Assessment of Traditional Asphalt Mixture Performance Using Natural Asphalt from Sulfur Springs

T his research utilized natural asphalt (NA) deposits from sulfur springs in western Iraq. Laboratory tests were conducted to evaluate the performance of an asphalt mixture incorporating NA and verify its suitability for local pavement applications. To achieve this, a combination of two types of NA, namely soft SNA and hard HNA, was blended to create a binder known as Type HSNA. The resulting HSNA exhibited a penetration grade that adhered to Iraqi specifications. Various percentages of NA (20%, 40%, 60%, and 80%) were added to petroleum asphalt. The findings revealed enhanced physical properties of HSNA, which also satisfied the requirements outlined in the Iraqi specifications for asphalt cement. Consequently, HSNA can serve as an asphalt binder to produce asphalt mixtures for flexible paving construction. Notably, HSNA mixtures exhibited greater Marshall stability and stiffness index when compared to traditional mixtures. The results from indirect tensile strength (ITS) and tensile strength ratio (TSR) tests indicated that the 80NA mixture displayed the highest ITS values and a TSR of 81.36%, surpassing the TSR of the mixture incorporating petroleum asphalt by 0.57%.


INTRODUCTION
Around 110 million tons of bitumen are required annually around the world.Bituminous pavements need a significant investment of time, money, and energy in construction, repair, and maintenance (Garcia et al., 2010).Hot mix asphalt (HMA) pavement experiences many issues during its service life, such as short and long-term aging caused by the mixing, storage, transportation, and placement of asphaltic mixtures as well as the inadequate resources of bitumen (Lu and Isacsson, 1998) Rock asphalt, a naturally occurring substance, can partially substitute conventional asphalt manufacturing HMA.Rock asphalt has generated interest across the globe as a result of its benefits in terms of lower prices and ease of use when making asphaltic mixtures.As a result of the actions of pressure, heat, oxidation, and bacteria over millions of years, petroleum or oil is infusing organically into rocks like limestone, creating rock asphalt.Therefore, asphalt binders and mineral fillers are the two major elements of rock asphalt.Rock asphalt is a dark substance readily crushable into powder European rocky asphalt-modified mixture and found that the high-temperature behavior, temperature susceptibility, and aging resistance of asphalt binder all dramatically improved with increasing rock asphalt content.North American rock asphalt, which (Huang, 2014) examined in terms of its microstructure, changed mechanism, and viscoelastic behavior, revealed that the modification effect of rock asphalt was very good.According to (Li et al., 2015), rock asphalt can reduce the relaxation potential and increase the stiffness of bitumen mastics.Iraqi NA is found in sulfur springs, especially in the northern and western regions along the banks of the Euphrates River.According to a study (Mandeel, 2012), adding phosphogypsum and cement kiln dust with a particle size of 100 mm to NA (Eyeen Aljeebal) at weights of 10, 20, 30, and 40% improves its ductility and viscosity.The best amount of this additive was 40%.Additionally, the viscosity and ductility of asphalt samples when chlorinated at various times (0.5, 1, and 1.5 hours), the preferred duration of chlorination is 1.5 hours, with a 40% addition of the material combinations.(Mahmood et al., 2007) investigated the characteristics of asphalt collected from sulfur asphalt springs in the Heet area.They also examined the natural samples' ultraviolet rays (UV) and infrared spectroscopy (IR) and contrasted them with the spectra of comparable petroleum samples derived from the Al-Doura Refinery.The findings reveal that natural asphalt and asphalt samples produced by processing Iraqi oil share several characteristics.The UV and IR analyses of the asphalt sample show the presence of heavy organic compounds present in asphalt obtained from refineries.This study intends to benefit from the NA resources produced naturally in the west of Iraq, representing untapped national wealth.The study aimed to determine the physical properties of NA and apply industrial treatment to improve those properties before using NA as an asphalt binder in local paving.

Traditional Asphalt
The most often used asphalt for paving in Iraq's central and southern regions is Asphalt Cement, with a penetration grade of 40-50 (AC (40-50)).It was delivered from the Al-Dora refinery, south of Baghdad.

Natural Asphalt
Two types of NA (soft and hard), as seen in Fig. 1, are transported from the Abu-Jeer region in Heet City, which is located in the western part of Iraq (Al-Anbar province).NA has considerably different physical characteristics than traditional asphalt produced in tightly regulated refineries.Notwithstanding the finding of a prior study by (Muttar et al., 2009), which claimed that the characteristics of springs NA are identical to those of industrial bitumen.Thus, using NA for flexible pavement production requires industrial treatments.

Fine and Coarse Aggregates
The aggregates required for this project are transported from the hot mix plant of Amanat Baghdad in Daurah.chosen gradation to create an identical, regulated gradation.The chosen gradation is depicted in Fig. 2. Table 1.displays the aggregates' physical characteristics.

Mineral Filler
The limestone filler of the study was shipped from a lime factory in Karbala, located in Iraq's southeast.Based on laboratory tests, the specific gravity of limestone filler was 2.7, and the limestone particles passing through sieve no.200 were larger than 95 percent of the total weight.

Natural Asphalt Treatment
The first stage of treatment for soft NA (SNA) involved stirring it in 500 ml steel containers throughout the two hours of oxidation in a hot oven at a temperature of 110 °C to ensure water expulsion.After the water has been removed from SNA, it is essential to do several tests to determine the substance's physical characteristics and whether employing NA in local HMA is appropriate.The two different NA (soft and hard) were mixed in a mixer at a constant temperature of 170°C for an hour at 1000 revolutions per minute (Erkus et al., 2020) during the second stage of treatment, as shown in Fig. 3. On the top of the cap, there is a thermostat attached to the heater plate that is submerged in bitumen through a channel.This process was done to get a mixture with penetration grade that meets the requirements of Iraqi specifications and then added to the conventional asphalt by 20, 40, 60, and 80% by weight of bitumen.

Asphalt Traditional Tests
To evaluate the performance of NA, tests such as penetration, flash point, softening point, specific gravity, and ductility were conducted following ASTM D-5, ASTM D-92, ASTM D-36, ASTM D-70, and ASTM D-113, respectively.The previous asphalt tests were conducted for traditional asphalt, soft NA (SNA), hard NA (HNA), hard and soft NA (HSNA) after they were mixed in the mixer and HSNA that was treated by mixing with traditional asphalt in several percentages.Bituminous mixtures containing 20%, 40%, 60%, and 80% HSNA are denoted as 20NA, 40NA, 60NA, and 80NA, respectively.

Thermo Scientific-Axia ChemiSEM Test
The elemental analysis of AC (40-50), NA, and treated NA was conducted using the Thermo Scientific Axia ChemiSEM Scanning Electron Microscope device, as seen in Fig. 4. Compared to conventional Scanning Electron microscopy (SEMs), the Thermo Scientific Axia ChemiSEM continuously gathers energy dispersive X-ray spectroscopy (EDS) data in the background.It processes the SEM and EDS data concurrently using special algorithms, enabling it to simultaneously display the morphology and elemental composition of the sample in realtime.EDS analysis, or EDX analysis, is an effective method for examining chemical composition at the microscale.EDS analyzes the X-rays produced when an electron beam scans over a sample in conjunction with scanning electron microscopy (SEM).This method can identify almost all of the elements in the periodic table.Applications ranging from process and quality control to failure analysis and basic research depend on the data offered by EDS.One elemental analysis technique that uses the distinctive X-rays produced by an electron beam is called elemental mapping.By depicting the distinctive X-ray intensities or elemental concentrations in two dimensions, the approach makes the distribution of the constituent elements in the specimen visible.In EDS, the characteristic X-ray spectra produced by the electron beam are recorded pixel by pixel when the electron beam is two-dimensionally scanned across a specimen area.To create an elemental map, these spectra depict pixel-by-pixel the target elements' computed concentrations or X-ray intensities (Vesseur, 2019).

Marshall Test
Specimens are prepared, compacted, and tested using the ASTM D6927-15 Marshall procedure.For each specimen, the aggregate gradation for the wearing course is mixed.After two hours of heating, the asphalt cement and aggregates are combined at temperatures up to 135 °C and 150 °C, respectively.The heated aggregate was coated with asphalt cement by adding various amounts of asphalt (4, 4.5, 5, 5.5, and 6% by aggregate weight).The mix was stirred for at least three minutes to achieve homogeneity; the aggregates were entirely covered with asphalt cement.In the Marshall test, a hot mixture is placed in the mold and compacted by a Marshall hammer for 75 blows on both sides of the specimen.Standard cylindrical molds measuring 102 mm in diameter and 64 mm in height are used, and they have been heated to 130°C for the test.

Moisture Damage Test
The adhesive and cohesive deterioration brought on by moisture in asphalt concrete can weaken the bonds between the aggregate and bitumen, reducing the load-bearing capacity of the pavement (Caro et al., 2008).The ASTM D 4867M-96 is used in this study to determine how moisture-sensitive asphalt concrete is.Six specimens with an air-void percentage of 7±1 % for each type of combination were selected.According to NCHRP Report No. 425 guidelines, each combination should be compacted to 7±1 % void before the test begins by adjusting the number of blows.In this research study, each mix should be compacted by adjusting the number of blows on 42 blows to reach the 7±1 % air voids.Three samples were put through a vacuum saturation at a level of 55-80% saturation, a 16-hour freeze-thaw cycle at -18°C, and a 24-hour immersion in a water bath at 60°C, then soaking in a water bath for 1 hour at 25±1 C˚ to adjust the temperature of the conditioned samples.The other three samples were submerged for 20 minutes in a 25 °C water bath.The tensile strength ratio, also known as the TSR, is calculated by dividing the tensile strength of the samples in the conditioned state by the tensile strength of the samples in the normal condition.The following Eqs.(1).and (2).can be used to determine the TSR value where: ITS is the indirect tensile strength, KPa P is the applied load required to fail the sample, N t is the sample height, mm D is the sample diameter, mm.TSR is the tensile strength ratio, % ITScond is the average ITS of the moisture-conditioned groups, KPa ITSuncond is the average ITS of the moisture-unconditioned groups, KPa

Asphalt Properties
The physical characteristics of AC (40-50), HNA, and SNA after water removal are depicted in Table 3.It should be noted that SNA displays high penetration and low viscosity values, so it cannot be used to produce HMA instead of traditional asphalt.On the other hand, HNA shows a very hard texture as its penetration value is less than the lower limit of the Iraqi specifications (SCRB, 2003).
The SNA was treated by combining it with various proportions of HNA to obtain a mixture (HSNA) with a penetration grade that meets Iraqi specifications (SCRB, 2003).After several attempts, the appropriate mixing ratio was determined to be 55% HNA and 45% SNA.As indicated in Table 4, HSNA does not meet the specification limits, so it was mixed with traditional asphalt in different proportions (20, 40, 60, and 80%) to enhance its properties.
The results demonstrated an improvement in the physical properties of HSNA, and it met Iraqi criteria for asphalt used in flexible pavement construction.As a result, HSNA can be employed as a building material in asphalt concrete constructions.

Thermo Scientific-Axia ChemiSEM Test Results
It is necessary to understand the chemical makeup of the NA and determine whether it is similar to that of conventional asphalt obtained from crude petroleum refineries to have widespread use of the NA for excellent performance.Table 5 shows the EDS elemental analysis of AC (40-50), NA, and treated NA.The results revealed that the NA and treated NA had larger heteroatoms, such as O, N, and S. The heteroatoms and their composition significantly impact the chemical and physical characteristics of asphalt binders.This will increase the stiffness of the binder.The larger amount of heteroatoms and, consequently, the higher degree of association and molecular organization in this NA may cause its improved high-temperature characteristics

Marshall Properties
The traditional and treated HSNA mixtures were prepared with optimum asphalt content (4.96%).Air voids (AV), voids filled with asphalt (VFA), voids in mineral aggregates (VMA), and bulk density are given in Table 6.All the mixtures meet the Iraqi specification (SCRB, 2003) regarding volumetric properties.

Moisture Damage Resistance
Fig. 10 provides the tensile strength values for all mixture types for unconditioned (dry) and conditioned specimens.According to the results, the mixture with 80% HSNA had better dry and conditioned tensile strength values than other mixtures among the specimens because adding HSNA stiffens the binder.Hence, the stiffness of the mixtures is increased by adding binders that have been treated with HSNA.As a result, adding HSNA to mixtures causes an increase in ITS.Fig. 11 displays the TSR values for each type of mixture used in this study.
Based on TSR values, all mixtures satisfied the Superpave requirements for the 80% lower TSR value limit.The mixture with 80% HSNA has the best TSR value.Moreover, it is slightly greater (by 0.57%) than the TSR of the traditional mixture.

CONCLUSIONS
In this study, NA was treated by mixing two types of NA (SNA and HNA) and then mixing it with different proportions of refined asphalt.The necessary tests were carried out for NA after receiving industrial treatments to determine its physical and chemical properties to be used for paving work.Bituminous mixes made with binders containing 20, 40, 60, and 80% NA by asphalt weight were subjected to mechanical testing, and the performances of the mixtures were compared.The following are the main conclusions: 1.The resulting HSNA had a penetration grade that met Iraqi requirements.After treating HSNA with petroleum asphalt, the physical properties of HSNA were enhanced.As a result, combining HSNA with refined asphalt in various proportions could yield asphalt that meets Iraqi specifications for asphalt used in road construction.
3. The treated HSNA mixture had the highest ITS values before and after conditioning.All mixes met the Superpave specifications for the 80% lower TSR value limit, and the 80NA mixture has the highest TSR.Moreover, it is slightly higher (by 0.57%) than the TSR of the traditional mixture.

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Flexible pavements are most frequently distressed due to traffic loads, environmental effects, fatigue cracking, rutting, and low-temperature cracking (Qadir, 2013; Al.ani and Al-bayati, 2017; Al-bayati and Lateif, 2017; Al-Azawee and Lateif, 2020; Samor and Sarsam, 2021).Recent research concentrated on improving The characteristics of NA through physical and chemical procedures for industrial applications.NA is an oil-based compound traveling through earth fissures from deep rock reservoirs to the surface.If NA reaches the earth's surface, it will cause bitumen springs, and If NA stays close to the surface, it will slowly oxidize, harden, and eventually become mineral bitumen, a solid and stiff substance.Rock asphalt, Trinidad Lake, and Gilsonite are the most widespread types of NA (Ameri et al., 2011).Gilsonite, a bituminous mineral, is black, brittle, and easily ground into powder (Ameri et al., 2011).The modifier gilsonite improves the bonding abilities and moisture resistance of HMA (Kök et al., 2012; Nasrekani et al., 2017; Jahanian et al., 2017; Lv et al., 2018; Lv et al., 2019).Gilsonite is a naturally occurring, dark-colored hydrocarbon made from crude oil.Gilsonite is brittle and hard due to its chemical composition, which contains asphaltenes (around 70%) (Kök et al., 2012).Gilsonite is less expensive than other modifiers, which can significantly lower the price of constructing a pavement (Akbari Nasrekani et al., 2016).Added Gilsonite to the asphalt binder, increasing its viscosity and rigidity.(Kök et al., 2011; Quintana et al., 2016).At high temperatures, gilsonite significantly improves the performance of asphalt binder; however, no positive effect has been observed at low and intermediate temperatures.(Aflaki et al., 2014; Yilmaz et al., 2017; Ameri et al., 2018).Trinidad Lake Asphalt (TLA) is renowned for having constant qualities, high viscosity and density, exceptional rheological characteristics, and the ability to mix effectively with other types of bitumen (Fengler et al., 2019).Due to their similar chemical makeup, TLA and petroleum bitumen are compatible and have strong temperature stability, chemical stability (good oxidation resistance), and water stability (good adhesivity) (Widyatmoko and Elliott, 2008; Feng et al., 2011).TLA is too hard to be used in bituminous blends alone, so it is typically blended in specific amounts with bitumen derived from petroleum (Widyatmoko et al., 2005; Russel et al., 2008; Cao et al., 2009; Zou et al., 2020).

(
Widyatmoko and Elliott, 2008).Due to its exceptional qualities, rock asphalt-modified asphalt has recently garnered interest in improving pavement performance (Arisona et al., 2016; Lv et al., 2018; Cai et al., 2018; Shi et al., 2018; Chunmei et al., 2018).Several studies have been conducted to evaluate the use of rock asphalt in producing HMA.(Zeng et al., 2018) investigated the behavior of a

Figure 1 .
Figure 1.Natural Asphalt from Abu-Jeer (a) Hard NA and (b) Soft NA.
According to the (SCRB, 2003), coarse aggregate has been produced in a variety of sizes ranging from ¾ in.(19mm) to No. 4 (4.75mm), and fine aggregate sizes range from No. 4 to No. 200.Aggregates were sieved and recombined in the lab to make the

Figure 10 .
Figure 10.The ITS for Unconditioned and Conditioned Mixtures.

Table 1 .
Physical Characteristics of Aggregates (Coarse and Fine).

Table 4 .
Physical Properties of HSNA after Treatment.

Table 6 .
Volumetric Properties of Mixtures.