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Evaluation of mixture characteristics of warm mix asphalt involving natural and synthetic zeolite additives
Construction and Building Materials 57 (2014) 38–44
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Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Evaluation of mixture characteristics of warm mix asphalt involving natural and synthetic zeolite additives Ali Topal a, Burak Sengoz a,⇑, Baha Vural Kok b, Mehmet Yilmaz b, Peyman Aghazadeh Dokandari c, Julide Oner c, Derya Kaya c a b c
Dokuz Eylul University, Faculty of Engineering, Department of Civil Engineering, 35160 Buca, Izmir, Turkey Fırat University, Faculty of Engineering, Department of Civil Engineering, 23119 Elazıg, Turkey Dokuz Eylul University, Graduate School of Natural and Applied Sciences, 35160 Buca, Izmir, Turkey
h i g h l i g h t s The utilization of zeolites decreases the optimum bitumen content. Zeolites improve the repetitive loading strength of bituminous mixtures. Zeolites improves permanent deformation ability and increases rigidity. Natural zeolite is an acceptable alternative to commercial synthetic zeolite.
a r t i c l e
i n f o
Article history: Received 15 November 2013 Received in revised form 17 January 2014 Accepted 24 January 2014 Available online 21 February 2014 Keywords: Warm mix asphalt Natural zeolite Synthetic zeolite Marshall stability Indirect tensile stiffness modulus Fatigue behavior
a b s t r a c t Concerning global warming and economical issues, many recent studies try to introduce innovative technologies applying lower temperatures with higher performance characteristics as alternative solutions for hot mix asphalt (HMA) applications. These new technologies generally named as warm mix asphalt (WMA) technologies implementing various techniques to reduce application temperatures in order to diminish harmful environmental effects of HMA applications and minimize construction costs. An effective technique to perform this task is to provide a foaming effect in mixing phase to increase workability by use of water containing additives such as zeolites. This paper investigates the feasibility of utilizing WMA containing natural zeolite additive in comparison with a commercial kind of synthetic zeolite. Marshall stability, indirect tensile stiffness moduli and fatigue behavior of WMA containing natural and synthetic zeolites have been analyzed and compared with HMA. Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction Most of the field pavement practices around the world consist of conventional hot mix asphalt (HMA). For the last decade, implementing of warm mix asphalt (WMA) technologies has gained popularity in Europe and in some other countries as well as in the USA. The goal of WMA technologies is to obtain required strength and durability which is equivalent to or even better than HMA pavements [1]. The use of WMA technologies offer many benefits to asphalt industries. Many studies have common sight about the various advantages of the utilization of WMA technologies. These advanta-
⇑ Corresponding author. Tel.: +90 232 301 7072; fax: +90 232 301 7253. E-mail address: [email protected] (B. Sengoz). http://dx.doi.org/10.1016/j.conbuildmat.2014.01.093 0950-0618/Ó 2014 Elsevier Ltd. All rights reserved.
ges are all originated from the major feature of WMA additives which is reducing the viscosity of the bitumen [2]. This reduction results in increasing workability and ease of use, ecological benefits due to less emissions and reduction in costs due to less energy use. In terms of workability, the reduced viscosity helps the aggregates to be coated more easily [3,4]. When discussing about environmental benefits, there are serious worries about the greenhouse gases emissions in HMA pavement applications. Due to lower application temperatures of WMA mixes, the emission of carbon dioxide (CO2) and other so called greenhouse gases are lowered in comparison with HMA mixes [5]. Besides, the evaporation of less heavy components of bitumen occurs less than conventional applications. This causes less odors in asphalt plants, therefore provides more pleasant working conditions. Builders comments also indicate that the fumes are rather less in WMA production in comparison with HMA production [6]. The fuel consumption
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of WMA technologies is rather less than conventional HMA mixtures. Energy consumption for WMA production has been reported as 60–80% of HMA production [4]. Some studies have also reported the range of 20–35% of savings in burner fuel with use of WMA technologies [5]. In asphalt industry, a common way of achieving lower application temperatures in order to produce WMA is the utilization of WMA additives. All of the current WMA additives facilitate lowering of production temperature by either lowering the viscosity and/or expanding the volume of the bitumen at a given temperature [7,8]. Nowadays, there are many WMA additives available on the market. One of these additives is categorized as synthetic zeolite. Zeolites due to their honeycomb microstructure can preserve water within their micropores and release it above the boiling point of water when heated. [5]. Hence, zeolites have been detected as suitable additives by asphalt industries in order to expand the volume of bitumen by foaming effect. Synthetic zeolite has been hydro-thermally crystallized. It contains about 18–21% water of crystallization which is released by increasing temperature above 85 °C. The expansion of water causes foaming of asphalt bitumen [9,10]. Natural zeolites are microporous, hydrated aluminosilicate minerals commonly used as commercial adsorbents [11]. Clinoptilolite is one of the most common natural zeolite comprising a microporous arrangement of silica and alumina tetrahedral which has large amount of pore space, high resistance to extreme temperatures and chemically neutral basic structure [11]. This study investigates the feasibility of utilizing WMA mixtures containing natural zeolite additive in comparison with a commercial kind of synthetic zeolite. Marshall stability, Indirect Tensile Stiffness Moduli (ITSM) and fatigue behavior of WMA specimens containing natural and synthetic zeolites have been analyzed and compared with HMA specimens. 2. Experimental
A kind of synthetic zeolite additive is manufactured in North America by PQ Corporation. Austerman et al. [9] and PQ Corporation [10] have reported that the maximum rate of this synthetic additive in base bitumen varies between 4% and 6% by weight of bitumen. The synthetic zeolite additive concentration in the base bitumen was chosen as 5% based on a past research made by PQ Corporation [10]. Natural zeolite WMA additive which is used in this study has been supplied from a Turkish local company in powder form. The complex formula of this natural zeolite is (Na3K3)(Al6Si30O72)27H2O. It forms as white to reddish tabular monoclinic tectosilicate crystals with a Mohs hardness of 3.5–4.0 and a specific gravity of 2.1–2.2. The content of natural zeolite in this study has been chosen as 5% by weight of bitumen in order to compare its fundamental characteristics with synthetic zeolite. The properties of natural zeolite are presented in Table 4. 2.2. Test methods 2.2.1. Conventional bitumen tests The base samples and the bitumen samples containing synthetic zeolite and natural zeolite additives were subjected to the following conventional bitumen tests; penetration (ASTM D5-06), ring and ball softening point (ASTM D36-95), thin film oven test (TFOT) (ASTM D 1754M-09), penetration and softening point after TFOT and storage stability test (EN 13399 (2010)) [12–14]. In addition, the temperature susceptibility of the bitumen samples has been calculated in terms of penetration index (PI) using the results obtained from penetration and softening point tests [22]. The effect of viscosity on asphalt bitumen’s workability is very important in selecting proper mixing and compacting temperatures. Brookfield Viscometer was employed to inspect the mixing and compaction temperatures in according to ASTM D4402-12 [23,24]. The test was performed at 135 °C and 165 °C. The temperatures corresponding to bitumen viscosities 170 ± 20 m Pa s and 280 ± 30 m Pa s were chosen as mixing and compaction temperatures respectively. 2.2.2. Mechanical properties The effect of synthetic zeolite and natural zeolite additives on the mechanical properties of WMA has been determined by Marshall method (ASTM D3549) in terms of stability, flow and air void content as well as by indirect tensile stiffness modulus test (BS DD 213) and indirect tensile fatigue test (BS DD ABF) [25–28]. The tests were conducted on WMA samples at recommended contents and on HMA as control samples. Asphalt concrete specimens were prepared with a compaction effort of 75 blows simulating heavy traffic loading conditions. The ITSM test is a non-destructive test that is used to evaluate the relative quality of materials and study the effect of temperature and loading rate. The ITSM Sm in MPa is defined as below [27];
Sm ¼ FðR þ 0:27Þ=LH
2.1. Materials The base bitumen with a 50/70 penetration grade was obtained from Aliaga/Izmir Oil Terminal of the Turkish Petroleum Refinery Corporation. In order to characterize the properties of the base bitumen, conventional test methods such as: penetration test (ASTM D5-06), softening point test (ASTM D36-95), thin film oven test (TFOT) (ASTM D1754-97), penetration and softening point after TFOT, etc. were performed [12–14]. These tests were conducted in conformity with the relevant test methods that are presented in Table 1. A mix of basalt and limestone aggregates provided from Dere Madencilik Inc. _ (Quarry located in Belkahve–Izmir/Turkey) was used in this study. In order to find out the properties of basalt and limestone aggregate, sieve analysis (ASTM C136), specific gravity (ASTM C127-07, ASTM C128-12), Los Angeles abrasion resistance test (ASTM C131-06), sodium sulfate soundness test (ASTM C88-05), fine aggregate angularity test (ASTM C1252-06) and flat and elongated particle tests (ASTM D4791-10) were conducted on basalt and limestone aggregates [15–21]. Physical properties of each kind are given in Table 2. Based on the associated test results, a mix gradation of basalt and limestone was intentionally chosen to provide desired performance in conformity with Turkish specifications concerning the Type 1 wearing course. Basalt plays the role of strengthening constituent as coarse aggregate while limestone participates in the fine aggregate framework. The gradation is given in Table 3.
ð1Þ
where F is the peak value of the applied vertical load (repeated load, N), H is the mean amplitude of the horizontal deformation (mm) obtained from five applications of the load pulse, L is the mean thickness of the test specimen (mm), and R is the Poisson’s ratio (assumed as 0.35). The test was performed by way of a universal testing machine (UTM) in deformation-controlled mode. The magnitude of the applied force was adjusted by the system during the first five conditioning pulses such that the specified target peak transient diametral deformation was obtained. An appropriate value was chosen to ensure that sufficiently high signal amplitudes were obtained from the transducers which would produce consistent and accurate results. Accordingly, this value was selected as 5 lm for this test. The rise time, which is measured from the origination of load pulse and denotes the duration of the applied load rising from zero to the maximum value, was set at 124 ms. The load pulse application was adjusted to 3.0 s. ITSM tests were conducted at three different temperatures (20 °C, 25 °C and 30 °C). The indirect tensile fatigue test is one of the constant stress test that characterizes the fatigue behavior of the mixture [29]. In this study, the fatigue test was performed in a controlled stress mode based on BS DD ABF standard [28]. The UTM was also used for this purpose. The loading frame was housed in an environmental chamber to control temperature during the test. The desired load level, load rate and load duration were controlled by a computer. The deformation of the specimen was monitored through linear variable-differential transducers (LVDTs). The LVDTs
Table 1 Properties of the base bitumen. Test
Specification
Results
Specification limits
Penetration (25 °C; 0.1 mm) Softening point (°C) Viscosity at (135 °C)-Pa s Thin film oven test (TFOT) (163 °C; 5 h) Change of mass (%) Retained penetration after TFOT (%) Softening point diff. after TFOT (°C) Specific gravity Flash point (°C)
ASTM ASTM ASTM ASTM
D5 D36 D4402 D1754
55 49.1 0.413
50–70 46–54 –
ASTM ASTM ASTM ASTM
D5 D36 D70 D92
0.04 25 5 1.030 +260
0.5 (max) – 7 (max) – 230 (min)
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Table 2 Physical properties of used aggregates. Test
Specification
Specific gravity (coarse agg.) Bulk Saturated surface dry Apparent Specific gravity (fine agg.) Bulk Saturated surface dry Apparent Specific gravity (filler) Los Angeles Abrasion (%) Flat and elongated particles (%) Sodium sulfate soundness (%) Fine aggregate angularity
ASTM C 127
Results
Limits
Limestone
Basalt
2.686 2.701 2.727
2.666 2.810 2.706
– – –
2.687 2.703 2.732 2.725 24.4 7.5 1.47 47.85
2.652 2.770 2.688 2.731 14.2 5.5 2.6 58.1
– – – – Max 35 Max 10 Max 10 Min 40
ASTM C 128
ASTM ASTM ASTM ASTM
C 131 D 4791 C 88 C 1252
Table 3 Gradation of the aggregates. Test
19–12.5 mm (Basalt)
12.5–5 mm (Basalt)
5–0 mm (Limestone)
Mixture ratio (%)
15
45
40
Gradation (3/4)00 (1/2)00 (3/8)00 No 4 No 10 No 40 No 80 No 200
100 35.7 2.5 0.4 0.3 0.2 0.15 0.10
100 100 89 16 1.2 0.7 0.4 0.2
100 100 100 100 81 33 22 13
Combined gradation (%)
Specification limits
100 90.5 80.5 47.3 33 13.5 9 5.3
100 83–100 70–90 40–55 25–38 10–20 6–15 4–10
Table 4 Physical properties and chemical structure of natural zeolite. Chemical structure SiO2
Al2O3
Fe2O3
K2O
H2O
CaO
MgO
Na2O
Ti
Ag
Content (%)
13.55
1.15
3.5
5.9
1.96
0.7
0.6
0.02
0.04
71.29
Physical properties Voids (%) Dimensions of the main channels (A)
Thermal stability
Ion exchange capacity (meq/g)
34
High
2.16
3.9 5.4
were clamped vertically onto the diametrical side of the specimen. A repeated dynamic compressive load at 350 kPa was applied to specimens at 20 °C, 25 °C and 30 °C test temperatures, across the vertical cross-section along the depth of the specimen using two loading strips 12.5 mm in width. Finally, the resulting total deformation corresponding to the applied force was measured.
3. Result and discussions 3.1. Conventional test results The conventional properties of the bitumen prepared with synthetic zeolite and natural zeolite additives are presented in Table 5 as a decrease in penetration and increase in softening point. The increase in softening point is favorable since bitumen with higher softening point may be less susceptible to permanent deformation (rutting) [30]. Synthetic zeolite and natural zeolite reduce temperature susceptibility (as determined by the penetration index–PI) of the bitumen. Lower values of PI indicate higher temperature susceptibility. Asphalt mixtures containing bitumen with higher PI are more resistant to low temperature cracking as well as permanent deformation [30]. Table 5 also indicates the decreased aging effect of zeolites. Compared to base bitumen, the addition of the zeolites decrease the retained penetration- value of the bitumen which simulates the aging of the bitumen during mixing of the aggregate, transportation to the landsite and com-
N
B (ppm) 30
paction in the field. This indicated that the addition of zeolites is less affected during short term aging. The detailed investigation of viscosity test involving natural and synthetic zeolite as well as organic and chemical WMA additive can be found in the study performed by the authors of this study [31]. The results of the research indicated that the addition of zeolites and other kinds of WMA additives decreased the mixing and compaction temperatures of the mixtures. It should be mentioned here that although the temperature reduction is determined by way of viscosity test [23] performed on the bitumen samples involving zeolites; the filler like structure of zeolite within the base bitumen is very delicate affecting the viscosity values. The ASTM standard regarding viscosity test [23] indicates the following statements in the case of determination of a bitumen involving filler like structure: – The single-operator precision (repeatability) standard deviation has been determined to be 21%. Therefore, two results obtained in the same laboratory, by the same operator using the same equipment, in the shortest practical period of time, should be considered not equivalent if the difference in the two results, expressed as a percent of their mean, exceeds 59.4%. – The multilaboratory precision (reproducibility) standard deviation has been determined to be 33.2%. Therefore, two results submitted by two different operators testing the same material
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A. Topal et al. / Construction and Building Materials 57 (2014) 38–44 Table 5 Conventional properties of bitumen prepared with warm mix asphalt additives. Property
Base bitumen
Syntetic zeolite additive content (%) 5
Natural zeolite content (%) 5
Penetration (1/10 mm) Softening point (°C) Penetration index (PI) Retained penetration after TFOT (%) Softening point difference after TFOT (°C) Storage stability (°C) Viscosity at 135 °C (Pa s) Viscosity at 165 °C (Pa s)
55 49.1 1.20 25 5 – 0.413 0.138
52 56 0.27 16 4.1 1.6 0.313 0.112
51 55 0.02 15 3.7 2 0.325 0.113
in different laboratories shall be considered not equivalent if the difference in the two results, expressed as a percent of their mean, exceeds 94.0%. As can be seen, the repeability of the viscosity test regarding filler like structure involving bitumen is low. Therefore it is recommended that the zeolites be added into the mixture rather than base bitumen and the temperature reduction should be determined through the compacted mixture at different temperature levels by taking the final density of the compacted specimen into account and comparing with the density of actual HMA. Within the scope of the study, the asphalt concrete samples are mixed and compacted taking into the temperature reduction through the viscosity test results gained from the study made by the authors which is around 6 °C and 8 °C regarding zeolites [31]. 3.2. Mechanical properties In this study, the optimum bitumen content related to HMA mixtures as well as WMA mixtures containing synthetic zeolite and natural zeolite were determined by the Marshall method, retrieved directly as the bitumen content corresponding to 4% air voids on content–air voids graphic based on second degree polynomial trendlines given in Fig. 1. The optimum bitumen content for HMA mixtures, WMA mixtures containing synthetic zeolite and natural zeolite were determined as 4.76%, 4.32%, and 4.56% respectively. The ITSM values at 20 °C, 25 °C and 30 °C temperatures for HMA mixtures and WMA mixtures containing synthetic zeolite and natural zeolite are shown in Fig. 2. As depicted in Fig. 2, the ITSM values of WMA mixtures containing synthetic zeolite and natural zeolite are higher than HMA mixtures at all tested temperatures. On the other hand, natural zeolite
has more effect in ITSM values in comparison to synthetic zeolite. The ITSM values of HMA mixtures and WMA mixtures containing synthetic zeolite and natural zeolite have significantly decreased by increase in temperature. The variation of ITSM values by temperature change is presented in Fig. 3. As can be seen in Fig. 3, the ITSM values of HMA mixtures and WMA mixtures containing natural zeolite and synthetic zeolite decreased by 57.11%, 46.48% and 41.23% respectively as the temperature hit 25 °C from 20 °C by 5 °C increase. This decrease is more significant at 30 °C. HMA mixture is more affected by temperature change in comparison to WMA mixtures. Among the WMA mixtures, the mixture prepared with bitumen containing natural zeolite are less affected by temperature change than the mixture prepared with bitumen containing synthetic zeolite. The graphs of load cycle numbers which caused the specimens to be cracked in the fatigue test at 20 °C, 25 °C and 30 °C are plotted in semi-logarithmic graphs and shown in Fig. 4 As depicted in Fig. 4, the load cycle numbers of WMA mixtures were more than the load cycle numbers of HMA mixture. This simply indicates that mixtures containing both kinds of zeolites tested within the scope of this study can tolerate more repetition of loads than HMA mixture. Comparing the effect of each additive based on the load cycle number separately, both additives have similar impact on the load cycle number since the synthetic zeolite has slightly better effect than natural zeolite at all temperatures. Although the load cycle numbers differ at all temperatures, the results were completely matched considering mixture kinds. The variation of load cycle numbers by temperature change is given in semi-logarithmic graphs in Fig. 5. As presented in Fig. 5, the load cycle numbers which caused the specimens to be cracked declined considerably as the temperature increased. All types of specimens traced similar decline in terms of load cycles by temperature change. Based on the load cycle
Fig. 1. Optimum bitumen contents corresponding to 4% air voids.
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Fig. 2. ITSM values of HMA mixture and WMA mixtures containing synthetic zeolite and natural zeolite.
Fig. 3. Variation of ITSM values by temperature change.
Fig. 4. Load cycle numbers of HMA mixture and WMA mixtures containing synthetic zeolite and natural zeolite.
A. Topal et al. / Construction and Building Materials 57 (2014) 38–44
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Fig. 5. Variation of load cycle numbers by temperature change.
Fig. 6. Permanent deformations corresponding load cycle numbers.
numbers, the specimens containing synthetic zeolite and natural zeolite have similar behavior in terms of temperature susceptibility. The deformation of the specimens was monitored through linear variable–differential transducers (LVDTs) during the indirect tensile fatigue test. The graphs for the load cycle number corresponding permanent deformation are given in Fig. 6 for HMA mixtures and WMA mixtures at 20 °C temperature. As shown in Fig. 6, HMA mixture and WMA mixtures containing natural zeolite and synthetic zeolite were cracked at approximate values of 4.3 mm, 4 mm, and 3.6 mm deformation strains respectively. The specimens prepared with both natural zeolite and synthetic zeolite WMA additives with ITSM values could withstand higher load cycles and have cracked at lower deformation strains. 4. Conclusions and recommendations Lowering mixing and compaction temperatures and consequently the reduction of energy costs as well as emissions are the dominant advantages of utilization of WMA technologies. The utilization of natural zeolite and synthetic zeolite helps in the reduction of viscosity values which in turn reduces the mixing and compaction temperature. The results obtained from Marshall design demonstrated that the optimum bitumen content decreases by use of zeolites. This decrease is more sensible for synthetic zeolite as there is a 0.44%
reduction in optimum bitumen content compared to HMA mixtures. This reduction can be described as an advantage of using WMA zeolite additives in terms of initial cost. ITSM values regarding HMA mixture and WMA mixtures showed that the utilization of zeolites generally increases the stiffness of mixtures. Besides, synthetic zeolite gives higher ITSM, load cycle number at 20 °C than 25 °C and 30 °C. It can be concluded that fatigue resistance and rutting performance is enhanced more with synthetic zeolite than the natural zeolite. On the other hand, the ITSM values of all mixtures tested within the scope of this study significantly decreased by increase in temperature. The utilization of synthetic zeolite and natural zeolite improves temperature susceptibility of mixtures in terms of stiffness. As well as PI values of bitumen containing natural zeolite, the mixture test results for specimens involving natural zeolite also exhibited that the use of natural zeolite potentially improves the temperature susceptibility. When evaluating the load cycle numbers which caused the specimens to be cracked, synthetic and natural zeolites improve the repetitive loading strength of bituminous mixtures. The load cycle numbers of all mixtures significantly decrease by increase in temperature. All mixtures show exhibit behavior against temperature change. Taking into consideration the deformation strains, WMA mixtures exhibit better performance under constant loading cycles. The utilization of synthetic and natural zeolites improves
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the ability of asphalt pavements against permanent deformation and increases the rigidity of bituminous mixtures. The formation of crack in lower deformation levels as a result of repetitive loading is an indicator for brittle susceptibility level of a specimen. It can be concluded that zeolite containing WMA mixtures exhibit better performance than HMA mixtures from many mechanical point of view such as indirect tensile stiffness moduli and the fatigue behavior. WMA mixtures containing synthetic zeolite and natural zeolite unveil similar mechanical characteristics. Natural zeolite can be considered as an alternative WMA additive to commercial synthetic zeolite. This study covers the mechanical characterization of zeolite involving WMA specimens mixed and compacted based on viscosity test approach. More research should be carried out by adding zeolites into the mixture rather than base bitumen and the temperature reduction of WMA should be determined through the compacted mixture at different temperature levels by taking the final density of the compacted specimen into account and comparing with the density of actual HMA. Acknowledgements This research was sponsored by the Scientific and Technological Research Council of TURKEY (TUBITAK) under the project number 110M567 for which the authors are greatly indebted. The findings and evaluations of the results of this study are not the official view of TUBITAK. References [1] Newcomb D. An introduction to warm-mix asphalt. National Asphalt Pavement Association; 2006. [2] Hurley GC, Prowell BD. Evaluation of potential process for use in warm mix asphalt. J Assoc Asphalt Paving Technol 2006;75:41–90. [3] Kristjansdottr O, Muench ST, Michael L, Burke G. Assessing potential for warmmix asphalt technology adoption. Transport Res Rec 2007;2040:91–9. [4] Rubio MC, Martinez G, Baena L, Moreno F. Warm mix asphalt: an overview. J Cleaner Prod 2012;24:76–84. [5] D’Angelo J, Harm E, Bartoszek J, Baumgardner G, Corrigan M, Cowsert J, et al. Warm-mix asphalt: European practice. American Trade Initiatives; 2008. [6] Croteau JM, Tessier B. Warm mix asphalt paving technologies: a road builder’s perspective. The 2008 Annual Conference of the Transportation Association of Canada, 2008. [7] Button JW, Estakhri C, Wimsatt A. A synthesis of warm-mix Asphalt, Texas Transportation Institute. The Texas A&M University; 2007. [8] Hurley GC, Prowell BD. Evaluation of SasobitÒ for use in warm mix asphalt. National Center for Asphalt Technology; 2005. [9] Austerman AJ, Mogawer WS, Bonaquist R. Evaluating the effects of warm mix asphalt technology additive dosages on the workability and durability of asphalt mixtures containing recycled asphalt pavement. Transportation Research Board 88th Annual Meeting, 2009. [10] Estakhri C, Button J, Alvarez AE. Field and laboratory investigation of warm mix asphalt in texas, Texas Transportation Institute. The Texas A&M University; 2010.
[11] Grace WR. Web site of Grace Co. Zeolite structure, 2010.. [12] ASTM D5-06. Standard test method for penetration of bituminous materials. West Conshohocken (PA), USA: American Society for Testing and Materials; 2006. [13] ASTM D36–95. Test method for softening point of bitumen (ring-and-ball apparatus). West Conshohocken (PA), USA: American Society for Testing and Materials; 2000. [14] ASTM D 1754M-09. Standard test method for effects of heat and air on asphaltic materials (thin-film oven test). West Conshohocken (PA), USA: American Society for Testing and Materials; 2009. [15] ASTM C136. Standard method for sieve analysis of fine and coarse aggregates. West Conshohocken (PA), USA: American Society for Testing and Materials; 2008. [16] ASTM C127-07. Standard test method for density, relative density (specific gravity), and absorption of coarse aggregate. West Conshohocken (PA), USA: American Society for Testing and Materials; 2007. [17] ASTM C128-12. Standard test method for density, relative density (specific gravity), and absorption of fine aggregate. West Conshohocken (PA), USA: American Society for Testing and Materials; 2012. [18] ASTM C131-06. Standard test method for resistance to degradation of small size coarse aggregate by abrasion and impact in the Los Angeles machine. West Conshohocken (PA), USA: American Society for Testing and Materials; 2006. [19] ASTM C88-05. Standard test method for soundness of aggregates by use of sodium sulfate or magnesium sulfate. West Conshohocken (PA), USA: American Society for Testing and Materials; 2005. [20] ASTM C1252-06. Standard test method for uncompacted void content of fine aggregate (as influenced by particle shape, surface texture, and grading). West Conshohocken (PA), USA: American Society for Testing and Materials; 2006. [21] ASTM D4791-10. Standard test method for flat particles, elongated particles, or flat and elongated particles in coarse aggregate. West Conshohocken (PA), USA: American Society for Testing and Materials; 2010. [22] Whiteoak D, Read JM. The shell bitumen handbook. London: Thomas Telford Services Ltd.; 2003. [23] ASTM D4402-12. Standard test method for viscosity determination of asphalt at elevated temperatures using a rotational viscometer. West Conshohocken (PA), USA: American Society for Testing and Materials; 2012. [24] Wu S, Cong P, Yu J, Luo X, Mo L. Experimental investigation of related properties of asphalt binders containing various flame retardants. Fuel 2006;85:1298–304. [25] ASTM D3549-11. Standard test method for thickness or height of compacted bituminous paving mixture specimens. West Conshohocken (PA), USA: American Society for Testing and Materials; 2011. [26] ASTM D6931-12. Standard test method for indirect tensile (IDT) strength of bituminous mixtures. West Conshohocken (PA), USA: American Society for Testing and Materials; 2012. [27] BS DD 213. Method for determination of the indirect tensile stiffness modulus of bituminous mixtures. Draft for development, London: British Standards Institution; 1993. [28] Bs DDABF. Method for determination of the fatigue characteristics of bituminous mixtures using indirect tensile fatigue. Draft for development. London: British Standards Institution; 1997. [29] Nejad FM, Aflaki E, Mohammadi MA. Fatigue behavior of SMA and HMA mixtures. Constr Build Mater 2010;24:1158–65. [30] Sengoz B, Isikyakar G. Analysis of styrene–butadiene–styrene polymer modified bitumen using fluorescent microscopy and conventional test methods. J Hazard Mater 2008;150:424–32. [31] Sengoz B, Topal A, Gorkem C. Evaluation of natural zeolite as warm mix asphalt additive and its comparison with other warm mix asphalt additives. Constr Build Mater 2013;43:242–52.
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Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Evaluation of mixture characteristics of warm mix asphalt involving natural and synthetic zeolite additives Ali Topal a, Burak Sengoz a,⇑, Baha Vural Kok b, Mehmet Yilmaz b, Peyman Aghazadeh Dokandari c, Julide Oner c, Derya Kaya c a b c
Dokuz Eylul University, Faculty of Engineering, Department of Civil Engineering, 35160 Buca, Izmir, Turkey Fırat University, Faculty of Engineering, Department of Civil Engineering, 23119 Elazıg, Turkey Dokuz Eylul University, Graduate School of Natural and Applied Sciences, 35160 Buca, Izmir, Turkey
h i g h l i g h t s The utilization of zeolites decreases the optimum bitumen content. Zeolites improve the repetitive loading strength of bituminous mixtures. Zeolites improves permanent deformation ability and increases rigidity. Natural zeolite is an acceptable alternative to commercial synthetic zeolite.
a r t i c l e
i n f o
Article history: Received 15 November 2013 Received in revised form 17 January 2014 Accepted 24 January 2014 Available online 21 February 2014 Keywords: Warm mix asphalt Natural zeolite Synthetic zeolite Marshall stability Indirect tensile stiffness modulus Fatigue behavior
a b s t r a c t Concerning global warming and economical issues, many recent studies try to introduce innovative technologies applying lower temperatures with higher performance characteristics as alternative solutions for hot mix asphalt (HMA) applications. These new technologies generally named as warm mix asphalt (WMA) technologies implementing various techniques to reduce application temperatures in order to diminish harmful environmental effects of HMA applications and minimize construction costs. An effective technique to perform this task is to provide a foaming effect in mixing phase to increase workability by use of water containing additives such as zeolites. This paper investigates the feasibility of utilizing WMA containing natural zeolite additive in comparison with a commercial kind of synthetic zeolite. Marshall stability, indirect tensile stiffness moduli and fatigue behavior of WMA containing natural and synthetic zeolites have been analyzed and compared with HMA. Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction Most of the field pavement practices around the world consist of conventional hot mix asphalt (HMA). For the last decade, implementing of warm mix asphalt (WMA) technologies has gained popularity in Europe and in some other countries as well as in the USA. The goal of WMA technologies is to obtain required strength and durability which is equivalent to or even better than HMA pavements [1]. The use of WMA technologies offer many benefits to asphalt industries. Many studies have common sight about the various advantages of the utilization of WMA technologies. These advanta-
⇑ Corresponding author. Tel.: +90 232 301 7072; fax: +90 232 301 7253. E-mail address: [email protected] (B. Sengoz). http://dx.doi.org/10.1016/j.conbuildmat.2014.01.093 0950-0618/Ó 2014 Elsevier Ltd. All rights reserved.
ges are all originated from the major feature of WMA additives which is reducing the viscosity of the bitumen [2]. This reduction results in increasing workability and ease of use, ecological benefits due to less emissions and reduction in costs due to less energy use. In terms of workability, the reduced viscosity helps the aggregates to be coated more easily [3,4]. When discussing about environmental benefits, there are serious worries about the greenhouse gases emissions in HMA pavement applications. Due to lower application temperatures of WMA mixes, the emission of carbon dioxide (CO2) and other so called greenhouse gases are lowered in comparison with HMA mixes [5]. Besides, the evaporation of less heavy components of bitumen occurs less than conventional applications. This causes less odors in asphalt plants, therefore provides more pleasant working conditions. Builders comments also indicate that the fumes are rather less in WMA production in comparison with HMA production [6]. The fuel consumption
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of WMA technologies is rather less than conventional HMA mixtures. Energy consumption for WMA production has been reported as 60–80% of HMA production [4]. Some studies have also reported the range of 20–35% of savings in burner fuel with use of WMA technologies [5]. In asphalt industry, a common way of achieving lower application temperatures in order to produce WMA is the utilization of WMA additives. All of the current WMA additives facilitate lowering of production temperature by either lowering the viscosity and/or expanding the volume of the bitumen at a given temperature [7,8]. Nowadays, there are many WMA additives available on the market. One of these additives is categorized as synthetic zeolite. Zeolites due to their honeycomb microstructure can preserve water within their micropores and release it above the boiling point of water when heated. [5]. Hence, zeolites have been detected as suitable additives by asphalt industries in order to expand the volume of bitumen by foaming effect. Synthetic zeolite has been hydro-thermally crystallized. It contains about 18–21% water of crystallization which is released by increasing temperature above 85 °C. The expansion of water causes foaming of asphalt bitumen [9,10]. Natural zeolites are microporous, hydrated aluminosilicate minerals commonly used as commercial adsorbents [11]. Clinoptilolite is one of the most common natural zeolite comprising a microporous arrangement of silica and alumina tetrahedral which has large amount of pore space, high resistance to extreme temperatures and chemically neutral basic structure [11]. This study investigates the feasibility of utilizing WMA mixtures containing natural zeolite additive in comparison with a commercial kind of synthetic zeolite. Marshall stability, Indirect Tensile Stiffness Moduli (ITSM) and fatigue behavior of WMA specimens containing natural and synthetic zeolites have been analyzed and compared with HMA specimens. 2. Experimental
A kind of synthetic zeolite additive is manufactured in North America by PQ Corporation. Austerman et al. [9] and PQ Corporation [10] have reported that the maximum rate of this synthetic additive in base bitumen varies between 4% and 6% by weight of bitumen. The synthetic zeolite additive concentration in the base bitumen was chosen as 5% based on a past research made by PQ Corporation [10]. Natural zeolite WMA additive which is used in this study has been supplied from a Turkish local company in powder form. The complex formula of this natural zeolite is (Na3K3)(Al6Si30O72)27H2O. It forms as white to reddish tabular monoclinic tectosilicate crystals with a Mohs hardness of 3.5–4.0 and a specific gravity of 2.1–2.2. The content of natural zeolite in this study has been chosen as 5% by weight of bitumen in order to compare its fundamental characteristics with synthetic zeolite. The properties of natural zeolite are presented in Table 4. 2.2. Test methods 2.2.1. Conventional bitumen tests The base samples and the bitumen samples containing synthetic zeolite and natural zeolite additives were subjected to the following conventional bitumen tests; penetration (ASTM D5-06), ring and ball softening point (ASTM D36-95), thin film oven test (TFOT) (ASTM D 1754M-09), penetration and softening point after TFOT and storage stability test (EN 13399 (2010)) [12–14]. In addition, the temperature susceptibility of the bitumen samples has been calculated in terms of penetration index (PI) using the results obtained from penetration and softening point tests [22]. The effect of viscosity on asphalt bitumen’s workability is very important in selecting proper mixing and compacting temperatures. Brookfield Viscometer was employed to inspect the mixing and compaction temperatures in according to ASTM D4402-12 [23,24]. The test was performed at 135 °C and 165 °C. The temperatures corresponding to bitumen viscosities 170 ± 20 m Pa s and 280 ± 30 m Pa s were chosen as mixing and compaction temperatures respectively. 2.2.2. Mechanical properties The effect of synthetic zeolite and natural zeolite additives on the mechanical properties of WMA has been determined by Marshall method (ASTM D3549) in terms of stability, flow and air void content as well as by indirect tensile stiffness modulus test (BS DD 213) and indirect tensile fatigue test (BS DD ABF) [25–28]. The tests were conducted on WMA samples at recommended contents and on HMA as control samples. Asphalt concrete specimens were prepared with a compaction effort of 75 blows simulating heavy traffic loading conditions. The ITSM test is a non-destructive test that is used to evaluate the relative quality of materials and study the effect of temperature and loading rate. The ITSM Sm in MPa is defined as below [27];
Sm ¼ FðR þ 0:27Þ=LH
2.1. Materials The base bitumen with a 50/70 penetration grade was obtained from Aliaga/Izmir Oil Terminal of the Turkish Petroleum Refinery Corporation. In order to characterize the properties of the base bitumen, conventional test methods such as: penetration test (ASTM D5-06), softening point test (ASTM D36-95), thin film oven test (TFOT) (ASTM D1754-97), penetration and softening point after TFOT, etc. were performed [12–14]. These tests were conducted in conformity with the relevant test methods that are presented in Table 1. A mix of basalt and limestone aggregates provided from Dere Madencilik Inc. _ (Quarry located in Belkahve–Izmir/Turkey) was used in this study. In order to find out the properties of basalt and limestone aggregate, sieve analysis (ASTM C136), specific gravity (ASTM C127-07, ASTM C128-12), Los Angeles abrasion resistance test (ASTM C131-06), sodium sulfate soundness test (ASTM C88-05), fine aggregate angularity test (ASTM C1252-06) and flat and elongated particle tests (ASTM D4791-10) were conducted on basalt and limestone aggregates [15–21]. Physical properties of each kind are given in Table 2. Based on the associated test results, a mix gradation of basalt and limestone was intentionally chosen to provide desired performance in conformity with Turkish specifications concerning the Type 1 wearing course. Basalt plays the role of strengthening constituent as coarse aggregate while limestone participates in the fine aggregate framework. The gradation is given in Table 3.
ð1Þ
where F is the peak value of the applied vertical load (repeated load, N), H is the mean amplitude of the horizontal deformation (mm) obtained from five applications of the load pulse, L is the mean thickness of the test specimen (mm), and R is the Poisson’s ratio (assumed as 0.35). The test was performed by way of a universal testing machine (UTM) in deformation-controlled mode. The magnitude of the applied force was adjusted by the system during the first five conditioning pulses such that the specified target peak transient diametral deformation was obtained. An appropriate value was chosen to ensure that sufficiently high signal amplitudes were obtained from the transducers which would produce consistent and accurate results. Accordingly, this value was selected as 5 lm for this test. The rise time, which is measured from the origination of load pulse and denotes the duration of the applied load rising from zero to the maximum value, was set at 124 ms. The load pulse application was adjusted to 3.0 s. ITSM tests were conducted at three different temperatures (20 °C, 25 °C and 30 °C). The indirect tensile fatigue test is one of the constant stress test that characterizes the fatigue behavior of the mixture [29]. In this study, the fatigue test was performed in a controlled stress mode based on BS DD ABF standard [28]. The UTM was also used for this purpose. The loading frame was housed in an environmental chamber to control temperature during the test. The desired load level, load rate and load duration were controlled by a computer. The deformation of the specimen was monitored through linear variable-differential transducers (LVDTs). The LVDTs
Table 1 Properties of the base bitumen. Test
Specification
Results
Specification limits
Penetration (25 °C; 0.1 mm) Softening point (°C) Viscosity at (135 °C)-Pa s Thin film oven test (TFOT) (163 °C; 5 h) Change of mass (%) Retained penetration after TFOT (%) Softening point diff. after TFOT (°C) Specific gravity Flash point (°C)
ASTM ASTM ASTM ASTM
D5 D36 D4402 D1754
55 49.1 0.413
50–70 46–54 –
ASTM ASTM ASTM ASTM
D5 D36 D70 D92
0.04 25 5 1.030 +260
0.5 (max) – 7 (max) – 230 (min)
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Table 2 Physical properties of used aggregates. Test
Specification
Specific gravity (coarse agg.) Bulk Saturated surface dry Apparent Specific gravity (fine agg.) Bulk Saturated surface dry Apparent Specific gravity (filler) Los Angeles Abrasion (%) Flat and elongated particles (%) Sodium sulfate soundness (%) Fine aggregate angularity
ASTM C 127
Results
Limits
Limestone
Basalt
2.686 2.701 2.727
2.666 2.810 2.706
– – –
2.687 2.703 2.732 2.725 24.4 7.5 1.47 47.85
2.652 2.770 2.688 2.731 14.2 5.5 2.6 58.1
– – – – Max 35 Max 10 Max 10 Min 40
ASTM C 128
ASTM ASTM ASTM ASTM
C 131 D 4791 C 88 C 1252
Table 3 Gradation of the aggregates. Test
19–12.5 mm (Basalt)
12.5–5 mm (Basalt)
5–0 mm (Limestone)
Mixture ratio (%)
15
45
40
Gradation (3/4)00 (1/2)00 (3/8)00 No 4 No 10 No 40 No 80 No 200
100 35.7 2.5 0.4 0.3 0.2 0.15 0.10
100 100 89 16 1.2 0.7 0.4 0.2
100 100 100 100 81 33 22 13
Combined gradation (%)
Specification limits
100 90.5 80.5 47.3 33 13.5 9 5.3
100 83–100 70–90 40–55 25–38 10–20 6–15 4–10
Table 4 Physical properties and chemical structure of natural zeolite. Chemical structure SiO2
Al2O3
Fe2O3
K2O
H2O
CaO
MgO
Na2O
Ti
Ag
Content (%)
13.55
1.15
3.5
5.9
1.96
0.7
0.6
0.02
0.04
71.29
Physical properties Voids (%) Dimensions of the main channels (A)
Thermal stability
Ion exchange capacity (meq/g)
34
High
2.16
3.9 5.4
were clamped vertically onto the diametrical side of the specimen. A repeated dynamic compressive load at 350 kPa was applied to specimens at 20 °C, 25 °C and 30 °C test temperatures, across the vertical cross-section along the depth of the specimen using two loading strips 12.5 mm in width. Finally, the resulting total deformation corresponding to the applied force was measured.
3. Result and discussions 3.1. Conventional test results The conventional properties of the bitumen prepared with synthetic zeolite and natural zeolite additives are presented in Table 5 as a decrease in penetration and increase in softening point. The increase in softening point is favorable since bitumen with higher softening point may be less susceptible to permanent deformation (rutting) [30]. Synthetic zeolite and natural zeolite reduce temperature susceptibility (as determined by the penetration index–PI) of the bitumen. Lower values of PI indicate higher temperature susceptibility. Asphalt mixtures containing bitumen with higher PI are more resistant to low temperature cracking as well as permanent deformation [30]. Table 5 also indicates the decreased aging effect of zeolites. Compared to base bitumen, the addition of the zeolites decrease the retained penetration- value of the bitumen which simulates the aging of the bitumen during mixing of the aggregate, transportation to the landsite and com-
N
B (ppm) 30
paction in the field. This indicated that the addition of zeolites is less affected during short term aging. The detailed investigation of viscosity test involving natural and synthetic zeolite as well as organic and chemical WMA additive can be found in the study performed by the authors of this study [31]. The results of the research indicated that the addition of zeolites and other kinds of WMA additives decreased the mixing and compaction temperatures of the mixtures. It should be mentioned here that although the temperature reduction is determined by way of viscosity test [23] performed on the bitumen samples involving zeolites; the filler like structure of zeolite within the base bitumen is very delicate affecting the viscosity values. The ASTM standard regarding viscosity test [23] indicates the following statements in the case of determination of a bitumen involving filler like structure: – The single-operator precision (repeatability) standard deviation has been determined to be 21%. Therefore, two results obtained in the same laboratory, by the same operator using the same equipment, in the shortest practical period of time, should be considered not equivalent if the difference in the two results, expressed as a percent of their mean, exceeds 59.4%. – The multilaboratory precision (reproducibility) standard deviation has been determined to be 33.2%. Therefore, two results submitted by two different operators testing the same material
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A. Topal et al. / Construction and Building Materials 57 (2014) 38–44 Table 5 Conventional properties of bitumen prepared with warm mix asphalt additives. Property
Base bitumen
Syntetic zeolite additive content (%) 5
Natural zeolite content (%) 5
Penetration (1/10 mm) Softening point (°C) Penetration index (PI) Retained penetration after TFOT (%) Softening point difference after TFOT (°C) Storage stability (°C) Viscosity at 135 °C (Pa s) Viscosity at 165 °C (Pa s)
55 49.1 1.20 25 5 – 0.413 0.138
52 56 0.27 16 4.1 1.6 0.313 0.112
51 55 0.02 15 3.7 2 0.325 0.113
in different laboratories shall be considered not equivalent if the difference in the two results, expressed as a percent of their mean, exceeds 94.0%. As can be seen, the repeability of the viscosity test regarding filler like structure involving bitumen is low. Therefore it is recommended that the zeolites be added into the mixture rather than base bitumen and the temperature reduction should be determined through the compacted mixture at different temperature levels by taking the final density of the compacted specimen into account and comparing with the density of actual HMA. Within the scope of the study, the asphalt concrete samples are mixed and compacted taking into the temperature reduction through the viscosity test results gained from the study made by the authors which is around 6 °C and 8 °C regarding zeolites [31]. 3.2. Mechanical properties In this study, the optimum bitumen content related to HMA mixtures as well as WMA mixtures containing synthetic zeolite and natural zeolite were determined by the Marshall method, retrieved directly as the bitumen content corresponding to 4% air voids on content–air voids graphic based on second degree polynomial trendlines given in Fig. 1. The optimum bitumen content for HMA mixtures, WMA mixtures containing synthetic zeolite and natural zeolite were determined as 4.76%, 4.32%, and 4.56% respectively. The ITSM values at 20 °C, 25 °C and 30 °C temperatures for HMA mixtures and WMA mixtures containing synthetic zeolite and natural zeolite are shown in Fig. 2. As depicted in Fig. 2, the ITSM values of WMA mixtures containing synthetic zeolite and natural zeolite are higher than HMA mixtures at all tested temperatures. On the other hand, natural zeolite
has more effect in ITSM values in comparison to synthetic zeolite. The ITSM values of HMA mixtures and WMA mixtures containing synthetic zeolite and natural zeolite have significantly decreased by increase in temperature. The variation of ITSM values by temperature change is presented in Fig. 3. As can be seen in Fig. 3, the ITSM values of HMA mixtures and WMA mixtures containing natural zeolite and synthetic zeolite decreased by 57.11%, 46.48% and 41.23% respectively as the temperature hit 25 °C from 20 °C by 5 °C increase. This decrease is more significant at 30 °C. HMA mixture is more affected by temperature change in comparison to WMA mixtures. Among the WMA mixtures, the mixture prepared with bitumen containing natural zeolite are less affected by temperature change than the mixture prepared with bitumen containing synthetic zeolite. The graphs of load cycle numbers which caused the specimens to be cracked in the fatigue test at 20 °C, 25 °C and 30 °C are plotted in semi-logarithmic graphs and shown in Fig. 4 As depicted in Fig. 4, the load cycle numbers of WMA mixtures were more than the load cycle numbers of HMA mixture. This simply indicates that mixtures containing both kinds of zeolites tested within the scope of this study can tolerate more repetition of loads than HMA mixture. Comparing the effect of each additive based on the load cycle number separately, both additives have similar impact on the load cycle number since the synthetic zeolite has slightly better effect than natural zeolite at all temperatures. Although the load cycle numbers differ at all temperatures, the results were completely matched considering mixture kinds. The variation of load cycle numbers by temperature change is given in semi-logarithmic graphs in Fig. 5. As presented in Fig. 5, the load cycle numbers which caused the specimens to be cracked declined considerably as the temperature increased. All types of specimens traced similar decline in terms of load cycles by temperature change. Based on the load cycle
Fig. 1. Optimum bitumen contents corresponding to 4% air voids.
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Fig. 2. ITSM values of HMA mixture and WMA mixtures containing synthetic zeolite and natural zeolite.
Fig. 3. Variation of ITSM values by temperature change.
Fig. 4. Load cycle numbers of HMA mixture and WMA mixtures containing synthetic zeolite and natural zeolite.
A. Topal et al. / Construction and Building Materials 57 (2014) 38–44
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Fig. 5. Variation of load cycle numbers by temperature change.
Fig. 6. Permanent deformations corresponding load cycle numbers.
numbers, the specimens containing synthetic zeolite and natural zeolite have similar behavior in terms of temperature susceptibility. The deformation of the specimens was monitored through linear variable–differential transducers (LVDTs) during the indirect tensile fatigue test. The graphs for the load cycle number corresponding permanent deformation are given in Fig. 6 for HMA mixtures and WMA mixtures at 20 °C temperature. As shown in Fig. 6, HMA mixture and WMA mixtures containing natural zeolite and synthetic zeolite were cracked at approximate values of 4.3 mm, 4 mm, and 3.6 mm deformation strains respectively. The specimens prepared with both natural zeolite and synthetic zeolite WMA additives with ITSM values could withstand higher load cycles and have cracked at lower deformation strains. 4. Conclusions and recommendations Lowering mixing and compaction temperatures and consequently the reduction of energy costs as well as emissions are the dominant advantages of utilization of WMA technologies. The utilization of natural zeolite and synthetic zeolite helps in the reduction of viscosity values which in turn reduces the mixing and compaction temperature. The results obtained from Marshall design demonstrated that the optimum bitumen content decreases by use of zeolites. This decrease is more sensible for synthetic zeolite as there is a 0.44%
reduction in optimum bitumen content compared to HMA mixtures. This reduction can be described as an advantage of using WMA zeolite additives in terms of initial cost. ITSM values regarding HMA mixture and WMA mixtures showed that the utilization of zeolites generally increases the stiffness of mixtures. Besides, synthetic zeolite gives higher ITSM, load cycle number at 20 °C than 25 °C and 30 °C. It can be concluded that fatigue resistance and rutting performance is enhanced more with synthetic zeolite than the natural zeolite. On the other hand, the ITSM values of all mixtures tested within the scope of this study significantly decreased by increase in temperature. The utilization of synthetic zeolite and natural zeolite improves temperature susceptibility of mixtures in terms of stiffness. As well as PI values of bitumen containing natural zeolite, the mixture test results for specimens involving natural zeolite also exhibited that the use of natural zeolite potentially improves the temperature susceptibility. When evaluating the load cycle numbers which caused the specimens to be cracked, synthetic and natural zeolites improve the repetitive loading strength of bituminous mixtures. The load cycle numbers of all mixtures significantly decrease by increase in temperature. All mixtures show exhibit behavior against temperature change. Taking into consideration the deformation strains, WMA mixtures exhibit better performance under constant loading cycles. The utilization of synthetic and natural zeolites improves
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the ability of asphalt pavements against permanent deformation and increases the rigidity of bituminous mixtures. The formation of crack in lower deformation levels as a result of repetitive loading is an indicator for brittle susceptibility level of a specimen. It can be concluded that zeolite containing WMA mixtures exhibit better performance than HMA mixtures from many mechanical point of view such as indirect tensile stiffness moduli and the fatigue behavior. WMA mixtures containing synthetic zeolite and natural zeolite unveil similar mechanical characteristics. Natural zeolite can be considered as an alternative WMA additive to commercial synthetic zeolite. This study covers the mechanical characterization of zeolite involving WMA specimens mixed and compacted based on viscosity test approach. More research should be carried out by adding zeolites into the mixture rather than base bitumen and the temperature reduction of WMA should be determined through the compacted mixture at different temperature levels by taking the final density of the compacted specimen into account and comparing with the density of actual HMA. Acknowledgements This research was sponsored by the Scientific and Technological Research Council of TURKEY (TUBITAK) under the project number 110M567 for which the authors are greatly indebted. The findings and evaluations of the results of this study are not the official view of TUBITAK. References [1] Newcomb D. An introduction to warm-mix asphalt. National Asphalt Pavement Association; 2006. [2] Hurley GC, Prowell BD. Evaluation of potential process for use in warm mix asphalt. J Assoc Asphalt Paving Technol 2006;75:41–90. [3] Kristjansdottr O, Muench ST, Michael L, Burke G. Assessing potential for warmmix asphalt technology adoption. Transport Res Rec 2007;2040:91–9. [4] Rubio MC, Martinez G, Baena L, Moreno F. Warm mix asphalt: an overview. J Cleaner Prod 2012;24:76–84. [5] D’Angelo J, Harm E, Bartoszek J, Baumgardner G, Corrigan M, Cowsert J, et al. Warm-mix asphalt: European practice. American Trade Initiatives; 2008. [6] Croteau JM, Tessier B. Warm mix asphalt paving technologies: a road builder’s perspective. The 2008 Annual Conference of the Transportation Association of Canada, 2008. [7] Button JW, Estakhri C, Wimsatt A. A synthesis of warm-mix Asphalt, Texas Transportation Institute. The Texas A&M University; 2007. [8] Hurley GC, Prowell BD. Evaluation of SasobitÒ for use in warm mix asphalt. National Center for Asphalt Technology; 2005. [9] Austerman AJ, Mogawer WS, Bonaquist R. Evaluating the effects of warm mix asphalt technology additive dosages on the workability and durability of asphalt mixtures containing recycled asphalt pavement. Transportation Research Board 88th Annual Meeting, 2009. [10] Estakhri C, Button J, Alvarez AE. Field and laboratory investigation of warm mix asphalt in texas, Texas Transportation Institute. The Texas A&M University; 2010.
[11] Grace WR. Web site of Grace Co. Zeolite structure, 2010.