Physico-mechanical properties of asphalt concrete incorporated with encapsulated cigarette butts PDF

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Physico-mechanical properties of asphalt concrete incorporated with encapsulated cigarette butts Abbas Mohajerani, Yasin Tanriverdi, Harin Nishamal Dissanayake, Lachlan Johnson, Damian Whitfield, Guy Thomson, Eilaf Alqattan, Ahmad Rezaei, Bao Thach Nguyen, Kee Kong Wong School of Engineering, Civil ...

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Physico-mechanical properties of asphalt concrete incorporated with encapsulated cigarette butts Abbas Mohajerani, Yasin Tanriverdi, Harin Nishamal Dissanayake, Lachlan Johnson, Damian Whitfield, Guy Thomson, Eilaf Alqattan, Ahmad Rezaei, Bao Thach Nguyen, Kee Kong Wong School of Engineering, Civil & Infrastructure Engineering, RMIT University, Melbourne, Australia

Corresponding author: E-mail address: [email protected]

Citation: Mohajerani, A. Tanriverdi, Y. Nguyen, B. Wong, K. Dissanayake, H. Johnson, L. Whitfield, D. Thomson, G. Alqattan, E. and Rezaei, A. 2017, 'Physico-mechanical properties of asphalt concrete incorporated with encapsulated cigarette butts', in Construction and Building Materials, Elsevier, Netherlands, vol. 153, pp. 69-80 ISSN: 0950-0618 https://researchbank.rmit.edu.au/view/rmit:44232

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Physico-mechanical properties of asphalt concrete incorporated with encapsulated cigarette butts Abbas Mohajerani, Yasin Tanriverdi, Harin Nishamal Dissanayake, Lachlan Johnson, Damian Whitfield, Guy Thomson, Eilaf Alqattan, Ahmad Rezaei, Bao Thach Nguyen, Kee Kong Wong School of Engineering, Civil & Infrastructure Engineering, RMIT University, Melbourne, Australia

ABSTRACT Discarded cigarette butts (CBs) are among the most common types of litter found around the world. As a possible solution to this problem, this study investigated the possibility of encapsulating CBs with different classes of bitumen and paraffin wax, and incorporating them into asphalt concrete (AC) for pavement construction. The idea behind encapsulation involves restricting the interaction of CBs with fluids and thus preventing chemical translocation. This paper presents and discusses the results of two investigations. The first involved assessing the effects of incorporating different amounts of CBs 3 3 3 (10Kg/m , 15Kg/m and 25Kg/m ) encapsulated with different classes of bitumen (C170, C320, C600) into an AC mix manufactured with Class 170 bitumen. The second involved assessing the effects of 3 incorporating 10Kg/m of CBs encapsulated with paraffin wax into AC mixes that were manufactured with different classes of bitumen (C170, and C320). All samples, including the control AC samples (no CBs), were tested for mechanical and volumetric properties, including stability, flow, resilient modulus, bulk density, maximum density, air voids, and voids in mineral aggregates. For the first investigation, 3 3 involving encapsulation of CBs with bitumen, using 10kg/m and 15kg/m of CBs in an asphalt mix gave results that satisfied the requirements for light, medium and heavy traffic conditions. For the second investigation, involving encapsulation of CBs with paraffin wax, the changes in mechanical 3 and volumetric properties for 10kg/m CBs only satisfied the light traffic conditions for road pavements. The reduction in bulk density of AC caused by incorporating encapsulated CBs, increases the porosity, particularly when encapsulating in higher grade bitumen, which, in turn, lowers its thermal conductivity. This helps reduce the Urban Heat Island effect in urban environments. Keywords: Asphalt concrete; Bitumen; Paraffin wax; Encapsulation; Cigarette butts

1.0 INTRODUCTION 1.1 Recycling Waste in Asphalt Concrete Asphalt concrete (AC), which is also known as asphalt or dense graded asphalt (Austroads 2007; VicRoads 2012), is commonly used in the construction of roads and pavements. It consists of up to 96% coarse and fine aggregates with the rest being filler and a bitumen binder (Austroads 2014). Asphalt is usually mixed, spread and compacted whilst hot, and is therefore classified as a Hot Mix Asphalt (VicRoads 2012). It has a continuous distribution of aggregate particle size and filler, and low design air void content, ranging from 3 – 7% (Standards Australia 2005). Rutting due to excessive permanent deformation, cracking due to fatigue, ravelling due to oxidation and hardening of the binder are common modes of failure for AC (Austroads 2014). Therefore, attempts to improve the performance of AC are constantly being investigated (Abtahi et al. 2010). The reuse and recycling of waste materials in asphalt mixes are gaining traction in the industry, and, despite complying with the required standards, are yet to achieve widespread adoption (Rebbechi & Green 2005; Roads and Civil Works Australia 2015).

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Crumb rubber from car tyres has been used internationally in asphalt mixes for many years (Oliver 1999), and has been successfully recycled into high strength concrete slabs. Experiments have confirmed that it improves the fire resistance in structural high strength concrete slabs by reducing the spalling damage caused by fire (Hernandez-Olivares et al. 2007). Recycled glass has also been investigated for use in AC. Pioneer Road Services (2007) confirmed that using recycled glass in asphalt helped reduce the time for an asphalt surface to dry after it rains because the glass particles provide an impervious barrier. Another practice; namely, the incorporation of pulverised computer circuit boards, has been shown to increase the strength of AC (Guo et al. 2009). A more interesting waste recycling practice involves the containment of nuclear and hazardous wastes. For example, bitumen has been used as an encapsulation medium for radioactive waste products in France, a technique that has been successfully practised for many decades (Courtois et al. 1996). Despite the potential benefits, several concerns arise when attempting to incorporate waste materials into Hot Mix Asphalt (HMA). Studies have shown that the inclusion of waste materials into HMA can affect the volumetric and mechanical properties of the mix (Waller 1993; Taylor et al. 2007). However, according to a study by Kriech (1990), traditional AC comprising aggregate, bitumen binder and filler has been shown to be a very benign material with little or no leachate properties of concern. Whilst little research has been undertaken to examine the leachate properties of asphalt mixes containing waste products, the findings suggest that the presence of bitumen in the mix restricts their interaction with water and reduces the translocation of the chemical disposition (Doyle 1979; Roffey & Norqvist 1991; Azizian et al. 2003). This indicates that bitumen is an excellent material to encapsulate waste materials, such as used CBs. Bitumen is a highly viscous fluid derived from the distillation of crude oil with pre-existing natural wax (Lu et al. 2008; Fazaeli et al. 2016). The factors that influence the effect of wax on bitumen are the bitumen’s chemical composition and rheological behaviour, the exposed temperature, and content, and the composition and crystallinity of the wax (Edwards et al. 2006; Wong & Li 2009). A study by Fazaeli et al. (2016) involved analysing the influence of Fischer-Tropsch paraffin (FT-paraffin) wax on bitumen. The results indicated that the performance of bitumen at high temperatures improved under the influence of FT-paraffin, resulting in the asphalt mixture having increased resistance to permanent deformation. As FT-paraffin is a flow improver, the viscosity of bitumen at high temperatures is reduced. Consequently, the mixing and compaction temperature of the asphalt mixture decreases, resulting in lower energy consumption and emissions (Edwards et al. 2006; Edwards 2009). According to Fazaeli et al. (2016), FT-paraffin has minimal influence on bitumen at intermediate and low temperatures. To avoid the possible detrimental effects from paraffin wax, it is best that the wax content in bitumen is limited and should not exceed 3% (Edwards 2009). In contrast, according to Wong and Li (2009), in Mainland China, three different grades (A, B and C) are used to classify bitumen, with C comprising up to 4.5% paraffin wax but with the restriction that it can only be used for roads with lower traffic than A and B. The effects of wax on the bitumen quality and mixture performance have been reported differently. The debate on waxy bitumen is further complicated by the lack of a precise definition for wax, the different types of wax, and the poor precision of the test methods (Lu & Redelius 2007; Wong & Li 2009).

1.2 Cigarette Butts Cigarette butts (CBs) are one of the most common types of litter found around the world (Clean Up Australia 2015; ANR 2016). According to estimations from Euromonitor International (2014), over 5.7 trillion cigarettes were consumed worldwide in 2013; and, each year, an estimated 4.5 trillion butts from the annual cigarette consumption are deposited somewhere in the environment (Eriksen et al.

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2015). This is equivalent to an estimated mass of approximately 1.2 million tonnes of CBs each year (Mohajerani et al. 2016). Although Euromonitor International (2011) expects the global cigarette market to fall by 8% between 2015 and 2050, the consumption of cigarettes is expected to increase by more than 50% by 2025, mainly due to an increase in the world population (Mohajerani et al. 2016). This would suggest that billions of cigarettes will still be on the market in the future, and will lead to a continuation of a large number of CBs being deposited in the environment. In Australia alone, excluding illegal cigarettes on the black market, 16.2 billion cigarettes were consumed in 2015 (Euromonitor International 2011, 2016), of which, approximately, 7 billion resulted in littered CBs (Clean Up Australia 2015; Keep Australia Beautiful 2016). The impact on the environment is exacerbated by the ubiquitous nature of CBs and long decomposition times. Plastic filaments, which are manufactured from synthetic fibres (cellulose acetate) derived from wood pulp, comprise 95% of CBs, and it is estimated that the decomposition of CBs varies from a couple of months to many years depending on the environmental factors (Buchanan et al. 1993; Gu et al. 1993; Puls et al. 2011; Robertson et al. 2012). Research indicates that the breakdown is at a reduced rate when the CBs are exposed to marine or freshwater conditions (Clean Up Australia 2015). According to EPA Victoria (2012); it takes up to 12 months for CBs to break down in freshwater and 5 years in seawater. This is a major environmental concern, especially considering that 85% of the litter found in waterfront precincts is cigarette litter (Sustainability Victoria 2013). Cigarette filters are designed to absorb and trap particular smoke components, including tar and toxic chemicals (Hoffmann et al. 1997). The difficulty of dealing with cigarette butt waste is a global issue that is faced by municipal authorities and community groups throughout the world. Unfortunately, the research into applications for its reuse remains in their infancy (Hager 2010), and commercially viable reuse is urgently required to ameliorate the ongoing effect arising from CB waste. Given the low chemical reactivity of asphalt (Kriech 1990; Kriech et al. 2002), and the large volume used in road and pavement construction, the addition of small quantities of waste materials, such as CBs, may result in viable applications in construction of flexible pavements while ridding the environment of this waste material. This paper presents and discusses the results of two investigations. The first involved assessing the effects of incorporating different amounts of CBs 3 3 3 (10kg/m , 15kg/m and 25kg/m ) into an AC mix manufactured with Class 170 bitumen after encapsulating them with different classes of bitumen (C170, C320, C600). The second part of the 3 investigation involved assessing the effects of incorporating 10kg/m of CBs encapsulated with paraffin wax into AC mixes manufactured with different classes of bitumen (C170, and C320).

2.0 MATERIALS AND METHODS 2.1 Asphalt concrete incorporated with bitumen encapsulated CBs 2.1.1 Encapsulation of CBs Prior to mixing the CBs with AC, the CBs were exposed to heat in an oven at 105°C for a period of 24 hours (Figure 1). This process dried the CBs and eliminated the moisture trapped inside them.

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Figure 1 – Some of the CBs used in this study After drying, the second stage involved encapsulating the CBs by saturating them in hot bitumen (heated to 150°C). As the characteristics of the bitumen constitute an important factor in the encapsulation of CBs, different classes of bitumen were used to compare and contrast their impact on AC. The classes of bitumen used were C170, C320 and C600 (Table 1). The C170 bitumen was provided by the Alex Fraser Group, and the C320 and C600 classes were provided by the Shell Company Pty Ltd of Australia. Table 1 – Viscosity of C170, C320 and C600 bitumen (Dickinson 1984; Standards Australia 2013a) Bitumen Class C170 C320 C600

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Viscosity (60 C, Pa.s) 140 – 200 260 – 380 500 – 700

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Viscosity (135 C, Pa.s) 0.25 – 0.45 0.4 – 0.65 0.6 – 0.85

Figure 2 below displays the CBs that were encapsulated and left to cool on baking paper. It was found that soaking the CBs over a 5-minute period allowed the hot bitumen to fully penetrate and be absorbed into the CBs.

Figure 2 – Some encapsulated CBs left to cool on Baking Paper When the CBs were encapsulated and added to the asphalt mix, some of the bitumen from the CBs became mobile and contributed to the overall free bitumen content in the asphalt mix. An excess of free bitumen in the asphalt mix would be contrary to the mix design and likely to have an impact on the mechanical and physical properties of the final specimen; hence, controlling the amount of bitumen released from the CBs was paramount. To minimise the effect of excess bitumen in the samples, the CBs were subjected to a compressive load in a press, prior to soaking them in hot bitumen. The compressive load was placed onto the CBs to force the air out of the CBs. This was 5

done to reduce the volume of voids within the CBs to minimise the amount of free bitumen absorbed and the amount subsequently released into the mix. The CBs were weighed before being placed into the bitumen and then weighed again afterwards. This allowed the exact weight of the bitumen absorbed to be determined. The viscosity of the bitumen is an important factor in terms of both encapsulating the toxic chemicals within the CBs and for controlling the excess bitumen in the asphalt mix. It was theorised that when CBs are soaked in low viscosity bitumen and added to the asphalt mix, a small amount of bitumen from the CBs would become mobile and would increase the mechanical and physical properties of AC, where a class C170 bitumen would have the lowest viscosity and a class C600 bitumen would have the highest viscosity (Dickinson 1984). 2.1.2 Asphalt Mix Preparation All the aggregates required for this investigation were provided by the Alex Fraser Group Pty Ltd. The 14mm mix for this study was prepared in accordance with Standards Australia (2005), AS2150. Table 2 below displays the primary aggregate types used in the mix, including their origin, the percentage of mix type used in the control mix, and the bulk particle density of each aggregate type. Table 2 – Distribution and bulk density of the aggregates used in the control mix 3

Material Type

Source

Percent Added (%)

Bulk particle density (t/m )

14mm 10mm 7mm Dust Sand Filler

Oaklands Junction Oaklands Junction Oaklands Junction Oaklands Junction Bacchus Marsh Sibelco Australia

21.0 14.0 21.0 30.0 13.0 1.0

2.960 2.960 2.660 2.640 2.600 2.760

In recognition of its wide use, it was decided to produce a Dense Grade Asphalt (DGA) mix. According to Austroads (2014), section 4.7.1, the mix design procedure for DGA involves initially preparing and conditioning a batch according to Standards Australia (2014c), AS2891.2.1. The procedure followed in accordance with the standard is explained below. Initially, the aggregates were placed in an oven at 105°C for 24 hours to remove any moisture that might be present. After drying the components of the asphalt mix, the aggregates and bitumen were placed in an oven along with the testing equipment and heated to 150°C for a minimum of one hour to ensure that they were all at the same temperature. Once all the required materials were heated to the required temperature, the aggregates were then mixed with the bitumen for a mixing time not exceeding 3 minutes. Then the asphalt mix and mould was conditioned for 1 hour at 150°C in the oven. Within 30 minutes of conditioning, the contents were mixed together with the required amount of encapsulated CBs. The total content of bitumen comprised 5.1% (by mass of total aggregates) of C170 bitumen, which was used in the AC mix and for encapsulating the CBs. According to Austroads (2007), aggregates form up to 96% by mass of an asphalt mix. In order to maintain this ratio, the aggregates were appropriately amended for the mixes to account for the addition of CBs. These AC 3 3 3 mixes comprised different amounts of encapsulated CBs (10kg/m , 15kg/m and 25kg/m ) in addition to the control group that had no CBs. 2.1.3 Compaction of AC samples After preparing and conditioning a batch, Austroads (2014) requires a sample to be compacted before testing by means of either Gyratory compaction (AS2891.2.2) or Marshall compaction (AS2891.5). This study undertook the Gyratory compaction method to compact all the samples before testing in accordance with Standards Australia (2014d), AS2891.2.2. 6

The AC samples were compacted using a Servopac gyratory compactor similar to the one displayed in Figure 3. Once the samples were placed in the mould, the gyratory compactor applied a vertical pressure of 240 KPa at a rate of 80 gyrations per minute. If the Marshall method was used instead of the Gyratory method, this would be equivalent to 50 blows with the Marshall hammer. An example of some compacted samples is shown in Figure 4.

Figure 3 – Servopac gyratory compaction machine (Austroads 2014)

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Figure 4 – Some samples manufactured with CBs of 10kg/m , 15kg/m , 25kg/m and no CBs (control) 2.1.4 Testing Once the compacted samples were prepared, testing was undertaken with the Marshall method in accordance with Standards Australia (2015a), AS2891.5. The Marshall method involved determining the stability and flow of AC. Initially, the specimens were placed in the water bath (60°C) for 30 to 40 minutes. They were then assembled (Figure 5) in preparation for testing the Marshall stability and flow. 7

Figure 5 – Specimen and breaking head assembled to undergo Marshall testing for stability and flow After assembly, a load was gradually applied to the specimen until the load began to decrease. Then, the maximum load (stability) reading and flow reading were recorded. Marshall Stability is defined as the maximum load carried by a compacted specimen tested at 60°C at a loading rate of 51mm/min. The Marshall Flow is defined as the vertical deformation of the specimen under load, measured from the start of the loading to the point at which the specimen’s stability is at its peak. Figure 6 below displays a representation of the flow and stability using the Marshall method.

Figure 6 – Flow and Stability measurements taken under testing (Austroads 2014) According to Austroads (2014), after the stability and flow tests are completed with the Marshall method, optional performance tests can be performed, such as the Resilient Modulus test. Figure 7 displays a sample placed in a testing rig that is ready to be tested to determine the resilient modulus. The resilient modulus of an asphalt sample is the characterisation of the stress-strain relationship within the material for rapidly applied loads, and quantifies the ability of the material to spread a load (Austroads 2014).

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Figure 7 – Sample in Resilient Modulus Testing Rig As bitumen is a ‘visco-elastic’ material (Austroads 2014), variations in the testing conditions, particularly temperature, have a significant impact on the resilient modulus results obtained. The test conditions, and the equipment and procedures fo...