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See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/287312521 ResearchGate Chapter 18: Energy Harvesting from Pavements" in Climate Change, Energy, Sustainability and Pavements Chapter in Green Energy and Technology October 2014 DOI: 10.1007/978-3-662-44719-2_18 CITATIONS 21 4 authors: Andrew Dawson AHH Enterprises 256 PUBLICATIONS 7,192 CITATIONS SEE PROFILE READS 7,756 Rajib B. Mallick Worcester Polytechnic Institute 191 PUBLICATIONS 5,132 CITATIONS SEE PROFILE Alvaro García RWTH Aachen University 181 PUBLICATIONS 5,924 CITATIONS Pejman Dehdezi WSP 21 PUBLICATIONS 472 CITATIONS SEE PROFILE All content following this page was uploaded by Rajib B. Mallick on 02 March 2016. The user has requested enhancement of the downloaded file. SEE PROFILE Published in: Climate Change, Energy, Sustainability and Pavements, 2014 Editors: Gopalakrishnan, Kasthurirangan, Steyn, Wynand JvdM, Harvey, John (Eds.) Energy Harvesting from Pavements Andrew Dawson¹, Rajib Mallick², Alvaro García Hernandez³, Pejman Keikhaei Dehdezi4 Abstract Against a background of the immense solar radiation incident with available pavement surfaces, the opportunity for energy to be harvested from pavements is investigated. While the emphasis is on the harvesting of solar-derived heat ener- gy, some attention is also paid to the collection of energy derived from displace- ment of the pavement by traffic and to solar energy converted directly to electrici- ty via photovoltaic systems embedded in pavements. Basic theory of heat collection is covered along with a discussion of the relevant thermal properties of pavement materials that affect heat transmission and storage in a pavement. Available technologies for pavement energy harvesting are reviewed and some of their advantages and limitations reviewed. The chapter continues with some de- scriptions of the ways in which the harvested energy can be stored and then used before ending with sections on evaporative cooling of pavements and system evaluation. 2 A. Dawson, R. Mallick, A. García, P. Keikhaei Dehdezi 1.1 Introduction With the increase in world population and industrialization, there has been a continuous increase in consumption of energy. Therefore, this important question is raised; will fossil energy resources (i.e. coal, oil, and gas) in the future account for the energy needed to survive and develop? Although opinions differ as to when fossil fuels will be depleted, there is no doubt that supplies are limited. Oil, one of the most consumable types of fossil fuels, is being consumed about one million times faster than it was made (Armstrong and Blundell, 2007). In addition, environmental pollution is a serious threat to vegetation, wild life, and human health. Generating energy from fossil fuels increases the level of car- bon dioxide into the upper earth atmosphere and causes anthropogenic climate change; an acceleration of the 'greenhouse effect' (Armstrong and Blundell 2007). The depletion of oil reserves, the need to arrest global warming, climate change, or ozone layer depletion caused by the combustion of fossil fuels, all mandate new thinking from all those with concerns for the future. Hence, governments and industries everywhere are striving, more than ever, to capture, harvest and generate energy in every possible way by discovering new potential energy supplies and reservoirs, and developing innovative technologies to extract the energy available from them. In terms of harvesting renewable ener- gy, there is none more researched than solar energy. The two most attractive things about solar energy are that it is an assured source of energy for the foresee- able future, and it is omnipresent on any exposed surface on the earth during day- light hours. To make the capture and harvesting of this energy feasible, the solar radiation needs to be of a minimum intensity for sufficient period of time during the year. While there are many areas of the world that are blessed with such sun- shine, harvesting technologies need to be of sufficient surface area to capture a meaningful amount of solar radiation. The most commonly used technology. photovoltaic cells – includes cells that themselves have a significant environmen- tal footprint (estimated energy payback times (energy generated/energy consumed to make and deliver) between 0.7 and 4 years and carbon footprints of between 15 and 38g CO2-equivalent per kWh generated) (de Wild-Scholten, 2003). - For these reasons it would be attractive to find an existing common material, existing in all parts of the world, of significant surface area that would be exposed to sunlight all year round and that has the ability to "hold" the energy in the form of “heat” that can be extracted. Pavements - asphalt and concrete, are such mate- rials. They cover millions of square kilometers all over the world and are exposed to the environment throughout the year. As an example, considering the total paved surfaces of 158,000 square kilometers in the US, then an average of 4.8 kil- owatt-hours (kWh) of incident solar radiation per square meter per day means that here are 758 terawatt-hours (TWh) of solar energy per day that is incident on pavements. These pavement surfaces, because of their relatively high absorptivity (and hence low reflectivity) and low conductivity, absorb a significant amount of 1 Energy Harvesting from Pavements 3 this radiation (as much as 80-90% of the energy reaching the earth's surface – see Figure 1.1) and then hold it as heat energy. Hot pavement surfaces, especially dur- ing warm weather, are common observations in most places of the world and are implicated in contributing to the Urban Heat Island (UHI) effect. Their surfaces emit that stored heat, particularly in evenings, leading to increased temperatures of adjacent buildings, use of more cooling energy, and hence depletion of fossil fuels, with consequent CO2 and particulate emissions (Wong & Chen 2009). Fur- thermore, hot pavements are more likely to experience structural and functional failures sooner, thus requiring more frequent maintenance. Moreover, rutting is a major temperature-related distress in asphalt pavements that occurs as a result of high temperature. Hence this heat absorption leads indirectly to greater consump- tion of natural resources and results in more harmful emissions that contribute to- wards climate change (Figure 1.2). Collecting heat from the pavement could re- duce the UHI effect and rutting potential of the asphalt pavement (Mallick et al. 2009; Wu et al. 2011). Surface Temperature (°C) 70 Asphalt Rubber Thin | Asphalt Rubber Thick 65 Asphalt Rubber Thin with White Paint Chip Seal Standard HMA Thin HMA Thick 60 60 55 59 50 50 45 HMA Thin with White Paint HMA Thick with White Paint Crumb-Rubber Concrete ☐☐ UTW Asphalt Rubber Thick with White Paint 30cm Concrete 40 + 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 Albedo Figure 1.1 Albedo for a range of pavement types in Phoenix, AZ (Cambridge Systematics, 2005). Notes: Albedo is the proportion of incident energy reflected, thus 100 x (1-Albedo) gives the percentage absorbed; HMA = Hot mix asphalt; UTW = Ultra-thin whitetopping (concrete) If this heat energy were to be extracted, two principle benefits would be ob- tained: 4 A. Dawson, R. Mallick, A. García, P. Keikhaei Dehdezi Elevated Emissions of Air Pollutants and Greenhouse Gases Fossil fuel power plants supply more power to meet demand and produces more pollutants, which are harmful to human health and increase air polution by forming ground level ozone/smog, fine particulate matter and acid rain; increases emissions of CO2 which contributes to global climate change Increased Energy Consumption in Offices and Homes Electricity demand for cooling increases 1.5-2.0% for every 0.6°C increase in air temperatures, starting from 20 to 25°C; 5-10% of community-wide demand for electricity is used to compensate for the heat island effect $11. Urban Heat Island Effect Compromised Human Health and Comfort Increased temperature and air pollution causes discomfort, respiratory difficulties, heat cramps, exhaustion, heat stroke and mortality; excerbates the impact of heat waves; death from excessive heat exposure>total deaths from hurricanes, lightning, tornadoes, floods and earthquakes in the US Impaired Water Quality Pavements above 38C increases temperature of rainwater from 21C to 35C; rainwater runoff drains into storm sewers and raises water temperature as it drains into streams, rivers, lakes and ponds, which causes negative effect, even fatal to aquatic life Asphalt mix layers which make up > 90% of pavements, rut under load at high temperatures, which leads to increased frequency of maintenance and rehabilitation; in concrete pavements variation of temperature along depth leads to an increase in curling stresses and potential of cracking Figure 1.2 Effects of high temperature in pavements (James 2002, Akbari, 2005) The energy could be used beneficially, allowing a reduction in fossil fuel- derived energy The energy would be removed from the location where it is currently causing a problem (both to the pavement and to the UHI) To give some context to the amount of solar radiation incidence on pavements, 758 TWh as mentioned above, consider that there are a little over 300 million households in the US using, on average, about 30 kWh of energy per day - a total of about 9 TWh. Thus it is apparent that the complete household consumption of energy in the US could be provided from pavements if only 1.2% of the solar en- ergy incident on the pavement could be captured! Also consider: 1. the fact that there is no need to set up a collector system to capture this en- ergy, (although there is a need for a system to “harvest” it), the system al- ready exists and is functioning as part of the transportation network! In- deed, as Figure 1.1 shows, pavement surfaces are among materials with low albedo (i.e. they don't reflect the energy back into the atmosphere well), so they are relatively efficient at energy collection without any spe- cial treatment. 2. that no additional material is needed for the solar "collector" and this means an avoidance of a significant amount of energy, money and time that are involved in the manufacturing process./n ResearchGate See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/330554205 Numerical Study on Influence of Piezoelectric Energy Harvester on Asphalt Pavement Structural Responses Article in Journal of Materials in Civil Engineering ⚫ March 2019 DOI: 10.1061/(ASCE)MT.1943-5533.0002640 CITATIONS 30 7 authors, including: Pengfei Liu RWTH Aachen University 156 PUBLICATIONS 2,352 CITATIONS SEE PROFILE READS 234 Qian Zhao Shenzhen University 9 PUBLICATIONS 230 CITATIONS SEE PROFILE Hailu Yang University of Science and Technology Beijing 58 PUBLICATIONS 753 CITATIONS Dawei Wang Harbin Institute of Technology 242 PUBLICATIONS 4,576 CITATIONS SEE PROFILE All content following this page was uploaded by Hailu Yang on 07 June 2022. The user has requested enhancement of the downloaded file. SEE PROFILE Numerical Study on Influence of Piezoelectric Energy Harvester on Asphalt Pavement Structural Responses Pengfei Liu, Ph.D.¹; Qian Zhao²; Hailu Yang, Ph.D.³; Dawei Wang, Ph.D., M.ASCE4; Markus Oeser, Ph.D., M.ASCE5; Linbing Wang, Ph.D., M.ASCE6; and Yiqiu Tan, Ph.D.7 Abstract: In recent years, energy harvesting technologies have been applied in pavement engineering. Piezoelectric energy harvesting in pavement aims to take advantage of the vehicle load on a road. Most of the existing theoretical and experimental research focused on the materials, structures, and shape of the energy harvesters to improve the efficiency of the output energy. However, few investigations have analyzed the compatibility of piezoelectric energy harvesters (PEHs) and pavement. This study investigated the influence of PEHS on the structural response of asphalt pavement. Three-dimensional (3D) tire-pavement interaction finite-element models with and without a PEH were constructed according to a previous demonstration project. Several critical points within the pavement structures were selected and their mechanical responses induced by the passing tire were compared and discussed. A parametric study analyzed the pavement responses to different traffic speeds, tire loads, and bonding conditions between the PEHS and asphalt layers. Two potential optimization solutions for the PEH were explored. The results showed that the influence of the PEH on the asphalt pavement performance is significant in terms of the horizontal and vertical strains and von Mises stresses. A PEH causes potential permanent damage initiation in its adjacent area within the pavement structure. The maximum values of the horizontal tensile strains appeared at the bottom of the asphalt surface course in all pavement models with a PEH. These conclusions offer basic information for improving the practical design of PEHs in asphalt pavement. DOI: 10.1061/(ASCE)MT.1943-5533.0002640. © 2019 American Society of Civil Engineers. Author keywords: Piezoelectric energy harvester; Finite-element method; Asphalt pavement; Dynamic analysis; Tire-pavement interaction model. Downloaded from ascelibrary.org by Dawei Wang on 01/13/19. Copyright ASCE. For personal use only; all rights reserved. Introduction Roads, as one of the most important types of infrastructure, play a key role in a country's economic growth. With the rapid urbanization Assistant Researcher, Institute of Highway Engineering, Rheinisch- Westfaelische Technische Hochschule Aachen Univ., Mies-van-der- Rohe-St. 1, Aachen D52074, Germany. Email: liu@isac.rwth-aachen.de ²Ph.D. Candidate, Graduate Research Assistant, National Center for Materials Service Safety, Univ. of Science and Technology Beijing, 30 Xueyuan Rd., Haidian District, Beijing 100083, China. Email: zhaoqian928 @126.com 3 Assistant Researcher, National Center for Materials Service Safety, Univ. of Science and Technology Beijing, 30 Xueyuan Rd., Haidian District, Beijing 100083, China. Email: 727930305@qq.com *Professor, School of Transportation Science and Engineering, Harbin Institute of Technology, 73 Huanghe Rd., Nangang District, Harbin 150090, China; Professor, Institute of Highway Engineering, Rheinisch-Westfaelische Technische Hochschule Aachen Univ., Mies-van-der-Rohe-St. 1, Aachen D52074, Germany (corresponding author). Email: wang@isac.rwth-aachen.de "Professor, Institute of Highway Engineering, Rheinisch-Westfaelische Technische Hochschule Aachen Univ., Mies-van-der-Rohe-St. 1, Aachen D52074, Germany. Email: oeser@isac.rwth-aachen.de °Professor, Joint USTB-Virginia Tech Laboratory on Multifunctional Materials, Univ. of Science and Technology Beijing, 30 Xueyuan Rd, Hai- dian District, Beijing 100083, China; Professor, Virginia Tech, Blacksburg, VA 24061. Email: wangl@vt.edu; lbwang@ustb.edu.cn Professor, School of Transportation Science and Engineering, Harbin Institute of Technology, 73 Huanghe Rd., Nangang District, Harbin 150090, China. Email: tanyiqiu@hit.edu.cn Note. This manuscript was submitted on July 13, 2018; approved on September 12, 2018; published online on January 14, 2019. Discussion period open until June 14, 2019; separate discussions must be submitted for individual papers. This paper is part of the Journal of Materials in Civil Engineering, ASCE, ISSN 0899-1561. © ASCE and updated information technology, significant changes have taken place in the field of transportation and infrastructure systems. For example, with the development of wireless sensor networks (WSNs) and intelligent transport system (ITS), an increasing num- ber of intelligent devices have been designed and added to the tradi- tional infrastructure. Thus, new challenges about powering the devices have been put forward as well. In recent years, energy harvesting technologies have attracted wide attention. Researchers developed different kinds of devices to transform light, wind, vibration, and heat from the environment into electricity (Batra et al. 2011; Chiarelli et al. 2015; Dakessian et al. 2016; Galchev et al. 2011; Kan et al. 2016; Wischke et al. 2011). Pavement always bears large numbers of axle loads during its lifetime, which contain abundant mechanical energy. Piezoelec- tric energy harvesting in pavement aims to take advantage of the vehicle load on the road. According to the piezoelectric effect of piezoelectric materials in pavement, its deformation caused by ve- hicles can be turned into electrical energy, for recycling and stor- age, and is one of the most popular pavement energy harvesting technologies (Faisal et al. 2016; Roshani et al. 2016; Sun et al. 2013). Zhao et al. (2010) designed a cymbal-shaped energy harvester for asphalt pavement and analyzed its performance at different sizes, and suggested that thicker piezoelectric transducers (PZTS) and smaller total cymbal size maximized efficiency. Yesner et al. (2016) provided an improved bridge transducer based on the cym- bal structure with a novel electrode design. The transducer con- sisted of a square PZT ceramic (32 × 32 × 0.2 mm) and steel caps. The prototype was made of 64 transducers and produced 2.1 mW under simulated traffic loadings. Moure et al. (2016) also calculated the exact output energy under different kind of traffic loading by cymbal harvesters. Based on indoor tests of the harvesters, they J. Mater. Civ. Eng. 04019008-1 J. Mater. Civ. Eng., 2019, 31(3): 04019008 Downloaded from ascelibrary.org by Dawei Wang on 01/13/19. Copyright ASCE. For personal use only; all rights reserved. calculated that the energy density of this technology could be be- tween 40 and 50 mWh/m². Zhao and Erturk (2013) presented two numerical methods of the electromechanical model of multilayer PZT stacks under harmonic and random vibrations. Yang et al. (2017b) designed a stacked mode for a piezoelectric energy har- vester (PEH) with a set of nine piezoelectric units in a package 300 x 300 x 68 mm. The open circuit voltage of the system reached 280 V during tests with a pressure testing machine and an accelerated instrument model mobile load simulator. Lv et al. (2015) investigated the behavior of PZT stacks embedded in as- phalt pavement using the finite-element method (FEM) with differ- ent parameters of stack size, and adopted a nylon package for the PZT stacks. The piezoelectric cantilever beam-type energy har- vester is supposed to perform better in bridge applications with an optimized design of its size and mass distribution (Karimi et al. 2016; Zhao et al. 2017). There are also demonstrated projects and research with PZT stack harvesters embedded in highways in the United States (Xiong and Wang 2016) and in China (Yang et al. 2018), both of which suggested that piezoelectric technology is a promising method for pavement energy harvesting. In addition, different piezoelectric materials such as polyvinylidene fluoride (PVDF) have been used for energy harvesting of sensors (Huang and Chen 2016). However, most of the existing theoretical and experimental re- search focused on the materials, structures, and shape of the energy harvesters to improve the efficiency of output energy (Yang et al. 2017a; Chen et al. 2016; Zhao et al. 2014). On the other hand, many experimental and numerical studies investigated the deterioration of traditional asphalt pavements (Liu et al. 2013, 2017a, c; Wang et al. 2017). As far as the authors know, few investigations have analyzed the performance and structural response of pavement embedded with PEHs, especially the reliability and durability for long-term service (Roshani et al. 2017; Chen and Anton 2017). With the popularization of PEHs in pavement engineering, it is in- creasingly important to determine the compatibility of PEHS and pavement, i.e., the relationship between a PEH and its influence on the performance of the host pavement. This paper focuses on the influence of PEHs on asphalt pave- ment response using the FEM. First, a demonstration project in pre- vious research is briefly introduced to show the application of PEHs in the practice. Then tire-pavement interaction finite-element (FE) models with PEHS and without PEHS in three dimensions are constructed according to the demonstration project, followed by verification using analytical and experimental methods. The mechanical responses of the asphalt pavements are comprehen- sively investigated based on the numerical simulation. Several critical points within the pavement structures are selected and their mechanical responses induced by passing tires are compared and discussed. A parametric study analyzes the pavement responses at different traffic speeds, tire loads, and bonding conditions between the PEH and asphalt layers. Two potential optimization solutions of the PEH are explored with the aim of reducing or delaying the potential premature damage caused within the pavement structure with the PEH. Finally, some general conclusions and recommen- dations are given. Methodology Demonstration Project A prefabricated PEH was embedded in the Ma-Zhao Highway, spe- cifically at K90 + 700, a highway near Zhaotong City in Yunnan Province, China. This is the site of a previous demonstration project © ASCE internal circuit board piezoelectric units packaging materials Fig. 1. Perspective illustration of the PEH. which was around 50 m in length. Taking into consideration the contact patch of tires, it was decided to design the PEH in a square shape with a side length of 0.3 m in order to improve the contact with vehicle wheels. The PEH was 0.08 m thick, which is margin- ally less than the sum of the asphalt surface and binder layers in the test site (0.1 m). The PEH was composed of four component parts: the packaging materials, the piezoelectric units, the internal circuit boards, and other components for sealing and fastening (Fig. 1). Piezoelectric material was the core component of the PEH, with a piezoelectric unit size of $20 × 23.2 mm, using piezoelectric ceramics PZT-5 H (Baoding Hongsheng Electronic Equipment, Baoding, Hebei, China). PA66-GF30 (Quadrant Plastics, Shanghai, China) is a kind of nylon reinforced with 30% glass fiber, which was selected as the material for the packaging of the PEH due to its high toughness, load resistance, and strength and its resistance to repeated shocks. There was an upper, middle, and lower layer to the protective layer, in which the upper layer directly undertook the vehicle load, the ground reaction force was supported by the lower layer, and the middle layer facilitated the holes for 12 piezoelectric units, desiccant positioning, and grooves for wires and the internal circuit board. The outputted power exited via a cable when the piezoelectric units were connected to the circuit board. A built-in rectifier circuit kept the output voltage positive. Water leakage was prevented by sealing the rectifier circuit with electronic glue. This was achieved via the application of a silicone gasket between the upper and lower encapsulation structures. To avoid stress concentration, a 0.04-m- diameter stainless steel gasket was inserted between the piezoelec- tric materials and wrapped in a protection package. Therefore, the PEH had good performance level in terms of compression, resis- tance to fatigue, and water resistance as a result of these methods. Light-emitting diodes (LEDs) were connected to the PEH to receive the piezoelectric power. Fig. 2 shows the PEH installation process, and the final state of the demonstration pavement is shown in Fig. 3. The demonstration project showed the high efficiency of the PEH; more information and results were given by Yang et al. (2018). Finite-Element Modeling of Tire-Pavement Interaction Models A 295/75R22.5 truck tire was selected to derive the mechanical response of asphalt pavement with and without a PEH under heavy traffic moving loads. Some features of the tire are listed in Table 1. Because this research focused specifically on the pavement re- sponse, a simplified model of the tire model was used, consisting of a detailed tread and a body section, without belts or cords, mounted on a rim. The tire was considered as elastic, and the rim considered J. Mater. Civ. Eng. 04019008-2 J. Mater. Civ. Eng., 2019, 31(3): 04019008 Reserving positions for PEHS during construction Covering the Slotting and coring for installation PEHS' zone with uniform protection layer Laying the cable and filling the seam Cleaning and levering the holes' bottom Putting PEHS in the pavement and compacting Fig. 2. Flowchart of PEH installation. as a rigid body, to help improve computational efficiency. The material properties of the tire are listed in Table 2. A two-dimensional cross section of a 295/75R22.5 tire was used to produce a three-dimensional (3D) model (Fig. 4). The rim was fixed upon a reference point on the tire's axis of rotation. It is help- ful in terms of providing the angular rotation boundary condition for the tire. The discretization of the tread and body section used 39,108 solid elements (C3D8 R). There were 73,635 nodes in total. Symmetrical tire-pavement interaction models were developed under the assumptions that the construction was free from defects, the pavement structure was in good condition, and the center of the tire passed directly over the PEH without any tire wander. It was important to analyze first the structural responses of the pavement without a PEH to provide a reference for the studies of the pave- ment structure with a PEH (Fig. 5). The element size in close prox- imity to the loading path was defined to be smaller than the global element size. The pavement model was 10 m in length and 1.85 m in width. Both ends and the right-hand side of the pavement (in the direction of traffic) were defined with symmetrical boundary conditions. The underside of the subgrade layer and the left-hand side (in the di- rection of traffic) of the pavement were fixed in all three directions. In addition to the interfaces between the PEH and asphalt layers, the three asphalt courses were fully bonded together. In order to permit only relative horizontal displacement at the interlayers, the interfaces between the asphalt base course and the subbase, and between the subbase and the subgrade, were partially bonded. Fur- ther details about the material properties and geometry of the pave- ment models are listed in Table 3. These material properties were measured from the specimens derived from the demonstration pavement, which was at a representative temperature of 25°C in the region in which the demonstration project was performed. In this initial study, the tire-pavement interaction model was used to predict the pavement response under one pass of the tire. The sim- ulation time was relatively short and the viscoelasticity of the pave- ment materials was not obvious. As a result, only elastic material properties were considered in this study. As mentioned in the previous section, the side length of the PEH was 0.3 m and its thickness was 0.08 m. The material properties of the PEH were considered to be the same as the properties of its protective pack- aging material, nylon (PA66 with 30% glass fiber), the density, E-modulus, and Poisson's ratio of which were 1,290 kg/m³, 5,900 MPa, and 0.34, respectively. Inflation of the tire, tire loading onto the pavement surface, and tire movement along the pavement were the three steps used in carrying out the simulation. All the simulations were carried out in Abaqus/Explicit version 2017. During the tire inflation step, the tire center was fixed and inflated to an internal surface pressure of 0.759 MPa, which happened in 4 s, while the tire was held at a defined distance above the pavement. Next, the tire was moved down to the pavement surface by applying axle loads and gravita- tional force on the reference point of the tire. The simulation time of the tire loading step was 8 s, which ensured that the tire was stable before rotation. Then a constant angular velocity was determined with respect to the reference point of the tire. The tire's constant rotation was converted into a longitudinal movement along the loading path using slip-free tire-pavement contact in Abaqus (2014). The duration of the tire rotation process was dependent on the traffic speed. More information about the tire-pavement in- teraction model was given by Liu et al. (2018a). Verification of FE Model A simulation was performed to validate the tire-pavement interac- tion model, during which the tire passed a ditch profile at a speed of 19.3 km/h. A water drainage ditch 0.69 m long and 0.12 m deep was used in determining the dynamic tire responses (Fig. 6). The curvature radius was 0.78 m and the dimensions of the pavement were 5 × 0.8 × 0.04 m. Results derived from Chae (2006) were directly comparison with the computational results in this study (Fig. 7), demonstrating that the vertical displacement response derived from the developed model was reasonable. Downloaded from ascelibrary.org by Dawei Wang on 01/13/19. Copyright ASCE. For personal use only; all rights reserved. © ASCE 14295. (a) (b) Fig. 3. Final state of the demonstration pavement: (a) close view of PEH embedded in the demonstration pavement; and (b) demonstration pavement with a passing car. 04019008-3 J. Mater. Civ. Eng., 2019, 31(3): 04019008 J. Mater. Civ. Eng. Table 1. Selected tire specifications Specification Overall diameter of tire Diameter of rim Section width of tire Thread depth Maximum load capacity Value and fluctuations (Liu et al. 2018b). Because the relative errors were 12% and -3.6%, respectively, they were within the error range. Thus, based on this criterion, the interaction model was verified. 0.97 m 0.5715 m 0.295 m 0.015 m 26.7 kN Table 2. Material properties of tire Parameter Thread and body section Density (kg/m³) 719 Poisson's ratio 0.3 Rim 8,000 0.3 80 E-modulus (MPa) Source: Data from Lin and Hwang (2004). Fig. 4. 3D tire model. 200,000 Data from experiments on the German Federal Highway Re- search Institute's test track further verified the developed model. Pressure load cells and strain gauges were buried at different depths during the test track construction to measure stresses and strains due to applied loads (Liu et al. 2017b). A moving tire with a speed of 30 km/h was used in the dynamic analysis undertaken in this study. The values from the simulation and the experimental measurements were compared (Table 4). A range of error of 20% was considered to allow for uncertainties Analyses and Discussions of Asphalt Pavement Structural Responses Mechanical Responses at Critical Points of Pavement Structures Some critical points in the pavement structures were selected to analyze the structural responses of asphalt pavements with and without the PEH. The horizontal tensile strain along the transverse direction of the traffic normally appears at the bottom of the asphalt layers and causes reflective cracking in asphalt pavements. As a result, for both pavement models, six points (C1-C6) at the center of the loading path and six points (E1-E6) at the edge of the load- ing path were selected. Points C1-C3 and E1-E3 were at the bot- tom of the asphalt binder course, whereas Points C4-C6 and E4-E6 were at the bottom of the asphalt base course. In the pavement model with the PEHs, C1, E1, E2, C3, E3, C4, E4, E5, C6, and E6 were located below the edges of the PEH (Fig. 8). Comparison of Critical Points at Bottom of Asphalt Binder Course The peak horizontal strains were derived from the FE simulations. Generally, the peak horizontal strains of the critical points were found when the tire was passing the corresponding critical points. In addition to the horizontal strains, the peak von Mises stresses were also determined from these critical points. Extensive use of the von Mises stresses enabled characterization of the yielding of the materials, and, therefore, the structure's permanent damage ini- tiation. The results are shown in Fig. 9. The letters p and t refer to the pavement model with the PEH and the traditional pavement model without the PEH, respectively. For example, Clp means the critical point in the pavement model with the PEH at location C1 mentioned previously; C1t means the critical point in the pave- ment model without the PEH at the corresponding location. At the bottom of the asphalt binder course, the horizontal strains derived from the critical points at the center of the loading path (C1-C3) were tensile in both the pavement with and without the PEH, whereas those derived from the edge of the loading path (E1-E3) were compressive [Fig. 9(a)]. This indicates that the points at the center of the loading path were prone to cracking in both pavement models. The peaks of the tensile strains derived from Downloaded from ascelibrary.org by Dawei Wang on 01/13/19. Copyright ASCE. For personal use only; all rights reserved. Traffic direction Traffic direction PEH (a) (b) Fig. 5. Different types of tire-pavement interaction models: (a) pavement model without PEH; and (b) pavement model with PEH. © ASCE 04019008-4 J. Mater. Civ. Eng., 2019, 31(3): 04019008 J. Mater. Civ. Eng./n Journal of Environmental Management xxx (xxxx) 116289 Contents lists available at ScienceDirect Journal of Environmental Management journal homepage: www.elsevier.com/locate/jenvman Environmental Management ELSEVIER Research article Recycling waste vehicle tyres into crumb rubber and the transition to renewable energy sources: A comprehensive life cycle assessment Quddus Tushara, Joao Santos, Guomin Zhang, Muhammed A. Bhuiyanª, Filippo Giustozzi ª, a School of Engineering, RMIT University, GPO Box 2476, Melbourne, VIC, 3001, Australia b Department of Construction Management and Engineering, University of Twente, Enschede, the Netherlands ARTICLE INFO ABSTRACT Keywords: Life cycle assessment (LCA) Crumb rubber (CR) Monte Carlo simulations Renewable energy Asphalt pavements Recycling This study conducts a comprehensive life cycle assessment (LCA) on converting waste vehicle tyres into recycled crumb rubber (CR) granules as an alternative polymer for enhancing asphalt properties. The LCA study has been performed on acquired industrial primary data by incorporating CR at different proportions of binder in one ton (1-ton) of asphalt mix following the wet method. The uncertainty analysis of design variables identified a rela- tively strong positive relation of emissions with the equipment energy consumption (r = 0.98). Monte Carlo sim- ulations evaluate the potential renewable sources (solar, hydro, and wind) in sequence over fossil fuels for the possible transition in the Australian grid by 2030 and 2050, as per the Paris Agreement. 71.91% reduction of CO2 emissions is achievable by recycling vehicle tyres into crumb rubber compared to landfill and incineration. Recy- cling by-products of CR production, such as steel and textile, significantly mitigates negative impacts. A decrease of 2.23% emissions was associated to the use of crumb rubber as a binder modifier in the asphalt mixture via the midpoint assessment. In endpoint LCA, a higher association of resource (US$) saving costs was observed than for other protective zones, i.e., human health and ecosystem damage. Recycling 466,000 tonnes of disposable waste tyres contributes to 16.1 million US$ worth of resource savings. An equitable industry-based LCA and uncer- tainty analysis of design parameters can assist in prioritizing suitable options to improve efficiency and future emission strategies on a global scale. 1. Introduction Over the last two decades, a growing interest in developing life cycle assessment (LCA) for road pavements has brought the analytical quan- tification of environmental impacts associated with recycled materials (Ma et al., 2021). The reliability of the LCA results depends to a large extent on decisions concerning the selection of proper functional units, system boundaries, data sources, and the quantification of associated uncertainties (Santero et al., 2011; Santos et al., 2015). An equitable in- dustry data-based assessment can help identify these gaps, thus offering a tailored and integrated comparative LCA solution rather than a sub- jective decision. Ultimately, the accuracy in conducting LCA will lead government bodies and private agencies towards successful paths of sustainable decision-making. Traditionally, the construction and maintenance of roads rely heav- ily on consuming significant quantities of virgin materials. This hap- pens in a context where an ever-increasing accumulation of waste mate- rials, lack of landfill space, and shortage of natural materials are being recorded. Within this context, the disposal of vehicle tyres wastage is now one of the prime environmental concerns that has to be adequately addressed. More than a billion tyres waste is generated around the world each year (İlkılıç and Aydın, 2011). Naturally, vehicle tyres in the environment are not readily decomposable. In addition, tyres com- bustion releases pollutants that are detrimental to human health, par- ticularly polycyclic aromatic hydrocarbons (PAHs), styrene, benzene, butadiene, and phenols (Reisman, 1997). Sometimes, waste tyres are then illegally disposed of either in landfills or burnt. Granulated crumb rubber (CR) derived from waste tyres has sparked interest as additive in bituminous mixes to reduce this impact (Dias et al., 2014). CR in as- phalt pavements is often considered a sustainable solution to reduce waste materials. CR acts as an alternative polymer to improve the per- formance of hot mix asphalt. An overview of the CR effects on rutting, stiffness, and fatigue resistance of the road pavement has been identi- fied by several studies (Arabani et al., 2018; Singh-Ackbarali, 2013; Zhang et al., 2020). Corresponding author. RMIT University, School of Engineering, 124 La Trobe St, VIC, 3000, Australia. E-mail address: filippo.giustozzi@rmit.edu.au (F. Giustozzi). https://doi.org/10.1016/j.jenvman.2022.116289 Received 16 February 2022; Received in revised form 30 August 2022; Accepted 13 September 2022 0301-4797/ 20XX Note: Low-resolution images were used to create this PDF. The original images will be used in the final composition. Q. Tushar et al. Identify the probabilistic distribution of input variables Determine the outcome based on input variations Run Monte Carlo simulations on the outcome Collection of simulations results Obtain sensitivity indices of design parameters Emphasize the influential parameter Fig. 1. Typical schematic diagram of performing sensitivity analysis for recy- cling facilities. End-of-life car and truck tyres (ELTs) are considered a substantial environmental hazard due to their potential impact on landfills (Yadav and Tiwari, 2019). Leaching compounds of dumped tyres are the possi- ble sources of soil contamination, surface water, and groundwater pol- lution. Tyres combustion releases pyrolytic oils and other harmful sub- stances into air, soil, and water. Even the disposal of tyres into piles be- comes an insect breeding ground, particularly mosquitoes, vermin, and others. Therefore, specific strategies have been developed for waste tyres landfill as monofils to reuse, recycle, and maximize energy recov- Journal of Environmental Management xxx (xxxx) 116289 ery (Matthews, 2006). Monofills comprise only specific waste materials that have to be separated from other waste materials. This study identi- fies the environmental impacts considering the consequences of waste tyres transportation and disposal at landfills, aiming to increase recy- cling. Monofills in Australia ensure the maximized recovery of scraped tyres from a specific area and improve ways of reducing contamination. However, the benefits of monofills will only be perceived if the storage of shredded and cut tyres will be advanced into reprocessing opera- tions. Tyre manufacturing industries consume a significant proportion of the world's natural or synthetic rubber. However, in many countries, most waste tyres are dumped into landfills due to the lower disposal cost. Still, there is a potential research gap in waste management re- garding waste tyres disposal and recycling because of their complex composition. The mixture of various ingredients including rubber, tex- tile and steel make tyres valuable resources. The general composition of a tyre includes elastomeric compounds (natural and synthetic rubber), carbon black, hydrocarbon oils, vulcanizing agent (sulphur com- pounds), sulphur accelerator, and protective antioxidizing agents as a stabilizer (Sienkiewicz et al., 2017). Moreover, this causes tyres to be resistant to natural degradation, resulting in landfills instability if not shredded. Recycling facilities for waste tyres provide the provisions for recov- ering these useful materials. The devulcanisation process is one that is used to regenerate granular rubber and reuse it as virgin materials (Nanjegowda and Biligiri, 2020). Mechanical grinding, cryogenic grind- ing (liquid nitrogen), wet grinding, and ozone cracking are also alterna- tive recycling processes. Recycled granular rubber can be used as modi- fiers and fillers in asphalt and concrete production. Its serviceability in the different mix design can be improved by further processing the granulated rubber through chemical, microbial, microwave, and ultra- sonic procedures. Other advanced disposal options include recovering energy, solids, oil, and gaseous products through pyrolysis, gasification, or combustion. However, the suggested approach of advanced disposal depends upon the acceptability of recycled resources, such as tyre- derived diesel, as alternative fuels on the current markets. Granulated crumb rubber is scrapped through the mechanical grind- ing process at the end of the tire's life cycle in a specialized plant (Valente and Sibai, 2019). The application of granulated tyre rubber in asphalt is known as CR asphalt technology. Two categories are involved in this technology; wet and dry process. Steel wire Waste Tyres collected Transportation to site Shredded tyres conveyed into Rasper Tyres conveyed into Barclay Shredder If tyres are not 6 conveyed back into shredder Yes No Bobcat relocates materials Classifier shredded tyres, into 6" or less Co-products of tyres recycling Magnetic screening and fibres separator Air conveyed chunks into Granulator Processing granules through Cracker Mill Fibres/textile (Polyester) Tyres shredded into 25mm chunks Crumb rubber production Bagging station Forklift relocates materials Fig. 2. System boundaries considered for the production of 1-ton crumb rubber from waste tires. 2 Q. Tushar et al. Journal of Environmental Management xxx (xxxx) 116289 Extraction of crude oil Allocation of distribution 60% for lighter products to further refining Aggregates extraction by crushing and screening Crude oil refining into bitumen Transportation of aggregates to storage or asphalt plant Transportation of bitumen from refinery to point of sale/ asphalt plant Allocation of distribution 40% for bitumen Heating and drying of aggregates Storage of bitumen Co-products of crumb rubber process (e.g. steel fibre and textile) Usage of aggregates to produce asphalt (95% by weight of the asphalt mix) Usage of bitumen to produce asphalt (5% by weight of the asphalt mix) Heating and blending bitumen with aggregates and CR proportions (5%, 10%, 15% and 20% by weight of the binder) Hot mix asphalt production Asphalt paving and rolling Waste tyre collection and processing at recycling facilities Crumb rubber (CR) production Fig. 3. System boundaries considered for the production of 1-ton of asphalt mixture. In the wet process, CR modified bitumen is known as asphalt rubber (AR), which has high viscosity and increased elasticity (Kang et al., 2015). AR is prepared in specialized mixers at about 180 °C with a cer- tain percentage of CR (usually more than 15% by weight of the total binder), depending on the desired properties of the final product (Qian and Fan, 2020). After curing, the prepared binder is mixed with aggre- gates to produce asphalt concrete. In the dry process, the main focus is improving the overall elastic re- sponse by integrating CR into the aggregate. CR contributes to increas- ing the load-bearing capability of asphalt pavements (Ateeq and Al- Shamma'a, 2016; Mohammadinia et al., 2018). The produced mixture comprises CR between 1% and 3% of dry aggregates weight, usually dense-graded to absorb the load (Xiao et al., 2018). However, the opti- mum binder ratio in this type of mixes is generally slightly higher than that of standard asphalt mixes that do not contain recycled rubber. Generally, pavement performance is influenced by the adhesive properties of the bitumen. Conventional bitumen consists of a limited range of rheological and durability properties, which are not sufficient to withstand pavement degradation under increasing trafficking and weathering (Giustozzi et al., 2015). Therefore, engineers and re- searchers are trying to seek out solutions for bitumen modifiers. Avail- able bitumen modifiers and additives used during construction include styrene-butadiene-styrene (SBS) and ethylene-vinyl acetate (EVA) (Diab and You, 2017; Eldouma and Xiaoming, 2021). The commercial use of these polymers in pavement construction enhances the relative cost due to these expensive materials. However, using alternative mate- rials in pavement construction such as CR has the potential to benefit the environment, improve the durability and properties of asphalt binder, and be cost-effective (Mashaan et al., 2011, 2014; Mashaan and Karim, 2013). The recent trend in road construction is to apply waste materials in roads to reduce fossil fuels, raw material consumption and avoid land- fills burden (Giani et al., 2015; Santos et al., 2021). Numerous LCA studies have already been conducted to quantify the potential environ- mental impacts of using recycled waste materials in road pavements construction (Butera et al., 2015; Cabeza et al., 2014; Li et al., 2019). Specifically, for crumb rubber in asphalt pavements, engineering prop- erties assessed and environmental concerns compared of asphalt mixes using rubber/plastic-modified binder with a commercial polymer- modified binder (Yu et al., 2014). Another study quantified the environ- mental impacts of dense- and gap-graded asphalt mixes combining crumb rubber with recycled asphalt pavement (RAP) materials (Farina et al., 2017). LCA focused on comparing the environmental perfor- mance of rubberized porous asphalt pavement incorporating recycling materials such as crumb rubber and waste plastic with conventional as- phalt mixes (Gulotta et al., 2019). The potential environmental impacts of asphalt mixes containing CR (vulcanised or devulcanised) and RAP were evaluated considering different degrees of binder activation of the aged binder through an LCA (Bressi et al., 2021). These results explain the associated impacts of rubber processing and bitumen content in as- phalt mixture is relatively higher than reclaimed asphalt pavement (RAP). However, the justification of resource consumption and emis- sions on the CR production has been neglected in these studies. Notwithstanding the merits of the aforementioned studies in ad- vancing the state-of-the-art on the application of the LCA methodology to quantify the environmental impacts of different asphalt mixes incor- porating CR, most of these studies relied on secondary data rather than on primary data obtained from industrial plants. The studies that did source data from industrial plants only provided single figures to ac- count for the entire CR production process, thereby falling short in cap- turing the contributions of the many recycling stages and processes in- volved. To the authors' best knowledge, none of the previous studies conducted a LCA study that looked at the crumb rubber production us- ing energy consumption and production data from tyre recyclers. The present research focuses on the comprehensive manufacturing process of recycling waste tyres into CR and emphasizes further reusing CR co- products (steel and fiber) to improve environmental scores. Previous studies have also not considered the uncertainties associated with crumb rubber production and how this is affected by various energy sources and electricity mixes. The latter aspect is particularly relevant because many countries are developing energy transition roadmaps to- ward more reliable and decarbonized energy systems. The uncertainty analysis of recycling facilities is similar for different types of applications. Typical steps of implementing sensitivity analysis 3 Q. Tushar et al. Table 1 LCI to produce 1-ton CR as per the Australian electricity grid mix. Step1: Recycled tires are transported to the site consumption Process Distance Consumption rate of fuel (Diesel) (km) Fuel Transportation 45 18.40 L per 100 km 8.28 L Fuel consumption 8.28 L of diesel Output recyclable waste tires (1.25 ton) Step2: Recycled tires conveyed into the Barclay Shredder (20 min) Electricity Journal of Environmental Management xxx (xxxx) 116289 mixed with hot bitumen in a mixing tank and finally poured onto the hot aggre- gate to produce hot mix asphalt. Before CR-modified bitumen is added to the ag- gregate in a batch mix plant, drying and heating of aggregates are necessary to minimize moisture content. The energy consumption associated with asphalt laying in the field is dependent on the amount of diesel used by the equipment during operation. The literature data shows a fuel consumption of approxi- mately 0.294 L per ton of asphalt laid by different vehicles. Table 2 Fossil fuels-based Renewables based generation electricity electricity Energy consumption LCI to produce and lay 1-ton of asphalt pavement. Process for Materials Unit Measurement References Barclay Coal Gas Oil Shredder (54%) Barclay 13.5 (20%) (2%) 5 0.5 2.25 Solar Wind Hydro (9%) 2.25 (9%) (6%) Aggregate extraction and transformation 1.5 25 kWh Shredder Electricity consumption Motor Classifier 0.675 4 Conveyor 1.08 0.25 0.4 0.025 0.1125 0.1125 0.04 0.18 0.18 0.075 0.12 1.25 kWh 2 kWh Diesel for equipment or vehicle operation MJ/ton aggregate Liter/ton aggregate 21.19 0.48 IVL (Swedish Environmental Research Institute) Huang (2007) belts Bitumen production and storage Energy 28.25 kWh Crude oil extraction MJ/ton 1779 Stripple (2001) Fossil fuels-based consumption Output 6-inch tire shreds (1.25 ton) Step3: Shredded tires conveyed into the Rasper (15 min) Electricity (Combustion of natural gas crude oil for steam generation) Crude oil refining (Electricity MJ/ton 90 Renewables based generation electricity electricity Energy consumption consumption) crude oil Diesel for transportation Liter/ton 3.9 Rasper Coal Gas Oil (54%) Rasper Motor 24.3 2 Conveyor 0.405 0.15 (20%) (2%) 9 0.9 4.05 0.015 0.0675 Solar Wind Hydro (9%) (9%) (6%) crude oil Bitumen storage MJ/ton 162 4.05 2.7 0.0675 0.045 45 kWh 0.75 kWh bitumen Asphalt mixing and drying aggregate belts Electricity consumption MJ/ton 25.2 Liter Bobcat Diesel in Energy consumption 45.75 kWh and 1.88-L diesel Output 25 mm tire chunks (1 ton), steel (0.2 ton), and fibers (0.05 ton) Step4: Tire chunks are conveyed into the Granulator (15 min) 1.88 L asphalt (Huang et al., 2009; Stripple, 2000) Fuel oil MJ/ton 251.3 asphalt Asphalt Placement Asphalt paver Three Rollers Liter/ton asphalt 0.042 0.047 Zapata and Gambatese (2005) Electricity Fossil fuels-based generation electricity Renewables based electricity Energy consumption Tack truck 0.073 Granulation Granulation Coal (54%) 14.85 Gas 5.5 Oil Solar Wind Hydro (20%) (2%) (9%) (9%) (6%) 0.55 2.475 2.475 1.65 Three pick up trucks One small loader One small broom 0.012 0.073 0.047 27.5 kWh motor Air Conveyor 0.675 0.25 0.025 0.1125 0.1125 0.075 1.25 kWh Energy 28.75 kWh consumption Output tire granules (1 ton) Step5: Tire granules are processed through the Cracker Mill (120 min) Gas Oil Solar Wind Hydro Renewables based electricity Energy consumption Electricity generation Fossil fuels-based electricity Cracker Mill Cracker Mill Coal (54%) 118.8 (20%) (2%) (9%) 44 4.4 (9%) (6%) 19.8 19.8 13.2 220 kWh motor Air Conveyor Cooler Industrial sieve 5.4 33.75 5.94 2 12.5 2.2 0.2 0.9 1.25 5.625 0.22 0.99 0.9 0.6 5.625 3.75 0.99 0.66 Forklift Diesel 10 kWh 62.5 kWh 11 kWh 0.1 L Energy consumption 303.5 kWh and 0.1-L diesel Output crumb rubber (1 ton) Energy Electricity consumption of 406.25 kWh and Fuel consumption consumption of 10.26-L diesel Relevant input data for the LCI of the asphalt mix was selected from previous studies, as shown in. Aggregates are extracted from a quarry using dedicated machinery and transported by heavy vehicles for crushing and sieving into dif- ferent-sized particles as per the requirements. In general, pavement construc- tion prefers crushed rocks due to the resulting fragmented shape, which causes greater interparticle friction and better adhesion to the binder. Bitumen is one of the crude oil refinery by-products where electricity is consumed for refining, diesel is used for transportation and natural gas combusted for generating heat. In the "wet process", obtained CR, normally pulverized to less than 0.6 mm, is in assessing the recycling performance are: identification of possible variations in input parameters, creation of a model for emissions, run- ning of deterministic models, assembly of simulations results, obtain sensitivity indices of inputs and outputs, and get indicators to prioritize the optimization process, as shown in Fig. 1. Variations in input uncer- tainties and probabilistic distribution are the main criteria for differen- tiating these processes. Maximum time sensitivity analysis is either neglected or not empha- sized in articulating recycling facilities' emissions. For example, the effi- ciency of machinery and equipment can be identified by a normal dis- tribution due to natural deterioration and ageing (Zhang and Lee, 2011). This phenomenon does not only increase energy consumption but also emissions. However, a uniform distribution is another possible way to estimate the emissions of the manufacturing processes in a recy- cling facility (Gottschalk et al., 2010). A two-dimensional Monte Carlo simulation is the feasible solution to combine these two types of distrib- utions (Normal and Uniform) as joint distribution (Tian, 2013). This study applies Monte Carlo simulations to the crumb rubber manufactur- ing process and electricity generation sources to emphasize the design parameter that can contribute to reducing emissions. For instance, the Australian government regards decarbonization as the most promising tool to comply with the 1.5 °C warming limit estab- lished in the Paris agreement (A. Denis et al., 2014). The agreement is only feasible by accomplishing an astonishing 91% renewable-based electricity generation contribution to the national electricity market (NEM) as early as 2030 (Vorrath, 2021). Australia aims to achieve a net-zero emission scenario by entirely phasing out fossil fuels with 100% renewable sources, replacing standard vehicles with electric ve- 4 Q. Tushar et al. 40 お Percentage contribution (%) 10 20 30 50 60 70 Journal of Environmental Management xxx (xxxx) 116289 Impact category Climate change Table 3 Life cycle impact assessment scores of 1-ton CR. Ozone depletion Terrestrial acidification Marine eutrophication Freshwater eutrophication Human toxicity Photochemical oxidant formation Particulate matter formation Terrestrial ecotoxicity Freshwater ecotoxicity Marine ecotoxicity Ionising radiation Agricultural land occupation Urban land occupation Natural land transformation Transportaion Barday Shredder Rasper Cracker Mill Fig. 4. Relative contribution (%) of the single processes to CR production emissions to the impact category scores. Granulation Water depletion Metal depletion Fossil depletion Unit Landfill 1 ton of crumb rubber (CR) production Manufacturing Valorisation of by-products Total Crumb Rubber Steel Textile kg CO2 eq 1230.88 kg CFC-11 eq 2.60E-06 kg SO2 eq 2.45E-01 kg P eq kg N eq kg 1,4-DB eq kg NMVOC -3.61E-05 3.77E-02 5.358 2.70E+01 345.67 1.09E-06 1.89E+00 3.83E-04 5.09E-02 22.937 -335.051 -1.51E-05 -1.28E+00 -1.27E-02 -3.03E-02 -25.221 kg PM10 eq 1.59E-01 kg 1,4-DB eq 4.47E-04 1.27E+00 5.53E-01 2.94E-03 -1.57E+00 -153.007 8.74E-07 -4.14E-01 1.19E-03 -9.18E-03 -0.178 -4.26E-01 -142.388 -1.31E-05 1.98E-01 -1.11E-02 1.14E-02 -2.462 -7.25E-01 -1.39E+00 -9.24E-02 -9.26E-01 -1.20E-02 -1.56E-04 -9.21E-03 kg 1,4-DB eq 1.83E-03 1.82E-01 -6.93E-02 -3.12E-02 8.15E-02 kg 1,4-DB eq kBq U235 eq m²a m²a m² m3 9.34E-03 1.30E-03 -1.44E+00 2.03E+00 4.94E-03 1.16E-01 1.93E-01 -1.72E-01 -3.02E-02 -9.27E-03 kg Fe eq kg oil eq 3.39E-01 -16.627 1.93E-03 5.29E+00 1.23E+01 5.05E-03 1.41 4.66E-01 96.038 -3.68E+00 -3.55E+00 -3.43E+00 -3.54E-02 -6.12E-01 -2.38E+02 -70.05 1.31E+00 -2.37E+00 1.09E+00 1.09E-01 2.51E-03 -2.45 -2.81E-01 -87.842 2.83E+00 8.98E+00 -2.78E-02 -1.65 -2.38E+02 -61.854 Climate change Ozone depletion Terrestrial acidification Freshwater eutrophication Marine eutrophication Human toxicity Photochemical oxidant formation Particulate matter formation Terrestrial ecotoxicity ORP Freshwater ecotoxicity Marine ecotoxicity Ionising radiation Agricultural land occupation Urban land occupation Natural land transformation Water depletion Metal depletion Fossil depletion hicles in the transportation sector, and using hydrogen instead of diesel for heavy-duty transport and industry sectors (Stéphanie Bouckaert et al., 2021). A detailed modeling report produced by a joint collaboration between Commonwealth Scientific and Industrial Research Organisa- tion (CSIRO), the Brattle Group, and ClimateWorks Australia describes possible transition scenarios as unstoppable to bring the NEM to more than 70% renewable energy by 2035 and over 90% by 2050. This study crucially analyses the impacts of the decarbonization strategy for CR manufacturing aligned with the temperature increase of 1.5 °C. The quantification of the effects of relative uncertainties around industrial production processes that consider alternative energy sources is re- quired to discontinue centralized fossil fuel power plants within the decade. There is a potential gap in justifying the environmental benefits of recycling waste tyres usage as crumb rubber modified asphalt. How- ever, primary data from recycling facilities provides the provision to verify the environmental impacts of crumb rubber production. To fill this research gap, the study conducts a comparative LCA on the indus- trial procedures of CR manufacturing and waste tyres landfills facilities. The Australasian life cycle inventory (AUSLCI) has been used to obtain 5/n CIC 2023 2nd International Conference on Civil Infrastructure and Construction (CIC 2023) 5-8 February, 2023 Qatar University, Doha, Qatar Development of a Comprehensive Pavement Design System for Roads in Wind and Solar Farms Ezio Santagata Ashghal Chair, Qatar University, Department of Civil and Architectural Engineering, Doha, Qatar; Full Professor, Politecnico di Torino, Department of Environment, Land and Infrastructure Engineering, Torino, Italy ezio.santagata@qu.edu.qa; ezio.santagata@polito.it Abstract Haissam Sebaaly Research Associate, Department of Engineering, Built Environment and Information Technology, University of Pretoria, Pretoria, South Africa haissam.sebaaly@tuks.co.za Vittorio Capozzi Head of Civil Infrastructural Engineering, ENEL Green Power S.P.A., Rome, Italy vittorio.capozzi@enel.com This paper briefly, illustrates the structure and contents of an ongoing research program aimed at developing a set of procedures and tools to be used for the design of pavements in renewable energy projects and mainly in wind and solar farms. Challenges related to this topic derive from the non- standard nature of several factors that affect the structural and functional performance of such pavements, with the consequent need of employing purposely defined prediction methods, design criteria and specifications. Further crucial aspects to be taken in account in the research program are related to the life cycle cost analysis of pavements, to be carried out in a multinational context by considering alternative scenarios according to an OPEX (operating expense) versus CAPEX (capital expenditure) philosophy. It is envisioned that results and deliverables of the project will contribute to the enhancement of the effectiveness of operations in wind and solar farms, optimizing investments and leading to the selection of more sustainable pavement solutions. Keywords: Renewable energy; Wind and solar farms; Pavement design; Performance prediction; OPEX versus CAPEX; Experimental tests; Sustainability 1 Introduction ENEL Green Power S.P.A. (hereafter indicated as “EGP") is a Company of the Italian utility group ENEL S.P.A. that develops and manages power generated from renewable resources worldwide. It is currently in charge of more than 1,200 power plants located in five continents, with assets in operation or under construction in 21 Countries. The overall worldwide energy capacity of EGP plants, either in operation or under construction, is of the order of 56 GW, deriving from a mix of renewable resources, which include wind (yielding approximately 33% of total capacity), solar (21%), hydroelectric (45%), geothermal(1.4%) and biomass (0.1%). In view of the impressive data indicated above, EGP can be considered one of the major private international players that are operating and investing resources in the global green energy transition, which will be crucial to react against ongoing climate change for a more sustainable future. As part of its efforts to improve the effectiveness of its investments and operations, since its foundation EGP has been constantly supporting research activities both of the fundamental and 905 applied type in multiple areas of engineering and earth science. In such a context, in 2021 it secured appropriate resources for the development of a comprehensive pavement design system for roads in wind and solar farms. Following a competitive bid that involved the participation of several invited research institutions specialized in the area of pavement engineering, the research contract was awarded to the Politecnico di Torino, Italy. Activities were commenced in April 2022 and are expected to be completed by the end of 2023. This paper briefly describes motivation, structure and contents of the abovementioned research program, with a synthetic illustration of specific challenges, inherent complexities, adopted approaches and expected deliverables. 2 Motivation The need for a comprehensive research program focused on pavement design for wind and solar farms originated from the status of engineering operations managed by EGP worldwide, in which critical issues were identified. As described in the following, such issues are related both to the structural evaluation of pavement solutions and to the analysis of corresponding cost. According to current practice, pavement design activities for each farm are carried out by Consultants designated by Contractors. Employed design procedures, such as the AASHTO 1993 method, are usually quite empirical and conservative, originally developed for standard roads and highways and lacking the possibility of taking in account the peculiar factors that characterize pavements to be constructed in wind and solar farms. These include non-standard and exceptionally high vehicle loadings, extreme climatic conditions, poor sub grade bearing capacity, and limited availability of high-quality materials. Further challenges that arise in the use of standard empirical methods stem from the need of implementing strengthening techniques, often unique to certain Countries, and of employing locally available recycled materials. Finally, complexity of design operations also derives from the need of differentiating pavement cross-section's as a function of the hierarchy and expected use of the different branches that compose the vast mobility network of a given farm. In such a context, it should be considered that these sites might have a remarkable land footprint, covering rural areas with an extension that for a reference energy capacity of 100 MW can be, depending upon the specific technology, of the order of 50-100 hectares for wind farms and of 150-250 hectares for solar farms. Corresponding infrastructures for internal mobility can form networks characterized by a significant extension, which in the worst-case scenario are constructed on uneven and steep terrain with potential ground instability. While considering current practice followed by Consultants in design operations, it was also observed that unfortunately structural design evaluations are seldom combined with analyses related to construction or life cycle costs, thereby preventing the true optimization of investments. Such a limitation needs to be overcome in the research program by defining a sound assessment procedure that includes alternative scenarios according to an OPEX (operating expense) versus CAPEX (capital expenditure) philosophy. In turn, these should be translated in operative plans that may entail, depending upon the case, stage construction, planned maintenance and scheduled rehabilitation. The ultimate goal of part of the program is to create guidelines to be implemented at the multinational level, thereby ensuring the consistency of choices made worldwide by designers and decision-makers. 3 Structure and Contents The research program is structured in multiple interconnected tasks, conceived to yield deliverables 906 that will be shared with Consultants, Contractors and EGP Technical Departments worldwide, with the added value of being reference milestones for future research activities. Further refinements of the scope and contents of each task may occur in the future phases of development as a function of achieved results. 3.1 Technical and Scientific Background The technical and scientific background of the research program was defined in Task 01, already completed at the time of preparation of this paper, which consisted in a bibliographical study carried out by thoroughly analysing international literature. Task outcomes were synthesised in a report (Politecnico di Torino, 2022) that contained a general description of infrastructures and pavements, a synthesis of the most common pavement design procedures, a review of technical information on component materials and layers, and a discussion of financial and environmental aspects. Contents of this report constitute the reference baseline for many of the other tasks included in the project. Given the scarcity of published documents focusing on pavements for wind and solar farms, literature analysis considered low-volume roads (LVRs) satisfying the mobility needs of local communities in rural areas, together with function-specific roads (FSRs) designed and constructed to serve the industry or to allow access to remote areas (such as mining haul roads, agricultural roads and forestry roads) Pretoria Department of Transport, (1990); Tannant & Regensburg, (2001); Thompson et al., (2019). In these contexts, it was recorded that studies and specifications generally refer either to “paved roads”, that entail the presence of flexible asphalt pavements and rigid concrete pavements, or to “unpaved roads", which can be further divided into the categories of gravel roads, driving surface aggregate (DSA) roads and earth roads. Additionally, it was noted that unpaved roads can be either unsealed or, in particular cases, sealed (by means of bituminous or non- bituminous surface treatments). Typical distresses were identified for all pavement types, highlighting their origin and their implications on structural and functional performance (FHWA, 2003, 2015). Finally, pavement selection criteria were discussed, showing that they can be generally expressed by referring to average daily traffic (ADT) or annual average daily traffic (AADT) (Pasindu et al., 2020). With respect to pavement design procedures, the literature review synthesized the principles and procedures more appropriate for pavement design of paved and unpaved roads. It was noted that while methods of the former group (such as AASHTO 1993 and those with a mechanistic framework) are well known to pavement engineers, those belonging to the latter group (such as those developed in Australia, Canada, Russia and South Africa) are more familiar to LVR and FSR specialists. Technical information on basic and mechanical characteristics of materials were collected by focusing on aggregates used in unbound layers (including those derived from recycling), mechanically and chemically stabilized soils, and geo synthetics. Whenever relevant, mechanical modelling methods, selection criteria and design principles were also reviewed. Finally, Task 01 addressed the themes of costs and environmental impact by introducing the basics of Life-Cycle Cost Analysis (LCCA) and Life Cycle Analysis (LCA). Preferred analysis approaches were highlighted, together with guidelines to be followed for interpretation of results. 3.2 Review of Current Practice Review of current practice in the design of EGP projects was carried out in Task 02 of the research 907 program, close to completion at the time of submission of this paper in which available pavement- related design documents of EGP wind and solar farms, in operation or in construction throughout the world, were analysed in detail. The ultimate goals of such a review were to identify existing conceptual gaps and inconsistencies, and to perform a comparative evaluation of the various pavement cross-sections by employing a common approach for the assessment of expected design life and construction costs. Outcomes of these analyses were synthesized in a specific report (Politecnico di Torino, 2023a) that will be further integrated towards the end of the research program by making use of more advanced design concepts and more comprehensive financial evaluation methods in accordance with the work developed as part of Tasks 03 and 04. It was observed that although design Consultants in most part make use of the AASHTO 1993 method, non-negligible inconsistencies exist with respect to the procedures followed, for both paved and unpaved roads, to compute (or assume) several input data. These are related to extraction of bearing capacity data from geological and geotechnical surveys (expressed in terms of CBR index and thereafter converted into resilient modulus), to the inclusion of seasonal effects that can account for changes of water content in the sub grade and unbound layers, to the assumption of meaningful layer coefficients for standard and non-standard materials, to the calculation of the number of Equivalent Single Axle Loadings (ESALS) in the design period, to the assignment of representative ESALS to different branches composing the network of transportation infrastructures (both temporary and permanent), and to the identification of acceptable serviceability at the end of the design life. Furthermore, it was confirmed that design Consultants seldom referred to stage construction or planned rehabilitation options, with a very limited attention to financial implication of their choices and with no formal value engineering assessment. Based on the review outcomes synthesized above, in Task 02 comparative analyses were carried out, for a selected number of representative EGP projects, by applying the AASHTO 1993 procedure in a uniform and consistent way, thus amending previous design choices according to a common rationale. Special attention was reserved to design ESALs, that were expected to show a relationship with extension of farms, length of the infrastructure network and total energy capacity. Further calculations were made by hypothesizing alternative scenarios based on terminal serviceability changes and introduction of stage construction. Construction and life cycle costs were computed for all considered cases, thereby leading to the preliminary identification of preferred general design strategies. It was concluded that in the absence of strict guidelines on the use of the AASHTO 1993 procedure, the likelihood of significantly overdesigning or under designing pavements has been extremely high, with the consequent waste of financial resources due to excessive expenses for construction (in the case of overdesign) or for early maintenance and rehabilitation (in the case of under design). As a consequence, while still working on the development and implementation of improved pavement design methods, clear guidelines on the use of AASHTO 1993 will be shared by EGP with design Consultants and Contractors. 3.3 Development of Pavement Design Procedures By taking in account the outcomes and conclusions of Task 02, specific pavement design procedures were purposely developed as part of Task 03, currently in its finalization stage (Politecnico di Torino, 2023b). These procedures present the distinctive character of including a sound mechanistic component based on the analysis of the results of specific experimental tests and environmental modelling activities, to be performed in the preliminary phases of site assessment, and to the evaluation of stresses and strains induced in pavement structures by vehicle loadings. 908 According to the philosophy adopted by the research team during their development, such procedures will yield results characterized by a higher reliability in comparison to empirical ones (such as AASHTO, 1993) but will also allow significant life cycle savings since the likelihood of overdesign or under design will be reduced. The new procedures were developed for both paved and unpaved roads, although in the former case the main focus was on asphalt pavements since in wind and solar farms rigid structures are exclusively used in pads and platforms or to overcome high gradients of the road alignment in critical locations. Damage mechanisms and their relevance to pavements in wind and solar farms were highlighted for the most frequently occurring categories of distresses (cracking, distortion and disintegration for paved roads; surface defects and structural defects in the case of unpaved roads) (FHWA, 2003; Paterson, 1991). Corresponding design evaluations were introduced in the form of analytical (transfer) functions and specific calculation procedures AASHTO, (2008); Austroads, (2017); La Vern, (2016); NCHRP, (2002); SRSMT, (2001); (Yapp et al., 1991) that constituted the backbone of the proposed methods. Appropriate guidance was provided with respect to the assessment of traffic loadings in the design life and climatic conditions, and the steps to be followed for design verification (possibly to be carried out iteratively until reaching optimization) were clearly illustrated. Details of the procedures will be shared in the near future with the international technical and scientific community according to EGP policies. 3.4 Improved Use of Pavement Design Methods and User-Friendly Implementation In order to make the best possible use of the pavement design procedures developed as part of Task 03, EGP requested to include in the research program specific tasks dedicated to the definition of guidelines for their improved use in adherence to the OPEX versus CAPEX philosophy (Task 04), to the creation of user-friendly software-based tools for their implementation into practice (Task 05), and to the formalization of a simple pavement design catalogue to be employed for budgeting purposes, in preliminary design, and in standard projects of limited importance (Task 06). Activities of these tasks are still in progress and related deliverables are expected to be finalized by the end of the second quarter of 2023. 3.5 Experimental Testing and Technical Specifications As per the requirements set by EGP, it was planned that activities related to the development of pavement design procedures and tools (comprised in Tasks 03 to 06) would be supported by experimental investigations (Task 07) and by the review and update of existing EGP technical specifications (Task 08). These activities were commenced in the early stages of the program and will continue throughout its development until the end of 2023. At the time of submission of this paper, activities of Task 07 have been exclusively carried out in the laboratory, mainly focusing on the physical and mechanical properties of sub grade soils and unbound and cement-treated materials for sub-bases and bases. Emphasis has been given to the assessment of the resilient modulus of granular materials by means of triaxial tests, exploring the full load spreading potential of these materials by operating on samples prepared with variable degrees of water saturation (representative of different climatic conditions and/or seasons) and of compaction level (representative of the variable effectiveness of construction operations). Relevant models are being fitted to experimental data to take in account their non-linearity in subsequent pavement design calculations. Samples currently being analysed were taken from two EGP farms (one wind and one solar project) and in two additional reference sites. 909/nThere are 4 Article files attached, you need to Summarize in 1-2 slides for each Article, but the total should be 6 slides only. Intrustions- When preparing your paper summary, please try to touch on the following: 1. Objectives of the paper 2. methodology and materials 3. main findings and conclusions 6:19 AM

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