Development of an asphalt concrete mixture for Asphalt Core Rockfill Dam

Construction and Building Materials 140 (2017) 301–309

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Development of an asphalt concrete mixture for Asphalt Core Rockfill Dam Jung-Woo Seo, Dae-Wook Park ⇑, Tri Ho Minh Le Dept. of Civil Engineering, Kunsan National University, 558 Daehak ro, Kunsan, Jeonbuk 54150, Republic of Korea

h i g h l i g h t s
Asphalt concrete mixtures designed for rockfill dam require higher bitumen content than that for road pavement.
The strength behavior and moisture resistant of test specimens were impacted considerably by filler content.
Confining pressure has a remarkable effect on triaxial compressive strength of asphalt concrete specimens.
A small change in air void content of asphalt concrete mix could results in significant increase in permeability property.

a r t i c l e

i n f o

Article history: Received 28 November 2016 Received in revised form 21 January 2017 Accepted 19 February 2017

Keywords: Asphalt Core Rockfill Dam Hot mix asphalt Triaxial strength Indirect tensile strength Permeability

a b s t r a c t The main objective of this paper is to develop asphalt concrete mixture and conduct performance tests for Asphalt Core Rockfill Dam (ACRD). Three conditions of mineral filler content have been used: 10, 12 and 14%, namely: F10, F12 and F14 respectively. The amount of optimum bitumen for each filler condition were determined by Marshall mix design method. The stress strain properties of the asphalt concrete (AC) were studied through Unconfined Compression Strength (UCS) Test, Indirect Tensile Test (IDT) and Triaxial Tests. Moisture susceptibility and water penetration were evaluated using Indirect Tensile Test and Permeability Test respectively. The result exhibits that the increase of filler content from 10 to 14% has significant effect on optimum asphalt content and properties of asphalt concrete mixture. Among all mixtures, mix F10 yielded highest strength behavior and moisture resistance. Result also suggests that asphalt concrete specimen was impervious to water (k value <108 mm/s) when the mixture was produced at air void content no larger than 4%, 3.4% and 3.6% in mix F10, F12 and F14 respectively. Ó 2017 Elsevier Ltd. All rights reserved.

1. Introduction The embankment dam using asphalt core was first developed in Germany in the 1960s. Since then, more than 150 ACRD dams have been built in many regions around the world but mostly in northern Europe, including several in Norway. The first dam with an asphalt core was completed in Norway in 1978, and nearly all large Norwegian embankment dams have been built using this method. Nowadays, many countries around the world have recognized the huge advantages of asphalt core dam and several asphalt core dam projects have been constructed. The Chinese developed their knowledge of the structures and built their first asphalt core dams in the 1970s. To date 13 dams of this type have been completed in China. In North America, Canada is the first country completing ⇑ Corresponding author. E-mail addresses: [email protected] (J.-W. (D.-W. Park), [email protected] (T.H.M. Le). http://dx.doi.org/10.1016/j.conbuildmat.2017.02.100 0950-0618/Ó 2017 Elsevier Ltd. All rights reserved.

Seo),

[email protected]

construction a dam of this type. After that, the biggest energy company in Canada Hydro Quebec has decided to construct several more dams of this design. Over the past few years detailed cost comparisons have been made between asphalt concrete core dams and their alternatives at the design stage of projects. For the Urar dam, completed in 1997 in Norway, tenders were submitted for a Roller-Compacted concrete (RCC) dam and a rockfill dam with asphalt core. When only considering contractor costs and additional spillway expenses, the asphalt core alternative turned out to be approximately 10% cheaper than the RCC option. For the Greater Ceres dam, completed in 1998 in South Africa, three alternatives were compared at the design stage: RCC, concrete faced and asphalt concrete core dams. The latter was chosen due to cost and because the dam was located in an earthquake region on a poor sandstone foundation. It seems quite probable that embankment dams with asphalt concrete cores are likely to find a more prominent place in future dam construction.

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In spite of the few economic data, this type of solution seems competitive, especially for locations where fine materials for the construction of a traditional core (clay) are scarce. Also, the increased use of asphalt concrete rather than earth core is partly due to the profession’s increased concern about internal erosion of earth core. By adjusting the bitumen content or the viscosity penetration, the viscoelastic-plastic properties can be tailored to local conditions and climate which makes asphalt core dams especially suited to seismically active areas, and on compressible foundations where stiffer structures like Concrete Face Rockfills Dam (CFRD) and RCC dam may not be suitable. The reservoir can be filled during construction, which is not feasible for an upstream facing alternative. Furthermore, overtopping of an asphalt core during construction will not have the dramatic consequences as for a clay core or an upstream facing solution. Vlad [12] presented that asphalt core embankment dams built on good foundation have outstanding record with no seepage problems or required maintenance. Wang and Höeg [13] suggested that asphalt concrete core not only offers virtually impervious and flexible characteristic but also resists to erosion and ageing. Especially, the self-healing ability can be provided by the viscoelasticplastic and ductile properties of asphalt core. This unique ability could prevent cracks develop in the core wall due to differential displacements (shear distortions) caused by severe earthquake loading. Asphalt concrete is also a very ‘‘forgiving” material in its behavior relieving itself of stress concentrations. The use of softer bitumen than in previous construction increases the self-sealing quality and allows lower operating temperatures and energy input during material production, transportation and core placement. Besides, some researches present another ideal advantage of asphalt core dam named joint-less core construction which dramatically enhance the dam quality. Furthermore, the core may be constructed in cold and rainy weather without construction delays. Therefore, asphalt core is a competitive and economically viable alternative in comparison with other traditional ones [11]. The mix design of asphalt concrete used in impervious facings and cores in embankment dam originated from road asphalt concrete experience [13]. However, there are significant differences between a road pavement and an interior dam core with respect to loading and environment conditions. The asphalt which is used on roads and airfields, where deterioration becomes evident in potholes etc, has a different composition to the asphalt used in dams. Inside a dam the asphalt is kept under virtually ideal conditions. Fairly constant temperatures without exposure to the sun and the rich, dense asphalt mix means that oxidation or hardening does not occur over time. Typically, the road asphalt concrete mixes consist of 4–6% bitumen by mineral weight, 4–8% filler material (<0.075 mm), and 20–40% fine aggregates (0.075–2.36 mm). The air voids content for road asphalt concrete after compaction is in the range of 3–10%. In the other hand, the asphalt concrete used in dam is required to be impervious and flexible and it consists of more fine aggregates, filler and bitumen than the asphalt concrete used in pavements. In previous designs of asphalt core dam (e.g. Höeg [13], Vlad [12]), these authors suggested the optimum asphalt content about 6.5 to 7.3% by mineral weight, <15% filler mineral (<0.075 mm), 35–52% fine aggregates (0.075–2.36 mm), 33–55% coarse aggregates (2.36–19 mm) and laboratory air void content no larger than 2% which will provide a virtually impervious asphalt concrete (permeability <10–8 mm/s). Particularly in recent years, construction of this type of dam in the seismic areas of the world such as Japan, China and Iran has caused researchers to focus on the dynamic behavior of asphalt cores. However, few researchers have investigated the stressstrain behavior of asphalt concrete used as watertight elements for dams by laboratory tests. Especially, very little has been reported on the research of filler content suitability for hydraulic

dense grade asphalt concrete with air porosity less than 3%. With parameters derived from the carried-out tests, the acceptable level of the rheological behavior and stress train properties of bituminous concrete mixes can be revealed. This research data can be very useful for geotechnical engineers to conduct numerical analyses and predict field performance of asphalt core dams for different situations.

2. Research objectives and scope The purpose of this paper is to systematically develop asphalt concrete mixture and conduct performance tests for ACRD. Preliminary studies have indicated the specific content of filler for ACRD, but lack of researches has clearly justified the effect of this mineral content to the properties of asphalt concrete mixture. Therefore, three filler content: 10, 12 and 14% were selected to evaluate in this study based on trial testing and previous experiences. The Marshall mix design method was conducted to determine the optimum asphalt binder content in each condition. The stress strain properties of the asphalt concrete were documented through Unconfined Compression Test, Indirect Tensile Test and Triaxial Tests. The ductility of the specimen after reaching peak strength and any strain weakening behavior of the mix was also evaluated to assure that the asphalt concrete exhibits flexible and ductile (not strain-softening) behavior required to adjust to dam deformations caused by static and dynamic loads and differential foundation settlements. Indirect Tensile Test and Permeability Test were carried out to determine the moisture susceptibility and water penetration respectively. Air void content also plays a very important role in the performance of asphalt concrete, especially the permeability. Air void content in asphalt concrete mixture was modified from approximately 2–8.5% to determine the influence of this content to the water penetration factor.

3. Material and methodology 3.1. Material HMA is a mixture of mineral aggregate and bituminous binder. Asphalt binder PG58-22 was used in this study as it is the most widely used in Korea. The specific density of coarse and fine aggregate is 2.647 and 2.671 respectively following the AASHTO T 84-10 [1] and AASHTO T 85-10 [2] standard. The nominal maximum size of 13 mm gradation was selected to enhance the design of impervious asphalt concrete. As mentioned before, there are three conditions of filler in this study: 10, 12, 14%. It is a combination of 50% pan and 50% mineral limestone which passing sieve #200. Based on preliminary asphalt core dam studies and experiences, the particle size distribution of aggregate designed for impervious core is shown in Table 1.

Table 1 Particle size distribution of aggregate.

*

Sieve size

Percent passing (%)

19 mm 13 mm 10 mm #4 #8 #30 #50 #100 #200

100 99 84 57 43 29 23 18 10/12/14*

Three different ratios of filler content: 10, 12 and 14%.

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J.-W. Seo et al. / Construction and Building Materials 140 (2017) 301–309 Table 2 Marshall mix design requirements.

*

Prepared specimens

Properties

Criteria limit

Optimum AC (%) Marshall stability (N) Flow (0.01 cm) VMA (%) VFA (%)

At 2%* >4900 N 20–50 >13% 80

Percentage of air voids.

)

Air voids (

Wet IDT test

Dry IDT test

Water (25 5 ; 2h)

Vacuum (13-67 kPa) Saturation degree (55-80%)

IDT test

Freezing (-18 ; 16h) Thawing (60 ; 24h)

Water

p

(25

Fig. 1. Mohr-Coulomb circle.

; 2h)

IDT test

3.2. Asphalt mixture design by Marshall method Wang and Höeg [13] concluded that the primary function of asphalt concrete used in a dam core is to create an impervious water-barrier, flexible and sufficiently ductile to accommodate the deformations imposed by the embankment, reservoir and foundation, without cracking during construction, impounding, operation, and earthquake loading. Therefore, hydraulic asphalt concrete is designed with a higher bitumen content than that in the mix used for road and airfield pavements that are subjected to very different loads and environmental conditions. Based on trial testing and previous experiences, the initial design binder content (Pb) for mix F10, F12 and F14 was 6, 6 and 6.3% respectively. Then, asphalt concrete samples were produced at Pb, Pb ± 0.5%, ±1% to determine optimum asphalt content. Therefore, there were 5 asphalt binder contents in each filler conditions with three replicates per asphalt content. Table 2 illustrates the Marshall mix design requirements in this research. According to Marshall mix design method, aggregate was first placed in the oven for more than 4 h, and less than one hour for asphalt binder at mixing temperature. After mixing, each sample was placed in the oven for 2 h at compaction temperature and compacted with a Marshall hammer. The specimens were stored at room temperature for 24 h and extruded from the mold prior to testing. The percent air voids, VMA, VFA, Marshall stability and flow values of the specimen were determined. Maximum specific gravity Gmm [5] and bulk specific gravity Gmb [3] of the mixture were also figured out. Table 2 illustrates the Marshall mix design requirements in this research. The air-void content (porosity) of the asphalt concrete in the dam core after compaction is required to be less than 3% to ensure a permeability coefficient less than about 1010 mm/s (almost impervious condition) [15]. However, laboratory specimens of the specified design mix should be required to show an air void content 2% to account for the difference in degree of compaction achieved in the laboratory and in the field [10]. Regards to this 2% air-void, optimum asphalt content was figured out in each filler

Tensile strength ratio Fig. 2. Wet and dry IDT test diagram.

condition. Therefore, the optimum asphalt content was 5.9%, 5.9% and 6.2% for mixes F10, F12 and F14 respectively. 3.3. Unconfined compressive strength test The test was designed with an attempt to investigate how large compressive strength the asphalt concrete specimen could undertake under different filler content ratio. Unconfined compressive strength (UCS) test of asphalt concrete is standardized in AASHTO T167 [4]. Test specimens were 100 mm in diameter and 150 mm in length prepared by gyratory compactor. Testing was conducted using a hydraulic-based universal testing machine. A straincontrolled at 2 mm/min rate of loading was applied along the axial direction of the asphalt mix cylinder and the test was conducted at ambient room temperature of 25 °C. 3.4. Indirect tension test (IDT test) In this research, the IDT test method is used to quantify the tensile strength of a cylindrical specimen in accordance with ASTM D6931-12 [7] and researches of Lubinda [17], [18], [19]. Two replicate samples were produced from each condition. The specimen geometry was 100 mm in diameter and 60 mm in length prepared by gyratory compactor. The testing mechanism of the IDT entails a compressive loading to be applied across the diameter of a test specimen using a Universal Testing Machine. This compressive load produces tensile stresses in the test specimen in a direction perpendicular to the vertical applied load with a constant deformation rate of 50.8 mm/min (2 in./min). The samples were tested at 25 °C in an environmental-control chamber.

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Upper timing mark

500ml

Graduated cylinder I.D. = 31.75 mm (1.25 in.)

h1

Lower timing mark

0ml

Clamp assembly 0.635mm thick lateral membrane was pressurized at 68.9 ± 3.4 kPa to ensure water would not flow laterally

Cap assembly

Hose bard fitting

Test specimen Height: 60mm Diameter: 150mm

h2

An air pump capable of applying 103.42 kPa (15psi)

Outlet pipe

Pressure gauge Quick connect

Fig. 3. Water Permeability Testing Apparatus [8].

3.5. Triaxial test

q¼

Triaxial compression tests should be carried out under different confining stresses to assure that the asphalt concrete exhibits flexible behavior required to adjust to dam deformations caused by static and dynamic loads [14]. Three compacted asphalt mixes named F10, F12 and F14 were used to conduct the triaxial compressive strength test. Two cylindrical replicates were used for each mix. The specimen geometry was 151 mm in length and 100 mm in diameter using gyratory compactor. Testing was conducted at three confining pressure, 35, 69 and 138 kPa in ambient temperature (25 °C). A strain-controlled at 2 mm/min rate of loading was applied along the axial direction of the asphalt mix cylinder. Testing was conducted using a hydraulic-based universal testing machine. The loading time, displacement and uniaxial stress were collected throughout the test. Testing was terminated at 12% strain to ensure that failure was occurred. Triaxial compression equations base on Mohr-Coulomb theory:

u u r1 ¼ r3 tan2 ð45 þ þ 2ctanð45 þ Þ 2

p¼

r1 þ r3 2

2

ð2Þ ð3Þ

r1  r3 2

u ¼ sin1 ðtanaÞ c¼

a

cosu

ð4Þ ð5Þ ð6Þ

where r1 is maximum principle stress, r3 minimum principle stress, C is cohesion, u is friction angle, a is the angle that the modified failure envelope makes with the horizontal, q and p is the vertical and horizontal stress coordinate. 3.6. Indirect tensile test for moisture susceptibility Moisture causes the loss of adhesion between the asphalt binder and the aggregate surface, and accelerates deterioration in the form of potholes and cracking. In the construction of Asphalt Core Rockfill Dam, this characteristic becomes more critical. Therefore, moisture susceptibility was investigated in this study using the AASHTO T 283–03 [6]. The damage due to moisture is controlled by the specific limits of the tensile strength ratios. All specimens were fabricated using the gyratory compactor and had air void contents of 7 ± 0.5%. Six replicates from each filler condition

305

95

14.5

90

14

VMA (%)

VFA (%)

J.-W. Seo et al. / Construction and Building Materials 140 (2017) 301–309

85 80

13.5

13 12.5

75

12

70 F10

F12

F10

F14

(a)

F12

F14

(b) 60

16000 14000

50

40

10000

30

8000 6000

20

4000

Flow (0.01cm)

Stability (N)

12000

10

2000

0

0 F10 Stability (kN)

F12

F14 Flow (mm)

(c) Fig. 4. VMA(a), VFA(b), Marshall stability and flow(c) test results.

Table 3 Summary of stability test results. Mix

F10 F12 F14

Stability Average (N)

Standard Deviation

C.O.V. (%)

14168 13344 11673

467.5 116.1 122.6

3.3 0.87 1.05

were produced and separated into two subsets, one subset for dry IDT test and the other for wet IDT test. The maximum indirect tensile force was recorded and the corresponding IDT strength of the asphalt concrete mixture was calculated. The tensile strength ratio (TSR) is determined from the dry and wet IDT test results [16]. A flowchart summarizing the experimental study was given in Fig. 2. 3.7. Permeability test In this study, the Florida Test Method (FM 5-565) [9] was followed to determine the permeability values. The permeability (hydraulic conductivity) of the test specimen was estimated using the Karol-Warner Asphalt permeameter. The testing is based on the falling head principle to estimate the water flow rate through the asphalt concrete specimen (Fig. 3). Base on Darcy’s law, the hydraulic conductivity can be estimated using equation below:

k¼

  aL h1  tc ln At h2

ð7Þ

where: k is coefficient of permeability (cm/s), a is inside crosssectional area of the buret, (cm2), L is average thickness of the test specimen (cm), A is average cross-sectional area of the test

specimen (cm2), t is elapsed time between h1 and h2 (s), h1 is initial head across the test specimen (cm), h2 is final head across the test specimen (cm) and tc is temperature correction for viscosity of water (cm). Three replicates (150 mm in diameter and 60 mm in height) of each mix were fabricated using gyratory compactor. Before permeability testing, superpave specimens were soaked in water to reach saturation. A sealing tube with a flexible latex membrane 0.635 mm (0.025 in.) thick was prepared to be capable of confining asphalt concrete specimens. An air pump capable of applying 103.42 kPa (15 psi) pressure was connected to apply vacuum to evacuate the air from the sealing tube/membrane cavity. Water from a graduated cylinder was allowed to flow through a saturated asphalt sample and time taken to reach a known change in head was recorded. The coefficient of permeability k was calculated using Eq. (7). For each replicate, permeability tests were conducted three times to report an average permeability value. Permeability values for the first and third test did not vary by more than 4% [8,16]. In this research, sample is considered to be impervious when the testing time was approaching 30 min with no sign of water level moving from the upper timing mark. 4. Results and discussion 4.1. Analysis of mix design properties The VMA, VFA, Marshall stability and flow test results were presented in Fig. 4. Generally, using optimum asphalt content at 2% air void, the Marshall mix design properties show acceptable values. All test specimens meet the requirement value in Marshall Stability with a minimum value of 4900 N and the flow value is in the range from 38 to 54 mm. As can be seen from Fig. 4a, 4b, there was an increase in VFA and VMA when the filler content was increased from 10 to 14%. Whereas, adding more filler content will

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J.-W. Seo et al. / Construction and Building Materials 140 (2017) 301–309

F10-1

F10-2

F12-1

3.5

2.5

Stress (MPa)

Stress (MPa)

3 2.5 2 1.5 1

2 1.5 1 0.5

0.5

0

0 0

2

4

6

0

8

2

Strain (%)

4

6

8

Strain (%)

(a)

(b)

F14-1

F14-2

3

2.5

2.5

2

Stress (MPa)

Stress (MPa)

F12-2

3

1.5 1 0.5

2 1.5 1 0.5

0

0 0

2

4

6

8

F10

F12

F14

Strain (%)

(c)

(d)

Fig. 5. UCS test result of mix: F10 (a), F12(b), F14(c) and peak stress comparison (d).

Table 4 Summary of average stress results. Mix

F10 F12 F14

Stress Average (MPa)

Standard Deviation

C.O.V. (%)

2.77 2.54 2.23

0.141 0.101 0.019

5.1 4 0.87

decrease the Marshall stability and flow value of asphalt concrete samples (Fig. 4c). Table 3 presents the average stability values along with standard deviation and COV. The test results showed low standard deviations. The COV values varied between 0.87 and 3.3% with an average of 1.74%. It can be concluded that the measurements were repeatable. 4.2. Strength behavior of asphalt concrete mixture Fig. 5 presents the unconfined compressive test results. Overall, the finding illustrates that there was a slight reduction in strength of asphalt concrete specimens when the filler was raised from 10 to 14%. The highest UCS of mixes F10, F12 and F14 were 2.87, 2.62 and 2.24 MPa respectively. As can be seen from Fig. 5(a)–(c), the stress-strain relationship was found to be almost similar in all test conditions. The compressive stress of asphalt concrete specimens increased with an increase in axial strain up to a certain peak. The maximum UCS of test specimens occurred at an axial strain approximately 3%. After reaching the peak strength, the UCS decreased with increasing axial strain. By examining stress-strain curves from Fig. 5a-c, all asphalt concrete samples yielded ductile behavior after reaching the peak stress. The average UCS values along with standard deviation and COV are exhibited in Table 4. The test results showed low standard deviations. With COV values

ranging from 0.87 to 5.1% and an average of 3.23%, the measurements were reasonably acceptable. The IDT test results is presented in Fig. 6. The general trend showed that higher filler content will results in lower tensile strength of test specimens (Fig. 6d). As can be seen from Fig. 6d, mix F10 yielded the highest IDT peak load of 7.01 kN, whereas the lowest IDT peak load of 6.14 kN was obtained by mix F14. However, all test specimens exhibited a relatively similar trend in the load-displacement curves (Fig. 6a–c). Result shows that IDT load increased with an increase in displacement up to a certain peak. After reaching the peak load, it decreased with increasing displacement and strain softening occurred. As can be seen from Table 5, the IDT load showed very low standard deviations. The alternation of COV values were between 0.47 and 3.3% with an average of 1.77%. It can be concluded that the measurements were repeatable. Fig. 7a presents the summary of triaxial test results of all mixes. It can be concluded that confining pressure has a significant impact on triaxial compressive strength of asphalt concrete mixture. At low level confining pressure of 35 kPa, triaxial test samples yielded relatively similar results with peak load of approximately 18.5 kN. When the confining pressure was enhanced to medium stress of 69 kPa, all filler combinations obtained a slight increase in strength with average peak load value of 19.3 kN. At highest confining pressure of 138 kPa, it is noticed that all mix achieved the highest compression strength with average peak load value of 20.6 kN. Also at this confining pressure, the strength between different filler combination started to vary obviously with mix F14 and F10 having the least and highest strength among all mixes, respectively. Results shows that the compressive strength of mix F10 increased up to 115% when confining pressure was enhanced from 35 to 138 kPa. However, the strength was slightly comparable in mix F14 regardless of confining pressure.

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F10-2

F12-1 8

6

6

Load (kN)

Load (kN)

F10-1

8

4 2

4

2

0

0 0

2 4 6 Displacement (mm)

8

0

2 4 6 Displacement (mm)

(a) F14-1

8

(b) F14-2

8

8

6

6

Load (kN)

Load (kN)

F12-2

4 2

4

2

0

0

0

2 4 6 Displacement (mm)

8

F10

F12

F14

(d)

(c) Fig. 6. IDT test result of mix: F10 (a), F12(b), F14(c) and peak load comparison (d).

Table 5 Summary of average IDT load results. Mix

F10 F12 F14

Load Average (kN)

Standard Deviation

C.O.V. (%)

7.1 6.224 6.148

0.234 0.029 0.095

3.3 0.47 1.54

The Mohr-Coulomb failure theory was used to obtain cohesion and friction angle value (Fig. 1). The presence of different filler content results in considerable variation in the cohesion C and friction angle u values of asphalt concrete specimens. It is observed that the cohesion C increased from 528 to 660 kPa when the filler changed from 10 to 14% (Fig. 7b). Fig. 7c represents the friction angle result of test specimens, the general trend showed that lower internal friction angle was obtained at higher filler content. The friction angle value of mix F10, F12 and F14 was 40, 32 and 29° respectively. Analysis revealed from triaxial test shows that the lower filler content provided mix F10 higher interlock and strength compared to mix F12 and F14. Table 6 presents the average unconfined compressive strength values along with standard deviation and COV. The COV values altered between 0.1 and 11% with an average of 4.45%, which reveals that the measurements were repeatable. As can be seen from Fig. 8, the influence of filler content on moisture resistance of test samples was obviously pronounced. It showed that adding more filler could result in the decrease of IDT stress and TSR value of all asphalt concrete samples. Comparisons of TSR values in Fig. 8 clearly indicates that mixture F10 achieved the highest moisture resistance due to higher strength acquired. Whereas mix F14 was severely affected by moisture with

33% reduction in IDT stress. Base on the result, mix F10, F12 and F14 has TSR values of 75%, 63%, and 67%, respectively. According to AASHTO T 283-03, only mix F10 meets the criteria of a minimum TSR value of 75%. The average IDT stress values along with standard deviation and COV are illustrated in Table 7. As can be seen from table 7, the COV values ranged from 1.9 to 12.3% with an average of 6%, which shows that the measurements were acceptable. 4.3. The effect of air void content on permeability property The relationship between permeability, filler and air-void content was evaluated shown in Table 8. The finding suggests that air void content has a significant impact on the water resistance of test specimens. It is noticeable that no water penetration was recorded in the test specimens when the air void content was ranged from 2 to nearly 3.5% in all filler combination. It can be concluded that those conditions are impervious to water. The permeability seemed to be relatively low at low air voids content, and it increased more dramatically with higher air voids in the mix. At 5.4 to 6% percent air void, the k value was 4.5  105 mm/s, 3.02  104 mm/s and 1.5  104 mm/s in the mix F10, F12 and F14 respectively. At approximately 8% air voids, a small change in this content could results in a remarkable increase in permeability. For examples, the permeability of mix F10 produced at 8.6% air void was 22 times higher than that at 6% percent air voids (9.9  104 mm/s compared to 4.5  105 mm/s). Based on preliminary researches recommendation (i.e. Vlad [12], Höeg [13]), asphalt concrete mixtures can be considered impervious and applied as water barrier when the permeability coefficient k is no larger than 108 mm/s. In this study, those mixtures produced at air void content higher than 5% do not meet this requirement regardless of the filler content.

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25

Load (kN)

20

F10

15

F12

10

F14

5 0

35

69

138

Confining pressure

(a) (deg.)

700

Cohession (kPa)

600 500

40

Friction Angle

30

400 300 200

100

20

10 0

0 F10

F12

F10

F14

F12

(b)

F14

(c)

Fig. 7. Triaxial test results: (a) Peak axial load and confining pressure relationship; (b) Cohesion; (c) Friction Angle.

Table 6 Summary of average triaxial load results. Mix

*

Load Standard deviation

C.O.V. (%)

F10

F10-35* F10-69 F10-138

18.74 19.95 21.71

1.893 0.028 0.166

10 0.1 1

F12

F12-35 F12-69 F12-138

18.61 19.22 20.44

1.223 0.729 0.113

7 4 1

F14

F14-35 F14-69 F14-138

18.27 18.5 19.72

2.019 0.589 0.603

11 3 3

F10a-35b:

(a)

: filler content;

(b)

Average (kN)

: confining pressure.

DRY

WET

TSR

12

100 Table 7 Summary of average IDT stress results.

80 10 60

9 8

40

7 20

6 5

0 F10

F12

F14

Fig. 8. TSR test result of mix F10, F12 and F14.

TSR (%)

IDT stress (kN)

11

Mix

IDT stress Average (kN)

Standard Deviation

C.O.V. (%)

Dry specimen F10 F12 F14

11.5 11.2 10.4

0.80 0.52 0.23

6.9 4.7 2.3

Wet specimen F10 F12 F14

8.6 6.9 7

0.70 0.13 0.86

8.2 1.9 12.3

J.-W. Seo et al. / Construction and Building Materials 140 (2017) 301–309 Table 8 Summary of Permeability test. Filler content

Air void content (%)

Permeability coefficient k (mm/s)

F10

2.05 2.9 4 6 8.6

<108 <108 <108 4.5  105 9.9  104

F12

2.01 2.5 3.4 5.4 8.4

<108 <108 <108 3.02  104 5.8  104

F13

2.03 2.9 3.6 5.4 8.4

<108 <108 <108 1.5  104 5.8  104

309

results in a considerable increase in coefficient k. Asphalt concrete specimens are considered to be impervious (k value <108 mm/s) when the mixture was produced at air void content no larger than 4%, 3.4% and 3.6% in mix F10, F12 and F14 respectively. In this study, permeability test specimens produced at higher 5% air void content do not reach the permeability coefficient criteria of 108 mm/s base on previous researches recommendation. (8) When designing asphalt concrete as an impervious core in rockfill dam, mix design with 10% filler content and air void below 3% is recommended to acquire desired permeability k-value of lower than 108 mm/s. Besides, based on this study, desired ACRD mixture should acquire the following property values: UCS of higher than 2.5 MPa; TSR value of higher than 75%; C value ranging from 500 to 600 kPa; friction angle value varying from 30 to 40° and Triaxial stress of higher than 18, 20 and 21.5 kN at confining pressure of 35, 69 and 138 kPa respectively.

5. Summary and conclusions This study aims to develop asphalt concrete mixture and conduct performance test designed for ACRD. Primary findings are summarized below: (1) Using optimum asphalt content at 2% air void, the Marshall mix design criteria, VMA, VFA, Marshall stability, flow results are acceptable. (2) By varying filler content from 10 to 14%, analysis shows that this mineral content has a significant effect on optimum asphalt content and properties of asphalt concrete mixture. The increase in filler content leads to the increase in optimum asphalt content requirement. When the filler content was raised from 10 to 14%, the required optimum asphalt content was altered from 5.9 to 6.2%. (3) In terms of UCS and IDT test, there was a slight reduction in strength when filler content was enhanced from 10 to 14%. However, all mixtures showed to follow the similar trend in stress-strain and load-displacement curve respectively. The stress (load) of asphalt concrete specimens increased with an increase in axial strain (displacement) up to a certain peak. After reaching the peak, the stress (load) decreased with increasing axial strain (displacement). Also, all test specimens showed relatively ductile plastic behavior after the peak strength level had been reached. (4) From triaxial test result, higher confining pressure resulted in higher compressive strength of asphalt concrete mixture. Also at higher confining pressure, the reduction in strength of test specimens when adding more filler content was more considerable. (5) Regards to cohesion C, the general trend showed that higher cohesion C was obtained at higher filler content. Meanwhile, the friction angle results exhibited the reverse trend. (6) For moisture susceptibility, the result suggests asphalt concrete mixture with 10% filler content showed highest resistance value. Moreover, only mix F10 meets the requirement of 75% of minimum TSR value. (7) The result base on permeability test shows that air void content has a remarkable influence on water penetration factor of asphalt concrete. A small change in this content could

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