An Application of Pulsed Power Technology and Subcritical Water to the Recycling of Asphalt Concrete

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1 Procedia Engineering Volume 143, 2016, Pages 1 9 Advances in Transportation Geotechnics 3. The 3rd International Conference on Transportation Geotechnics (ICTG 2016) An Application of Pulsed Power Technology and Subcritical Water to the Recycling of Asphalt Concrete Rétyce I.H.D.T. Amoussou 1*, Mitsuru Sasaki 2 and Mitsuhiro Shigeishi 1 1 Graduate School of Science and Technology, Kumamoto University, Kumamoto, JAPAN 2 Institute of Pulsed Power Science, Kumamoto University, Kumamoto, JAPAN dodjy7@yahoo.fr, msasaki@chem.kumamoto-u.ac.jp, shigeishi@civil.kumamoto-u.ac.jp Abstract In order to resolve the issues related to the recycling of asphalt concrete, this study focuses on the application of pulsed power technology and subcritical water to the recovery of asphalt from asphalt concrete lumps. At the result, the recycled aggregate over 5mm with asphalt content of approximately 0.99% was produced using pulsed power technology. Furthermore, the application of subcritical water to recover asphalt from the residues of pulsed power discharge inside of asphalt concrete lumps resulted in an about 91% pure asphalt recovery rate and recycled fine aggregate with pure asphalt content of less than 0.5%. Keywords: Asphalt, asphalt concrete recycling, pulsed power technology, subcritical water, recycled aggregate 1 Introduction After a given time in service, the deteriorated asphalt concrete pavement is removed by milling or excavation from roads to become asphalt concrete waste (Cheung, 2003). Next, asphalt concrete waste has to be deprived from any other unwanted type of waste. The reprocessed asphalt concrete wastes become the reclaimed asphalt pavement (RAP). The reprocessing consists in crushing and screening the asphalt concrete waste collected. RAP can be recycled by adding it to new asphalt mixes. Owing to the fact that CO 2 emission and energy consumption regarding virgin binder production represent more than 80 % and 70 % respectively of the whole virgin mixture manufacturing process, the higher the RAP content of the recycled asphalt pavement, the higher the amount of reduced CO 2 emission and energy savings compared to producing virgin mixtures (Lee, 2011; Horvath, 1998). Hendricks, et al. demonstrated that the recycling of RAP can save approximately 37.9 liters of asphalt per ton of recycled mix * Created the first stable version of this document Corresponding author Corresponding author Selection and peer-review under responsibility of the Scientific Programme Committee of ICTG 2016 c The Authors. Published by Elsevier B.V. doi: /j.proeng

2 (Hendricks, 2005). However, not only could the RAP have a high moisture content compromising the cold-in-place recycling process (Horvath, 1998) but also it could be contaminated by salt and oil residues (Tam, 2006). Owing to its high stiffness and variability in aggregate gradation, RAP influences the volumetric and low temperatures properties of hot-mix asphalt (Santucci, 2007; Horvath, 1998), and decreases the recycled asphalt pavement cracking resistance (Huang, 2011). As regards polymer modified asphalt (JMAA, 2007); a mixture of virgin asphalt and a polymer modifier, it is resistant to the existing recycling and treatments methods due to the lack of accurate knowledge of the behavior of recycled modified asphalt binder in the recycled mix and requires the implementation of appropriate recycling methods that match its properties (Watson, 2011; Kubo, 2009). As a result, asphalt recovery from asphalt concrete wastes would improve the quality of recycled mixes, minimize the need for virgin mineral aggregate and the expenses associated with foreign crude oil exportation especially in the case of Japan that is well-known as a developed country without significant natural resources (Hesham, 2012). For this reason, pulsed power was discharged into straight and modified asphalt concrete specimens with asphalt content of 5% underwater. As a result, the recycled aggregate with asphalt content of approximately 1% originating from the asphalt concrete control specimens was produced using pulsed power technology (Amoussou, 2015). In line with previous studies where authors proposed an ideal asphalt concrete recycling to resolve the issues related to modified asphalt concrete recycling (Amoussou, 2015), this research work set as goals to: separate asphalt concrete lumps into recycled aggregate and the residues containing asphalt using pulsed power technology; assess the applicability of pulsed power technology to separate recycled aggregate from asphalt concrete lumps; recover asphalt from the above-mentioned residues with the aid of subcritical water; evaluate the properties of the recovered asphalt. This paper explains how to reproduce the aggregate from asphalt concrete lumps with the aid of pulsed power technology and subcritical water. 2 Material and Methods Asphalt and aggregate were separated from asphalt concrete lumps using pulsed power discharge and subcritical water as described in Figure 1. Pulsed power discharge Subcritical water Asphalt concrete lumps Residues containing asphalt Recycled coarse and fine aggregate Figure 1: Asphalt and aggregate separation process Asphalt 2

3 Figure 2: Asphalt concrete lumps Samples were composed of pieces of asphalt concrete lumps (Figure 2) obtained from the recycling plant of private company, Fukuoka Kensetsu-Gouzai Co., Ltd. located in Yatsushiro city, Japan. At this plant, asphalt concrete lumps are received from various construction sites along Yatsushiro city and the surrounding Kumamoto prefecture areas. 2.1 Pulsed Power Discharge Pulsed power is a scheme where stored energy is discharged as electrical energy into a load in a single short pulse or as short pulses with a controllable repetition rate (Akiyama, 2003; Bluhm, 2006). It is a less energy consuming and environmentally friendly technique which enables the transmission of considerable amount of electrical power during a relatively short time (Shigeishi, 2013). Pulsed power was discharged underwater into approximately 2.5 kg of pieces of asphalt concrete lumps (Figure 3) according to three discharge conditions namely Nos.1, 2, and 3 with total discharged energy of 720, 1080, and kj respectively were applied on the asphalt concrete lumps. As it is shown in Figure 3, products obtained after discharging pulsed power into the residues were labeled recycled aggregate over 5 and 2.5mm, and residues under 2.5 mm (Amoussou, 2015). Figure 3: Pulsed power discharge procedure Exclusive of the residues under 2.5mm, density and water absorption tests were performed on recycled aggregate over 5 and 2.5 mm according to Japan industrial standards (JIS) regulations and guidelines namely JIS A 1109 and JIS A 111 (JSMS, 2008). Asphalt was recovered from recycled aggregate over 5 and 2.5mm, and residues under 2.5 mm at the Kumamoto Prefectural Center of Constructional Technology to determine their asphalt contents. 3

4 2.2 Subcritical Water Recovery of Asphalt from the Residues The critical temperature and pressure of water are 374 C and MPa respectively. Below the critical point water is found in its subcritical state. The supercritical region is that above the critical point. Sub-and supercritical water is an environmentally friendly alternative to conventional harmful and toxic organic solvents. Furthermore, an abundance of water exists on earth at affordable price. Moreover, easy and efficient water recycling methods have been established (Wakayama, 2005). Asphalt was recovered from approximately 7.86% asphalt content residues under 2.5 mm. During the recovery an autoclave MMJ-500 (OM LABTECH, Co., Ltd., Japan) with a batch-type reactor of internal volume of 500ml was used (Figure 4). About 50 g of the asphalt concrete residues and 100ml of water were loaded in the autoclave. After that, the autoclave was heated to 300 C for 3h. Then, the heater was turned off and the system was allowed to cool down to room temperature. The authors refrained from stirring during the treatment but the mixture inside the autoclave was stirred during cooling at 450 rpm. Figure 4: Subcritical water recovery set-up After cooling, the contents of the autoclave were separated into liquid, recycled aggregate and recovered asphalt by suction filtration. Soon afterwards, recycled aggregate and recovered asphalt were dried at 105 C in an oven and room temperature respectively for 24 hours. Eventually, recycled aggregate and recovered asphalt were weighed. a) Recycled aggregate b) Residues under 2.5 mm Figure 5: Products of pulsed power discharge into asphalt concrete lumps After subcritical water recovery of asphalt from the residues under 2.5 mm (Figure 5-b), asphalt contents of recovered asphalt and corresponding recycled fine aggregate were determined according to 4

5 the asphalt ignition method (ASTMD , 2010) using an electrical furnace KBF626N1 (Koyo Thermo Systems Co., Ltd., Japan). To determine the properties of the recovered asphalt, penetration, softening point, and ductility tests were conducted at the above-mentioned constructional center. 3 Results and Discussion 3.1 Evaluation of Recycled Aggregate and Residues produced by Pulsed Power Discharge Recycling rates for discharge conditions Nos. 1, 2, and 3 were 96.5, 95.2, and 94.2 % respectively. These results show that recycling rate decreased when the pulsed power discharged energy increased. Figure 6 shows the distribution of recycled aggregate (Figure 5-a) and residues under 2.5 mm (Figure 5-b). A close investigation of Figure 6 has revealed that the amount of residues under 2.5 mm increases when discharged energy increases probably due to the substantial decrease of the amount of recycled aggregate over 5 mm. Recycled aggregate over 5mm Recycled aggregate over 2.5mm Residues under 2.5 mm Pulsed power energy -kj % 12% 34 % 31.0 % 9 % 13.5% 79% 57 % 55.5 % Figure 6: Distribution of aggregate and residues a) Oven dry density b) Water absorption Figure 7: Properties of recycled aggregate 5

6 The results of oven-dry density tests are displayed in Figure 7-a). Recycled aggregate over 2.5 mm has higher oven-dry density compared to the recycled aggregate over 5mm. However, at kj as pulsed power discharged energy recycled aggregate over 5mm is as good as recycled aggregate over 2.5 mm with 2.53 g/cm 3 as oven-dry density. In addition, both oven-dry densities increase with the increasing pulsed power discharged energy. The results of water absorption tests are shown in Figure 7-b). The lower water absorption ratio 0.87 % was observed at kj for recycled aggregate over 5 mm. At 1080 kj recycled aggregate over 5 and 2.5 mm has approximately the same water absorption. These results highlight the fact that recycled aggregate quality improves with the increasing pulsed power discharged energy. As it is shown in Figure 8 residues under 2.5 mm had the highest asphalt content compared to recycled aggregate over 5 and 2.5 mm. The results of the asphalt content tests suggest that asphalt binder has been significantly separated from the pieces of asphalt concrete lumps by pulsed power discharge as parts of the residues under 2.5 mm For instance, at kj as discharged energy asphalt contents of recycled aggregate over 5 and 2.5 mm were 0.99 and 1.35 %, respectively. As Pulsed power discharged energy increases, the asphalt contents of recycled aggregate over 5 and 2.5 mm residues decreases simultaneously highlighting the above-discussed decrease of the recycling rate when pulsed power discharged energy increases. Asphalt content (%) Recycled aggregate over 5mm Recycled aggregate over 2.5mm Residues under 2.5mm Pulsed power energy-kj Figure 8: Asphalt contents in recycled aggregate The results of oven-dry density, water absorption, and asphalt contents tests related to the asphalt concrete lumps are consistent with those of pulsed power discharge inside asphalt concrete control specimens performed by the authors (Amoussou, 2015). These results suggest the on-site applicability of pulsed power technology to separate asphalt from asphalt concrete lumps. 3.2 Characteristics of the Recovered Asphalt by Subcritical Water Asphalt was recovered mainly as spheroids. They were composed of pure asphalt and residual fine aggregate. An image of a recovered spheroid is shown in Figure 9-a). The application of the asphalt ignition method on the recovered spheroids revealed that their pure asphalt content was about 29 %. 6

7 a) Recovered spheroid b) A part of the recovered pure asphalt Figure 9: Recovered asphalt In other words, the recovered spheroids contained about 71 % residual fine aggregate. Figure 9-b) is a picture of a part of the pure asphalt recovered from the spheroids. Its physical properties are summarized in Table 2. To evaluate the recovery rate of the pure asphalt, its mass balance was calculated using equation 1: A o = A RA + A AG + A WL (1) Where A o is the pure asphalt content of about 50 g of residues (g); A RA is the pure asphalt content of corresponding recovered spheroids (g); A AG is the pure asphalt content of the corresponding recycled aggregate (g); A WL is the pure asphalt content in water and lost portions of the residues (g). Table 1 illustrates pure asphalt mass balance in terms of percentage. A RA /A o (%) A AG /A o (%) A WL /A o (%) Table 1: Asphalt mass balance Penetration (1/10 mm) Softening point ( 0 C) Ductility (cm) Table 2: Physical properties of the recovered asphalt Comparison of these results with the standard properties of straight and polymer modified asphalt (JMAA, 2007) showed that the recovered pure asphalt had a relatively high softening point and low ductility. Therefore, it may contain some polymer modifiers. Furthermore, these results demonstrate that the recovered pure asphalt needs proper rejuvenation in order to be reused as material for making recycled asphalt concrete. Moreover, the application of the above-mentioned subcritical water conditions produced recycled fine aggregate with pure asphalt content of 0.22 %. That is to say the purity of the recycled fine aggregate was about %. 4 Conclusions In summary, to confirm the applicability of pulsed power technology at separating asphalt from asphalt concrete lumps, pulsed power was discharged inside asphalt concrete lumps obtained from a recycling plant in Kumamoto, Japan. The main findings of this study demonstrate that the quality of the recycled aggregate improved with an increase in the total discharged energy. At kj as 7

8 pulsed power discharge energy, recycled coarse aggregate of asphalt content less than 1% was produced. Next, about 91 % of the pure asphalt contained in the residues of pulsed power discharge inside of the asphalt concrete lumps could be recovered using subcritical water. This recovery resulted in recycled fine aggregate with pure asphalt content smaller than 0.5 %. Quality tests performed on the recovered asphalt demonstrate that it still contained some polymer modifiers and residual fine aggregate. Consequently, it needs adequate rejuvenation before being used as material for making recycled asphalt concrete. It should be noted that in this study the authors have not been able to evaluate the asphalt loss in the water inside the pulsed power discharge apparatus. Further work should investigate the decomposition of polymer modified asphalt into base asphalt and polymer modifier using sub-and supercritical fluids. Concerning water contamination, it is crucial to design suitable recycling apparatus that will match asphalt concrete wastes recycling and allow water filtration to collect the products remaining in the water inside the pulsed power discharge apparatus. Acknowledgements The authors would like to express their sincere gratitude towards Mr. Daizou Fukuoka, president of Fukuoka Kensetsu-Gozai located in Yatsushiro-shi, Kumamoto, Japan for providing the asphalt concrete lumps utilized in this study. The authors gratefully acknowledge the contributions of Dr. Yuichi Tomoda, Mr. Yoshinori Toda, and Mr. Yasuo Miyazaki, Graduate School of Science and Technology, Kumamoto University, Japan for helping with the experiments. References Cheung, H.K. (2003). Use of recycled asphalt pavement- A practical approach to asphalt Recycling, pp-1-9. Lee, N., Chou, C., & Chen, K. (2011). Benefits in Energy Savings and CO2 reduction by using reclaimed asphalt pavement. TRB 2012 Annual Meeting. Horvath, A. & Hendrickson, C. (1998). Comparison of environmental implications of asphalt and steel-reinforced concrete pavements.transportation Research Record, 1626, pp Hendricks, C.F. & Janssen, G.M.T. (2005). Does recycling fit with sustainable use?, Achieving sustainability in construction. Dhir, R.K., Dyer, D.T., Newlands, M.D. (Eds.), pp Tam, V. & Tam, C.M. (2006). A review on the viable technology for construction waste recycling. Resources Conservation & Recycling. Vol. 47, pp Santucci, L. (2007). Recycling Asphalt Pavements - A Strategy Revisited. TechTopic, 8. Huang, B., Shu, X., & Vukosavljevic, D. (2011). Laboratory Investigation of Cracking Resistance of Hot-Mix Asphalt Field Mixtures Containing Screened Reclaimed Asphalt Pavement. Journal of Materials in Civil Engineering, Vol. 23, No. 11, pp Japan Modified Asphalt Association (JMAA). (2007). Japan Modified Asphalt Association Standards, Quality and Test Methods of Polymer Modified Asphalt for Road Pavement. Watson, E.D. (2011). Literature review of hot in-place recycling. Florida Department of Transportation. Kubo, K. (2009). Pavement Team, Public Works Research Institute, Japan: Recycling in Japan. Hesham, A. & Sobhan, K. (2012). On the Road to Sustainability: Properties of Hot-in-place Recycled Superpave Mix. Publication and Presentation at the 91st Annual TRB Meeting, pp Amoussou, R., Ishimatsu, K., Oyama, N., & Shigeishi, M. (2015). Separation of aggregate from asphalt concrete using pulsed power technology. Int. J. of GEOMATE, Vol.9, No.1 (Sl. No. 17), pp

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