Executive Summary
This proposal is written in response to the request for developing solutions for a sustainable engineering problem. In this proposal, the team has identified that Singapore has been increasingly generating waste rubber tires which amount to about 30000 tonnes yearly. Currently, 92% of the total waste tires generated are recycled through innovative methods and importation to neighbouring countries for incineration, and the remaining 8% are being discarded onto Semakau Landfill. This shows that the current waste rubber tires management is partly recycling and partly through undesirable methods such as burning and disposing of the used tires which encompass environmental and aesthetic aspects. As a result, these methods will cause land and air pollution in Singapore and its neighbouring countries.
In the interest of achieving 100% recycling rate of waste rubber tires, the team proposes the implementation of YARJ Green Asphalt, which incorporates crumb rubber into bituminous pavements. With YARJ Green Asphalt, it will allow a continuous recycling cycle and a reduction in harmful gas emission. When designed appropriately, it has the potential to reduce noise pollution, better drainage and an increment of the roads’ lifespan which means lesser road maintenance. Hence, YARJ Green Asphalt supports economic development without compromising environmental pollution and provides quality infrastructure. Challenges of YARJ Green Asphalt include higher placement and compaction temperature, storage of crumb rubber modified bitumen and hazardous emissions by rubberized asphalt mixture. All these challenges can be resolved through a different use of machinery and have been proven through case studies. Both primary and secondary research, including survey questionnaires and existing research papers, were used and included to support the team’s proposal.
In view of Singapore’s movement under the Zero
Waste Masterplan, this proposal aims to resolve the waste rubber tires situation
and improve its waste management system, and thus executing Singapore’s mission
to be a zero-waste nation.
1.0 Introduction
1.1 Background Information
Rapid population growth, along with increasing productivity and consumption has aggravated waste production and accumulation. This will lead to waste pollution which is an ongoing environmental concern around the globe, affecting countries and mother earth.
In 2017, Singapore produced 7.7 million tonnes of waste (NEA, 2019). Generally, the waste is incinerated at waste to energy incineration plants and ash and other non-incinerable waste are dumped at Singapore’s only landfill. This process of burning the waste would leave a big carbon footprint that contributes to global warming (Watch: where does, 2018) and at the current rate of waste growth, Semakau Landfill will be filled up by 2035 (NEA, 2019).
Due to the severity of waste pollution in Singapore, the National Environment Agency (NEA) have designated 2019 as the year “Towards Zero Waste” (NEA, 2019). Under this movement, the NEA has published the Zero Waste Masterplan to raise awareness of waste pollution in Singapore and to educate and persuade the citizens to do their part to reduce waste pollution.
In a study on waste management, it is reported that approximately 1.5 billion waste rubber tires are being discarded yearly in the world (Williams, 2013). The issue with waste rubber tires being dumped in a landfill is that it takes over 50 years to decompose naturally, also burning rubber releases dangerous and carcinogenic pollution to the atmosphere (Korzeniewski, 2009). Therefore, recycling rubber tires effectively and environmentally friendly is of utmost importance for the world.
Regarding waste rubber tires in Singapore, the increasing number of cars in Singapore has boosted tire production, and this led to immense stockpiles of waste rubber tires generated every year. As reported in 2017, Singapore had produced a massive amount of waste rubber tires, which amassed to 35,900 tonnes (NEA, 2017). Singapore is currently recycling 92% of the 35,900 tonnes which leaves the remaining 8% which is approximately 2900 tonnes of waste rubber tires that are not being recycled. Although the recycling rate of waste rubber tires is stated at 92%, the value is not accurate as a Singapore considered exportation to be as part of the recycling rate. Hence, it does not portray the real value of recycling through environmentally friendly implementations. Over the years, the recycling rate seems to be increasing for waste rubber tires, but the values reported does not take into consideration the cumulative discarded waste rubber tires over time. Figure 1 shows the statistic of waste rubber tires in Singapore.
Figure 1. Statistics on waste rubber tire generated VS waste rubber tire recycled (NEA, 2017)
Presently, waste rubber tires in Singapore are being discarded mainly through exportation to neighbouring countries and incineration plants while the remaining are being dumped in Semakau Landfill (ZeroWaste SG, 2008). These methods of disposal help Singapore in clearing the waste rubber tires but are not feasible as a long-term solution as it creates additional environmental problems and solid waste pollution. Through exportation, neighbouring countries processed the tires through incineration which would help them attain fuel but, in the process, emanate toxic gases into the surrounding and consequently leads to health endangerment. This results in urgency for the government and relevant companies dealing with rubber tires to adopt environmentally friendly solutions to ensure that the recycling rate for waste rubber tires is kept at 100% to reduce carbon footprint and save landfill spaces.
Aligned with the Zero Waste nation idea, YARJ Green Insight’s ideal situation is to fully utilize waste rubber tire by incorporating waste rubber tires into the bituminous pavement mixtures.
1.2 Problem Statement
Singapore’s current method of recycling these waste rubber tires is not environmentally friendly. We are exporting the waste rubber tires overseas to be incinerated resulting in air pollution, and locally there is still 8% of the waste rubber tires being dumped at the landfill, which results in land pollution. The waste rubber tire situation would affect not only the country but also the earth if not dealt with appropriately.
1.3 Purpose Statement
The purpose of our proposed submission is to notify LTA about the negative environmental impacts that come along with waste rubber tires and persuade it that by incorporating crumb rubber into asphalt, Singapore can achieve 100% recycle rate of waste rubber tires in an environmentally friendly manner.
2.0 Proposed Solution
YARJ Green Insight’s proposed solution to recycle waste rubber tires efficiently is through our designed product called YARJ Green Asphalt. YARJ Green Asphalt incorporates waste crumb rubber tires into asphalt pavements as seen in Figure 2.
| Figure 2. Close up animation of crumb rubber in asphalt pavements |
It was observed through secondary research that the properties of crumb rubber have the potential of improving the road quality when designed appropriately. Therefore, a series of trials and experiments are conducted to ensure that YARJ Green Asphalt performance meets the standard of conventional pavements. YARJ Green Asphalt is a strategic and environmentally friendly way of recycling waste rubber tires without compromising the integrity of the roads.
Figure 3. Overview of YARJ Green Asphalt
2.1 Plan of Action
YARJ Green Insight is committed to ensuring that YARJ Green Asphalt is suitable for Singapore’s asphalt pavements. As such, to ensure the quality of YARJ Green Asphalt is of an adequate standard, YARJ Green Insight will be performing the necessary procedures and experiments to verify the properties of YARJ Green Asphalt. Refer to Appendix A for the full experimental procedure.
YARJ Green Insight will firstly obtain crumb rubber to incorporate it into the bitumen and conduct bitumen testing to evaluate the optimum crumb rubber content. Secondly, a suitable mix design will be selected and blended with the crumb rubber modified bitumen (CRMB) in different proportion with the mix design to create YARJ Green Asphalt samples for testing. Combining different percentage of the CRMB and aggregates allow us to evaluate the optimum CRMB and aggregates ratio which will be the final product.
2.2 Materials and Methods
2.2.1 Obtaining crumb rubber
Crumb rubbers are generally known as the finer recyclable grains of a rubber tire. There are two methods for attaining crumb rubber, and they are ambient mechanical grinding and cryogenic grinding, refer to Appendix A for obtaining crumb rubber processes. These two methods of obtaining crumb rubbers can be integrated into one system to maximise the benefits and to reduce overall costs. Although the crumbs obtained from cryogenic grinding are smaller and smoother, it is not as cost efficient as ambient mechanical grinding. (Putman & Amirkhanian, 2006)
2.2.2 Bitumen Selection Process
Waste crumb rubber will be mixed into the bitumen used in preparing the YARJ Green Asphalt mix. As such YARJ Green Insight needs to evaluate the available types of bitumen and select the most suitable bitumen to incorporate the crumb rubber with.
| Figure 4. Bitumen sample |
Types of bitumen
There are several types of bitumen used such as pen 60/70, Polymer Modified Bitumen (PMB), and Performance Grade 76. Each bitumen has different properties, and its properties reflect its quality. Comparing these three mixes, Pen 60/70 bitumen is a suitable option as it is of lower quality as compared to the rest. This meant that improving the quality of this bitumen would be more significant. Pen 60/70 bitumen will be used as the base, and its properties will be designed and modified using crumb rubber to achieve a quality that is comparable to PG 76. Refer to Appendix B for qualities of bitumen.
Crumb rubber modified bitumen sample testing
YARJ Green Insight needs to conduct several experiments to evaluate the properties of the crumb rubber modified bitumen (CRMB). Four critical experiments, viscosity test, hardness test, ductility test and elasticity recovery test would be conducted on the bitumen samples with different crumb rubber content percentage.
By carrying out the experiments, YARJ Green Insight would be able to obtain the experimental data to evaluate the optimum binder content which is the percentage of crumb rubber to be added. Refer to Appendix B for experiment process information.
2.2.3 Aggregate selection process
About 85-95% of any paving mixtures are the aggregates, and these aggregates provide the paving mixture with its strength and durability. Therefore, it is necessary to select a suitable mix design that will compliment well with the crumb rubber modified bitumen. (Refer to figure 5).
Comparison of road mix
Figure 5. Comparison of road mix
As the information in figure 5 illustrates (Land Transport Authority, 2010). OGW mix design would be a better selection as it has a broader application and many benefits. OGW mix has high air voids which provides space for the crumb rubber to integrate into the mix which improves bonding between aggregates.
With
the OGW mix design is selected, sieve analysis would be conducted to obtain the
correct percentage of different size aggregates to produce YARJ Green Asphalt.
2.2.4 YARJ Green Asphalt Production & Testing
Mixing process
Upon achieving the optimum crumb rubber bitumen content and the correct aggregate percentage, this will be mix together. There are specifically two mixing processes; they are the dry mixing and wet mixing process. YARJ Green Insight believes that for small batching testing, the dry process would be more desirable as it is cost effective and uses consumes lesser energy which fits well with a trial and error procedure. The dry process will enhance and speed up the process of determining the suitability and the right amount of compound mixture needed. Refer to Appendix C for experiment process information.
Figure 6. Dry Mix Process
Upon full adoption, YARJ Green Insight believes that wet process will be a better choice as it uses more crumb rubber and has a lesser reaction time between aggregates, crumb rubber and bitumen. In addition, the wet process will produce a finer quality sample. Implementation of the wet process will take much more energy and cost but will produce a higher quality of asphalt pavement. Refer to Appendix C for experiment process information.
Figure 7. Wet Mix Process
YARJ Green Asphalt Testing
To test the properties of YARJ Green Asphalt, 4 technical tests will be conducted on samples with different proportion of aggregates and CRMB. The 4 tests are the Cantabro test, indirect tensile test, resilient modulus test and the dynamic creep test. The results of these tests will provide specific information on the exact proportion of aggregates and CRMB to be used. The results will in evidently result in the optimum balance between waste rubber and the quality of the road. Refer to Appendix D for experimental process information.
3.0 Benefits of Proposed Solution (YARJ Green Asphalt)
The benefits of YARJ Green Asphalt are explained in detail in the paragraphs below.
3.1 Environmental benefits of YARJ Green Asphalt implementation
3.1.1 Continuous recycling of waste rubber tires
YARJ Green Asphalt is designed to be an ongoing method to fully utilise waste rubber tires. With Singapore’s massive road infrastructure and a constant need for maintaining roads, a massive amount of crumb rubber will be needed to accomplish this project. This method of sustainability will turn scrap rubber tires into a much valued resource. In addition, with this method being implemented, there will be a relief of the Semakau Landfill. (Svoboda, J., 2018)
3.1.2 Reducing emission of harmful gases
With YARJ Green Asphalt in place, the need for exporting waste rubber tires internationally will be obsolete. The tires that are export for incineration would instead be brought into service of the YARJ Green Asphalt. This will diminish the emission of harmful gases to the surrounding. Not only does YARJ Green Asphalt reduce damage caused to the environment, but it also helps improve the condition of the air and health of the citizen. (Zero Waste Singapore, 2008)
3.2 Technical benefits of YARJ Green Asphalt implementation
3.2.1 Better drainage
With the crumb rubber being in amalgamated with the bitumen of the road, air voids will be created and thus increasing the porosity of the roads. With this air voids, rainwater can easily seep through the roads to ensure much drier roads for safer driving. (Certin, 2013)
3.2.2 Increment of the life span of the roads and cost-effectiveness.
The implementation of YARJ Green Asphalt will increase the lifespan of roads. With crumb rubber being integrated into the bitumen, the bonding within the structure will be strengthened and thus increasing the durability of the road. With the increase in road strength and durability that YARJ Green Asphalt entails, there will be a lesser need for regular maintenance which will reduce the overall upkeep cost. (Presti, 2013)
3.2.3 Reduction of noise pollution
YARJ Green asphalt is also designed to reduce noise pollution. As noise is a vibration, the air voids in YARJ Green Asphalt will work brilliantly to mitigate and disrupt the vibration produced. The crumb rubber content in YARJ Green Asphalt also acts as a cushion to soak up the noise. As high-rise buildings are located near the highway where there is constant traffic flow, noise mitigation will be deeply appreciated by the citizens. (Shatanawi, 2008)
4.0 Proposal Evaluation
In this portion, the feasibility and concerns of the proposed solution YARJ Green Asphalt will be evaluated and discussed.
4.1 Current implementation of Crumb Rubber Modified Asphalt (CRMA)
4.1.1 Case study (Overseas implementation)
CRMA usage has been widely implemented in many countries since its first development in Arizona, USA in the 1960s. Countries like Sweden, Germany, France and many others have adopted the implementation of adding crumb rubber into asphalt. Due to advantages such as cost reduction and better performance against conventional asphalt (Presti, 2013).
4.1.2 Case Study (Singapore’s implementation)
Recently in Singapore, CRMA are being field tested on a portion of the West Coast Highway. The single lane of crumb rubber modified asphalt is being tested by SamWoh, where they evaluate the noise generated by the tires and the roads. Apart from the noise levels, they are also checking to see if there will be any major cracks or deformities in the road.
4.2 Concerns about YARJ Green Asphalt implementation
4.2.1 Higher placement & compaction temperature
Construction may be more challenging, as temperature requirements are more critical. Asphalt mixtures with high viscosity modified bitumen (CRMB) must be compacted at higher temperatures compared to traditional asphalt. This is because, like polymers, rubber stiffens the binders at high temperatures. Also, coarse gap-graded mixtures may be more resistant to compaction due to the stone nature of the aggregate structure. As such a higher temperature is required to construct YARJ Green Asphalt. In order to withstand the higher temperature, vibratory steel wheel rollers are used instead of rubber-tired rollers (Dennis, 2016).
4.2.2 Storage of Crumb Rubber Modified Asphalt
There is a tendency for the crumb rubber & asphalt to separate during storage & transportation which affects the homogenous properties of the asphalt. As such to prevent this from occurring maintaining heat & agitation is required until the application of the crumb rubber modified asphalt (Presti, 2013).
4.2.3 Hazardous emissions by rubberized asphalt mixture
Studies performed by the National Institute
for Occupational Safety and Health (NIOSH), and Federal Highways Administration
(FHWA), studied that the use of rubberised
asphalt does not appear to increase health risks to paving personnel. In these studies,
it concludes that the risks associated with the use of CRMA products were
negligible and emission exposures in CRMA operations did not differ from those
of conventional asphalt pavements. In addition
it was also stated that the effect of CRMA on emissions is relatively small in
comparison to the effects of other variables. Those variables
include the fuelling rate of the dryer, mix temperature, asphalt throughput
rate and asphalt binder content (Presti,2013).
5.0 Methodology and Procedure
5.1 Primary Research
Primary research in the form of an online survey questionnaire was conducted by interviewing the team’s targeted audience and providing details to them of the ongoing situation of waste rubber tires in Singapore before they are required to fill in the survey. A total of 50 car owners including SIT students, professors, the campus’ vendors and the general public were chosen as survey participants as they are the stakeholders that have contributed to the increasing numbers of used tires. The survey intends to find out the understanding of car owners regarding the use of their tires and highlight the current situation of waste rubber tires in Singapore which has always been an overshadowed issue by other materials due to media even though it plays an indispensable role in our modes of transportation.
The team also interviewed Mr Moe, a member of the research and development committee of Samwoh who has much experience and expertise on crumb rubber modified asphalts. His studies on rubberized material which he emphasized that waste rubber tires are flexible and durable which are properties that have the potential to improve the quality of our road infrastructure. Hence, he proposed the implementation of the design feature in SIT campus grounds to be used as a testing field and collection of data.
5.2 Secondary Research
Secondary research in the form of
studying and evaluating existing research data and projects was conducted with
the main source of the research based on an online research paper by the collaboration
of Samwoh Corporation and Singapore Polytechnic. The research paper “Crumb
Rubber Modified Bitumen in Open-Graded
Wearing Course of Flexible Pavement”, (Lwin and Utomo, 2017) served as a source
of credibility for the proposal with documented comprehensive information and
experimental data and analysis on the performance of incorporating waste crumb
rubber tires into bitumen.
6.0 Conclusion
Singapore being a developed country, the number of cars produced yearly will only increase. With an increase in the number of vehicles, it would lead to higher production and disposal of rubber tires. Despite the efforts that Singapore has invested in reducing scrap rubber tires, these methods are either not ecological or sustainable. Tonnes of waste rubber tires are being sold internationally to be incinerated for fuel which will release harmful gases that will affect the livelihood of the people and the environment. Currently, there is still 8% of rubber tires that are yet to be recycled and ended up discarded to Semakau Landfill. If rectifications are not taken immediately, it is estimated that Semakau Landfill will be filled by the year 2035.
Apart from the immense amount of waste rubber tires generated yearly, Singapore also faced a problem whereby green spaces are suppressed to make land for road infrastructure and paved areas. This results in flooding of road surfaces due to the increased surface runoff, the increase in surface runoff will increase the chances of flooding and will be dangerous for road users due to hydroplaning. Hence, the issue of waste rubber tires and hydroplaning means that an integrated solution is required to tackle both issues.
YARJ Green Insight developed the idea of YARJ Green Asphalt upon conducting countless in-depth research to address the issues while adhering to the requirements set by LTA. This research has included the meticulous selection of bitumen, aggregate and comparison amongst a wide spectrum of different mixes to obtain the optimal product. The idea of YARJ Green Asphalt revolves around the incorporation of crumb rubber tires into the paved areas, and the property of the affected areas is seen to have multiple upgrades in terms of structural properties such as ductility and strength without affecting the structural integrity. Besides having better structural strength, YARJ Green Asphalt also administer secondary benefits such as faster drainage of water, noise reduction and cost-effectiveness.
The establishment of YARJ Green
Asphalt will not only serve as a method to fully utilise waste rubber tires; it
is also a continuous process where new scrap tires will be put into good use.
With the benefits that YARJ Green Asphalt entails, YARJ Green Insight believes
that the implementation of YARJ Green Asphalt will be a massive breakthrough to
relief the landfill and for Singapore to achieve 100% recycling rate of rubber
tires.
7.0 References
Cetin, A. (2013). Effects of crumb rubber size and concentration on performance of porous asphalt mixtures. International Journal of Polymer Science 2013 (1265). doi:10.1155/2013/789612.
Crumb rubber information. (2019) Scrap Tire News. Retrieved from https://www.scraptirenews.com/crumb.php
Dennis, L.C. (2016). Introduction to rubberized asphalt. Slide player. Retrieved from https://slideplayer.com/slide/6890606/
International journal of physical sciences (2019). Academic Journals. doi:0.5897/IJPS
Korzeniewski, J. (2009). Sobering Statistics: How long will it take for your car to decompose. Autoblog. Retrieved from https://www.autoblog.com/2009/04/17/sobering-statistics-how-long-will-it-take-for-your-car-to-decom/
Kumar, A. (2016). Crumb rubber modified bitumen (CRMB). Slideshare. Retrieved from https://www.slideshare.net/AshwaniKumar292/crumb-rubber-modified-bitumen-crmb-61820238
Land Transport Authority (2010). Engineering group materials and workmanship specification for civil and structural works. Retrieved from https://www.lta.gov.sg/content/dam/ltaweb/corp/Industry/files/EGD09104A1-Overall.pdf
Ministry of the Environment and Water Resources (2019). Managing our waste – Landfill. Retrieved from https://www.mewr.gov.sg/topic/landfill
Mohd, R.I., Katman, H.Y., Mohamed, R.K. & Koting S. (2013). A review on the effect of crumb rubber addition to the rheology of crumb rubber modified bitumen. Advances in Materials Science and Engineering 2013(3). doi: 10.4236/ojce.2017.72010
National Environment Agency (2019). Waste management and overall recycling. Retrieved from https://www.nea.gov.sg/our-services/waste-management/waste-statistics-and-overall-recycling
Presti, D.L. (2013). Recycled tyre rubber modified bitumens for road asphalt mixtures: A literature review. Constructions and building materials, 49. doi: 10.1016/j.conbuildmat.2013.09.007
Putman, B.J. & Amirkhanian, S.N. (2006). Crumb rubber modification of binders: interaction and particle effects. Retrieved from https://www.researchgate.net/publication/228375092_Crumb_rubber_modification_of_binders_interaction_and_particle_effects
Recycling of scrap tyres for asphalt road construction. (2017). Samwoh. Retrieved from https://samwoh.com.sg/success-stories/case-studies/research-projects/533-recycling-of-scrap-tyres-for-asphalt-road-construction.html
Shatanawi, K. (2008). The effects of crumb rubber particles on highway noise reduction – A laboratory study. All Dissertations. Retrieved from https://tigerprints.clemson.edu/cgi/viewcontent.cgi?referer=https://www.google.com/&httpsredir=1&article=1268&context=all_dissertations
Silvrano, A.D.N., Marcio, M.F., Jorge, C.P. & Paula, A.A.P. (2006). Influence of crumb rubber gradation on asphalt rubber properties. Retrieved from http://www.civil.uminho.pt/transportinfra/publications/2006_(AR2006)_Neto_Farias_Pais_Pereira.pdf
South Central Iowa Solid Waste Agency (2016). The problem with waste tires. Retrieved from https://sciswa.org/the-problem-with-waste-tires/
Svoboda, J., Václavík, V., Dvorský, T., Klus, L. & Zajac, R. (2018). The potential utilization of the rubber material after waste tire recycling. IOP Conference Series: Materials Science and Engineering. 385. 012057. 10.1088/1757-899X/385/1/012057.
Tan, K. W., Ong, M. J. K., Ho, S. J. & Kan, M. (2016). Is your waste a waste? Asian Management Insight, 3(2). Retrieved from https://cmp.smu.edu.sg/ami/article/20161208/your-waste-waste
Watch: Where does all your rubbish go? (2018). The Straits Times. Retrieved from https://www.straitstimes.com/singapore/where-does-all-your-rubbish-go
Williams, P.T. (2013). Pyrolysis of waste tyres: A review. Waste Management, Volume 33, Issue 8 (2013), Pages 1713-1728. https://doi.org/10.1016/j.wasman.2013.05.003
Zafar, S. (2019). Crumb rubber from waste tires. Clean Tech Solutions. Retrieved from https://www.cleantechloops.com/what-is-crumb-rubber/
The art of Effective Communication 