1. Introduction
According to Meteorological Service Singapore, Singapore is situated near the equator and has a typically tropical climate, with abundant rainfall, high and uniform temperatures, and high humidity all year round. Singapore has been facing flooding issues occasionally due to the increase in the average temperature and change in precipitation related to global warming. As a result, members of the community of Singapore Institute of Technology (SIT) faces similar “ponding” issues whereby storm water are left stagnant on the surface of the walkways for a period whenever there are heavy recurring rains.
The current walkway is made of conventional concrete which has an impermeable surface. Conventional concrete is unable to allow water to seep through and this will lead to “ponding” issues. Hence, there is a decrease in friction on the surface of these walkways when “ponding” occurs and in turn jeopardising the safety of the community. With these walkways being impermeable, it causes inconvenience for the SIT community as footwears and clothes gets drenched while walking along the walkways. With that, the walkways are unable to facilitate SIT’s population under these heavy downpour circumstances based on observations and personal experiences.
To overcome this issue, pervious walkway should be introduced to overcome “ponding”. Pervious walkways are made from concrete which consist of well graded aggregates. This allows water to seep through the voids as compared to conventional concrete which has little to no voids. Also, the voids from the concrete ensure that the surface of the pervious walkway is rougher as compared to conventional concrete and this in turn increases the friction of the walkway. With this, the permeable surface of pervious walkway allows storm water to drain through its surface and seep into the soil below therefore, reducing “ponding” and with the rougher surface, it improves the safety of the community by reducing chances of slip and fall.
2. Problem Statement
SIT community should be able to walk without difficulties on concrete walkways that are anti-slip and dry. To prevent slip and fall incidents from happening in SIT@Dover, having pervious walkways will mitigate ‘ponding’ whenever it rains. However, there are no pervious walkways in the campus and this results in various instances where slip and fall are prone to happen. SIT’s Division of Estate should therefore replace the impermeable walkway to a pervious walkway to prevent the problem at hand.
3. Purpose Statement
The aim of this report is to propose to SIT’s Division of Estates the implementation of pervious walkways along the walkway connecting the back gate and USC to reduce the inconvenience and to create a safer walking environment for the community.
4. Current Implementation
Both figure 1 and 2 shows the current implementation of the walkway. Figure 2 depicts the dry state of the area whereas figure 1 shows the “ponding” problem that is evident especially after it rains. This is because the current material used is conventional concrete and due to its impermeable surface, storm water is just left to dry, thus making it inconvenient for users to walk across.
Proposed Solution
The team has proposed a solution to replace the current implementation with pervious walkways. The walkway connecting the back gate and USC is chosen as it is prone to “ponding”, as seen in figure 1, especially during heavy recurring rains which happens frequently these days.
As the current concrete used along the walkways are conventional concrete, the replacement with a Neupave C30/37 well graded concrete which consist of compressive strength of 30MPa (Megapascal), will enable storm water to be drained into the collecting basins underneath the walkway. Apart from that, this concrete has a rougher surfacing due to its pores which in turn improves the overall safety for the community by increasing the friction on the surface.
To ensure that this proposed solution could be implemented in an effective manner, the chosen walkway will be used as a test bed for this project. This is so that SIT’s division of estates are assured that the area considered as a “prototype” is fully located in SIT@Dover’s campus.
5.1 Technical Information
Pervious walkways differ from conventional walkways as it allows water to infiltrate through the surface, thus preventing “ponding.” How this is achieved is by using pervious concrete instead of conventional concrete. A pervious concrete mixture contains little to no sand, creating a substantial void content. By using sufficient paste to coat and bind the aggregate particles together, it creates a system of highly permeable, interconnected voids that drains water quickly. According Typically, between 15 to 25% voids are achieved in the hardened concrete (Pervious Concrete Pavement, 2011) Water to cement (w/c) ratio is used to determine the amount of water and cement accordingly. Ordinary concrete typically has a w/c of 0.6 to 0.7 whereas pervious concrete has a ratio of 0.28 to 0.4. The lower the w/c means the mix is more ‘dry’ therefore creating more voids for water to seep through.
5.2 Benefits of Pervious Walkway
5.2.1 Reduces storm water runoff
Permeable pavements help re-establish a more natural hydrologic balance and reduce runoff volume by trapping and slowly releasing precipitation into the ground instead of allowing it to flow into storm drains and out to receiving drains as effluent. This same process also reduces the peak rates of discharge by preventing large, fast pulses of precipitation through the storm water system.
5.2.2 Improve discharge water quality
Permeable pavement can reduce the concentration of some pollutants either physically (by trapping it in the pavement or soil), chemically (bacteria and other microbes can break down and utilize some pollutants), or biologically (plants that grow in-between some types of pavers can trap and store pollutants).
5.2.3 Reduce overall project cost
The implementation of pervious concrete provides lower overall costs as no underground piping and storm drains are needed. The low life-cycle costs of pervious concrete can be compared with regular concrete such that it has an equal life expectancy to that of regular concrete; 20 to 40 years when correctly installed.
5.2.4 Provide friction
Additionally, as pervious concrete has a rougher surfacing as compared to a conventional concrete due to pores on the surface, it will be able to provide the friction needed to avoid users from slipping especially during heavy rains and therefore, reducing the probability of a slip and fall incidents.
5.3 Limitations of Pervious Walkway
Though there are various benefits to using pervious concrete, there are certain restrictions that comes from this proposed idea.
Pervious walkways should be properly designed to accommodate the amount of storm water runoff that is expected in the area. If not adequately designed, the water table below the pavement can rise, preventing storm water from being absorbed into the ground. Certain types of pervious pavements require frequent maintenance due to the possibility that solids and particles may get trapped and clog pavement pores.
The team interviewed fellow lecturer at SIT@Dover, Dr Feijin, who specialises in concrete materials and design. He mentioned that because pervious concrete has such a high void content, its overall strength is generally lower than that of regular concrete and is not recommended on heavy loading areas. In view that this project is to be implemented along the sheltered walkway leading towards USC from the back gate, utilizing pervious concrete at this area would not be an issue as no heavy loading is applied there.
Lastly, the team gathered relevant facts regarding the usage of pervious concrete from a professional engineer, Teo Yong Boon, in SamWoh Corporation Pte Ltd that specialises in ready-mix concrete. He explained that the main drawback of using pervious concrete is maintenance. As mentioned in the article “Permeable Pavement: The Pros and Cons You Need to Know,” The concrete is prone to clogging due to sand and fine particles. As a result, an industrial vacuum would be needed to unclog these particles. If this is not carried out appropriately, water would start to ‘pond’ on the surface, defeating the whole idea of reducing ‘ponding’ occurrence.
5. Potential Solutions
Besides incorporating pervious concrete, there are various other potential solutions that could be considered. Such examples include sloping the walkway, whereby a slope of certain gradient is constructed along the walkway for surface water to flow into the nearby drains. Stamped concrete is another alternative that could be implemented. It is basically a patterned and/or textured concrete to look like a brick, wood or any texture desired. This method is cheap and has the least maintenance compared to the rest. Apart from that, ease of installation is also an advantage for this method. It is also longer lasting than most of the other alternatives.
6.1 Limitations of Potential Solutions
The process of creating a gradient for a slope may affect the community as they are unable to travel along the pavement while it is being reconstructed. Also, current drains as shown in Figure 4 would probably need to be enlarge as gradient is introduced, the surface water runoff increase and when the drains could not handle the input, it would clog and floods the area.
Durability of stamped concrete is an issue as it has low durability compared to other surfaces and methods. This is a rather a more relevant method for creating customize looks for patio, pool side tiles or even backyard as it focuses more on aesthetic rather than solving the issue at hand.
6. Methods/Procedure
To ensure sufficient knowledge is gained before recommending the use of pervious concrete, research was done to ensure the team had an in depth understanding. The team narrowed down the research and decided to search on the guidelines provided by Building Construction Authority (BCA) regarding floor surfaces, standard measurements in Singapore when it comes to how smooth or rough the floor can be, and factors contributing to a “slip and fall” incident.
7.1 Primary Research
Survey and interviews were carried out by the team to get sufficient data to prove that this is an ongoing problem in SIT@Dover as seen in Appendix A.
7.2 Secondary Research
According to the guidelines provided by (BCA), it is stated on the code of accessibility, “In the Built Environment 2007,” floor surfaces shall –
(a) be stable, firm, level and slip-resistant;
(b) not have any projection, drop or unexpected variation in level;
The guideline also provided grading of the slip resistance of some of the typical materials used for floor finishes. Attached as Appendix C.
7. Conclusion
Though there are certain limitations that pervious concrete brings such as clogging of the pores. This limitation can be resolved by using an industrial vacuum. As compared to conventional concrete, pervious concrete does not require drains and piping to redirect storm water. Instead, pervious concrete enables storm water to seep through and be drained into the collecting basins underneath the walkway. This will in turn reduce the overall cost of the system.
As mentioned in the proposed solution found under section 5.0, the compressive strength of pervious concrete is 30 MPa. The strength makes it suitable for the chosen walkway as there is no high imposed dead load such as building acting on it.
To conclude, reconstructing the current walkway with pervious concrete instead is certainly the optimum solution to overcome slip and fall incidents in SIT. As safety is always the number one priority in all places, the community should never feel unsafe especially when walking along the school premises.
References
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BA Contracts Pte Ltd. (2017). Permeable pavers at Hort Park. Retrieved from http://bac.com.sg/permeable-pavers-hort-park-singapore
Building and Construction Authority. (n.d). Quality standards. Retrieved from https://www.bca.gov.sg/qm/quality.html
Concrete Network. (n.d). Economic Benefits. Retrieved from https://www.concretenetwork.com/pervious/economic_benefits.html
FindLaw. (n.d). Slip and fall accidents overview. Retrieved from http://injury.findlaw.com/torts-and-personal-injuries/slip-and-fall-accidents-overview.html
GreenBlue Urban. (n.d). Permeable pavement: The pros and cons you need to know. Retrieved from https://www.greenblue.com/na/permeable-pavement-the-pros-and-cons-you-need-to-know/
Meteorological Service Singapore. (n.d). Climate of Singapore. Retrieved from http://www.weather.gov.sg/climate-climate-of-singapore/
Neupave. (n.d). Permeable pavers [Brochure]. Retrieved from http://bac.com.sg/wp-content/uploads/2016/05/Neupave.pdf
