Development of a New Road Safety Barrier Coverage manufactured from Used Tyres. A Technical, Economical and Environmental Assessment.

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1 Development of a New Road Safety Barrier Coverage manufactured from Used Tyres. A Technical, Economical and Environmental Assessment. Moral A. a, Irusta R. a,b a Environmental Division, CARTIF Foundation, Boecillo Technology Park p. 205, Valladolid, Spain b Department of Chemical Engineering and Environmental Technology, ETSII, University of Valladolid, Valladolid, Spain albmor@cartif.es, rubiru@cartif.es ABSTRACT Road safety barriers can be defined as any device installed on a road whose purpose is to provide a certain level of containment to a vehicle out of control, moreover to limit the damage and injuries to both the vehicle occupants and other road users. The morphology of these containment systems makes them particularly dangerous to motorcycle users, so a protection system has been developed to avoid the injuries and to reduce the impact consequences in an accident. The impact absorber system proposed in this work includes a high percentage of granulated rubber from post consumer tyres (PCTs) and a thermoplastic binder matrix obtained from thermoplastic polyolefins chemical recycling, both mixed using an injection system to produce the final protective element. The design of the protective cover was carried out using the Taguchi s Parameter Design method and considering a L18 orthogonal array taking into account material and process factors. The final impact absorber consist of a thermoplastic matrix including granulated rubber from post-consumer tyres that provides at least, 20 % impact absorption in a collision. Further, the coverage provides protection against the edges of the traditional safety barrier, responsible for severe injuries. An economical study was carried out, proving the economic feasibility of the cover performing, taking into account to the social purpose of the device. In the other hand, the Life Cycle Assessment of the coverage showed that avoiding 6,3% of the mortal impacts in Spain would compensate the environmental impact of km of poor quality Spanish roads coverage. Keywords: Impact absorption, Injection system, Life cycle assessment, Post-consumer tyres valorization, Protection system, Safety barriers. INTRODUCTION The aim of this work comes up from a double motivation. On one hand, the global production of tyres and the difficulties associated with their management once they have been used has been identified as one of the most serious environmental problems in the last years. A tyre needs a large amount of energy to be produced and also leads to environmental pollution if it is not properly recycled or treated, being part, generally, of uncontrolled landfills. On the other hand, the media, statistics from many road users platforms and other information sources have shown concern about the security systems existing on the roads. Although a road safety barrier is a device that provides a certain level of retention to a vehicle out of control, many of the road users find it inappropriate and even dangerous due to its design.

2 These barriers were designed thinking about vehicles of four or more wheels, but it is not a safety system for motorcycles or bicycles. After identifying the problem from an environmental point of view (dangerous disposal scenarios for post-consumer tyres) and from the social-safety point of view (serious damages and injuries due to the design of the safety barriers), it started out the idea of performing a protection element for the road safety barrier. This work tries to take the opportunity of the good properties of rubber obtained from Post Consumer Tyres (PCTs), finding an application in the development of an impact absorber system for the horizontal steel sheet of the road safety barriers, using materials 100 % from recycling. The problem associated with rubber from PCTs is its thermosetting properties. Rubber is vulcanised during tyre manufacturing (using sulphur in most of the cases). This process provides rubber the good properties and quality, but also its thermosetting nature. Thermosetting materials can not be reprocessed applying temperature, unlike thermoplastics. There are several studies about rubber devulcanization, (ultrasound techniques, chemical processes and stress methods), but these methods are still in the experimental stage and there are no warranties or favorable economic conditions in their use. This fact promoted the necessity of finding a binding material responsible of the consistency and compaction of tyre scraps. The use of a thermoplastic matrix (a polyolefin obtained from the mechanical recycling) enables the above-mentioned binder effect, making the rubber from PCTs act as filler in the mixture. There are several studies about rubber-thermoplastic blends, using different thermoplastics, rubber scraps particle size and different rubber/plastic ratios. According to Liu et al. (2001), the ratio of rubber in the mixture influences primarily on mechanical properties such as tensile strength. The studies carried out by Ismail et al. (2002) also determine a decrease of Young's Modulus as the percentage of rubber in the mixture increases, resulting in contrast to an increase in elongation properties at high percentages of rubber (60%). Bartczak et al. (1999), Adhikari, et al. (2000) and Liu et al. (2001) agree on the reduction of tensile strength with the increase in the rubber particle size, and a slight decrease in the elongation with rubber particles of larger size. The results obtained by Choudhury et al. (1996), Duhaime et al. (1996), for rubber devulcanization and its subsequent influence showed no substantial improvements in mechanical properties, taking into account the cost associated with those techniques. METHODS During this work, the following materials and equipments were used: - Rubber scraps from post consumer tyres provided by RENECAL company, located in Palencia (Spain). This company works crushing tyres and removing the different materials of the tyre (rubber, steel and fibers). The scrap were developed in two range sizes, 0,5-2 mm and 2,5-4 mm. - Thermoplastic proceeding from mechanical recycling was supplied by SERNAPLAS, company dedicated to the mechanical recycling of polyolefins. - Injection equipment MINI DEU 250 H55, 25 Tn clamping force and 25 cm 3 theoretical volume of injection in PS. This equipment preformed the test pieces during the DOE. - Injection equipment Husky 10000, 1100 Tn clamping force, and a theoretical mass of injection of g in PS. This equipment preformed the prototype pieces.

3 Methods developed during this work were: - The experiences at lab scale were preformed according an Orthogonal Array L18, following Taguchi s Parameters Design methodology. - For the evaluation of the variable responses obtained from the L18 experiences, the software ANOVA TM was used. - For the design of the prototype piece the software FEM CATIA was used, in order to determine the influence of the cover proposed in the tense-deformational behaviour of the safety barrier. - The LCA has been carried out using the commercial software of Life Cycle Assessment SimaPro 7.0, using as method of evaluation the Ecoindicator'99, egalitarian version (Goedkoop et al., 2000). RESULTS AND DISCUSSION Technical assessment The first stage of this work was to define the formulation of the new material. A DOE was performed taking into account material and process variables. In table 1 it can be seen the control factors and levels selected to carry out the Parameter Design. Table 2 shows the L18 orthogonal array selected taking into account the levels of freedom required Mould cooling time Thermoplastic nature Rubber particle size Thermoplastic ratio Back Load pressure Table 1. Factors and levels FACTORS TE s NT - G mm PT % Table 2. L18 Orthogonal array* LEVELS 1 L18 TE NT G PT CC TH VI PM CC kg f/cm Screw temperature TH ºC 7 Injection speed VI cm 3 /s 8 Pressure Maintenance PM kg f/cm *This is a fractional factorial design, very useful in this type of experimentation, reducing the number of trials from 3 7 x2 to 18. In table 3 it can be seen the mechanical characterization results for the test pieces at lab scale. These results were analysed using ANOVA TM software, which results are shown in table 4. According to the Analysis of Variance, material variables (NT,G and PT) are the key variables in this study, offering the best results for polypropylene thermoplastic, high values of scrap particle size and medium-high values of thermoplastic percentage.

4 Table 3. Material Characterization of the test pieces obtained according the L18 orthogonal array Hardness Elongation failure Breaking load Fatigue Compression Tear strength 0 to 100 % kg/cm 2 nº cycles % N/mm 0 to 100 L , ,9 22,8 33 L , ,6 24,1 33 L , ,5 24,3 32 L , ,5 12,6 33 L , ,9 15,1 32 Table 4. Results of ANOVA for each response value Resilience *Rho (%) Source L , ,2 20,2 34 TE - 0,6 4,2 - - L , ,8 7,7 27 NT 17,1 39, ,7 - L , ,4 16,6 32 G 12,1 8,6 8,1 - - L , ,1 12,2 34 PT 28,8 20,4 29,5 18,4 - L , ,4 28,1 34 CC - 6,8 2,3 - - L , ,8 20,1 34 TH ,9 L , ,4 21,3 34 VI - 20,1 3,6 - - L , ,4 20,3 35 PM - 1,6 11,8 - - L , ,6 21,6 33 TexNP - 1, L , ,5 21,9 25 <e> 41,9 0,4 3,1 16,8 75,1 L , ,3 16,9 30 L , ,9 12,6 32 L , ,2 11,7 30 The design of the protective cover was obtained using the software CATIA (finite elements method), in an impact simulation according to the Spanish standard UNE , obtaining a protective cover design that provides a theoretical 20-25% of impact absorption in crashes. Environmental assessment The functional unit for the assessment was 1 m of the protection system. As it was aforementioned, the study was carried out using the commercial software SimaPro 7.0, evaluation method Ecoindicator 99 egalitarian version (Goedkoop et al., 2000). Figure 1 shows the traditional steel safety barrier assessment. The materials and process stage presents the highest impacts, while the end of life stage (which includes a 70% of steel recycling) avoids impacts to the environment. Figure 2 shows the environmental impact of the coverage developed, taking into account two scenarios: Esc 1 (considering the avoided burdens to the impact of using residual rubber and plastic) and Esc 2 (assuming that the impact of raw materials is zero). Two scenarios were selected due to the uncertainty of rubber and plastic recycling data. In LCA is usual to associate zero impact to the materials from recycling process. As it can be seen, Esc 2 presents higher contributions to the environmental impact of the final product, so the Esc. 2 will be selected to obtain the environmental assessment conclusions (the most unfavourable scenario). In the figure 3 it can be seen the impact combining the impact of the traditional safety barrier and the coverage (taking into account the two assessment scenarios). The main differences were associated to the carcinogens, respiratory inorganics and radiation category. In the other hand the impacts were similar in ozone layer, ecotoxicity, land use, minerals and fossil fuels in both scenarios. Hardness Elongation to failure Breaking load Tear strength Compression *Rho is the influence of the factors to the final response variable value and interactions

5 100% 80% Caracterization (%) 60% 40% 20% 0% -20% -40% -60% C OR IR CG R DO ET A/E S M F -100 Impact catego ries M aterials and processes Installation/Use Distribution End of life Caracterization (%) Esc. 1 Esc. 2 C OR IR CG R DO ET A/E S M F Impact catego ries M aterials and processes Installation /Use Distribution End of life C Carcinogens CG Global warming ET Ecotoxicity M Minerals OR Respiratory organics R Radiation A/E Acidification/Eutrophization F Fossil fuels IR Respiratory inorganics DO Ozone layer S Land use Figure 1. Characterization of traditional safety barrier. Figure 2. Characterization of the coverage barrier (Esc. 1 and Esc.2). The impacts associated to human health (figure 4) shows a high contribution of the coverage (Esc 2) in carcinogens and respiratory inorganics. Caracterization (%) C OR IR CG R DO ET A/E S M F Impact categories Traditional safety barrier Coverage Esc. 1 Coverage Esc. 2 Human health damage (DALY) 1,60E-05 1,44E-05 1,28E-05 1,12E-05 9,60E-06 8,00E-06 6,40E-06 4,80E-06 3,20E-06 1,60E-06 0,00E+00 C OR IR CG R DO Impact categories Traditional safety barrier Traditional safety barrier + coverage (Esc 2) Figure 3. Characterization of traditional safety barrier and coverage linkage (Esc.1 and Esc. 2). Figure 4. Comparative Human Health Damage of 1m traditional safety barrier and 1m traditional safety barrier&coverage (Esc. 2). These results imply a difference between the traditional safety barrier + coverage and the traditional barrier of DALY = 1, years /m. According to the Spanish Ministry of Public Administrations, there are km of poor quality and/or dangerous road in Spain. This means that avoiding 6,3% of the mortal accidents caused on the traditional safety barrier would be enough to compensate the environmental impact of the new proposed coverage. Economical assessment The economic analysis of the process has taken into account two contributions. On the one hand, the immobilized equipment for milling and screening rubber from PCTs, the

6 thermoplastic mechanical recycling and the injection process (5 years amortization time), and secondly, the energy consumption of this equipment. The cost associated with the equipment is 1,24 /m, and the energy cost is 0,82 /m, so the total cost is 2,06 /m CONCLUSSIONS The protecting cover is composed 100% from recycled material, scraps from PCTs and a thermoplastic polyolefin from mechanical recycling. This mixture is performed using injection techniques. The protective cover offers a minimum of 20 % of absorption of direct impact, but bearing in mind that direct impact usually occurs in the low part of the safety barrier, the efficiency of the cover remains in secondary impacts (of minor intensity that the direct ones), and as protector of the horizontal steel sheet edges. In the process of injection, the temperature of the screw, the back loading pressure and the time of cooling are the most important parameters that must be controlled to carry out a correct injection. The thermoplastic/rubber ratio is the most relevant factor of the study. Hardness, breaking load and tear resistance are proportional to the thermoplastic added. The main impacts in coverage Life Cycle Assessment are associated to carcinogens, respiratory inorganics and climate change. Avoiding the 6,3% of the mortal accidents caused in the km of the traditional safety barrier would be enough to compensate the environmental impact of the proposed coverage. The cost associated to the manufacturing is reasonable taking into account the social benefits that the product can offer. ACKNOWLEDGEMENTS This study has been supported by the Spanish Ministry of the Environment in its programme of Development and Technological innovation Nº /2005/3-B REFERENCES Adhikari B., De D., Maiti S. (2000). Reclamation and recycling of waste rubber. Prog. Polym. Sci. (25) Bartczak Z., Argon A.S., Cohen R.E., Weinberg M. (1999). Toughness mechanism in semicrystalline polymer blends: I High density polyethylene toughned with rubbers. Polymer (40) Choudhury NR, Bhattachrya SN (1996). Plast Rubber Compos Process Appl (25) 448. Duhaime JRM, Baker WE (1996). Plast Rubber Compos Process Appl (15) 87. Goedkoop M., Spriensma R. (2000) The Eco-indicator 99 A damage oriented method for Life Cycle Impact Assessment. Methodology Report. 2nd edition. PRé Consultants B.V. Ismail H. Suryadiansya (2002). Thermoplastic elastomers based on polypropylene/natural rubber and polypropilene /recycle rubber blends. Polymer Testing (21) Liu, H.S., Mead J.L., (2001). Process development of scrap rubber /Thermoplastic blends. Chelsea Center for Recycling and economic Development Technical Research Program.