural Engineering, Universiti Kebangsaan Malaysia, Selangor, Malaysia Faculty of Civil Engineering & Construction Research Alliance, Universiti Teknologi Malaysia, Johor, Malaysia d Dept. of Civil Engineering, Kansas State University, 2124 Fiedler Hall, Manhattan, KS 66506-5000, United States b c
h i g h l i g h t s We investigate moisture-induced damage of HMA under tropical climatic conditions. The Modified Lottman and SPT dynamic modulus tests were used to assess moisture susceptibility of HMA. Superpave mixes show better resistance to rutting compared to the Marshall mixes. SPT dynamic modulus test is recommended for Superpave mixture characterisation in tropical climatic countries.
a r t i c l e
i n f o
Article history: Received 19 July 2013 Received in revised form 30 September 2013 Accepted 4 October 2013 Available online 27 October 2013 Keywords: Marshall mix design Superpave mix design Simple Performance Test Moisture-induce damage Tensile strength ratio
a b s t r a c t A major concern for highway industries in tropical climatic countries is the excessive moisture-induced damage to hot-mix asphalt (HMA) pavements as a result of frequent passes by heavy axle loads. Therefore, in this study, two different approaches, the Superpave and Marshall mix design methods, were used to design HMA mixes and a comparison was made to identify how susceptible these mixtures are to moisture damage. The Modified Lottman test and Simple Performance Test (SPT) were performed on unconditioned and conditioned specimens tailored to suit tropical climatic conditions, omitting freeze and thaw. The Modified Lottman test showed that the tensile strength values of Superpave-designed mixtures are higher than Marshall-designed mixtures. The tensile strength ratio (TSR) values decreased from unconditioned to conditioned specimens, suggesting that there is damage to the mixtures. The results also show good agreement between the TSR and ESR in the two tests, with a coefficient of determination value of 0.78. This relationship indicates that the SPT dynamic modulus test was effective and suitable to evaluate the lab-measured moisture susceptibility of HMA mixes. Since the dynamic modulus test provides a full characterisation of the mix over a broad range of temperatures and loading frequencies, this test is highly recommended for Superpave mixture characterisation in tropical climatic conditions. Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction The tremendous development in the national infrastructure network in Malaysia over the last decade has led to an increase in road construction. Asphaltic road dominates the overall surfacing types at 87,626 km, and there are only 343 km of concrete roads. The other 3651 km are earth or gravel roads. Federal roads stretch over 16,509 km, while state roads cover 104,112 km [1]. The conventional Marshall design method for hot-mix asphalt (HMA) mixes has been used for decades by the Malaysian Public ⇑ Corresponding author. Tel.: +60 3 8921 6447; fax: +60 3 8921 6147. E-mail addresses: [email protected] (J. Ahmad), [email protected] (N.I.M. Yusoff). 0950-0618/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.conbuildmat.2013.10.017
Works Department (PWD) to construct pavements, following the JKR/SPJ/2008 standard specification [2]. Although these pavements are still in service, a large amount of money is allocated for maintenance work annually due to pavement distress, which sometimes occurs prematurely due to increasing traffic loads and wet tropical climatic conditions. With the successful implementation of the Superpave method in the USA, it is very timely for the Malaysian PWD to initiate a paradigm shift to adopt a better mix design system for HMA pavements that suit tropical climatic conditions. Recently, a number of studies have been conducted outside the USA to evaluate the feasibility and performance of Superpave-designed mixtures. For instance, a study was conducted in Taiwan to compare the volumetric and mechanical performance properties of Superpave mixtures and typical Taiwan mixtures (TTM) using
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the Marshall method [3]. It was found that the binder content of the Superpave-designed mixtures is lower than TTM Marshall-designed mix, and TTM mixtures exhibit low densification values. In Jordan, a research study proved the superiority of Superpave mixes over Marshall mixes [4]. A study in India showed that the Superpave gyratory compactor (SGC) is capable of achieving a lower air void content than can be achieved by the mechanical Marshall Hammer compactor. This study also found that Superpave mixes have a lower asphalt binder content than Marshall mixes [5]. Khan and Kamal [6] found that Superpave mixtures exhibit better creep resistance compared to Marshall mixtures in flexible pavement in Pakistan. A study was conducted based on the Iraq road specification and the results indicate that Superpave mixes have a lower asphalt content than Marshall mixes. As a result, Superpave mixes are better from an economic point of view than Marshall mixes [7]. However, one of the major concerns related to HMA deformation is moisture-induced damage. Moisture infiltrating a wearing course may cause detachment of the asphalt film from the aggregate surface and weaken the binder adhesion through an emulsification process under heavy traffic and elevated temperature conditions. Hence, extensive laboratory tests to identify moisture damage have been developed over the years. Initially, in the late 1940s, the immersion compression test on compacted mixtures was developed. The National Cooperation Highway Research Project (NCHRP) Report 589 [8] stated that the significant impact of climate and traffic on moisture damage was discovered in the 1960s through the research work of Johnson [9], Schmidt and Graf [10], Jiminez [11] and Lottman [12]. In 1981, a test involving repeated water pressure to simulate the behaviour of saturated HMA was developed by Jiminez and further modified by Tunnicliff and Root [13]. This resulted in a quantitative method of laboratory testing that is currently widely accepted, known as the Modified Lottman test (AASHTO T283 or ASTM D4867). Currently, the AASHTO T283 is incorporated in the Superpave mix design system as the principal moisture susceptibility test method. Other fundamental tests to predict moisture damage are reported in the work of Ensley et al. [14] and Terrel and Al-Swailmi [15], which resulted in the use of the Environmental Conditioning System (ECS). In the 1990s, the Hamburg Wheel Tracking Device (HWTD) was introduced and gained popularity in predicting moisture damage in HMA mixes submerged under water [16,17]. However, the mix’s success was reported by highway agencies in the United States, resulting in continued research to refine the procedures and to investigate other alternatives. Under the NCHRP Project 9-34, a new test was proposed, believed to better simulate environment and traffic factors to evaluate the water susceptibility of HMA mixtures. Solaimanian [18] evaluates moisture damage by combining the ECS and Simple Performance Test (SPT). However, the ECS system is costly and complex to use [19]. In a recent study, the results show that the SPT without the ECS conditioning system is able to correlate with the AASHTO T283 test [20]. In Malaysia, no specific test has been developed as a standard specification for road works by the Malaysian PWD to determine HMA moisture damage. In an effort to identify the moisture damage susceptibility of Malaysian mixes, both the Modified Lottman (AASHTO T283) and SPT dynamic modulus tests without the ECS conditioning system were conducted to evaluate how susceptible these HMA mixtures are to moisture damage. This study does not consider low temperature environments because the temperature in Malaysia rarely falls below 30 °C in daylight hours and usually lies within the range of 35–45 °C [21]. Rutting and resilient modulus tests were conducted using a wheel tracking device and the Indirect Tensile Modulus test to evaluate and compare the mix properties of Superpave- and Marshall method-designed HMA mixes.
2. Experimental design 2.1. Materials selection Two granite aggregate sources were selected in this study, representing the central and southern parts of Peninsular Malaysia. Quarry Selangor (QS) Granite quarry is located in the central part in the vicinity of Kuala Lumpur, and another quarry, Quarry Johor (QJ), is located in the southern part of Peninsular Malaysia. These two quarries supply aggregates for road construction in the central and southern regions of Peninsular Malaysia. Aggregate properties were evaluated for compliance with both mix design systems. According to PWD specifications, only granite aggregates are permissible for use in the asphalt wearing course. Two different gradations with different nominal maximum aggregate size (NMAS) were selected, as shown in Figs. 1 and 2. To enable a comparison of the volumetric properties and rutting performance between the mixes, the gradations for all mixtures were purposely selected to fall within the upper and lower limits, complying with both Superpave and PWD Marshall grading requirements. A total of eight mixes were designed, of which four were Superpave-designed mixes and the rest were Marshall mixes. Since the climatic conditions in Malaysia are fairly consistent throughout the country, the supply of Performance Graded (PG) asphalt binder in this region is based on higher temperatures. The asphalt binders of Performance Grade (PG) 64 and PG 70 used are equivalent to Penetration Grade (PEN) 80/100 (B1) and PEN 60/70 (B2) respectively. The properties of both binders, which follow the requirements of PWD specifications and road works, are summarised in Table 1. Table 2 shows the test design matrix for both the PWD Marshall and Superpave mixtures used in this study. 2.2. Mix design The standard Marshall mix design procedure from the Malaysian PWD road works specifications was employed to design the HMA mixes. Fifteen specimens for each mix were prepared with blended mineral aggregates at an increment of 0.5% binder from 4% to 7% by weight of mixture. The mixing temperature was 165 and 150 °C for binder types B1 and B2 respectively. No aging is required for the Marshall mix design method prior to compaction. The optimum binder content (OBC) of these mixtures was estimated, corresponding to 4% design air voids, bulk density, voids filled with asphalt (VFA) and flow values. The OBC of QS and QJ mixtures ranged from 5.6% to 6.2% and 5.4% to 6.0% respectively. The volumetric properties of all PWD Marshall mixes conformed to PWD criteria, as tabulated in Table 3. Superpave-designed mixtures, when blended at OBC, should yield acceptable volumetric properties at 4% air voids based on the established Superpave criteria at the design number of gyrations. The mixing temperature of B1 and B2 binder types was 150 and 165 °C respectively. Short-term aging is required for Superpave mixtures for approximately two hours prior to compacting using the Superpave gyratory compactor (SGC). The OBC for Superpave-designed mixtures was established from the volumetric properties which include voids in mineral aggregates (VMA), VFA, air voids and dust proportion (DP). The volumetric properties of the design mixtures corresponding to OBC for Superpave-designed mixtures are shown in Table 4. The OBC for QS ranged from 5.1% to 5.7% and 5.5% to 6.4% for QJ mixes. The results show that QS and QJ mixtures comply with all Superpave and PWD Marshall criteria requirements except for the 9.5-QJ B1 and B2 Superpave mixes, which do not meet the VFA criteria. Further investigations were conducted to determine how susceptible these mixtures are to moisture damage. 2.3. Wheel tracking test The dry wheel tracking test was conducted using a Wessex wheel tracking device for which a mold was fabricated to hold the SGC rut specimen. The height of the SGC rut mold follows exactly the original slab mold of the Wessex wheel tracking device. This is to avoid any inaccuracy during the rutting test. Approximately 3700 g of Superpave or Marshall mix was compacted to 7 ± 0.5% air voids to make a cylindrical specimen with a diameter of 150 mm and final height of 65 mm. This was accomplished by putting a given amount of mixture in the SGC mold and compacting it to the specified height. The specimens were left to cool at room temperature for 24 h after compaction. The air void content was also determined before conducting the test to meet the test requirements. The specimens were then trimmed and paired to fit in the wheel tracking mold. Care was taken to make sure that the specimens fitted into the mold exactly. The rut test was conducted at 60 °C since the initial tests at 40 °C showed negligible rut depths. Prior to testing, the specimens were conditioned for at least four hours at test temperature. The specimens were subjected to simulated traffic with a simple harmonic motion by applying 525 N load for one hour. 2.4. Indirect tensile resilient modulus test The specimens were fabricated at OBC and the resilient modulus test was conducted to evaluate rutting at 40 °C using an IPC UTM-5 machine, according to ASTM 4123. These specimens were subjected to a cyclic load with a sinusoidal wave
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100 90
PWD Marshall Upper Envelope
Percent Passing
80 70 60 50
PWD Marshall Lower Envelope
Superpave Upper Limit
40 30
Superpave Lower Limit
20 10
25.00
19.00
12.50
9.50
4.75
2.36
1.18
0.60
0.075 0.15 0.30
0
Sieve Size (mm) Fig. 1. NMAS 12.5 mm gradation.
100 90
PWD Marshall Upper Envelope
Percent Passing
80 70 60
Superpave Upper Limit
PWD Marshall Lower Envelope
50 40
Superpave Lower Limit
30 20 10
12.50
9.50
4.75
2.36
1.18
0.60
0.30
0.075 0.15
0
Sieve Size (mm) Fig. 2. NMAS 9.5 mm gradation.
Type
PEN 80-100 (B1)
PEN 60-70 (B2)
Criteria
shape, and the test sequence consisted of five conditioning pulses followed by five loading pulses when data acquisition took place. The load was applied for a period of 0.1 s with a rest period of 0.9 s. The horizontal and vertical deformations were measured by means of extensometers and LVDTs respectively.
Penetration at 25 °C (0.1 mm) Softening point (°C) R & B Rotational viscosity (original) Rotational viscosity (RTFO)
84
68
–
2.5. Modified Lottman test
43 0.35 Pa s
42 0.45 Pa s
0.6 Pa s
0.7 Pa s
48–56 3 Pa s Max 3 Pa s Max
For the dynamic modulus test, all specimens were prepared at OBC and compacted using the SGC with initial diameter of 150 mm and height of 165 mm. The specimens were then cored to a diameter of 100 mm and both ends were sawed to a height of 150 mm to achieve the right dimensions for the dynamic modulus test, as shown in Fig. 3. This ‘‘ideal’’ geometry was derived based on specimen size and aggregate size effect studies conducted by previous researchers [22]. Before
Table 1 Binder properties.
Table 2 Test design matrix for Superpave and PWD Marshall mixes. No.
Factor
Details
1
Aggregate gradation
Superpave and PWD gradation limits
2 3 4
Mix design method Aggregate source Binder type (PWD specification)
Superpave and PWD Marshall mix design method Quarry Selangor (QS) and Quarry Johor (QJ) Penetration Grade 80/100 (denoted as B1) Penetration Grade 60/70 (denoted as B2)
12.5 mm NMAS 9.5 mm NMAS
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Table 3 Volumetric properties of PWD Marshall mixtures. Parameter
12.5-QS-B1
12.5-QS-B2
9.5-QS-B1
9.5-QS-B2
PWD criterion
Quarry QS OBC (%) Stability (kN) Flow (mm) VMA (%) VFA (%)
5.6 10.2 3.5 16.2 75
5.9 10.1 3.5 16.8 75
6.1 10.2 3.2 17.2 75
6.2 11.0 3.3 17.5 77
– >8 kN 2–4 mm – 70–80
Quarry QJ OBC (%) Stability (kN) Flow (mm) VMA (%) VFA (%)
5.4 13.2 2.8 14.9 79
5.4 13.1 3.5 14.8 80
6.0 9.7 3.2 16.4 75.8
5.9 12.3 3.2 15.9 80
– >8 kN 2–4 mm – 70–80
Table 4 Volumetric properties of Superpave mixtures. Mix design properties
12.5-QS-B1
12.5-QS-B2
9.5-QS-B1
9.5-QS-B2
Criterion
Quarry QS OBC (%) Air voids (%) VMA (%) VFA (%) Dust proportion
5.1 4.0 14.9 73.1 0.8
5.3 4.0 15.8 74.4 0.8
5.4 4.0 15.7 74.6 0.8
5.7 4.0 16.5 75.7 0.7
– – 14.0 min* 65–75** 0.6–1.2
Quarry QJ OBC (%) Air voids (%) VMA (%) VFA (%) Dust proportion
5.5 4.0 16.0 74.9 0.8
5.5 4.0 16.0 75.0 0.8
6.4 4.0 17.6 76.5 0.7
6.3 4.0 17.4 77 0.7
– – 14.0* min 65–75** 0.6–1.2
Note: B1 – asphalt binder Penetration Grade 80/100; B2 – asphalt binder Penetration Grade 60/70. For 9.5 mm (3/800 ) nominal maximum size mixtures, the specified minimum VMA is 15.0. For design traffic levels 3–30 million ESALs, (9.5 mm) 3/800 nominal maximum size mixtures, the specified VFA range shall be 65–76%.
*
**
conditioning, the displacement transducers were glued to gauge points on the cylindrical specimens to measure axial deformation, as shown in Fig. 4. For the Modified Lottman test, PWD Marshall and Superpave specimens were prepared according to individual standard mix design procedures. For moisture-induced damage, the air voids of all test specimens were within 0.5% of the required air void content of 7.0%. The specimens for each mixture type were divided into wet and dry subsets [23]. The dry or control subsets were conditioned at 25 °C in a plastic bag submerged in a water bath for two hours before testing. The wet subset was subjected to vacuum saturation; it took approximately four to five minutes to achieve between 70% and 80% saturation levels. The saturated specimens were then placed in a water bath at 60 °C for 24 h and then at 25 °C for another two hours prior to testing. The degree of saturation was measured by weight from the equation below.
%S ¼
100ðW SSD W D Þ Va
ð1Þ
Where %S is the degree of saturation, WSSD is the saturated surface dry weight of the specimen after vacuum saturation, WD is the initial dry specimen weight and Va is the volume of air voids in the specimen. The indirect tensile strength (ITS) test is applied on dry and wet specimens and specifies a tensile strength ratio (TSR) of at least 0.8. The TSR can be calculated as follows:
Tensile Strength Ratio ¼
Swet Sdry
ð2Þ
where Swet and Sdry are the conditioned and unconditioned tensile strengths respectively. 2.6. Simple Performance Test (SPT) The SPT dynamic modulus test procedure follows the test protocols described in NCHRP Project 9-19, Superpave Support and Performance Models Management [24]. The conditioning procedures are similar to the Modified Lottman test specimens. However, extra care should be taken to avoid detachment of the glued LVDT gauge holders from the specimen. The dynamic modulus of conditioned (Ewet) and unconditioned (Edry) values were obtained from the tests conducted at six different frequencies by applying a sinusoidal compressive load on the specimen in a cyclic manner. The test was conducted at 25 °C on each specimen, with loading frequen-
Fig. 3. Cored and trimmed SPT specimen. cies of 25, 10, 5, 1, 0.5 and 0.1 Hz. The dynamic stress applied is 100 kPa and it is important to attain axial strains between 75 and 150 microstrains throughout the testing process. Prior to testing, the specimens must be placed in the testing chamber until the effective temperature and contact stress are achieved. It is also important to ensure that the specimens are placed in the centre under the loading platens. A continuous uniaxial sinusoidal compressive stress at selected test frequency is then applied to the unconfined cylindrical test specimen. The linear viscoelastic stress–strain relationship of the HMA specimen is defined as the complex modulus (E). The absolute value of the complex modulus |E|, also known as the dynamic modulus, is defined as the ratio of maximum (peak) dynamic stress (r0) to peak recoverable axial strain (e0) [24]. The angle by which the peak recoverable strain lags behind the peak dynamic stress is referred to as the phase angle, /. The phase angle is an indicator of the viscous and elastic properties of the material being evaluated. Mathematically, the dynamic modulus and phase angle equation is expressed as:
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12.5-B1
100mm
12.5-B2
7
120 o
Transducers located apart around circumference of
9.5-B1
9.5-B2
6.4
6.5
70mm
150mm
120 o
Rut Depth (mm)
6 5
4.3
4.1
4 3 2
3
2.7 1.6
0.8
1 0 Fig. 4. Schematic diagram of LVDT dimensions of specimen.
jE j ¼
ð3Þ
ti tp
ð4Þ
where r0 is the maximum peak dynamic stress, e0 is the peak recoverable strain, ti is the average lag time between a cycle of stress and strain and tp is the average time for a stress cycle. In order to develop master curves for each frequency and test temperature, a sigmoidal function was used to fit the time-dependent dynamic modulus from the equation below.
log ðE Þ ¼ d þ
a
ð5Þ
1 þ ebþcðlog tr Þ
where E is the dynamic modulus, d is the minimum value of E , (d + a) is the maximum value of E*, b and c are parameters that describe the shape of sigmoidal function and tr is the time of loading at the reference temperature. Time of loading, tr, can be estimated using the following equation:
log tr ¼ log
QS-Mar sh all
Fig. 5. Comparison between Superpave and Marshall mixes.
r0 e0
/ ¼ 360
QS-Su p er pav e
t aT
ð6Þ
where t is the time of loading at a given temperature and aT is the temperature shift factor. Numerical optimisation is used to solve the variables d, a, b and c as well as the shift factors aT using the Solver function in Microsoft Excel.
3. Results and discussion 3.1. Rutting resistance Fig. 5 shows that the rutting values of the Superpave mixtures varies from 0.8 mm to 3.0 mm, compared to the Marshall mixtures with high rutting values ranging from 4.1 mm to 6.5 mm. This obviously indicates the higher resistance of Superpave mixtures compared to Marshall mixtures. In addition, the results also show that NMAS 9.5 mm grading for a particular mixture has lower rutting values compared to NMAS 12.5 mm mixtures. Asphalt binder type also contributed to the rutting resistance. In this study, HMA with asphalt binder type B2 exhibited better rutting resistance than asphalt binder type B1. In Fig. 6, the wheel tracking rates for both Marshall and Superpave mixes were compared. According to Faustino et al. [25], two parameters are considered in a wheel tracking test to ensure that the performance of materials is correctly assessed. The wheel tracking rate is measured as the primary measure of the resistance to permanent deformation, and the maximum rut depth is a secondary measure. This is important, because different mixtures may deform differently, and some mixtures may rut excessively at the early stage of the rutting test compared to the latter part of the test. In this study, the results show that different types of gradation do not have an adverse effect on the wheel tracking rate; however, different types of binder and mix design method show variability in the results of wheel tracking rate. It can be seen that the Superpave mixes have a lower wheel tracking rate compared to Marshall-designed mixes.
An independent t-test analysis was also conducted to compare the superiority of the mix design method used to design the HMA mix statistically. The null hypothesis is that the mean rutting of Superpave-designed HMA mixes and Marshall-designed mixes is equal (H0: lSuperpave = lMarshall). The Levene’s test for equality of variances shows that the population variance is equal and the t-value is considered to test for the null hypothesis. The results show that the p-value is 0.000, less than 0.05, hence the null hypothesis was rejected, indicating that the mean difference between the two different mix design methods is significant. This indicates that Superpave-designed mixtures are less resistant to rutting compared to Marshall-designed mixtures. 3.2. Resilient modulus The resilient modulus is an important variable used to measure pavement response in terms of dynamic stresses corresponding to strains. During testing, both horizontal and vertical deformations were measured from both sides of the specimen, and the resilient modulus was calculated accordingly. This test was analysed to compare and characterise Superpave- and Marshall-designed HMA mixes tested at two temperatures, namely 25 and 40 °C. At 25 °C, the resilient modulus is an indication of the mixture’s resistance to fatigue, whereas the resilient modulus at 40 °C indicates the mixture’s resistance to rutting. The resilient modulus values are higher for QS Superpave-designed mixtures compared to Marshall-designed mixtures when tested at 25 °C. The results in Fig. 7 show that as the pulse repetition period during loading time decreases from 0.1 s to 0.3 s, the resilient modulus values also decrease. From the graph, the 9.5-B2-SP mix is the least susceptible to fatigue with the highest resilient modulus value of 3721 MPa, followed by 12.5-B2-SP, 9.5-B1-SP, 12.5-B1-SP, 12.5-B2- Marshall, 12.5-B1-Marshall, 9.5-B2-Marshall and 9.5-B1-Marshall. As temperature increases, the difference in resilient modulus is more notable, with a decline in stiffness at 40 °C. At the higher temperature, almost all Superpave mixtures showed a higher resilient modulus value compared to Marshall mixtures. The difference in the resilient modulus values at the higher temperature indicates that Superpave mixtures are less susceptible to rutting than Marshall mixtures. At a pulse repetition period of 0.1 s in the resilient modulus test, the results show that the mixture most resistant to rutting is 9.5-B2-SP, with the highest resilient modulus value of 728 MPa, followed by 12.5-B2-SP, 9.5-B1-SP, 12.5-B1-SP, 12.5-B2Marshall, 9.5-B2-Marshall, 9.5-B1-Marshall, and 12.5-B1-Marshall. With regards to the binder types used, mixtures with binder type B2 are stiffer and have the highest resilient modulus values for both Marshall and Superpave mixtures. It was estimated that
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Fig. 6. Wheel tracking rates of mixes.
the average resilient modulus values of Superpave mixtures are 30% higher when tested at 25 °C and approximately 32% higher at 40 °C compared to Marshall mixtures. In general, the resilient modulus results for QJ mixtures are lower compared to QS mixtures at similar test temperatures, as shown in Fig. 8. An independent t-test analysis was also conducted to compare Superpave and Marshall mixtures to evaluate HMA mix stiffness. The null hypothesis is that the stiffness of Superpave-designed HMA mixes and Marshall-designed mixes are the same (Ho: lSuperpave = lMarshall). The Levene’s test for equality of variances shows that the population variance is equal and the t-value is considered to test for the null hypothesis. The results showed that the two-tailed significance level is 0.009, hence the null hypothesis is rejected. This indicates that the mean difference between the
Superpave-designed mixes and the Marshall-designed mixes is significant. 3.3. Modified Lottman test The moisture susceptibility test was conducted on all mixtures at the OBC for each individual mix. All specimens tested were produced to have an air voids content in the range of 7 ± 0.5%. The trend shows that the TSR of all specimens decreased from the unconditioned to conditioned specimens, indicating deterioration in the mixtures, affecting the strength of the HMA mixes. The effects of the unconditioned and conditioned response from AASHTO T283 test were assessed using the statistical t-test. The null hypothesis for this analysis is that the mean difference in the mean
Fig. 7. Resilient modulus of QS HMA mixes.
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Fig. 8. Resilient modulus of QJ HMA mixes.
Table 5 Moisture susceptibility test results for Superpave and PWD mixes. Mix Type
ITS (kPa) Dry
TSR (%) Conditioned
ITS (kPa) Dry
Superpave mixtures
TSR (%) Conditioned
Marshall mixtures
Quarry QS
12.5-B1 12.5-B2 9.5-B1 9.5-B2
625.7 670.6 702.2 640.0
514.1 635.1 616.0 633.2
82.2 94.7 87.7 98.9
461.4 464.5 543.9 516.2
460.5 452.0 535.8 498.4
99.8 97.3 98.5 96.6
Quarry QJ
12.5-B1 12.5-B2 9.5-B1 9.5-B2
564.1 630.1 – –
286.5 380.8 – –
50.8 60.4 – –
522.1 509.6 538.4 566.2
400.7 459.3 421.8 494.8
77.9 90.1 78.3 87.4
strength for both unconditioned and conditioned data is equal. The results of the analyses show that the p-values for Marshall and Superpave mixtures are 0.003 and 0.031 respectively, which is less than 0.05. Hence, the mean difference between the unconditioned and conditioned specimens is significant, therefore the null hypothesis is rejected. This also indicates that moisture conditioning has a significant effect on reducing the tensile strength of the mixtures. It should also be noted that a higher TSR value does not mean that the mix is less susceptible to moisture damage
and vice versa. The ITS test is an indicator of the tensile strength of HMA mixes. Table 5 summarises the tensile strength and tensile TSR of all QS and QJ HMA mixtures. The TSR result is an indication that the HMA mixture is susceptible to moisture damage. In this study, QS-Superpave and QS-Marshall mixtures met the required minimum 80% tensile strength ratio (TSR) value specified in AASHTO T283. Although TSR values are generally higher for QS-Marshall mixes compared to QS-Superpave mixes, this does not mean that QS-Marshall mixes are less
Fig. 9. Specimen after moisture susceptibility test.
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Minimum
TSR (%)
100 80 60 40 20 0 12.5-B1
12.5-B2
9.5-B1
9.5-B2
Mix Type QJ-SPave
QJ-PWD
QS-SPave
QS-PWD
Fig. 10. TSR limit for PWD and Superpave mixes.
susceptible to moisture damage. The indirect tensile strength test showed that QS-Superpave mixtures exhibit higher tensile strength values than QS-Marshall mixtures. For QJ mixes, no results are available for 9.5-QJ mixes because they do not meet the Superpave mixture design criteria and are therefore not included in any performance test. Except for the 12.5-QJ-B2-Marshall and 9.5-QJ-B2-Marshall mixes, all other QJ mixes did not meet the TSR minimum requirement of 80%. This obviously shows that QJ-Superpave mixtures and QJ-Marshall-B1 type mixtures are more susceptible to moisture damage. Although no thorough investigation was conducted to analyse the interface within the mixtures, this phenomenon is related to the properties of the aggregates. Since QJ aggregate is weaker compared to QS aggregate, some particles could have been crushed during compaction. The fractured surface without any binder coating is exposed to water and moisture damage occurs gradually within the HMA mix, as shown in Fig. 9. A graphical presentation showing the TSR limit for Marshall and Superpave mixtures is shown in Fig. 10. From this test, it can be summarised that binder type affects the strength of the mix. Almost all of the HMA mixes using B2 binder type passed the minimum TSR limit except for 12.5-B2-QS mix. This indicates that binder B2, which is stiffer, improves the quality of HMA mixes. The tensile strength values are also higher compared to B1-type mixes. The results also showed that good quality aggregates are also important to mitigate moisture damage in HMA mixes. Fig. 11 shows a strong correlation between ITS dry and wet strength. It appears that the data is somewhat scattered and the regression line diverges slightly away from the line of equality as strength increases. The effect of the unconditioned and conditioned response from the AASHTO T283 test was assessed using the statistical t-test. The null hypothesis for this analysis was that the mean difference in the mean strength for both unconditioned and conditioned data was equal. The results of the analyses show that the p-values for PWD and Superpave mixtures are 0.023 and 0.038 respectively, which is less than a = 0.05. Hence, the mean difference between unconditioned and conditioned specimens is significant; therefore the null hypothesis is rejected. This also indicates that moisture conditioning has a significant effect in reducing the tensile strength of mixtures.
Fig. 11. Dry strength versus wet strength (pooled data).
Master Curve QS Mix (Before & After Conditioning) 8000 12.5-B1-SPave-Dry 12.5-B1-SPave-Wet
7000
12.5-B2-SPave-Dry 12.5-B2-SPave-Wet
6000
9.5-B1-SPave-Dry 9.5-B1-SPave-Wet
5000
9.5-B2-SPave-Dry 9.5-B2-SPave-Wet
4000
12.5-B1-PWD-Dry 12.5-B1-PWD-Wet
3000
12.5-B2-PWD-Dry 12.5-B2-PWD-Wet
2000
9.5-B1-PWD-Dry 9.5-B1-PWD-Wet
1000
9.5-B2-PWD-Dry 9.5-B2-PWD-Wet
0 0.01
0.1
1
Reduce Frequency Fig. 12. SPT dynamic modulus before and after conditioning QS mixes.
10
E* (MPa)
120
Tensile Strength Ratio of QS and QJ Mix PWD vs Superpave Mix
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J. Ahmad et al. / Construction and Building Materials 50 (2014) 567–576
Master Curve QJ Mix (Before & After Conditioning) 6000 12.5-B1-SPave-Dry
5000
12.5-B1-SPave-Wet 12.5-B2-SPave-Wet
4000
12.5-B1-PWD-Dry 12.5-B1-PWD-Wet 12.5-B2-PWD-Dry
3000
12.5-B1-PWD-Wet
E* (MPa)
12.5-B2-SPave-Dry
9.5-B1-PWD-Dry
2000
9.5-B1-PWD-Wet 9.5-B2-PWD-Dry 9.5-B2-PWD-Wet
1000
0 0.01
0.1
1
10
Reduce Frequency Fig. 13. SPT dynamic modulus before and after conditioning QJ Mixes.
for both PWD and Superpave. The null hypothesis was rejected because the mean difference between the unconditioned and conditioned specimens is significant. This also indicates that moisture conditioning has a significant effect in reducing the stiffness of the HMA mixtures. The retained dynamic modulus stiffness ratio, ESR and TSR values obtained for all mixtures are given in Table 4. The ESR were calculated from the ratio of dynamic modulus, E*, values before and after conditioning. Since the tests were conducted at six different frequencies, the ESR results for each mix type were averaged. The ESR of the conditioned dynamic modulus to that of the unconditioned dynamic modulus value is given in the following equation:
140 120 100
R2 = 0.70
TSR
80 60 40
ESR ¼
20 0 0
20
40
60
80
100
120
140
ESR Fig. 14. TSR versus ESR.
3.4. SPT dynamic modulus test A decrease in the dynamic modulus values were evident for conditioned specimens compared to unconditioned specimen. This is an indication of deterioration in the asphalt-aggregate interaction due to moisture infiltrating the specimen. The master curves plotted for conditioned and unconditioned QS and QJ mixes for all mix design types are shown in Figs. 12 and 13. With regards to the mix design method, the results show that Superpave-designed mixtures have higher dynamic modulus values at all temperatures and frequency conditions compared to PWD Marshalldesigned mixtures of the same mix group. It was also noted that higher dynamic modulus values are obvious for B2 binder-type mixtures compared to mixtures utilising binder type B1, and QS mixtures exhibited higher dynamic modulus values compared to QJ mixtures. A t-test statistical analysis was also performed to determine the effectiveness of the SPT dynamic modulus test in differentiating between the conditioned and unconditioned response of the mixtures. The results of the analyses show that the p-values = 0.00
Ewet Edry
ð7Þ
where ESR is the E* ratio, Edry is the average dynamic modulus of the unconditioned subset and Ewet is the average dynamic modulus of the conditioned subset. The TSR and ESR results were plotted and the results from the two test methods and the trend agree with a study conducted using the SPT dynamic modulus to evaluate moisture damage in HMA mixes but with additional freeze–thaw conditioning [19]. The line of linear regression shows a rather good relationship with the coefficient of determination, R2, value of 0.70 (Fig. 14). This indicates that the dynamic modulus test can be used to assess the moisture susceptibility of HMA mixtures. 4. Conclusions This research was conducted to assess the moisture susceptibility of asphaltic mixtures using indirect tensile strength and dynamic modulus tests. The results indicate that dynamic modulus tests using SPT but without the ECS system can be used to evaluate the moisture susceptibility of asphaltic mixtures. Additionally, the following conclusions can be drawn: The SPT dynamic modulus test can be used to assess the moisture susceptibility of asphaltic mixtures based on the retained dynamic modulus stiffness ratio (ESR). The correlation from the scatter plot graph shows a good relationship between the TSR and ESR of the asphaltic mixtures with an R2 value of 0.70.
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Asphalt binder PEN 60–70 (B2) had higher dynamic modulus values compared to HMA mixtures using PEN 80–100 (B1) binder. Superpave-designed mixtures show higher ITS values compared to Malaysian PWD Marshall-designed mixtures. Superpave-designed mixtures require less asphalt binder compared to Marshall-designed mixtures. The resilient modulus values for Superpave mixtures are higher than Marshall mixtures, especially for fine gradation mixes using PEN 60/70 asphalt binder type. Superpave mixtures are less susceptible to permanent deformation (rutting) compared to Marshall mixtures from the wheel tracking test.
Acknowledgments The authors would like to acknowledge the Ministry of Science, Technology and Innovations (MOSTI), Malaysia for funding this research study under the eScience grant. References [1] Office of Engineering and Highway Operations R&D, FHWA-RD-90-019 Road Engineering Association of Asia and Australasia, ‘‘Statistical Profile of REAAA Member Countries’’ REAAA News, p. 7, PP2372/12/2009(022739). Report 2009. [2] Malaysian Public Works Department. Standard specification for road works: Section 4 – flexible pavement JKR/SPJ/2008-S4, Kuala Lumpur; 2008. [3] Wang JN, Kennedy TW, McGennis RB. Volumetric and mechanical performance properties of Superpave mixtures. J Mater Civ Eng 2000;12:238–44. [4] Asi IM. Performance evaluation of Superpave and Marshall asphalt mix designs to suite Jordan climatic and traffic conditions. Constr Build Mater 2007;21:1732–40. [5] Swami BL, Mehta YA, Bose S. A comparison of the Marshall and Superpave design procedure for materials sourced in India. Int J Pavement Eng 2004;5:163–73. [6] Khan KM, Kamal MA. Impact of Superpave mix design method on rutting behaviour of flexible pavement in Pakistan. Arab J Sci Eng 2008;33:379–90. [7] Ahmed NG, Ismail NM. Comparative evaluation for mix design of Marshall and Superpave methods. J Eng Dev 2009;13:1–20. [8] NCHRP 589. Improved conditioning and testing procedures for HMA moisture susceptibility. National Cooperative Highway Research Program; 2007.
[9] Johnson DL. Debonding of water saturated asphalt concrete caused by thermally induced pore pressure. MSc Thesis. University of Idaho; 1969. [10] Schmidt RJ, Graf PE. The effect of water on the resilient modulus of asphalt treated mixes. Proc Assoc Asphalt Paving Technol 1972;41:118–62. [11] Jiminez RA. Testing for debonding of asphalt from aggregates. Transport Res Rec 1974;515:1–17. [12] Lottman RP. Predicting moisture-induced damage to asphaltic concrete. NCHRP Report No. 192. Washington, DC: Transportation Research Board; 1995. [13] Tunnicliff D, Root R. Performance of anti-stripping additives in asphaltic concrete mixtures. NCHRP Report No. 274, Washington DC; 1984. [14] Ensley EK, Petersen JC, Robertson RE. Asphalt aggregate bonding energy measurements by microcalorimetric methods. Thermochimica Acta 1984;77:95–107. [15] Terrel RL, Al-Swailmi S. Water sensitivity of asphalt aggregate mixes test selection SHRP-A-403, Washington DC; 1994. [16] Aschenbrener T. Evaluation of Hamburg wheel-tracking device to predict moisture damage in hot mix asphalt. Transport Res Rec 1995:193–201. [17] Aschenbrener T, McGennis RB, Terrel RL. Comparison of several moisture susceptibility tests to pavements of known field performance. J Assoc Asphalt Paving Technol 1996;64:163–208. [18] Solaimanian M, Fedor D, Bonaquist R, Soltani A, Tandon V. Simple performance test for moisture damage prediction in asphalt concrete. J Assoc Asphalt Paving Technol 2006;75:316–46. [19] Nadkarni AA, Kaloush KE, Zeiada WA. Using dynamic modulus test for moisture susceptibility evaluation of asphalt mixtures. Trans Res Rec: J Trans Res Board 2009;2127:29–35. [20] Buchanan MS, Vernon MM. Laboratory accelerated stripping simulator for hot mix asphalt. Report No. FHWA/MSDOT-RD-04-167. Mississippi State University; 2005. [21] Witczak MW, Bonaquist R, Van Quintus H, Kaloush K. Specific geometry and aggregate size laboratory test study. NCHRP 9-19, Task C, Team Report SLS3. Tempe, AZ: Arizona State University; 1999. [22] American Association of State Highway and Transportation Officials (AASHTO). Standard method of test for resistance of compacted asphalt mixtures to moisture-induced damage T283. Standard Specifications for Transportation Materials and Methods of Sampling and Testing, American Association of State Highway and Transportation Officials, Washington DC; 2002. [23] Witczak MW, Kaloush K, Pellinen T, El-Basyouny M, Von Quintus H. NCHRP 465: simple performance test for Superpave mix design. Washington, DC: Transportation Research Board, National Highway Research Council; 2002. [24] Al-Swailmi S, Terrel RL. Evaluation of water damage of asphalt concrete mixtures using the environmental conditioning system (ECS). J Assoc Asphalt Paving Technol 1992;61:405–45. [25] Faustino RP, Valencia NR, O’Connell MJ, Ford W. Making effective use of volcanic ash in road-building in the Philippines. Proc Eastern Asia Soc Transport Stud 2005;5:868–76.
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Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Investigation into hot-mix asphalt moisture-induced damage under tropical climatic conditions Juraidah Ahmad a, Nur Izzi Md. Yusoff b,⇑, Mohd Rosli Hainin c, Mohd Yusof Abd Rahman a, Mustaque Hossain d a
Institute for Infrastructure Engineering and Sustainable Management (IIESM), Faculty of Civil Engineering, Universiti Teknologi MARA, Selangor, Malaysia Dept. of Civil & Structural Engineering, Universiti Kebangsaan Malaysia, Selangor, Malaysia Faculty of Civil Engineering & Construction Research Alliance, Universiti Teknologi Malaysia, Johor, Malaysia d Dept. of Civil Engineering, Kansas State University, 2124 Fiedler Hall, Manhattan, KS 66506-5000, United States b c
h i g h l i g h t s We investigate moisture-induced damage of HMA under tropical climatic conditions. The Modified Lottman and SPT dynamic modulus tests were used to assess moisture susceptibility of HMA. Superpave mixes show better resistance to rutting compared to the Marshall mixes. SPT dynamic modulus test is recommended for Superpave mixture characterisation in tropical climatic countries.
a r t i c l e
i n f o
Article history: Received 19 July 2013 Received in revised form 30 September 2013 Accepted 4 October 2013 Available online 27 October 2013 Keywords: Marshall mix design Superpave mix design Simple Performance Test Moisture-induce damage Tensile strength ratio
a b s t r a c t A major concern for highway industries in tropical climatic countries is the excessive moisture-induced damage to hot-mix asphalt (HMA) pavements as a result of frequent passes by heavy axle loads. Therefore, in this study, two different approaches, the Superpave and Marshall mix design methods, were used to design HMA mixes and a comparison was made to identify how susceptible these mixtures are to moisture damage. The Modified Lottman test and Simple Performance Test (SPT) were performed on unconditioned and conditioned specimens tailored to suit tropical climatic conditions, omitting freeze and thaw. The Modified Lottman test showed that the tensile strength values of Superpave-designed mixtures are higher than Marshall-designed mixtures. The tensile strength ratio (TSR) values decreased from unconditioned to conditioned specimens, suggesting that there is damage to the mixtures. The results also show good agreement between the TSR and ESR in the two tests, with a coefficient of determination value of 0.78. This relationship indicates that the SPT dynamic modulus test was effective and suitable to evaluate the lab-measured moisture susceptibility of HMA mixes. Since the dynamic modulus test provides a full characterisation of the mix over a broad range of temperatures and loading frequencies, this test is highly recommended for Superpave mixture characterisation in tropical climatic conditions. Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction The tremendous development in the national infrastructure network in Malaysia over the last decade has led to an increase in road construction. Asphaltic road dominates the overall surfacing types at 87,626 km, and there are only 343 km of concrete roads. The other 3651 km are earth or gravel roads. Federal roads stretch over 16,509 km, while state roads cover 104,112 km [1]. The conventional Marshall design method for hot-mix asphalt (HMA) mixes has been used for decades by the Malaysian Public ⇑ Corresponding author. Tel.: +60 3 8921 6447; fax: +60 3 8921 6147. E-mail addresses: [email protected] (J. Ahmad), [email protected] (N.I.M. Yusoff). 0950-0618/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.conbuildmat.2013.10.017
Works Department (PWD) to construct pavements, following the JKR/SPJ/2008 standard specification [2]. Although these pavements are still in service, a large amount of money is allocated for maintenance work annually due to pavement distress, which sometimes occurs prematurely due to increasing traffic loads and wet tropical climatic conditions. With the successful implementation of the Superpave method in the USA, it is very timely for the Malaysian PWD to initiate a paradigm shift to adopt a better mix design system for HMA pavements that suit tropical climatic conditions. Recently, a number of studies have been conducted outside the USA to evaluate the feasibility and performance of Superpave-designed mixtures. For instance, a study was conducted in Taiwan to compare the volumetric and mechanical performance properties of Superpave mixtures and typical Taiwan mixtures (TTM) using
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the Marshall method [3]. It was found that the binder content of the Superpave-designed mixtures is lower than TTM Marshall-designed mix, and TTM mixtures exhibit low densification values. In Jordan, a research study proved the superiority of Superpave mixes over Marshall mixes [4]. A study in India showed that the Superpave gyratory compactor (SGC) is capable of achieving a lower air void content than can be achieved by the mechanical Marshall Hammer compactor. This study also found that Superpave mixes have a lower asphalt binder content than Marshall mixes [5]. Khan and Kamal [6] found that Superpave mixtures exhibit better creep resistance compared to Marshall mixtures in flexible pavement in Pakistan. A study was conducted based on the Iraq road specification and the results indicate that Superpave mixes have a lower asphalt content than Marshall mixes. As a result, Superpave mixes are better from an economic point of view than Marshall mixes [7]. However, one of the major concerns related to HMA deformation is moisture-induced damage. Moisture infiltrating a wearing course may cause detachment of the asphalt film from the aggregate surface and weaken the binder adhesion through an emulsification process under heavy traffic and elevated temperature conditions. Hence, extensive laboratory tests to identify moisture damage have been developed over the years. Initially, in the late 1940s, the immersion compression test on compacted mixtures was developed. The National Cooperation Highway Research Project (NCHRP) Report 589 [8] stated that the significant impact of climate and traffic on moisture damage was discovered in the 1960s through the research work of Johnson [9], Schmidt and Graf [10], Jiminez [11] and Lottman [12]. In 1981, a test involving repeated water pressure to simulate the behaviour of saturated HMA was developed by Jiminez and further modified by Tunnicliff and Root [13]. This resulted in a quantitative method of laboratory testing that is currently widely accepted, known as the Modified Lottman test (AASHTO T283 or ASTM D4867). Currently, the AASHTO T283 is incorporated in the Superpave mix design system as the principal moisture susceptibility test method. Other fundamental tests to predict moisture damage are reported in the work of Ensley et al. [14] and Terrel and Al-Swailmi [15], which resulted in the use of the Environmental Conditioning System (ECS). In the 1990s, the Hamburg Wheel Tracking Device (HWTD) was introduced and gained popularity in predicting moisture damage in HMA mixes submerged under water [16,17]. However, the mix’s success was reported by highway agencies in the United States, resulting in continued research to refine the procedures and to investigate other alternatives. Under the NCHRP Project 9-34, a new test was proposed, believed to better simulate environment and traffic factors to evaluate the water susceptibility of HMA mixtures. Solaimanian [18] evaluates moisture damage by combining the ECS and Simple Performance Test (SPT). However, the ECS system is costly and complex to use [19]. In a recent study, the results show that the SPT without the ECS conditioning system is able to correlate with the AASHTO T283 test [20]. In Malaysia, no specific test has been developed as a standard specification for road works by the Malaysian PWD to determine HMA moisture damage. In an effort to identify the moisture damage susceptibility of Malaysian mixes, both the Modified Lottman (AASHTO T283) and SPT dynamic modulus tests without the ECS conditioning system were conducted to evaluate how susceptible these HMA mixtures are to moisture damage. This study does not consider low temperature environments because the temperature in Malaysia rarely falls below 30 °C in daylight hours and usually lies within the range of 35–45 °C [21]. Rutting and resilient modulus tests were conducted using a wheel tracking device and the Indirect Tensile Modulus test to evaluate and compare the mix properties of Superpave- and Marshall method-designed HMA mixes.
2. Experimental design 2.1. Materials selection Two granite aggregate sources were selected in this study, representing the central and southern parts of Peninsular Malaysia. Quarry Selangor (QS) Granite quarry is located in the central part in the vicinity of Kuala Lumpur, and another quarry, Quarry Johor (QJ), is located in the southern part of Peninsular Malaysia. These two quarries supply aggregates for road construction in the central and southern regions of Peninsular Malaysia. Aggregate properties were evaluated for compliance with both mix design systems. According to PWD specifications, only granite aggregates are permissible for use in the asphalt wearing course. Two different gradations with different nominal maximum aggregate size (NMAS) were selected, as shown in Figs. 1 and 2. To enable a comparison of the volumetric properties and rutting performance between the mixes, the gradations for all mixtures were purposely selected to fall within the upper and lower limits, complying with both Superpave and PWD Marshall grading requirements. A total of eight mixes were designed, of which four were Superpave-designed mixes and the rest were Marshall mixes. Since the climatic conditions in Malaysia are fairly consistent throughout the country, the supply of Performance Graded (PG) asphalt binder in this region is based on higher temperatures. The asphalt binders of Performance Grade (PG) 64 and PG 70 used are equivalent to Penetration Grade (PEN) 80/100 (B1) and PEN 60/70 (B2) respectively. The properties of both binders, which follow the requirements of PWD specifications and road works, are summarised in Table 1. Table 2 shows the test design matrix for both the PWD Marshall and Superpave mixtures used in this study. 2.2. Mix design The standard Marshall mix design procedure from the Malaysian PWD road works specifications was employed to design the HMA mixes. Fifteen specimens for each mix were prepared with blended mineral aggregates at an increment of 0.5% binder from 4% to 7% by weight of mixture. The mixing temperature was 165 and 150 °C for binder types B1 and B2 respectively. No aging is required for the Marshall mix design method prior to compaction. The optimum binder content (OBC) of these mixtures was estimated, corresponding to 4% design air voids, bulk density, voids filled with asphalt (VFA) and flow values. The OBC of QS and QJ mixtures ranged from 5.6% to 6.2% and 5.4% to 6.0% respectively. The volumetric properties of all PWD Marshall mixes conformed to PWD criteria, as tabulated in Table 3. Superpave-designed mixtures, when blended at OBC, should yield acceptable volumetric properties at 4% air voids based on the established Superpave criteria at the design number of gyrations. The mixing temperature of B1 and B2 binder types was 150 and 165 °C respectively. Short-term aging is required for Superpave mixtures for approximately two hours prior to compacting using the Superpave gyratory compactor (SGC). The OBC for Superpave-designed mixtures was established from the volumetric properties which include voids in mineral aggregates (VMA), VFA, air voids and dust proportion (DP). The volumetric properties of the design mixtures corresponding to OBC for Superpave-designed mixtures are shown in Table 4. The OBC for QS ranged from 5.1% to 5.7% and 5.5% to 6.4% for QJ mixes. The results show that QS and QJ mixtures comply with all Superpave and PWD Marshall criteria requirements except for the 9.5-QJ B1 and B2 Superpave mixes, which do not meet the VFA criteria. Further investigations were conducted to determine how susceptible these mixtures are to moisture damage. 2.3. Wheel tracking test The dry wheel tracking test was conducted using a Wessex wheel tracking device for which a mold was fabricated to hold the SGC rut specimen. The height of the SGC rut mold follows exactly the original slab mold of the Wessex wheel tracking device. This is to avoid any inaccuracy during the rutting test. Approximately 3700 g of Superpave or Marshall mix was compacted to 7 ± 0.5% air voids to make a cylindrical specimen with a diameter of 150 mm and final height of 65 mm. This was accomplished by putting a given amount of mixture in the SGC mold and compacting it to the specified height. The specimens were left to cool at room temperature for 24 h after compaction. The air void content was also determined before conducting the test to meet the test requirements. The specimens were then trimmed and paired to fit in the wheel tracking mold. Care was taken to make sure that the specimens fitted into the mold exactly. The rut test was conducted at 60 °C since the initial tests at 40 °C showed negligible rut depths. Prior to testing, the specimens were conditioned for at least four hours at test temperature. The specimens were subjected to simulated traffic with a simple harmonic motion by applying 525 N load for one hour. 2.4. Indirect tensile resilient modulus test The specimens were fabricated at OBC and the resilient modulus test was conducted to evaluate rutting at 40 °C using an IPC UTM-5 machine, according to ASTM 4123. These specimens were subjected to a cyclic load with a sinusoidal wave
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100 90
PWD Marshall Upper Envelope
Percent Passing
80 70 60 50
PWD Marshall Lower Envelope
Superpave Upper Limit
40 30
Superpave Lower Limit
20 10
25.00
19.00
12.50
9.50
4.75
2.36
1.18
0.60
0.075 0.15 0.30
0
Sieve Size (mm) Fig. 1. NMAS 12.5 mm gradation.
100 90
PWD Marshall Upper Envelope
Percent Passing
80 70 60
Superpave Upper Limit
PWD Marshall Lower Envelope
50 40
Superpave Lower Limit
30 20 10
12.50
9.50
4.75
2.36
1.18
0.60
0.30
0.075 0.15
0
Sieve Size (mm) Fig. 2. NMAS 9.5 mm gradation.
Type
PEN 80-100 (B1)
PEN 60-70 (B2)
Criteria
shape, and the test sequence consisted of five conditioning pulses followed by five loading pulses when data acquisition took place. The load was applied for a period of 0.1 s with a rest period of 0.9 s. The horizontal and vertical deformations were measured by means of extensometers and LVDTs respectively.
Penetration at 25 °C (0.1 mm) Softening point (°C) R & B Rotational viscosity (original) Rotational viscosity (RTFO)
84
68
–
2.5. Modified Lottman test
43 0.35 Pa s
42 0.45 Pa s
0.6 Pa s
0.7 Pa s
48–56 3 Pa s Max 3 Pa s Max
For the dynamic modulus test, all specimens were prepared at OBC and compacted using the SGC with initial diameter of 150 mm and height of 165 mm. The specimens were then cored to a diameter of 100 mm and both ends were sawed to a height of 150 mm to achieve the right dimensions for the dynamic modulus test, as shown in Fig. 3. This ‘‘ideal’’ geometry was derived based on specimen size and aggregate size effect studies conducted by previous researchers [22]. Before
Table 1 Binder properties.
Table 2 Test design matrix for Superpave and PWD Marshall mixes. No.
Factor
Details
1
Aggregate gradation
Superpave and PWD gradation limits
2 3 4
Mix design method Aggregate source Binder type (PWD specification)
Superpave and PWD Marshall mix design method Quarry Selangor (QS) and Quarry Johor (QJ) Penetration Grade 80/100 (denoted as B1) Penetration Grade 60/70 (denoted as B2)
12.5 mm NMAS 9.5 mm NMAS
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J. Ahmad et al. / Construction and Building Materials 50 (2014) 567–576
Table 3 Volumetric properties of PWD Marshall mixtures. Parameter
12.5-QS-B1
12.5-QS-B2
9.5-QS-B1
9.5-QS-B2
PWD criterion
Quarry QS OBC (%) Stability (kN) Flow (mm) VMA (%) VFA (%)
5.6 10.2 3.5 16.2 75
5.9 10.1 3.5 16.8 75
6.1 10.2 3.2 17.2 75
6.2 11.0 3.3 17.5 77
– >8 kN 2–4 mm – 70–80
Quarry QJ OBC (%) Stability (kN) Flow (mm) VMA (%) VFA (%)
5.4 13.2 2.8 14.9 79
5.4 13.1 3.5 14.8 80
6.0 9.7 3.2 16.4 75.8
5.9 12.3 3.2 15.9 80
– >8 kN 2–4 mm – 70–80
Table 4 Volumetric properties of Superpave mixtures. Mix design properties
12.5-QS-B1
12.5-QS-B2
9.5-QS-B1
9.5-QS-B2
Criterion
Quarry QS OBC (%) Air voids (%) VMA (%) VFA (%) Dust proportion
5.1 4.0 14.9 73.1 0.8
5.3 4.0 15.8 74.4 0.8
5.4 4.0 15.7 74.6 0.8
5.7 4.0 16.5 75.7 0.7
– – 14.0 min* 65–75** 0.6–1.2
Quarry QJ OBC (%) Air voids (%) VMA (%) VFA (%) Dust proportion
5.5 4.0 16.0 74.9 0.8
5.5 4.0 16.0 75.0 0.8
6.4 4.0 17.6 76.5 0.7
6.3 4.0 17.4 77 0.7
– – 14.0* min 65–75** 0.6–1.2
Note: B1 – asphalt binder Penetration Grade 80/100; B2 – asphalt binder Penetration Grade 60/70. For 9.5 mm (3/800 ) nominal maximum size mixtures, the specified minimum VMA is 15.0. For design traffic levels 3–30 million ESALs, (9.5 mm) 3/800 nominal maximum size mixtures, the specified VFA range shall be 65–76%.
*
**
conditioning, the displacement transducers were glued to gauge points on the cylindrical specimens to measure axial deformation, as shown in Fig. 4. For the Modified Lottman test, PWD Marshall and Superpave specimens were prepared according to individual standard mix design procedures. For moisture-induced damage, the air voids of all test specimens were within 0.5% of the required air void content of 7.0%. The specimens for each mixture type were divided into wet and dry subsets [23]. The dry or control subsets were conditioned at 25 °C in a plastic bag submerged in a water bath for two hours before testing. The wet subset was subjected to vacuum saturation; it took approximately four to five minutes to achieve between 70% and 80% saturation levels. The saturated specimens were then placed in a water bath at 60 °C for 24 h and then at 25 °C for another two hours prior to testing. The degree of saturation was measured by weight from the equation below.
%S ¼
100ðW SSD W D Þ Va
ð1Þ
Where %S is the degree of saturation, WSSD is the saturated surface dry weight of the specimen after vacuum saturation, WD is the initial dry specimen weight and Va is the volume of air voids in the specimen. The indirect tensile strength (ITS) test is applied on dry and wet specimens and specifies a tensile strength ratio (TSR) of at least 0.8. The TSR can be calculated as follows:
Tensile Strength Ratio ¼
Swet Sdry
ð2Þ
where Swet and Sdry are the conditioned and unconditioned tensile strengths respectively. 2.6. Simple Performance Test (SPT) The SPT dynamic modulus test procedure follows the test protocols described in NCHRP Project 9-19, Superpave Support and Performance Models Management [24]. The conditioning procedures are similar to the Modified Lottman test specimens. However, extra care should be taken to avoid detachment of the glued LVDT gauge holders from the specimen. The dynamic modulus of conditioned (Ewet) and unconditioned (Edry) values were obtained from the tests conducted at six different frequencies by applying a sinusoidal compressive load on the specimen in a cyclic manner. The test was conducted at 25 °C on each specimen, with loading frequen-
Fig. 3. Cored and trimmed SPT specimen. cies of 25, 10, 5, 1, 0.5 and 0.1 Hz. The dynamic stress applied is 100 kPa and it is important to attain axial strains between 75 and 150 microstrains throughout the testing process. Prior to testing, the specimens must be placed in the testing chamber until the effective temperature and contact stress are achieved. It is also important to ensure that the specimens are placed in the centre under the loading platens. A continuous uniaxial sinusoidal compressive stress at selected test frequency is then applied to the unconfined cylindrical test specimen. The linear viscoelastic stress–strain relationship of the HMA specimen is defined as the complex modulus (E). The absolute value of the complex modulus |E|, also known as the dynamic modulus, is defined as the ratio of maximum (peak) dynamic stress (r0) to peak recoverable axial strain (e0) [24]. The angle by which the peak recoverable strain lags behind the peak dynamic stress is referred to as the phase angle, /. The phase angle is an indicator of the viscous and elastic properties of the material being evaluated. Mathematically, the dynamic modulus and phase angle equation is expressed as:
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12.5-B1
100mm
12.5-B2
7
120 o
Transducers located apart around circumference of
9.5-B1
9.5-B2
6.4
6.5
70mm
150mm
120 o
Rut Depth (mm)
6 5
4.3
4.1
4 3 2
3
2.7 1.6
0.8
1 0 Fig. 4. Schematic diagram of LVDT dimensions of specimen.
jE j ¼
ð3Þ
ti tp
ð4Þ
where r0 is the maximum peak dynamic stress, e0 is the peak recoverable strain, ti is the average lag time between a cycle of stress and strain and tp is the average time for a stress cycle. In order to develop master curves for each frequency and test temperature, a sigmoidal function was used to fit the time-dependent dynamic modulus from the equation below.
log ðE Þ ¼ d þ
a
ð5Þ
1 þ ebþcðlog tr Þ
where E is the dynamic modulus, d is the minimum value of E , (d + a) is the maximum value of E*, b and c are parameters that describe the shape of sigmoidal function and tr is the time of loading at the reference temperature. Time of loading, tr, can be estimated using the following equation:
log tr ¼ log
QS-Mar sh all
Fig. 5. Comparison between Superpave and Marshall mixes.
r0 e0
/ ¼ 360
QS-Su p er pav e
t aT
ð6Þ
where t is the time of loading at a given temperature and aT is the temperature shift factor. Numerical optimisation is used to solve the variables d, a, b and c as well as the shift factors aT using the Solver function in Microsoft Excel.
3. Results and discussion 3.1. Rutting resistance Fig. 5 shows that the rutting values of the Superpave mixtures varies from 0.8 mm to 3.0 mm, compared to the Marshall mixtures with high rutting values ranging from 4.1 mm to 6.5 mm. This obviously indicates the higher resistance of Superpave mixtures compared to Marshall mixtures. In addition, the results also show that NMAS 9.5 mm grading for a particular mixture has lower rutting values compared to NMAS 12.5 mm mixtures. Asphalt binder type also contributed to the rutting resistance. In this study, HMA with asphalt binder type B2 exhibited better rutting resistance than asphalt binder type B1. In Fig. 6, the wheel tracking rates for both Marshall and Superpave mixes were compared. According to Faustino et al. [25], two parameters are considered in a wheel tracking test to ensure that the performance of materials is correctly assessed. The wheel tracking rate is measured as the primary measure of the resistance to permanent deformation, and the maximum rut depth is a secondary measure. This is important, because different mixtures may deform differently, and some mixtures may rut excessively at the early stage of the rutting test compared to the latter part of the test. In this study, the results show that different types of gradation do not have an adverse effect on the wheel tracking rate; however, different types of binder and mix design method show variability in the results of wheel tracking rate. It can be seen that the Superpave mixes have a lower wheel tracking rate compared to Marshall-designed mixes.
An independent t-test analysis was also conducted to compare the superiority of the mix design method used to design the HMA mix statistically. The null hypothesis is that the mean rutting of Superpave-designed HMA mixes and Marshall-designed mixes is equal (H0: lSuperpave = lMarshall). The Levene’s test for equality of variances shows that the population variance is equal and the t-value is considered to test for the null hypothesis. The results show that the p-value is 0.000, less than 0.05, hence the null hypothesis was rejected, indicating that the mean difference between the two different mix design methods is significant. This indicates that Superpave-designed mixtures are less resistant to rutting compared to Marshall-designed mixtures. 3.2. Resilient modulus The resilient modulus is an important variable used to measure pavement response in terms of dynamic stresses corresponding to strains. During testing, both horizontal and vertical deformations were measured from both sides of the specimen, and the resilient modulus was calculated accordingly. This test was analysed to compare and characterise Superpave- and Marshall-designed HMA mixes tested at two temperatures, namely 25 and 40 °C. At 25 °C, the resilient modulus is an indication of the mixture’s resistance to fatigue, whereas the resilient modulus at 40 °C indicates the mixture’s resistance to rutting. The resilient modulus values are higher for QS Superpave-designed mixtures compared to Marshall-designed mixtures when tested at 25 °C. The results in Fig. 7 show that as the pulse repetition period during loading time decreases from 0.1 s to 0.3 s, the resilient modulus values also decrease. From the graph, the 9.5-B2-SP mix is the least susceptible to fatigue with the highest resilient modulus value of 3721 MPa, followed by 12.5-B2-SP, 9.5-B1-SP, 12.5-B1-SP, 12.5-B2- Marshall, 12.5-B1-Marshall, 9.5-B2-Marshall and 9.5-B1-Marshall. As temperature increases, the difference in resilient modulus is more notable, with a decline in stiffness at 40 °C. At the higher temperature, almost all Superpave mixtures showed a higher resilient modulus value compared to Marshall mixtures. The difference in the resilient modulus values at the higher temperature indicates that Superpave mixtures are less susceptible to rutting than Marshall mixtures. At a pulse repetition period of 0.1 s in the resilient modulus test, the results show that the mixture most resistant to rutting is 9.5-B2-SP, with the highest resilient modulus value of 728 MPa, followed by 12.5-B2-SP, 9.5-B1-SP, 12.5-B1-SP, 12.5-B2Marshall, 9.5-B2-Marshall, 9.5-B1-Marshall, and 12.5-B1-Marshall. With regards to the binder types used, mixtures with binder type B2 are stiffer and have the highest resilient modulus values for both Marshall and Superpave mixtures. It was estimated that
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Fig. 6. Wheel tracking rates of mixes.
the average resilient modulus values of Superpave mixtures are 30% higher when tested at 25 °C and approximately 32% higher at 40 °C compared to Marshall mixtures. In general, the resilient modulus results for QJ mixtures are lower compared to QS mixtures at similar test temperatures, as shown in Fig. 8. An independent t-test analysis was also conducted to compare Superpave and Marshall mixtures to evaluate HMA mix stiffness. The null hypothesis is that the stiffness of Superpave-designed HMA mixes and Marshall-designed mixes are the same (Ho: lSuperpave = lMarshall). The Levene’s test for equality of variances shows that the population variance is equal and the t-value is considered to test for the null hypothesis. The results showed that the two-tailed significance level is 0.009, hence the null hypothesis is rejected. This indicates that the mean difference between the
Superpave-designed mixes and the Marshall-designed mixes is significant. 3.3. Modified Lottman test The moisture susceptibility test was conducted on all mixtures at the OBC for each individual mix. All specimens tested were produced to have an air voids content in the range of 7 ± 0.5%. The trend shows that the TSR of all specimens decreased from the unconditioned to conditioned specimens, indicating deterioration in the mixtures, affecting the strength of the HMA mixes. The effects of the unconditioned and conditioned response from AASHTO T283 test were assessed using the statistical t-test. The null hypothesis for this analysis is that the mean difference in the mean
Fig. 7. Resilient modulus of QS HMA mixes.
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Fig. 8. Resilient modulus of QJ HMA mixes.
Table 5 Moisture susceptibility test results for Superpave and PWD mixes. Mix Type
ITS (kPa) Dry
TSR (%) Conditioned
ITS (kPa) Dry
Superpave mixtures
TSR (%) Conditioned
Marshall mixtures
Quarry QS
12.5-B1 12.5-B2 9.5-B1 9.5-B2
625.7 670.6 702.2 640.0
514.1 635.1 616.0 633.2
82.2 94.7 87.7 98.9
461.4 464.5 543.9 516.2
460.5 452.0 535.8 498.4
99.8 97.3 98.5 96.6
Quarry QJ
12.5-B1 12.5-B2 9.5-B1 9.5-B2
564.1 630.1 – –
286.5 380.8 – –
50.8 60.4 – –
522.1 509.6 538.4 566.2
400.7 459.3 421.8 494.8
77.9 90.1 78.3 87.4
strength for both unconditioned and conditioned data is equal. The results of the analyses show that the p-values for Marshall and Superpave mixtures are 0.003 and 0.031 respectively, which is less than 0.05. Hence, the mean difference between the unconditioned and conditioned specimens is significant, therefore the null hypothesis is rejected. This also indicates that moisture conditioning has a significant effect on reducing the tensile strength of the mixtures. It should also be noted that a higher TSR value does not mean that the mix is less susceptible to moisture damage
and vice versa. The ITS test is an indicator of the tensile strength of HMA mixes. Table 5 summarises the tensile strength and tensile TSR of all QS and QJ HMA mixtures. The TSR result is an indication that the HMA mixture is susceptible to moisture damage. In this study, QS-Superpave and QS-Marshall mixtures met the required minimum 80% tensile strength ratio (TSR) value specified in AASHTO T283. Although TSR values are generally higher for QS-Marshall mixes compared to QS-Superpave mixes, this does not mean that QS-Marshall mixes are less
Fig. 9. Specimen after moisture susceptibility test.
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Minimum
TSR (%)
100 80 60 40 20 0 12.5-B1
12.5-B2
9.5-B1
9.5-B2
Mix Type QJ-SPave
QJ-PWD
QS-SPave
QS-PWD
Fig. 10. TSR limit for PWD and Superpave mixes.
susceptible to moisture damage. The indirect tensile strength test showed that QS-Superpave mixtures exhibit higher tensile strength values than QS-Marshall mixtures. For QJ mixes, no results are available for 9.5-QJ mixes because they do not meet the Superpave mixture design criteria and are therefore not included in any performance test. Except for the 12.5-QJ-B2-Marshall and 9.5-QJ-B2-Marshall mixes, all other QJ mixes did not meet the TSR minimum requirement of 80%. This obviously shows that QJ-Superpave mixtures and QJ-Marshall-B1 type mixtures are more susceptible to moisture damage. Although no thorough investigation was conducted to analyse the interface within the mixtures, this phenomenon is related to the properties of the aggregates. Since QJ aggregate is weaker compared to QS aggregate, some particles could have been crushed during compaction. The fractured surface without any binder coating is exposed to water and moisture damage occurs gradually within the HMA mix, as shown in Fig. 9. A graphical presentation showing the TSR limit for Marshall and Superpave mixtures is shown in Fig. 10. From this test, it can be summarised that binder type affects the strength of the mix. Almost all of the HMA mixes using B2 binder type passed the minimum TSR limit except for 12.5-B2-QS mix. This indicates that binder B2, which is stiffer, improves the quality of HMA mixes. The tensile strength values are also higher compared to B1-type mixes. The results also showed that good quality aggregates are also important to mitigate moisture damage in HMA mixes. Fig. 11 shows a strong correlation between ITS dry and wet strength. It appears that the data is somewhat scattered and the regression line diverges slightly away from the line of equality as strength increases. The effect of the unconditioned and conditioned response from the AASHTO T283 test was assessed using the statistical t-test. The null hypothesis for this analysis was that the mean difference in the mean strength for both unconditioned and conditioned data was equal. The results of the analyses show that the p-values for PWD and Superpave mixtures are 0.023 and 0.038 respectively, which is less than a = 0.05. Hence, the mean difference between unconditioned and conditioned specimens is significant; therefore the null hypothesis is rejected. This also indicates that moisture conditioning has a significant effect in reducing the tensile strength of mixtures.
Fig. 11. Dry strength versus wet strength (pooled data).
Master Curve QS Mix (Before & After Conditioning) 8000 12.5-B1-SPave-Dry 12.5-B1-SPave-Wet
7000
12.5-B2-SPave-Dry 12.5-B2-SPave-Wet
6000
9.5-B1-SPave-Dry 9.5-B1-SPave-Wet
5000
9.5-B2-SPave-Dry 9.5-B2-SPave-Wet
4000
12.5-B1-PWD-Dry 12.5-B1-PWD-Wet
3000
12.5-B2-PWD-Dry 12.5-B2-PWD-Wet
2000
9.5-B1-PWD-Dry 9.5-B1-PWD-Wet
1000
9.5-B2-PWD-Dry 9.5-B2-PWD-Wet
0 0.01
0.1
1
Reduce Frequency Fig. 12. SPT dynamic modulus before and after conditioning QS mixes.
10
E* (MPa)
120
Tensile Strength Ratio of QS and QJ Mix PWD vs Superpave Mix
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J. Ahmad et al. / Construction and Building Materials 50 (2014) 567–576
Master Curve QJ Mix (Before & After Conditioning) 6000 12.5-B1-SPave-Dry
5000
12.5-B1-SPave-Wet 12.5-B2-SPave-Wet
4000
12.5-B1-PWD-Dry 12.5-B1-PWD-Wet 12.5-B2-PWD-Dry
3000
12.5-B1-PWD-Wet
E* (MPa)
12.5-B2-SPave-Dry
9.5-B1-PWD-Dry
2000
9.5-B1-PWD-Wet 9.5-B2-PWD-Dry 9.5-B2-PWD-Wet
1000
0 0.01
0.1
1
10
Reduce Frequency Fig. 13. SPT dynamic modulus before and after conditioning QJ Mixes.
for both PWD and Superpave. The null hypothesis was rejected because the mean difference between the unconditioned and conditioned specimens is significant. This also indicates that moisture conditioning has a significant effect in reducing the stiffness of the HMA mixtures. The retained dynamic modulus stiffness ratio, ESR and TSR values obtained for all mixtures are given in Table 4. The ESR were calculated from the ratio of dynamic modulus, E*, values before and after conditioning. Since the tests were conducted at six different frequencies, the ESR results for each mix type were averaged. The ESR of the conditioned dynamic modulus to that of the unconditioned dynamic modulus value is given in the following equation:
140 120 100
R2 = 0.70
TSR
80 60 40
ESR ¼
20 0 0
20
40
60
80
100
120
140
ESR Fig. 14. TSR versus ESR.
3.4. SPT dynamic modulus test A decrease in the dynamic modulus values were evident for conditioned specimens compared to unconditioned specimen. This is an indication of deterioration in the asphalt-aggregate interaction due to moisture infiltrating the specimen. The master curves plotted for conditioned and unconditioned QS and QJ mixes for all mix design types are shown in Figs. 12 and 13. With regards to the mix design method, the results show that Superpave-designed mixtures have higher dynamic modulus values at all temperatures and frequency conditions compared to PWD Marshalldesigned mixtures of the same mix group. It was also noted that higher dynamic modulus values are obvious for B2 binder-type mixtures compared to mixtures utilising binder type B1, and QS mixtures exhibited higher dynamic modulus values compared to QJ mixtures. A t-test statistical analysis was also performed to determine the effectiveness of the SPT dynamic modulus test in differentiating between the conditioned and unconditioned response of the mixtures. The results of the analyses show that the p-values = 0.00
Ewet Edry
ð7Þ
where ESR is the E* ratio, Edry is the average dynamic modulus of the unconditioned subset and Ewet is the average dynamic modulus of the conditioned subset. The TSR and ESR results were plotted and the results from the two test methods and the trend agree with a study conducted using the SPT dynamic modulus to evaluate moisture damage in HMA mixes but with additional freeze–thaw conditioning [19]. The line of linear regression shows a rather good relationship with the coefficient of determination, R2, value of 0.70 (Fig. 14). This indicates that the dynamic modulus test can be used to assess the moisture susceptibility of HMA mixtures. 4. Conclusions This research was conducted to assess the moisture susceptibility of asphaltic mixtures using indirect tensile strength and dynamic modulus tests. The results indicate that dynamic modulus tests using SPT but without the ECS system can be used to evaluate the moisture susceptibility of asphaltic mixtures. Additionally, the following conclusions can be drawn: The SPT dynamic modulus test can be used to assess the moisture susceptibility of asphaltic mixtures based on the retained dynamic modulus stiffness ratio (ESR). The correlation from the scatter plot graph shows a good relationship between the TSR and ESR of the asphaltic mixtures with an R2 value of 0.70.
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Asphalt binder PEN 60–70 (B2) had higher dynamic modulus values compared to HMA mixtures using PEN 80–100 (B1) binder. Superpave-designed mixtures show higher ITS values compared to Malaysian PWD Marshall-designed mixtures. Superpave-designed mixtures require less asphalt binder compared to Marshall-designed mixtures. The resilient modulus values for Superpave mixtures are higher than Marshall mixtures, especially for fine gradation mixes using PEN 60/70 asphalt binder type. Superpave mixtures are less susceptible to permanent deformation (rutting) compared to Marshall mixtures from the wheel tracking test.
Acknowledgments The authors would like to acknowledge the Ministry of Science, Technology and Innovations (MOSTI), Malaysia for funding this research study under the eScience grant. References [1] Office of Engineering and Highway Operations R&D, FHWA-RD-90-019 Road Engineering Association of Asia and Australasia, ‘‘Statistical Profile of REAAA Member Countries’’ REAAA News, p. 7, PP2372/12/2009(022739). Report 2009. [2] Malaysian Public Works Department. Standard specification for road works: Section 4 – flexible pavement JKR/SPJ/2008-S4, Kuala Lumpur; 2008. [3] Wang JN, Kennedy TW, McGennis RB. Volumetric and mechanical performance properties of Superpave mixtures. J Mater Civ Eng 2000;12:238–44. [4] Asi IM. Performance evaluation of Superpave and Marshall asphalt mix designs to suite Jordan climatic and traffic conditions. Constr Build Mater 2007;21:1732–40. [5] Swami BL, Mehta YA, Bose S. A comparison of the Marshall and Superpave design procedure for materials sourced in India. Int J Pavement Eng 2004;5:163–73. [6] Khan KM, Kamal MA. Impact of Superpave mix design method on rutting behaviour of flexible pavement in Pakistan. Arab J Sci Eng 2008;33:379–90. [7] Ahmed NG, Ismail NM. Comparative evaluation for mix design of Marshall and Superpave methods. J Eng Dev 2009;13:1–20. [8] NCHRP 589. Improved conditioning and testing procedures for HMA moisture susceptibility. National Cooperative Highway Research Program; 2007.
[9] Johnson DL. Debonding of water saturated asphalt concrete caused by thermally induced pore pressure. MSc Thesis. University of Idaho; 1969. [10] Schmidt RJ, Graf PE. The effect of water on the resilient modulus of asphalt treated mixes. Proc Assoc Asphalt Paving Technol 1972;41:118–62. [11] Jiminez RA. Testing for debonding of asphalt from aggregates. Transport Res Rec 1974;515:1–17. [12] Lottman RP. Predicting moisture-induced damage to asphaltic concrete. NCHRP Report No. 192. Washington, DC: Transportation Research Board; 1995. [13] Tunnicliff D, Root R. Performance of anti-stripping additives in asphaltic concrete mixtures. NCHRP Report No. 274, Washington DC; 1984. [14] Ensley EK, Petersen JC, Robertson RE. Asphalt aggregate bonding energy measurements by microcalorimetric methods. Thermochimica Acta 1984;77:95–107. [15] Terrel RL, Al-Swailmi S. Water sensitivity of asphalt aggregate mixes test selection SHRP-A-403, Washington DC; 1994. [16] Aschenbrener T. Evaluation of Hamburg wheel-tracking device to predict moisture damage in hot mix asphalt. Transport Res Rec 1995:193–201. [17] Aschenbrener T, McGennis RB, Terrel RL. Comparison of several moisture susceptibility tests to pavements of known field performance. J Assoc Asphalt Paving Technol 1996;64:163–208. [18] Solaimanian M, Fedor D, Bonaquist R, Soltani A, Tandon V. Simple performance test for moisture damage prediction in asphalt concrete. J Assoc Asphalt Paving Technol 2006;75:316–46. [19] Nadkarni AA, Kaloush KE, Zeiada WA. Using dynamic modulus test for moisture susceptibility evaluation of asphalt mixtures. Trans Res Rec: J Trans Res Board 2009;2127:29–35. [20] Buchanan MS, Vernon MM. Laboratory accelerated stripping simulator for hot mix asphalt. Report No. FHWA/MSDOT-RD-04-167. Mississippi State University; 2005. [21] Witczak MW, Bonaquist R, Van Quintus H, Kaloush K. Specific geometry and aggregate size laboratory test study. NCHRP 9-19, Task C, Team Report SLS3. Tempe, AZ: Arizona State University; 1999. [22] American Association of State Highway and Transportation Officials (AASHTO). Standard method of test for resistance of compacted asphalt mixtures to moisture-induced damage T283. Standard Specifications for Transportation Materials and Methods of Sampling and Testing, American Association of State Highway and Transportation Officials, Washington DC; 2002. [23] Witczak MW, Kaloush K, Pellinen T, El-Basyouny M, Von Quintus H. NCHRP 465: simple performance test for Superpave mix design. Washington, DC: Transportation Research Board, National Highway Research Council; 2002. [24] Al-Swailmi S, Terrel RL. Evaluation of water damage of asphalt concrete mixtures using the environmental conditioning system (ECS). J Assoc Asphalt Paving Technol 1992;61:405–45. [25] Faustino RP, Valencia NR, O’Connell MJ, Ford W. Making effective use of volcanic ash in road-building in the Philippines. Proc Eastern Asia Soc Transport Stud 2005;5:868–76.