Evaluation of incorporating oil shale filler aggregate into hot mix asphalt using Superpave mix design

Construction and Building Materials 101 (2015) 359–379

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Evaluation of incorporating oil shale filler aggregate into hot mix asphalt using Superpave mix design Mohammed O.J. Azzam a,⇑, Ziad Al-Ghazawi b a b

Dept. of Chemical Engineering, Jordan University of Science and Technology, P.O. Box 3030, Irbid 22110, Jordan Dept. of Civil Engineering, Jordan University of Science and Technology, P.O. Box 3030, Irbid 22110, Jordan

h i g h l i g h t s

g r a p h i c a l a b s t r a c t


Replacement of filler size limestone

aggregate with oil shale is promising.
The properties of modified HMA have

either remained acceptable (not changed) or improved.
Rutting and fatigue resistances for some tested compositions increased by around 50%.
Incorporation of oil shale into HMA pavement has a positive overall economic potential.

a r t i c l e

i n f o

Article history: Received 25 June 2015 Received in revised form 21 August 2015 Accepted 15 October 2015

Keywords: Oil shale Hot mix asphalt Pavement Superpave Creep Fatigue

a b s t r a c t The world is on the run looking for new energy resources, improvements and conservation on current energy resources while at the same time trying to keep the environment safe and clean, keeping in mind the economic constraints of all the above. Recycling and minimization of waste produced from the above activities are among top priorities for policy makers. Oil shale is on the rise as an additional source of energy. This sector of the industry has not yet reached maturity and still under development. One application of oil shale is the direct combustion, where fine oil shale is produced as a waste and considered an environmental hazard. This investigation proposed the incorporation of such filler size oil shale into hot mix asphalt (HMA). The study used Superpave design method. The study included resilient modulus, creep and fatigue measurements. The results showed a mixed performance where, depending on the HMA formulation, the inclusion of oil shale filler produced better performance than the control limestone filler whereas other formulations showed the contrary. Ó 2015 Elsevier Ltd. All rights reserved.

1. Introduction There are so many worldwide attempts to look for other than fossil fuel resources of energy. Terminologies such as wind energy [65,24], photovoltaic cells and solar energy [29,78,42], geothermal ⇑ Corresponding author. E-mail addresses: [email protected] (M.O.J. Azzam), [email protected] (Z. Al-Ghazawi). http://dx.doi.org/10.1016/j.conbuildmat.2015.10.071 0950-0618/Ó 2015 Elsevier Ltd. All rights reserved.

energy [79,20], ocean waves [60,75], biofuels [41,51,38] and of course nuclear energy [21,69] are becoming familiar to the young before the old generations. There is tremendous research and development work done and still being done on these areas. Despite all of the above, it seems that the world dependence on fossil fuel as the primary source of energy is going to stay for some time. Shale gas [33,71,70,30] and shale oil [45,11,62] are on the rising side of relatively new fossil fuel resources.

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Table 1 Properties of asphalt binder. Property

Value

Test method

Penetration, at 25 °C, 0.1 mm Ductility, at 25 °C, cm Viscosity, at 135 °C, Pa s Softening Point, °C Flash Point, °C Fire Point, °C Specific Gravity, at 25 °C

66 104 0.355 53 298 314 1.009

ASTM ASTM ASTM ASTM ASTM ASTM ASTM

D5 D113 D4402 D36 D92 D92 D70

Shale gas production is in the news, however, shale oil is still under development. There are several technologies used in RD&D (Research, Development & Demonstration) projects in the USA, Estonia, China, and other countries to recover shale oil and gas from oil shale deposits [18] such as the underground mining and surface retorting (used by OSEC – Oil Shale Exploration Co. and

in situ conversion process (ICP) using self-contained heaters (used by Shell). Jordan ranks third in the world with respect to oil shale resource estimates [17]. Jordan’s supply of energy depends heavily on imported oil and natural gas. Oil shale is considered a major possible alternative source of energy in Jordan which has an estimated 50 billion tons of geological proven reserves of oil shale that is widely distributed all over the country [27]. Oil shale is a layered sedimentary rock that contains significant quantities of kerogen. Jordanian oil shale is mainly composed of calcium compounds (calcium carbonate content is about 40–70%), in addition to sulfur compounds (around 3%), organic matter (total organic matter is about 20%), silicon compounds (around 5–25%). When heated to temperatures above 480 °C, the kerogen in the shale decomposes producing shale oil, gas and spent shale. The average oil content of oil shale is generally in the range of 5–15% [27].

Fig. 1. (a) Rotational viscosity (RV) instrument; (b) dynamic shear rheometer (DSR) instrument, note a test sample shown at the bottom of the figure; (c) bending beam rheometer (BBR), (d) BBR test sample.

M.O.J. Azzam, Z. Al-Ghazawi / Construction and Building Materials 101 (2015) 359–379 Table 2 Rotational viscosity (RV) of used asphalt binder. Temperature (°C)

RV (cP)

135 160

355 158

Table 3 DSR test results for 60/70 original asphalt binder.

a

Test temperature (°C)

(G*/sin d) before RTFOa (kPa)

Superpave criteria

58 64 70

4.5 2.1 0.92

Minimum of 1.0 kPa for original asphalt binder

RTFO stands for Rolling Thin Film Oven.

Table 4 DSR test results for 60/70 RTFO-aged asphalt binder. Test temperature (°C)

(G*/sin d) after RTFO (kPa)

Superpave criteria

58 64 70

11.6 4.15 1.8

Minimum of 2.2 kPa for RTFO-aged asphalt binder

Table 5 DSR test results for 60/70 PAVa-aged asphalt binder.

a

Test temperature (°C)

(G*/sin d) after PAV (kPa)

Superpave criteria

25 28 31 34

650 520 380 270

Maximum of 5000 kPa for PAV-aged asphalt binder

PAV stands for Pressure Aging Vessel.

Table 6 BBR test results for 60/70 PAV-aged asphalt binder. Test temperature (°C)

At 60 s Creep stiffness (MPa)

m – value

0 6 Superpave criteria

18.6 15.2 Maximum of 300 MPa

0.35 0.28 Minimum of 0.300

Table 7 Asphalt binder performance grade (PG). Asphalt binder

Performance grade (PG)

60/70

64–10

One way of making use of oil shale is by direct combustion of oil shale from mining sites to power plants in the same way as coal [68,43,40]. This is being done for example in Estonia which has one of the highest grade deposits in the world with an average heating value of about 8.3 MJ/kg [15,10]. The above method requires crushing, grinding, milling and classification activities to be done on oil shale rocks which generate fine sizes of particles of oil shale that are not only not useful in the above power

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generation processes, but also may be considered an environmental hazard. Another method of benefitting from oil shale is the extraction of shale oil from oil shale. Many investigations have been done and are still being done on this method [56,23,9,3,6]. A third way of using oil shale is to incorporate it in concrete mixes. Jordanian oil shale contains 50–60% ash. This high value has motivated some researchers to investigate the use of this oil shale in the production of cement or as an additive to concrete. For example, Al-Otoom [8] has reported a reduction in the required cement clinkering reactions temperature when oil shale was added to the clinker mixture during production, and hence a potential cost reduction in the production of Portland cement. In another investigation by Smadi and Haddad [66], spent oil shale that resulted from a retorting operation at 600 °C was added to concrete mixes. The study reported that the compressive strength of investigated concrete was not affected significantly. On the other hand, spent oil shale ash was reported to have poor cementing properties. In a previous investigation by Khedawi et al. [37], who investigated the addition of oil shale ash to Pozzolanic cement, the cement activity was not promising due to the fact that commercial Pozzolanic cement had a higher cement activity than the modified cement with oil shale ash. A fourth way of benefitting from oil shale is to incorporate it in asphalt pavement mixtures, which is the subject of this work. Several investigators studied the effect of employing shale oil (not oil shale) in asphalt and/or asphalt pavement mixtures. For example, Mahboub et al. [44] conducted a feasibility study to establish possible paving applications of oil extracted from eastern shale (Kentucky, USA) by the KENTORT II process. They concluded that depending on the viscosity of employed shale oil the asphalt properties exhibited desirable or undesirable behavior. The authors recommended further studies to fully characterize the binder and mixture properties of investigated shale oil. In another study, Thomas et al. [67] made a comparative field assessment of shale oil-modified asphalt with polymer-modified asphalts. The authors concluded that even though the properties were comparative, the cost of the shale oil-modified asphalt was much lower. Katamine [34] on the other hand, investigated the rheological properties of conventional asphalt binder in comparison to the same binder but modified with shale oil obtained from Jordanian oil shale. The study concentrated on evaluation of deformation resistance of hot mix asphalt. He adopted Marshall design method for sample preparation and testing, in addition to the immersion wheel tracking machine. He concluded that the shale oil binders should be treated before being used because they displayed inconsistent physical properties. Regarding the subject of hot mix asphalt (HMA) pavement investigations, the literature is rich of varieties of research conducted in this area. For example, aggregate replacements; such as cement kiln dust, coal waste powder, waste glass and glass fiber scrap [49,50,64,14,76] were investigated. Others have investigated the use of recycled waste materials; such as recycled concrete and recycled bricks [25,57,59,19]; into the aggregate, or recycled asphalt shingles, waste plastics or reclaimed asphalt binder, into the asphalt binder [2,31,54,39,80,81,46]. One investigation even considered using sludge waste in HMA [7]. Other investigations were concerned with asphalt binder modified with polymers; such as polyethylene, polyethylene terephthalate, ethylene vinyl acetate and rubber [55,52,12,26,82], or non-polymeric materials; such as bio-oil and monoethylene and diethylene glycols [72,16], and more recently with nano-materials; such as carbon nanotubes (CNT), carbon nanofibers (CNF), nanoclays, nanosilica and nano-titanium dioxide [13,63,35,74,73]. Some investigations were even done on improving the testing methods of HMA [36,22,61], or on the

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Fig. 2. XRD-pattern of investigated limestone aggregate.

Table 8 Chemical composition (X-ray fluorescence (XRF)) of limestone and oil shale aggregates. Component

Limestone aggregate (wt.%)

Oil shale (wt.%)

Fe2O3 MnO TiO2 CaO K2O P2O5 SiO2 Al2O3 MgO Na2O SO3 Cl L.O.I.

0.39 0.006 0.05 51.49 0.09 0.033 2.20 0.56 3.08 0.015 0.078 0.90 42.0

1.36 0.001 0.19 23.60 0.47 2.97 32.20 3.15 0.45 0.38 – – 35.20

interpretations of the results of such tests [4], or on HMA mixing process conditions [58]. It is worth reemphasizing at this point that Jordan has limited oil resources; however, it has enormous reserves of oil shale. Approximately, 40–60% of Jordanian land contains different sources of oil shale. Currently, Jordan is moving ahead with major projects that are to exploit this national treasure (projects with JOSCO and Enefit companies). During the mining process of oil shale, some of these projects are expected to produce very fine particles of oil shale. Some of these fine sizes are considered an environmental and health hazards. One key solution to these expected hazards is to incorporate these harmful sizes of oil shale powder into HMA pavements. The objective of this work was to study the effect of replacing classical limestone filler aggregate of HMA pavement with oil shale filler. The investigation used Superpave design method. Major investigation parameters included resilient modulus, creep and fatigue.

Fig. 3. Thermal gravimetric analysis (TGA) of limestone aggregate.

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Fig. 4. Scanning electron micrograph (SEM) image of a sample of limestone (top left) and its elemental analysis using EDS technique (top right), and the elements count pattern (bottom).

2. Materials and methods 2.1. Asphalt binder The asphalt binder employed in this study was obtained from Jordan Oil Refinery Company, Jordan. Table 1 shows its properties. 2.1.1. Asphalt binder evaluation according to Superpave criteria 2.1.1.1. Rotational viscosity. Rotational viscosity of used asphalt binder in this investigation was measured using a Brookfield instrument (Fig. 1) at both 135 and 160 °C. The results are presented in Table 2. Based on this data, it was determined that the mixing temperature range is 152–160 °C, while the compaction temperature range is 138–145 °C.

2.1.1.2. Dynamic shear rheometer (DSR). The dynamic shear rheometer (DSR) is used to investigate the viscous and elastic behavior of asphalt binders at different temperatures (Fig. 1). The DSR test employs a thin asphalt binder sample inserted between two circular plates. The upper plate oscillates back and forth across the sample at 10 rad/s (1.59 Hz) to create a shearing action while the lower plate is fixed. DSR tests were conducted on un-aged, rolling-thin-film-oven (RTFO) aged and pressure-aging-vessel (PAV) aged asphalt binder samples. Tables 3–5 show the results of DSR test before aging and after aging. 2.1.1.3. Bending beam rheometer (BBR). The BBR test gives a measure of low temperature stiffness and relaxation properties of asphalt binders (see Fig. 1 for equipment and sample shape) which indicates an asphalt binder’s ability to resist low temperature cracking. The bending beam rheometer test results are shown in Table 6.

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M.O.J. Azzam, Z. Al-Ghazawi / Construction and Building Materials 101 (2015) 359–379 When combining the weight percentages of CaO and L.O.I. (loss on ignition) of Table 8 for limestone, one obtains 93 wt.%, indicating that calcite was the dominant component of the used limestone. A QUANTA FEG 450 scanning electron microscope was used to investigate how the aggregate looks like on a micro-scale. Fig. 4 shows a sample scanning electron micrograph (SEM) image of a sample of limestone (top left) and its elemental analysis using energy-dispersive X-ray spectroscopy (EDX) technique (top right), and the elements count pattern (bottom). Combining the wt.% of C, O and Ca (the major elements of calcite), one obtains 90 wt.%, confirming the above results of XRF and XRD.

Fig. 5. Sultani oil shale mine.

2.1.1.4. Asphalt binder performance grade (PG). Based on the results of the above tests, the performance grade of the asphalt binder used in this investigation was determined to be as shown in Table 7.

2.2. Aggregate 2.2.1. Limestone Limestone aggregate was obtained from a local mine (Ajloun, North of Jordan). It was sieved into standard sizes and then mixed according to standard gradations to be incorporated in the HMA pavement mixtures. Representative and homogenized samples of the above limestone were taken for the analysis presented below. X-ray diffraction (XRD) of limestone was performed using a HiltonbrooksÒ generator with a PhilipsÒ X’Pert Pro PW 3040n60 diffractometer with an automatic divergence slit, and Cu anode producing X-rays of wavelength k = 1.54 Å. Fig. 2 presents the above XRD-pattern. As expected, it is observed from the XRD-pattern that calcite is the dominant material. The chemical composition of the used limestone was obtained by X-ray fluorescence (XRF) according to ASTM C1271–99, and is given in Table 8. XRF for the samples utilized a Philips PW1404 Wavelength Dispersive Sequential XRF Spectrometer controlled by Philip X40 software. The composition indicated that limestone is primarily composed of calcite with small quantities of dolomite and silica. Fig. 3 shows the thermo-gravimetric analysis (TGA) of the above limestone confirming the calcite domination of its components. It is observed from XRF results that CaO is the dominant material confirming the XRD results presented in Fig. 2.

2.2.2. Oil shale Oil shale was obtained from Sultani mine (Fig. 5), south of Jordan. The shale bed is about 32 m thick and has an overburden of an average of 70 m [32]. The shale was obtained in several rock sizes (from about 1 g to 10 kg rocks). The rocks were crushed, milled, and then sieved into several sizes. The chemical composition of the above oil shale was obtained by XRF, using the same ASTM standard method and equipment as that for limestone, and is given in Table 8. Figs. 6 and 7 show the XRD-pattern and TGA of investigated oil shale aggregate respectively. The XRD analysis shows that the major mineral composition of the oil shale is calcite, silica, magnetite, in addition to small quantities of clay and rutile, therefore, it is believed that oil shale, with its high content of calcite, can represent a suitable replacement of aggregates in HMA pavement formulations. Combining the weight percentages of CaO and L.O.I. (loss on ignition) of Table 8 for oil shale, one obtains 59 wt.%, indicating that calcite was the dominant component of the used oil shale, however, not as dominant as in limestone. The weight loss profile, presented in Fig. 7, consisted of four regions. The first region was below 200 °C which represented the loss of volatile materials and interlayer water. The second region existed between 200 and 480 °C, where oil shale organic matter decomposition and volatilization took place. The third region was between 480 and 600 °C, where cracking of heavy hydrocarbons was expected to have taken place. Finally, the fourth region was above 600 °C which corresponded to the dissociation of clay materials and the carbonate minerals components of the oil shale specimen which is a highly endothermic reaction. It is also clear that calcination is taking place at the same temperature as that observed in Fig. 3 for limestone (around 700 °C). Fig. 8 shows a sample SEM image of a sample of oil shale (top left) and its elemental analysis using EDX technique (top right), and the elements count pattern (bottom). Combining the wt.% of C, O and Ca (the major elements of calcite), one obtains 68 wt.%, confirming the above results of XRF and XRD. To find out the oil content of oil shale, Fischer assay method was used. The method heats up a sample of oil shale to 500 °C in an aluminum container, and the distilled components of the oil shale, namely; water, oil and gas; are passed through a condenser where oil and water are condensed while gas is not. Fischer assay analysis of the investigated oil shale (Table 9) shows that it has a moderate oil content of about 12%. 2.2.3. Surface Area of limestone and oil shale Surface areas of both limestone and oil shale that were used in this investigation were measured. The instrument used is made by Quantachrome Corporation. Liquid nitrogen was used as the adsorbate for surface area measurement. Fig. 9

Fig. 6. XRD-pattern of investigated oil shale aggregate.

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Fig. 7. Thermal gravimetric analysis (TGA) of oil shale aggregate.

shows sample adsorption isotherms for both oil shale and limestone filler aggregates (for particles passing mesh number 200; i.e., diameters < 74 lm). Multipoint BET was used in the calculations. Sample weight was around 1 g. Table 10 presents the results of the surface area measurements for both limestone and oil shale. The table reports the surface area calculated by several methods, namely, multi-point BET (Brunauer, Emmett and Teller), single point BET, Langmuir, t-method-Halsey, and DR (Dubinn–Rudashkevic) methods. Each of these methods has its assumptions for surface area calculations. In general, it is observed that the calculated surface areas by all these methods were very close to each other. In general, it can be observed that both limestone and oil shale particles have low surface areas. This observation was also supported by noticing that the surface area remains almost constant without significant changes with respect to the different investigated particle sizes of limestone indicating a poor porosity as indicated by the above surface area data. It can also be observed that the surface area of oil shale is 3.5–4 times higher than limestone. Specifically, oil shale particles of pan size (<0.074 mm) had an average surface area of 10.7 m2/g compared to 2.79 m2/g for limestone (according to multi-point BET method); which is 3.8 times higher, and therefore indicating that oil shale particles have relatively higher porosity than limestone. This particle size (<0.074 mm) of oil shale was selected for the more detailed work of this study. The cumulative pore volume measurement data for both limestone and oil shale are presented in Table 11. It is observed from this table that the cumulative pore volume of oil shale pan size (<0.074 mm) particles is 0.0431 ml/g compared to 0.00661 ml/g for limestone; which is more than 6.5 times higher. The same trend was also observed for the cumulative pore area of particles <0.074 mm where it was 26.194 m2/g for oil shale and 6.27 m2/g for limestone; which is 4.2 times higher; indicating a larger surface area of oil shale compared to limestone. The above analysis suggests that oil shale may require more asphalt binder in hot mix asphalt.

2.2.4. Aggregate particles properties There are several popular tests used to identify and quantify aggregate properties. Among the most popular are:






Flat and elongated particles in coarse aggregate Coarse aggregate angularity Fine aggregate angularity The Los Angeles abrasion test Sand equivalent test

2.2.4.1. Flat and elongated particles in coarse aggregate (ASTM D4791). An elongated particle is usually defined as one that exceeds a 5:1 length-to-width ratio. Flat and elongated particles can cause HMA problems because they tend to reorient and break under compaction. Therefore, they are normally restricted to some maximum percentage. The test is done on a characteristic sample with a caliper device and a two-step process. The longest dimension is measured first on one end of the caliper. Then, based on the position of the pivot point, the other end of the caliper is automatically

sized to the fixed length-to-width ratio. If the aggregate is able to pass between the bar and caliper it fails the test (Fig. 10). The standard test for flat or elongated particle is: ‘‘ASTM D 4791: Flat or Elongated Particles in Coarse Aggregate”. Course aggregate (limestone in our case) having sizes greater than ⅜00 were collected and separated into the ranges specified in Table 12. One hundred (100) particles of each size range are collected. Then these particles are separated into two groups. Group one contains particles that are flat and elongated using a 5:1 ratio in accordance with ASTM D4791 (maximum to minimum dimension ratio greater than five), whereas, group two is the other particles that do not satisfy the criteria of group one. Then, the percentage flat and elongated particles is calculated using the following equation:

Pfe ¼ ðM fe =M t Þ  100 where Pfe = percent flat and elongated particles; Mfe = mass of the flat and elongated particles; Mt = mass of the sample.Table 12 presents the results of this test. It is clear that the coarse aggregate used in this study satisfied the requirement of being less than 10%. 2.2.4.2. Coarse aggregate angularity (ASTM D5821). In this test, a sample retained on the 4.75 mm (mesh No. 4) sieve is collected and the number of particles with fractured faces is compared to the number of particles without fractured faces. A fractured face is defined as an ‘‘angular, rough, or broken surface of an aggregate particle created by crushing, by other artificial means, or by nature”. In order for a face to be considered fractured it must constitute at least 25% of the maximum cross-sectional area of the rock particle. The standard test for percentage fractured face is: ‘‘ASTM D5821: Determining the Percentage of Fractured Particles in Coarse Aggregate”. Table 13 shows the results of this test. It is clear from these results that the used coarse aggregate passes the minimum requirement of 80%. 2.2.4.3. Fine aggregate angularity (ASTM C1252 and AASHTO T304). Superpave design method tests for uncompacted void content of fine aggregate, which gives an indication of fine aggregate particle shape and surface texture. The test involves filling a 100 mL cylinder with fine aggregate (passing the 2.36 mm (mesh No. 8) sieve) by pouring it from a funnel at a fixed height (Fig. 10). After filling, the mass of aggregate in the cylinder is measured and a void content is calculated. The standard test for fine aggregate angularit is: ‘‘AASHTO T 304 and ASTM C 1252: Uncompacted Void Content of Fine Aggregate”. In this investigation, the uncompacted void content percentage was found to be 43.6%, which is higher than the 40% minimum requirement. 2.2.4.4. The Los Angeles abrasion test (ASTM C535). This test is used to characterize toughness and abrasion resistance. The Los Angeles abrasion done on the reference all-limestone system was 33% and therefore satisfied the Jordanian regulation specification of being less than a maximum 35% [47]. 2.2.4.5. Sand equivalent test (ASTM D2419). This test (Fig. 10) shows the relative proportions of fine dust or claylike materials in aggregate. The higher the sand equivalent value the better the aggregate. The sand equivalent test was performed on

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Fig. 8. Scanning electron micrograph (SEM) image of a sample of oil shale (top left) and its elemental analysis using EDS technique (top right), and the elements count pattern (bottom).

Component

wt.%

and 15. The test results are shown in Fig. 11. Despite the rough observation that the addition of oil shale to the aggregate reduced the sand equivalent, it is very clear that all investigated compositions satisfied the sand equivalent requirements. Note: Superpave mix design requires sand equivalent values not less than 40 [1].

Total water Total oil Spent shale Gas loss

2.0 12.07 81.30 4.63

2.3. Superpave sample preparation, compaction and testing

Table 9 Oil shale Fischer assay analysis (according to ISO 647 standard).

several aggregate compositions including the all-limestone aggregate and the limestone/oil shale mixed aggregate having the compositions presented in Tables 14

2.3.1. Sample Preparation and compaction In the Superpave method, several trial aggregate-asphalt binder blends are made, each containing a different asphalt binder content. Then, by evaluating the performance of each trial blend, an optimum asphalt binder content is selected.

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Each sample was heated to the required mixing temperature (around 160 °C in our case), aged for a short time (up to 4 h) and then compacted with a Superpave gyratory compactor (Fig. 12). This device applies pressure to a sample through a hydraulically or mechanically operated load. Key parameters of the gyratory compactor are:

Adsorption/Desorption Isotherms Volume Adsorbed @ STP (ml/g)

25 Adsorpon Isotherm (Oil Shale) 20


Sample shape and size: cylinder having a diameter of 150 mm, and a height of about 115 mm. Note that this sample size is much larger than those used for the classical Marshall method (Fig. 12).
Load is flat and circular with a diameter of 149.5 mm.
Compaction pressure is around 600 kPa.
Number of blows varies (75–109 in this study).
Simulation method: The load is applied to the sample top and covers almost the entire sample top area. The sample is inclined at 1.25° and rotates at 30 rpm as the load is continuously applied. This helps achieve a sample particle orientation that is somewhat like that achieved in the field after roller compaction.

Desorpon Isotherm (Oil Shale) Adsorpon Isotherm (Limestone)

15

367

Desorpon Isotherm (Limestone)

10

5

0 0

0.2

0.4

0.6

0.8

1

P/Po Fig. 9. Adsorption/desorption isotherms of nitrogen on particles of oil shale and limestone particles (size < 0.074 mm).

To obtain the optimum asphalt content for the all-limestone aggregate, two gradations (gradations 1 and 2) were formulated to represent high and low traffic conditions respectively. Tables 16 and 17 show the selected gradations. Three different aggregate weights were selected namely, 4400, 4600 and 4800 g. The asphalt content was fixed at 5.4 wt.% (note: this was the optimum asphalt content for a previously done Marshall HMA design). The percentage air voids was measured for each selected weight and for each gradation. Then the aggregate weight that gave 4% air voids was selected for each gradation. The results are presented in Fig. 13. It was determined from Fig. 13 that aggregate weights of 4570 and 4680 g for gradations 1 and 2 respectively, produced the required 4% air voids for the selected 5.4 wt.% asphalt content.

Fig. 10. (a) Flat and elongated test setup; (b) fine aggregate angularity setup; (c and d) sand equivalent test setup and cylinder.

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Table 10 Results of surface area measurements of both limestone and oil shale. Sieve size (mesh no.)

Retained on mesh size (mm)

Average particle size (mm)

Surface area Multi-point BET (m2/g)

Limestone Pass #4; Retained on #8 Pass #8; Retained on #16 Pass #16; Retained on #50 Pass #50; Retained on #100 Pass #100; Retained on #200 Pass #200; Retained on Pan

2.38 1.19 0.297 0.149 0.074 Pan

Pan

t-Method – Halsey (m2/g)

Langmuir (m2/g)

3.57 1.785 0.744 0.223 0.112 <0.074

1.65 1.34 2.08 3.01 2.90 2.79

1.60 1.28 2.01 2.92 2.74 2.66

2.38 1.91 2.98 4.29 4.19 4.06

1.85 1.45 2.15 3.18 3.29 3.23

2.29 0.42

2.20 0.67

3.301 1.02

2.52 0.81

3.09 0.94

<0.074

10.70

15.75

14.96

Average= Standard deviation= Oil shale Pass #200; Retained on Pan

Single point BET (m2/g)

10.12

DR method (m2/g) 2.26 1.81 2.80 4.02 3.91 3.75

14.64

Table 11 Results of pore size measurements of both limestone and oil shale. Sieve size (Mesh No.)

Retained on mesh size (mm)

Limestone Pass #4; Retained on #8 Pass #8; Retained on #16 Pass #16; Retained on #50 Pass #50; Retained on #100 Pass #100; Retained on #200 Pass #200; Retained on Pan

Average particle size (mm)

2.38 1.19 0.297 0.149 0.074 Pan Average= Standard deviation=

Oil Shale Pass #200; Retained on Pan

Pan

Pore size data Pore volume (cumulative) (ml/g)

Pore diameter (average) (nm)

Pore area (cumulative) (m2/g)

3.57 1.785 0.744 0.223 0.112 <0.074

0.00353 0.00295 0.00397 0.00569 0.00618 0.00661

6.60 6.76 6.31 6.42 6.53 7.31

3.21 2.69 3.92 5.42 6.19 6.27

0.00482 0.00153

6.65 0.36

4.62 1.55

<0.074

0.0431

13.69

Table 12 Flat and elongated test results according to ASTM D4791. (A maximum of 10% flat and elongated is allowed.)

26.19

Table 14 Aggregate design composition and size distribution.

Particles size range (inch)

Mass fraction of flat and elongated particles

Flat and elongated (%)

Sieve size (passing)

1–¾ ¾–½ ½–⅜

0 0 0

0 0 0

Inch or Sieve No.

(mm)

Weight (g)

Weight%

100 ¾00 ½00 ⅜00 No. No. No. No. No. No.

(25.4) (19.05) (12.7) (9.52) (4.76) (2.38) (1.19) (0.297) (0.149) (0.074)

60 174 150 270 180 126 108 24 48 60

5 14.5 12.5 22.5 15.0 10.5 9 2 4 5

Total = 1200 g

Total = 100%

Table 13 Course aggregate angularity test results according to ASTM D5821. Particles size range (inch)

Mass% of particles having zero fractured faces

Mass% of particles having one fractured face

Mass% of particles having two fractured faces

1–¾ ¾½ ½⅜

1 0 0

12 10 13

87 90 87

1⅜

0.7

11.9

87.4

Fig. 14 shows how the optimum asphalt content was obtained for gradation composition 1 for the case of all filler size (size < sieve no. 200) limestone replaced by oil shale of the same size. It was concluded from Fig. 14 that the optimum asphalt content for this case was 6.8 wt.%. Following the procedure to determine the proper Superpave aggregate gradation and optimum asphalt content combination, the following gradations and asphalt contents were determined to give the required percent air voids of 4% (Table 18). Table 18 presents the compositions of the gradations that were used for the rest of this investigation.

4 8 16 50 100 200

Weight of Particles (passing selected sieve size and retained on the next)

Eight samples of each weight for each trial composition from Table 18 were prepared (a total of 32) and compacted using Superpave gyratory compactor (Fig. 12) for a number of gyrations of 75. The samples were given the following code numbering:
Grade 1: Low traffic design. ➢ 8 samples of composition 1 with all limestone aggregate (denoted as grade ‘‘1A”). ➢ 8 samples of composition 1 with oil shale replacing ‘‘No. 200–Pan” sieve size aggregate (denoted as grade ‘‘1B”).

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M.O.J. Azzam, Z. Al-Ghazawi / Construction and Building Materials 101 (2015) 359–379 Table 15 Test specimens fine/filler compositions (Distribution given in Table 14). Sample ID codea

Sieve size (passing), [mesh #]

Weight (g) of Particles (passing selected sieve size and retained on the next) [the percentages are with respect to the total weight of aggregate] Lime stone

a

Oil shale

Weight (g)

Weight%

Weight (g)

Weight%

OS0.00

200

60

5.00

0

0

OS1.25

200

45

3.75

15

1.25

OS2.50

200

30

2.50

30

2.50

OS5.00

200

0

0

60

5.00

OS4.50

100 200

24 30

2.00 2.50

24 30

2.00 2.50

OS5.50

50 100 200

12 24 30

1.00 2.00 2.50

12 24 30

1.00 2.00 2.50

OS9.00

100 200

0 0

0 0

48 60

4.00 5.00

OS11.0

50 100 200

0 0 0

0 0 0

24 48 60

2.00 4.00 5.00

OS20.0

16 50 100 200

0 0 0 0

0 0 0 0

108 24 48 60

9.00 2.00 4.00 5.00

OS45.5

4 8 16 50 100 200

0 0 0 0 0 0

0 0 0 0 0 0

180 126 108 24 48 60

15.0 10.5 9.00 2.00 4.00 5.00

Sample ID code: ‘‘OS” is Oil Shale, ‘‘#.##” is overall wt.% of oil shale in the sample.

80

Sand Equivalent

Sand Equivalent

75 70 65

71

70

66

66

65

60

60

60 55

73

57 54

50 45 40

Sample ID Code Fig. 11. Sand equivalent test results of investigated samples.


Grade 2: High traffic design. ➢ 8 samples of composition 2 with all limestone aggregate (denoted as grade ‘‘2A”). ➢ 8 samples of composition 2 with oil shale replacing ‘‘No. 200–Pan” sieve size aggregate (denoted as grade ‘‘2B”).

Each of the above samples was cut in half (perpendicular to the z-axis) to double the number of samples to be subjected to the following tests to be done on a universal testing machine (Fig. 12):
Resilient modulus (MR)
Dynamic creep
Fatigue

2.3.2. Resilient modulus (MR) This test is a measure of the expected flexibility of HMA with respect to traffic loading. The test was done by applying a repeated compressive load pulse with a haversine shape. The loading period was 0.1 s followed by a resting period of 0.9 s (which gives a total loading cycle of 1 s). The load was applied vertically in the vertical diametral plane of a cylindrical sample as prepared in Section 2.3.1. The average axial dynamic load was 1.1 kN. The resulting permanent and resilient horizontal deformations of the sample were measured continuously. The resilient modulus was then calculated using the following equation:

MR ¼ Pðm þ 0:27Þ=ðt  DHÞ where MR = modulus of resilience (MPa); P = repeated load (N); m= Poisson’s ratio (usually assumed to be 0.35 for HMA); t = thickness of sample (mm); DH = recoverable horizontal deformation (mm).

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Fig. 12. (a) Superpave gyratory compactor and Superpave mold; (b) Marshall sample (left) and Superpave sample (right); (c) universal testing machine (UTM) used for Superpave samples tests.

Table 16 Composition of gradation 1 of aggregate containing only limestone. Sieve size

Pass (%)

Retained (%)

Accumulated (%)

4400

4600

4800

1 1–¾ ¾–½ ½–3/8 3 /8–No. 4 No. 4–No. 8 No. 8–No. 16 No. 16–No. 30 No. 30–No. 50 No. 50–No. 100 No. 100–No. 200 No. 200–Pan

100 96 85 65 50 30 20 15 10 8 5 0

0 4 15 35 50 70 80 85 90 92 95 100

0 4 11 20 15 20 10 5 5 2 3 5

0 176 484 880 660 880 440 220 220 88 132 220

0 184 506 920 690 920 460 230 230 92 138 230

0 192 528 960 720 960 480 240 240 96 144 240

100

4400

4600

4800

4400

4600

4800

0 2 10 13 20 10 10 10 5 5 8 7

0 88 440 572 880 440 440 440 220 220 352 308

0 92 460 598 920 460 460 460 230 230 368 322

0 96 480 624 960 480 480 480 240 240 384 336

100

4400

4600

4800

Total

Aggregate weight (g)

Table 17 Composition of gradation 2 of aggregate containing only limestone. Sieve size

1 1–¾ ¾–½ ½–3/8 3 /8–No. 4 No. 4–No. 8 No. 8–No. 16 No. 16–No. 30 No. 30–No. 50 No. 50–No. 100 No. 100–No. 200 No. 200–Pan

Pass (%)

100 98 88 75 55 45 35 25 20 15 7 0

Retained (%)

0 2 12 25 45 55 65 75 80 85 93 100

Total

This test was done at three different temperatures, namely, 30, 40 and 50 °C. 2.3.3. Dynamic creep This test is a measure of HMA resistance to permanent deformation. In this test a repeated pulsed uniaxial stress/load was applied on a cylindrical sample (as prepared in Section 2.3.1) and the resulting deformations in the same axis

Accumulated (%)

Aggregate weight (g)

were measured using linear variable displacement transducers (LVDTs). The stress level was set at 69 kPa, and the test continued for 26,000 cycles (1 s per cycle). The samples were put in a controlled temperature chamber for at least 4 h before testing to make sure that they reached the testing temperature. This test was done at three different temperatures, namely, 30, 40 and 50 °C.

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for 10,000 cycles. Fatigue failure was defined as the number of cycles to reach 50% of initial creep modulus. To assure stability of the data, the first 200 cycles were neglected and the initial creep modulus was that at cycle number 200. The fatigue tests were conducted at 20, 25 and 30 °C. The samples were put in a controlled temperature chamber for at least 4 h before testing to make sure that they reached the testing temperature.

5

(a) Gradation 1

% Air Voids

4.5 4

2.4. Scanning electron micrographs

3.5

To further understand and analyze the results, scanning electron microscopy (SEM) images for HMA containing only limestone and HMA containing oil shale (blank limestone and blank oil shale were also done for comparison), both for grade 1 of investigated compositions, were taken. A SEM, model Quanta FEG 450 (Fig. 15), was used in obtaining the images.

3 2.5 2 4300

4400

4500

4600

4700

4800

4900

Weight of Aggregate (g)

3.1. Resilient modulus

5

% Air Voids

4.5

(b) Gradation 2

4 3.5 3 2.5 2 4300

4400

4500

4600

4700

3. Results and discussion

4800

4900

Weight of Aggregate (g) Fig. 13. Percentage air voids vs. weight of aggregate (all limestone).

2.3.4. Fatigue Fatigue test measures the disturbance on HMA produced by the accumulation of a high number of loads. The test was done by applying a repeated compressive load pulse with a haversine shape. The loading period was 0.1 s followed by a resting period of 0.9 s (which gives a total loading cycle of 1 s). The load was applied vertically in the vertical diametral plane of HMA cylindrical sample (as prepared in Section 2.3.1). The deviator stress was set at 69 kPa, and the test was continued

It is observed from Table 19 and Fig. 16 that, for both grades 1 and 2, HMA containing oil shale (grades 1B and 2B) had higher resilient modulus than HMA containing only limestone (grades 1A and 2A) at all investigated temperatures with an almost one exception for the 40 °C case where the values for grade 2 (2A and 2B) were close to each other indicating almost similar behavior. This observation indicated that HMA containing oil shale was expected to have better resistance to rutting. It is worth noting here that the above results were generally either the same or better than results found by other investigators [48,49,13,77] for all investigated grades. The relative performance of HMA containing oil shale with respect to that containing only limestone is presented in Table 20 [indicated as percentage increase (positive values) or decrease (negative values) of investigated property with respect to control limestone case]. It is concluded from Table 20 that, from resilient modulus results, the overall performance with respect to rutting resistance was expected to be around 52% and 21% better for the case of HMA containing oil shale compared to that of the control HMA which contained only limestone (no oil shale) for both grades 1 and 2 respectively. 3.2. Creep modulus It is very clear from Table 19 and Fig. 17 that for all investigated temperatures, grade 1B was more resistant to rutting than grade 1A. This result is consistent with the above resilient modulus

12

% Air Voids

10 8 6 4 2 0 3

4

5

6

7

8

9

Asphalt wt. % Fig. 14. Percentage air voids vs. asphalt wt.% for the case of oil shale filler size (all limestone) replacing all limestone of the same size.

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Table 18 Compositions of Superpave samples. Composition 1 Sieve Size

Pass (%)

Retained (%)

1 1–3=4 3= 4 –½ ½–3/8 3 /8–No. 4 No. 4–No. 8 No. 8–No. 16 No. 16–No. 30 No. 30–No. 50 No. 50–No. 100 No. 100–No. 200 No. 200–Pan

100 96 85 65 50 30 20 15 10 8 5 0

0 4 15 35 50 70 80 85 90 92 95 100

Accumulated (%)

Total Optimum asphalt content for reference all limestone aggregate

5.4 wt.% asphalt of total mixture

Optimum asphalt content for filler limestone aggregate replaced by filler oil shale

6.8 wt.% asphalt of total mixture

Weight 4570 g

0 4 11 20 15 20 10 5 5 2 3 5

0 183 503 914 686 914 457 228 228 91 137 228

100

4570

Accumulated (%)

Weight 4680 g

Composition 2 Sieve size

Pass (%)

Retained (%)

1 1–3=4 3= 4 –½ ½–3/8 3 /8–No. 4 No. 4–No. 8 No. 8–No. 16 No. 16–No. 30 No. 30–No. 50 No. 50–No. 100 No. 100–No. 200 No. 200–Pan

100 98 88 75 55 45 35 25 20 15 7 0

0 2 12 25 45 55 65 75 80 85 93 100

Total Optimum asphalt content for reference all limestone aggregate

5.4 wt.% asphalt of total mixture

Optimum asphalt content for filler limestone aggregate replaced by filler oil shale

6.8 wt.% asphalt of total mixture

results. On the other hand, for grade 2, grade 2A showed better resistance to rutting compared to grade 2B, which is contrary to the results indicated by the resilient modulus. Since it is known that the creep modulus is a more accurate measure for rutting resistance than the resilient modulus, it is concluded that grade 1B is the better rutting resistance for low traffic conditions while grade 2A is the better rutting resistance for high traffic conditions. It is concluded from Table 20 that, from creep modulus results the overall performance with respect to rutting resistance is expected to be better than 53% for the case of HMA containing oil shale for grade 1 (low traffic conditions) compared to that of the control HMA which contains only limestone (no oil shale). On the other hand, the overall performance with respect to rutting resistance is expected to be around 55% worse than for the case of HMA containing oil shale for grade 2 (low traffic conditions) compared to that of the control HMA which contained only limestone (no oil shale). However, for all cases, creep results of this investigation were generally much better than other reported results [53,5,28]. Fig. 18 shows original data for accumulated strain (%) of one sample of each investigated composition and temperature under creep test conditions. This figure demonstrates the traditional logarithmic rise of accumulated strain vs. number of cycles. On the other hand, Fig. 19 reports the accumulated strain (permanent strain, %) for the creep modulus calculations.

0 2 10 13 20 10 10 10 5 5 8 7

0 94 468 608 936 468 468 468 234 234 374 328

100

4680

3.3. Fatigue It is observed from Fig. 20 that the control (all limestone) grade 1A had more fatigue resistance compared to the same grade 1 containing oil shale (grade 1B) for the cases of 20 and 25 °C, whereas the reverse is true for the case of 30 °C. On the other hand grade 2B (containing oil shale) had better fatigue resistance compared to the control all limestone grade (grade 2A) for the 20 and 25 °C cases, while the reverse is true for the case of 30 °C. It is concluded from Table 20 that fatigue resistance is expected to be 3–4 times better for grade 2B compared to grade 2A for the 30 and 40 °C conditions. The above results are generally either around similar to or better than reported values of other HMA systems [13,49,46]. Fig. 21 shows selected original data for some fatigue tests. In summary, grade 2B is the better material regarding fatigue resistance, while grade 1B is the better material with respect to creep resistance. 3.4. SEM images Fig. 22 shows SEM images for HMA containing only limestone and HMA containing oil shale (blank limestone and blank oil shale are also shown for comparison) both for grade 1 of investigated compositions. The images of HMA containing filler size oil shale as a replacement of limestone showed relatively better asphalt

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Fig. 15. The SEM machine (left). The interior chamber of the SEM (right). Note where the samples are located in the photo in the right.

Table 19 Performance of Superpave hot mix asphalt (HMA) samples. ‘‘A” is for all limestone aggregate. ‘‘B” is for oil shale replacing limestone filler size. Sample codea

Temperature (°C)

Accumulated strain (%)

Resilient modulus, MR (MPa)

Creep modulus (MPa)

Fatigue (number of cycles to failure)b

1A

20 25 30 40 50

– – 0.1995 0.1215 0.0280

– – 3374 1808 2020

– – 33 107 270

5180 5160 550 – –

1B

20 25 30 40 50

– – 0.0150 0.0110 0.0090

– – 5539 3273 2262

– – 709 693 412

750 1060 1080 – –

2A

20 25 30 40 50

– – 0.0210 0.0250 0.0445

– – 3756 4213 2786

– – 350 522 280

530 600 950 – –

2B

20 25 30 40 50

– – 0.0505 0.0410 0.0540

– – 4301 3967 4349

– – 158 237 129

2460 3160 380 – –

a

The meanings of these codes are found in the previous paragraph. Fatigue failure is defined as the number of cycles to reach 50% of initial creep modulus. To assure stability of the data, the first 200 cycles were neglected and the initial creep modulus was that at cycle number 200. b

coverage compared to the all limestone case. This observation supports the above conclusion that HMA containing filler size oil shale has a relatively better performance than the control case containing no oil shale.

4. Economic evaluation Using the standard design of asphalt pavement in Jordan of 5 cm overlay thickness and a lane width of 3.6 m, then:

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Resilient Modulus (MR) 7000

Resilient Modulus (MPa)

30°C 6000

50°C

5540

5000 4000

40°C

4300

4210 3270

3370

3970

4350

3760 2790

3000 1810

2260

2020

2000 1000 0 1A

1B

2A

2B

Sample Composition (Grade Code) Fig. 16. Resilient modulus of investigated Superpave samples.

Table 20 Relative resilient modulus, creep and fatigue of HMA containing oil shale (Grades B) to that containing no oil shale (Grade A). Temperature (°C)

Grade number

Percentage change in resilient modulus (%)

Percentage change in creep modulus (%)

Percentage change in fatigue (%)

30

1 2

+64 +14

+2050 55

85 +360

40

1 2

+81 6

+550 55

79 +430

50

1 2

+12 +56

+53 54

+96 60

Creep Modulus 900

30°C

Creep Modulus (MPa)

800

709

700

50°C

693

600

522

500

412 350

400

280

270

300

237 158

200 100

40°C

129

107 33

0 1A

1B

2A

2B

Sample Composition (Grade Code) Fig. 17. Creep modulus of investigated Superpave samples.

Volume of 1 km of lane = 0.05  3.6  1000 = 180 m3/1 km lane. Mass of aggregate and asphalt in 180 m3 lane (for the case of no oil shale): (180 m3)  (2.320 metric ton/m3) = 418 metric ton/1 km lane. Note: the word ‘‘metric” will be dropped to simplify the units. (where the 2.320 ton/m3 is the bulk specific gravity of the all limestone HMA control samples).

Mass of aggregate and asphalt in 180 m3 lane (for the case with oil shale): (180 m3)  (2.260 ton/m3) = 407 metric ton/1 km lane. (where the 2.260 metric ton/m3 is the bulk specific gravity of the samples containing oil shale). In this investigation the control HMA (no oil shale) had an optimum asphalt content (OAC) of 5.4 wt.% (Table 18), while the OAC

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0.25

1A1-30C

Accumulated Strain (%)

0.2

1A2-40C 1A3-50C 2A1-30C

0.15

2A2-40C 2A3-50C 0.1

1B1-30C 1B2-40C 1B3-50C

0.05

2B1-30C 2B2-40C 2B3-50C

0 0

5000

10000

15000

20000

25000

30000

Number of Cycles Fig. 18. Original data for accumulated strain (%) of one sample of each investigated composition and temperature.

Accumulated Strain (%) Accumulated Strain (%)

0.25 0.2

0.200

0.15

0.122

30C

40C

50C

0.1 0.044

0.05

0.028

0.0150.0110.009

0.050

0.041

0.054

0.0210.025

0 1A

1B

2A

2B

Sample Composition (Grade Code) Fig. 19. Percentage accumulated strain (%) of investigated Superpave samples.

Fatigue Fatigue (no. of cycles to failure)

6000 5180

20°C

5160

25°C

30°C

5000 4000 3160 3000

2460

2000

1060 1080

1000

550

750

530 600

950 380

0 1A

1B

2A

Sample Composition (Grade Code) Fig. 20. Fatigue results of investigated Superpave samples.

2B

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16000 1A6-20C

Creep Modulus (MPa)

14000

1A7-25C 12000

1A8-30C 2A6-20C

10000

2A7-25C

8000

2A8-30C

6000

1B6-20C 1B7-25C

4000

1B8-30C 2000

2B6-20C 2B7-25C

0 0

2000

4000

6000

8000

10000

2B8-30C

Cycle No. Fig. 21. Original data used for finding the fatigue of one sample of each investigated composition and temperature.

of the investigated samples containing oil shale was 6.8 wt.%. Therefore, Quantity of needed asphalt binder for the case with no oil shale is: 418  5.4/(100  5.4) = 24 metric ton of asphalt binder par kilometer lane. Quantity of needed asphalt binder for the case with oil shale is: 407  6.8/(100  6.8) = 30 metric ton of asphalt binder par kilometer lane. Quantity of needed aggregate (for the case of no oil shale) will be: 418  24 = 394 metric ton of aggregate per kilometer lane. Quantity of needed aggregate (for the case with oil shale) will be: 407  30 = 377 metric ton of aggregate per kilometer lane. In this study, the replaced aggregate were those passing sieve having mesh number 200, this replacement equals 5% of total aggregate weight for grade 1B (Table 18), while for grade 2B the replacement was 7%. Therefore, Mass of needed oil shale for grade 1B is: 377  0.05 = 19 metric ton of oil shale per kilometer of lane. Mass of needed oil shale for grade 2B is: 377  0.07 = 26 metric ton of oil shale per kilometer of lane. The average price (for last year 2014) for one metric of asphalt is 80 JD/metric ton of asphalt binder (note: 1 JD = 1.4 USD), while the average price of aggregate is 20 JD/metric ton of aggregate. An estimated value of replacing limestone with oil shale is: 10 JD/metric ton (assuming no extra cost for purchasing the oil shale). Using the above data for the same design criteria (no change in other operational values for using oil shale) the initial cost would be: Cost of normal HMA (all limestone, i.e., no oil shale): = 24  80 + 394  20 = 9800 JD/kilometer lane Cost of HMA containing filler size oil shale according to grade 1B (Table 18): = 30  80 + 358  20 + 19(20 + 10) = 10,130 JD/kilometer lane Cost of HMA containing filler size oil shale according to grade 2B (Table 18): = 30  80 + 351  20 + 26(20 + 10) = 10,200 JD / kilometer lane

It is noted here that grades 1B and 2B are around 3% and 4% more expensive than the control case (no oil shale) respectively. However, adding oil shale to HMA more than doubles the fatigue resistance (Table 19) of asphalt mix (grade 2B; i.e., high traffic case) for temperatures lower than 30 °C (a condition satisfied in most regions of Jordan). This result is expected to at least delay the beginning of maintenance time which is reflected in lower maintenance cost over the life of the applied asphalt mix. This decrease in maintenance cost is expected to much offset the incurred extra cost of incorporating the filler oil shale. In addition, one needs to remember that this use of filler size oil shale is helping preventing an expected environmental hazard when oil shale projects become operational. 5. Conclusions In this work, the incorporation of oil shale filler aggregate into the HMA pavement formulation was investigated using Superpave design method. Comparison of filler oil shale aggregate to the all limestone control samples was made.
It is concluded, from resilient modulus results, that the overall performance with respect to rutting resistance is expected to be around 52% and 21% better for the case of HMA containing oil shale compared to that of the control HMA which contained only limestone (no oil shale) for both grades 1 and 2 respectively.
It is also concluded, from creep modulus results, that the overall performance with respect to rutting resistance is expected to be better than 53% for the case of HMA containing oil shale for grade 1 (low traffic conditions) compared to that of the control HMA which contains only limestone (no oil shale). On the other hand, the overall performance with respect to rutting resistance is expected to be around 55% worse than for the case of HMA containing oil shale for grade 2 (low traffic conditions) compared to that of the control HMA which contained only limestone (no oil shale).
Fatigue resistance is expected to be 3–4 times better for grade 2B compared to grade 2A for the 30 and 40 °C conditions.
In summary, grade 2B is the better material regarding fatigue resistance, while grade 1B is the better material with respect to creep resistance.

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(A1)

(B1)

(A2)

(B2)

(A3)

(B3)

(A4)

(B4)

377

Fig. 22. A1 is an SEM image of blank limestone. A2, A3, and A4 are SEM images of HMA containing only limestone. B1 is an SEM image of blank oil shale. B2, B3 and B4 are SEM images of HMA containing filler size oil shale.

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Finally, it is expected that at least one of the investigated formulas (grade 2B) is more economical than the case containing no oil shale.

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