Executive Summary
This report aims to propose to the Land Transport Authority (LTA) to replace expressways with porous asphalt containing steel slag. Primary research focused on surveys and interviews revealed that flooding is a major cause of concern on expressways, especially in terms of the safety of motorists. Porous asphalt is an asphalt mix which allows water that has collected on the road and/or pavement surface to flow through the road into a water collection point below the road surface. This serves to reduce water ponding and floods that may occur by allow stormwater to flow through the porous asphalt.
There were many suggestions on the improvisation of the use of porous asphalt to turn it into a more sustainable element in road construction as the limited resources in the world progressively deplete. Substitution of materials with recycled aggregates as well as non-potable applications in buildings for the stormwater collected are suitable means of integrating sustainability into road engineering. The benefits and sustainability of this proposal would hence be used to persuade LTA to replace traditional asphalt roads with porous asphalt containing steel slag.
1. Introduction
1.1. Background Information
Flash floods are considered to be of major inconvenience to motorists, exacerbated by the limited land we have in Singapore. Singapore, being one of the most densely populated countries in the world, has seen a growing transport demand among individual road users, logistic firms and public transportation agencies in the city. These users “expect reliable and safe road infrastructure for traveling from one location to another and transporting goods and people” (Hartmann & Ling, 2016). However, due to the city’s tropical climate, Singapore receives abundant rainfall, which has been steadily rising over the years (see Appendix A). This increase in frequency and intensity of rain, in conjunction with the increase in the car population in Singapore, is a catalyst for road accidents - wet road conditions reduces the friction car tyres have against the road surface. According to a study led by Chow, Cheong and Ho (2016), this in turn leads to higher chances of causing traffic disruption due to road flooding from storms.
The same authors showed that there was a total of 212 flood events reported in Singapore from 1965 to 2015, with only seven years that were absent of recorded newsworthy flood events. According to Chow et al. (2016), 30.2% of the historical extent of flooding during the fifty-year period was categorized and defined as flash floods (Appendix B).
These floods have led to the development of alternative techniques to increase the drainage capability of surfaces, such as the use of porous asphalt. Porous asphalt is a type of asphalt that allows water to permeate through its surface into a collection pond below the pavement. Water-permeable asphalt is made possible by controlling and/or changing the amount of materials used in conventional asphalt mixes, such as the fine and coarse aggregates, along with some variations in construction methods to produce the desired outcome of reducing surface runoff. Porous asphalt has the capacity to conserve water, reduce runoff and promote infiltration which cleanses stormwater, all of which are acquired from the relatively high porosity and permeability of the porous pavement layers (Fwa, Lim & Tan, 2015). According to Hesami et al. (2013), a number of completed or ongoing studies on warm-mix asphalt and steel slag asphalt mixtures have been conducted all over the world.
Exemplifying the advantages our proposed porous asphalt would contribute toward sustainability, such as introducing recycled by-products in the production process. Our team will focus on the use of recycled steel slag. Non-potable use for the water collected from the asphalt after rain (Hammes, Thives & Ghisi 2018), together with recycled steel slag (which will be discussed in later sections), are sustainable aspects of porous asphalt that can serve to urge the Land Transport Authority (LTA) to consider porous asphalt as an alternative to the conventional road asphalt currently being used.
1.2. Problem Statement
According to a survey done by our team in SIT@Dover, flash floods have always been of major inconvenience to motorists in on expressways in Singapore (see Appendix D). With the aim of being a sustainable city, porous asphalt should be implemented on expressways not only to mitigate the occurrence of floods, but also as a sustainable measure by introducing recycled steel slag aggregates in the production process as well as providing non-potable use for the water collected from the asphalt.
1.3. Purpose Statement
The purpose of this report is to propose to LTA the implementation of porous asphalt on expressways in Singapore to reduce the occurrence of floods in areas that has a lack of thorough drainage systems. The proposed methodologies and application of porous asphalt roads would demonstrate to LTA that porous asphalt not only mitigates the occurrence of floods, it can also be presented as a sustainable approach to mitigate road flooding as it acts as a stormwater management where water will permeate through the ground surface into a collection pond below.
2. Proposed Solution
2.1. Porous Asphalt Roads
Our team’s proposed solution to mitigate the occurrence of floods is the implementation of porous asphalt on roads especially on areas where there is lack of sufficient drainage systems such as expressways. Expressways in Singapore have drains that are located only on the road shoulders. Therefore, incorporating porous asphalt can be a strategic stormwater management system - its unique functional benefits include having the capacity to conserve water, reduce runoff and promote infiltration, which cleanses stormwater simultaneously. These properties are acquired from the relatively high porosity and permeability of the porous pavement layers (Fwa, Lim & Tan, 2015).
2.1.1. Recycled Steel Slag
Our team proposes for the substitution of crushed stone aggregates with steel furnace slag. According to Ahmedzade & Sengoz (2009), steel slag, when used as coarse aggregate, improves the mechanical properties of asphalt mixtures. The results of different tests conducted with steel slag indicated that steel slag mixtures have excellent engineering properties such as greater toughness, hardness and ultimate tensile strength. Currently, steel slag is supplied by NatSteel Asia, the only steel mill in Singapore, as a by-product of reinforcement bar production. It is treated by NSL Chemicals Ltd (formerly known as NatSteel Envirotech Pte Ltd).
2.1.2. Application
Our team proposes to LTA for porous asphalt to be implemented as a pilot study on a small section (400m span) of road at the western regions of Singapore, relatively further away from the Central Business District (CBD) where traffic congestion is more likely to occur. Instead of using a traditional asphalt mix, our proposed porous asphalt mix can be used during the maintenance of roads.
3. Benefits of Proposed Solution
4.1. Case Study
According to Takahashi (2013), the number of traffic accidents on wet surface conditions in Japan since 1998 has decreased drastically because of the spread of porous asphalt used widely across the expressways (see Appendix C). Due to the wet surface caused by rain, the loss of vehicle control at high-speed travel was one of the main reasons for traffic accidents. At that time, Japan’s growing economy and with it the unexpected increase in the number of vehicles led to many surfaces of expressways in Japan being severely damaged.
4.2. Challenges
Porous asphalt may seem to be highly efficient and sustainable to the environment, but there are drawbacks and limitations to porous asphalt, the primary one being the lack of strength of porous asphalt as compared to regular asphalt.
4.2.1. Strength
The large amount of pore size in the porous asphalt mix allows water seepage through the surface, but significantly reduces the strength of the road surface (Mo et al., 2010).
To overcome this challenge, our team has suggested for the porous asphalt mix to be implemented on highway roads instead. The reduced congestion in traffic and a swifter road flow, as compared to road junctions, will be a good fit for the use of porous asphalt.
5. Methodology and Procedure
Our team conducted primary and secondary research to supplement our research. Primary research includes interviews with industry experts and a survey conducted by our team in SIT@Dover. Secondary research includes articles and research papers accessed from online libraries.
5.1. Primary Research
According to an interview done on March 6, 2019 with Teo Yong Boon, the Laboratory Manager for Samwoh Corporation Pte Ltd, porous asphalt is not currently being implemented on expressways on a large enough scale. Also, a survey done by our team in SIT@Dover revealed that 95.6% out of 45 responders agreed that floods caused inconveniences for them on expressways.
5.2. Secondary Research
Sources of secondary research include research articles and online journals which are relevant sources that support the contents of this proposal. An example of an article is by Fwa, Lim & Tan (2015) which discussed the characteristics of porous asphalt and pervious concrete pavement materials. Another relevant source is by Hesami et al. (2015), where the laboratory investigation discusses warm-mix asphalt mixtures containing steel slag aggregates. The figures as listed in the appendices were sourced from Meteorological Service Singapore (2018) and several other academic articles.
6. Conclusion
The upward trend of increasing annual rainfall that is expected in Singapore due to changes in the global climate will be a major cause of ponding and flooding on roads in the future. There is a compelling need to prevent ponding and flooding and hence accidents from occurring on expressways where drainage systems could only be found on road shoulders. While our proposed porous asphalt solution aims to mitigate floods by reducing ponding on expressways, it is can also be presented as a sustainable approach towards mitigating floods. Sustainable aspects of the proposed solution include the potential of stormwater collection and its various non-potable uses in buildings, and the usage of recycled steel-slag aggregates to aid in strengthening and improving the durability of the asphalt mix.
References
Ahmedzade, P., & Sengoz, B. (2009). Evaluation of steel slag coarse aggregate in hot mix asphalt concrete. Journal of Hazardous Materials, 165(1-3), 300-305.
https://doi.org/10.1016/j.jhazmat.2008.09.105
Chan, F. K. S., Chuah, C. J., Ziegler, A. D., Dąbrowski, M., & Varis, O. (2018). Towards resilient flood risk management for Asian coastal cities: Lessons learned from Hong Kong and Singapore. Journal of Cleaner Production, 187, 576-589.
https://doi.org/10.1016/j.jclepro.2018.03.217
Chen, J., & Wei, S. (2016). Engineering properties and performance of asphalt mixtures incorporating steel slag. Construction and Building Materials, 128, 148–153. https://doi.org/10.1016/j.conbuildmat.2016.10.027
Chow, W. T., Cheong, B. D., & Ho, B. H. (2016). A multimethod approach towards assessing urban flood patterns and its associated vulnerabilities in Singapore. Advances in Meteorology, 2016. http://dx.doi.org/10.1155/2016/7159132
Fwa, T. F., Lim, E., & Tan, K. H. (2015). Comparison of permeability and clogging characteristics of porous asphalt and pervious concrete pavement materials. Transportation Research Record, 2511(1), 72-80.
https://journals.sagepub.com/doi/abs/10.3141/2511-09
Hammes, G., Thives, L., & Ghisi, E. (2018). Application of stormwater collected from porous asphalt pavements for non-potable uses in buildings. Journal of Environmental Management, 222, 338–347.
https://doi.org/10.1016/j.jenvman.2018.05.094
Hartmann, A., & Ling, F. Y. Y. (2016). Value creation of road infrastructure networks: A structural equation approach. Journal of Traffic and Transportation Engineering (English edition), 3(1), 28-36.
https://doi.org/10.1016/j.jtte.2015.09.003
Hesami, S., Ameri, M., Goli, H., & Akbari, A. (2015). Laboratory investigation of moisture susceptibility of warm-mix asphalt mixtures containing steel slag aggregates. International Journal of Pavement Engineering, 16(8), 745-759.
https://doi.org/10.1080/10298436.2014.953502
Meteorological Service Singapore (n.d.). Past climate trends.
http://www.weather.gov.sg/climate-past-climate-trends
Public Utilities Board. (2012). Report on Key Conclusions and Recommendations of the Expert Panel on Drainage Design and Flood Protection Measures. Retrieved on March 5, 2019
https://www.pub.gov.sg/Documents/fullReport.pdf
T. L. Chow, Winston & D. Cheong, Brendan & Ho, Beatrice. (2016). A Multimethod Approach towards Assessing Urban Flood Patterns and Its Associated Vulnerabilities in Singapore. Advances in Meteorology. 2016. 1-11.
https://doi.org/10.1155/2016/7159132
Takahashi, S. (2013). Comprehensive study on the porous asphalt effects on expressways in Japan: based on field data analysis in the last decade. Road Materials and Pavement Design, 14(2), 239-255.
https://doi.org/10.1080/14680629.2013.779298
There were many suggestions on the improvisation of the use of porous asphalt to turn it into a more sustainable element in road construction as the limited resources in the world progressively deplete. Substitution of materials with recycled aggregates as well as non-potable applications in buildings for the stormwater collected are suitable means of integrating sustainability into road engineering. The benefits and sustainability of this proposal would hence be used to persuade LTA to replace traditional asphalt roads with porous asphalt containing steel slag.
1. Introduction
1.1. Background Information
Flash floods are considered to be of major inconvenience to motorists, exacerbated by the limited land we have in Singapore. Singapore, being one of the most densely populated countries in the world, has seen a growing transport demand among individual road users, logistic firms and public transportation agencies in the city. These users “expect reliable and safe road infrastructure for traveling from one location to another and transporting goods and people” (Hartmann & Ling, 2016). However, due to the city’s tropical climate, Singapore receives abundant rainfall, which has been steadily rising over the years (see Appendix A). This increase in frequency and intensity of rain, in conjunction with the increase in the car population in Singapore, is a catalyst for road accidents - wet road conditions reduces the friction car tyres have against the road surface. According to a study led by Chow, Cheong and Ho (2016), this in turn leads to higher chances of causing traffic disruption due to road flooding from storms.
The same authors showed that there was a total of 212 flood events reported in Singapore from 1965 to 2015, with only seven years that were absent of recorded newsworthy flood events. According to Chow et al. (2016), 30.2% of the historical extent of flooding during the fifty-year period was categorized and defined as flash floods (Appendix B).
These floods have led to the development of alternative techniques to increase the drainage capability of surfaces, such as the use of porous asphalt. Porous asphalt is a type of asphalt that allows water to permeate through its surface into a collection pond below the pavement. Water-permeable asphalt is made possible by controlling and/or changing the amount of materials used in conventional asphalt mixes, such as the fine and coarse aggregates, along with some variations in construction methods to produce the desired outcome of reducing surface runoff. Porous asphalt has the capacity to conserve water, reduce runoff and promote infiltration which cleanses stormwater, all of which are acquired from the relatively high porosity and permeability of the porous pavement layers (Fwa, Lim & Tan, 2015). According to Hesami et al. (2013), a number of completed or ongoing studies on warm-mix asphalt and steel slag asphalt mixtures have been conducted all over the world.
Exemplifying the advantages our proposed porous asphalt would contribute toward sustainability, such as introducing recycled by-products in the production process. Our team will focus on the use of recycled steel slag. Non-potable use for the water collected from the asphalt after rain (Hammes, Thives & Ghisi 2018), together with recycled steel slag (which will be discussed in later sections), are sustainable aspects of porous asphalt that can serve to urge the Land Transport Authority (LTA) to consider porous asphalt as an alternative to the conventional road asphalt currently being used.
1.2. Problem Statement
According to a survey done by our team in SIT@Dover, flash floods have always been of major inconvenience to motorists in on expressways in Singapore (see Appendix D). With the aim of being a sustainable city, porous asphalt should be implemented on expressways not only to mitigate the occurrence of floods, but also as a sustainable measure by introducing recycled steel slag aggregates in the production process as well as providing non-potable use for the water collected from the asphalt.
1.3. Purpose Statement
The purpose of this report is to propose to LTA the implementation of porous asphalt on expressways in Singapore to reduce the occurrence of floods in areas that has a lack of thorough drainage systems. The proposed methodologies and application of porous asphalt roads would demonstrate to LTA that porous asphalt not only mitigates the occurrence of floods, it can also be presented as a sustainable approach to mitigate road flooding as it acts as a stormwater management where water will permeate through the ground surface into a collection pond below.
2. Proposed Solution
2.1. Porous Asphalt Roads
Our team’s proposed solution to mitigate the occurrence of floods is the implementation of porous asphalt on roads especially on areas where there is lack of sufficient drainage systems such as expressways. Expressways in Singapore have drains that are located only on the road shoulders. Therefore, incorporating porous asphalt can be a strategic stormwater management system - its unique functional benefits include having the capacity to conserve water, reduce runoff and promote infiltration, which cleanses stormwater simultaneously. These properties are acquired from the relatively high porosity and permeability of the porous pavement layers (Fwa, Lim & Tan, 2015).
2.1.1. Recycled Steel Slag
Our team proposes for the substitution of crushed stone aggregates with steel furnace slag. According to Ahmedzade & Sengoz (2009), steel slag, when used as coarse aggregate, improves the mechanical properties of asphalt mixtures. The results of different tests conducted with steel slag indicated that steel slag mixtures have excellent engineering properties such as greater toughness, hardness and ultimate tensile strength. Currently, steel slag is supplied by NatSteel Asia, the only steel mill in Singapore, as a by-product of reinforcement bar production. It is treated by NSL Chemicals Ltd (formerly known as NatSteel Envirotech Pte Ltd).
2.1.2. Application
Our team proposes to LTA for porous asphalt to be implemented as a pilot study on a small section (400m span) of road at the western regions of Singapore, relatively further away from the Central Business District (CBD) where traffic congestion is more likely to occur. Instead of using a traditional asphalt mix, our proposed porous asphalt mix can be used during the maintenance of roads.
3. Benefits of Proposed Solution
There are 3 benefits of the proposed solution, namely, the reduced impact of ponding and floods, stormwater management and the use of a recycled by-product: steel slag.
3.1. Reducing impact of ponding and floods
The higher porosity and hence void content of porous asphalt as compared to the conventional asphalt mix will allow the seepage of rainwater through the road surface. This will maintain a relatively dry surface with little ponding. Reduced ponding on the road surface hence allows for a safer driving experience as car tyres are less likely to skid against a wet road surface.
3.2. Stormwater management
The collection of stormwater from under porous asphalt roads can be collected for non-potable use in buildings, such as “flushing urinals and toilets” in a building, which led to savings of 53% to 54% of potable water (Hammes, Thives & Ghisi, 2018). This would make porous asphalt roads dual-purpose and sustainable due to its ability to prevent ponding and recycle water simultaneously.
3.3. Recycled by-product: Steel Slag
According to Chen and Wei (2016), the use of steel slag as a coarse aggregate substitute could improve the engineering properties of asphalt mixtures with higher durability, higher skid resistance and has longer road lifespan resulting in lesser carbon emissions. Furthermore, steel slag has angular and rough textured particles that would improve the interlocking mechanism and provide good mechanical properties such as the tensile strength and hardness of the end product.
4. Proposal Evaluation
The higher porosity and hence void content of porous asphalt as compared to the conventional asphalt mix will allow the seepage of rainwater through the road surface. This will maintain a relatively dry surface with little ponding. Reduced ponding on the road surface hence allows for a safer driving experience as car tyres are less likely to skid against a wet road surface.
3.2. Stormwater management
The collection of stormwater from under porous asphalt roads can be collected for non-potable use in buildings, such as “flushing urinals and toilets” in a building, which led to savings of 53% to 54% of potable water (Hammes, Thives & Ghisi, 2018). This would make porous asphalt roads dual-purpose and sustainable due to its ability to prevent ponding and recycle water simultaneously.
3.3. Recycled by-product: Steel Slag
According to Chen and Wei (2016), the use of steel slag as a coarse aggregate substitute could improve the engineering properties of asphalt mixtures with higher durability, higher skid resistance and has longer road lifespan resulting in lesser carbon emissions. Furthermore, steel slag has angular and rough textured particles that would improve the interlocking mechanism and provide good mechanical properties such as the tensile strength and hardness of the end product.
4. Proposal Evaluation
4.1. Case Study
According to Takahashi (2013), the number of traffic accidents on wet surface conditions in Japan since 1998 has decreased drastically because of the spread of porous asphalt used widely across the expressways (see Appendix C). Due to the wet surface caused by rain, the loss of vehicle control at high-speed travel was one of the main reasons for traffic accidents. At that time, Japan’s growing economy and with it the unexpected increase in the number of vehicles led to many surfaces of expressways in Japan being severely damaged.
4.2. Challenges
Porous asphalt may seem to be highly efficient and sustainable to the environment, but there are drawbacks and limitations to porous asphalt, the primary one being the lack of strength of porous asphalt as compared to regular asphalt.
4.2.1. Strength
The large amount of pore size in the porous asphalt mix allows water seepage through the surface, but significantly reduces the strength of the road surface (Mo et al., 2010).
To overcome this challenge, our team has suggested for the porous asphalt mix to be implemented on highway roads instead. The reduced congestion in traffic and a swifter road flow, as compared to road junctions, will be a good fit for the use of porous asphalt.
5. Methodology and Procedure
Our team conducted primary and secondary research to supplement our research. Primary research includes interviews with industry experts and a survey conducted by our team in SIT@Dover. Secondary research includes articles and research papers accessed from online libraries.
5.1. Primary Research
According to an interview done on March 6, 2019 with Teo Yong Boon, the Laboratory Manager for Samwoh Corporation Pte Ltd, porous asphalt is not currently being implemented on expressways on a large enough scale. Also, a survey done by our team in SIT@Dover revealed that 95.6% out of 45 responders agreed that floods caused inconveniences for them on expressways.
5.2. Secondary Research
Sources of secondary research include research articles and online journals which are relevant sources that support the contents of this proposal. An example of an article is by Fwa, Lim & Tan (2015) which discussed the characteristics of porous asphalt and pervious concrete pavement materials. Another relevant source is by Hesami et al. (2015), where the laboratory investigation discusses warm-mix asphalt mixtures containing steel slag aggregates. The figures as listed in the appendices were sourced from Meteorological Service Singapore (2018) and several other academic articles.
6. Conclusion
The upward trend of increasing annual rainfall that is expected in Singapore due to changes in the global climate will be a major cause of ponding and flooding on roads in the future. There is a compelling need to prevent ponding and flooding and hence accidents from occurring on expressways where drainage systems could only be found on road shoulders. While our proposed porous asphalt solution aims to mitigate floods by reducing ponding on expressways, it is can also be presented as a sustainable approach towards mitigating floods. Sustainable aspects of the proposed solution include the potential of stormwater collection and its various non-potable uses in buildings, and the usage of recycled steel-slag aggregates to aid in strengthening and improving the durability of the asphalt mix.
References
Ahmedzade, P., & Sengoz, B. (2009). Evaluation of steel slag coarse aggregate in hot mix asphalt concrete. Journal of Hazardous Materials, 165(1-3), 300-305.
https://doi.org/10.1016/j.jhazmat.2008.09.105
Chan, F. K. S., Chuah, C. J., Ziegler, A. D., Dąbrowski, M., & Varis, O. (2018). Towards resilient flood risk management for Asian coastal cities: Lessons learned from Hong Kong and Singapore. Journal of Cleaner Production, 187, 576-589.
https://doi.org/10.1016/j.jclepro.2018.03.217
Chen, J., & Wei, S. (2016). Engineering properties and performance of asphalt mixtures incorporating steel slag. Construction and Building Materials, 128, 148–153. https://doi.org/10.1016/j.conbuildmat.2016.10.027
Chow, W. T., Cheong, B. D., & Ho, B. H. (2016). A multimethod approach towards assessing urban flood patterns and its associated vulnerabilities in Singapore. Advances in Meteorology, 2016. http://dx.doi.org/10.1155/2016/7159132
Fwa, T. F., Lim, E., & Tan, K. H. (2015). Comparison of permeability and clogging characteristics of porous asphalt and pervious concrete pavement materials. Transportation Research Record, 2511(1), 72-80.
https://journals.sagepub.com/doi/abs/10.3141/2511-09
Hammes, G., Thives, L., & Ghisi, E. (2018). Application of stormwater collected from porous asphalt pavements for non-potable uses in buildings. Journal of Environmental Management, 222, 338–347.
https://doi.org/10.1016/j.jenvman.2018.05.094
Hartmann, A., & Ling, F. Y. Y. (2016). Value creation of road infrastructure networks: A structural equation approach. Journal of Traffic and Transportation Engineering (English edition), 3(1), 28-36.
https://doi.org/10.1016/j.jtte.2015.09.003
Hesami, S., Ameri, M., Goli, H., & Akbari, A. (2015). Laboratory investigation of moisture susceptibility of warm-mix asphalt mixtures containing steel slag aggregates. International Journal of Pavement Engineering, 16(8), 745-759.
https://doi.org/10.1080/10298436.2014.953502
Meteorological Service Singapore (n.d.). Past climate trends.
http://www.weather.gov.sg/climate-past-climate-trends
Public Utilities Board. (2012). Report on Key Conclusions and Recommendations of the Expert Panel on Drainage Design and Flood Protection Measures. Retrieved on March 5, 2019
https://www.pub.gov.sg/Documents/fullReport.pdf
T. L. Chow, Winston & D. Cheong, Brendan & Ho, Beatrice. (2016). A Multimethod Approach towards Assessing Urban Flood Patterns and Its Associated Vulnerabilities in Singapore. Advances in Meteorology. 2016. 1-11.
https://doi.org/10.1155/2016/7159132
Takahashi, S. (2013). Comprehensive study on the porous asphalt effects on expressways in Japan: based on field data analysis in the last decade. Road Materials and Pavement Design, 14(2), 239-255.
https://doi.org/10.1080/14680629.2013.779298
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