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 (Straits Time, 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% approximately 2900 tonnes of waste rubber tires that are not being recycled. Even though the recycling rate seems to be increasing for waste rubber tires, 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
Presently, waste rubber tires in Singapore are being discarded mainly through exportation to neighboring 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, neighboring 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 an 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’s ideal situation is to fully utilize waste rubber tire by incorporating it into our roads without degrading the current quality of roads in Singapore.
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 them that Green Asphalt will be able to help Singapore to achieve 100% recycle rate of waste rubber tires in an environmentally friendly manner.
2.0 Proposed Solution
YARJ’s proposed solution to recycle waste rubber tires efficiently is through our designed product called Green Asphalt. Green Asphalt incorporates waste crumb rubber tires into asphalt pavements as seen in Figure 2. 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 Green Asphalt performance meets the standard of conventional pavements. 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 Green Asphalt
2.1 Plan of Action
YARJ is committed to ensuring that Green Asphalt is suitable for Singapore’s asphalt pavements. As such, to ensure the quality of Green Asphalt is of an adequate standard, YARJ will be performing the necessary procedures and experiments to verify the properties of Green Asphalt. Refer to Appendix A for full experimental procedure.
YARJ 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 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. (reference-how you know the about cryogenic grinding)
2.2.2 Bitumen Selection Process
Waste crumb rubber will be mixed into the bitumen used in preparing the Green Asphalt mix. As such YARJ needs to evaluate the available types of bitumen and select the most suitable bitumen to incorporate the crumb rubber with.
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 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 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, these aggregates provide the paving mixture its strength and durability. Therefore, it is necessary to select a suitable mix design that will compliment well with the crumb rubber modified bitumen. (reference-how you know 85%-95% are aggregates)
Comparison of road mix (reference-how you know the all these contents)
| W3B Mix | Open Graded Wearing Mix | |
| Gradation Graph | ||
| Properties | Dense graded mixture, with equally mix proportion of fine and coarse aggregates. | Open graded mix, with 60% and above of coarse aggregates. |
| Usage | Normal roads. | Expressways and other specifics type of roads. |
| Benefits | High contact point between aggregates. | Ability to drain water. |
| Production Temperature | 165°C | 180°C |
| Compaction temperature | 135°C | 150°C |
| Air voids | 3-5% | 7-9% |
Based on table x. OGW mix design would be a better selection as it has a broader application and many benefits. OGW mix has high air voids this provides space for the crumb rubber to integrate into the mix which improves bonding between aggregates.
With the mix design selected, sieve analysis would be conducted to obtain the correct percentage of different size aggregates to produce Green Asphalt.
2.2.4 Green Asphalt Production & Testing
Mixing process
Upon achieving the optimum crumb rubber bitumen content and the correct aggregate percentage, we will mix them together. There is specifically two mixing process, they are the dry mixing and wet mixing process. YARJ believes that for small batching testing, the dry process is more suitable as the advantages such as it being cost effective and uses less energy fits well with a trial and error procedure. 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 5 Dry Mix Process
Upon full adoption, YARJ 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, 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. (further details can be found in benefits section).
Figure 6 Wet Mix Process
Green Asphalt Testing
To test the
properties of 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 (Green Asphalt)
The benefits of Green Asphalt are explained in detail in the paragraphs below.
3.1 Continuous recycling of waste rubber tires
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 of 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 valuable resource. In addition, with this method being implemented, there will be a relief of the Semakau Landfill. (reference)
3.2 Reduce emission of harmful gases
With Green Asphalt in place, the need of exporting waste rubber tires internationally will be obsolete. The tires that are export for incineration would instead be brought into service of the Green Asphalt. This will diminish the emission of harmful gases to the surrounding. Not only does Green Asphalt reduce damage cause to the environment, it also helps improve the condition of the air and health of the citizen. (reference)
3.3 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 a much drier roads for safer driving. (reference)
3.4 Increment of life span of the roads and cost effectiveness.
The implementation of 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 Green Asphalt entails, there will be a lesser need for regular maintenance which will reduce the overall upkeep cost. (reference)
3.4 Reduction of noise pollution
Green asphalt is also designed to reduce noise
pollution. As noise is a vibration, the air voids in Green Asphalt will work
brilliantly to mitigate and disrupt the vibration produced. The crumb rubber
content in Green Asphalt also act as a cushion to soak up the noise. As high-rise
buildings are located near the highway where there is a constant heavy traffic
flow, noise mitigation will be deeply appreciated by the residents. (reference)
4.0 Proposal Evaluation
In this portion, the feasibility and draw backs of the proposed solution Green Asphalt will be evaluated and discussed.
4.1 Case study
4.1.1 Overseas implementation
Rubberised asphalt 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 the conventional asphalt. (reference)
4.1.2 Singapore’s implementation
Recently in Singapore, crumb rubber modified roads 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.
4.1.3 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 Green Asphalt. In order to withstand the higher temperature, vibratory steel wheel rollers are used instead of rubber-tired rollers (Dennis, 2016).
4.1.4 Storage of crumb rubber modified bitumen
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).
4.1.5 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, campus’ vendors
and general public were chosen as survey participants as they are the
stakeholders that have contributed to the increasing numbers of used tires. The
intention of the survey is 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 interviewed Mr Moe, a member of the research and development committee of Samwoh. He has 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, M.A. and Utomo, H.D., 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. Besides that, other secondary researches includes
literature review and online publications that explains Singapore’s insight on
the issue, elaboration of the feasibility and drawbacks of the solution and
case studies on the implementation by other countries, The Straits Times
(2018), MEWR (2019), Nottingham Transportation Engineering Center (2013) and
Centre for Transportation Research, Faculty of Engineering, University of
Malaya (2013).
6.0 Conclusion
With Singapore being a developed country, the amounts of cars being produced yearly will only increase. This would lead to a higher production and disposal of rubber tires. Despite the efforts that Singapore has invest to reduce 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 environment. Currently, there is still an 8% of rubber tires that are yet to be recycled and ended up discarded to Pulau Semakau landfill. If further actions are not being taken immediately, Pulau 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 increase of surface runoff, the increase of 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 meant that an integrated solution is required to tackle both issues.
YARJ had come up with the idea of Green Asphalt upon conducting detailed experiments and countless in-depth researches to address these issues while adhering to the requirements set by LTA. These researches include meticulous selection of bitumen and aggregate and comparison amongst a wide spectrum of different mixes to obtain the optimum product. The idea of 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, Green Asphalt also administer secondary benefits such as faster drainage of water, noise reduction and cost effectiveness.
The establishment of 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 Green
Asphalt entails, YARJ believes that the implementation of Green Asphalt will be
a huge breakthrough to relief the landfill and for Singapore to achieve 100%
recycling rate of rubber tires.
The art of Effective Communication 