Technical Report Final

1.0 Introduction

1.1 Background

This proposal is developed in response to the call for engineering problem solution. for creating solutions towards reducing the amount of waste specifically plastic to landfill in Singapore.

As Singapore’s human population has been increasing at a staggering rate of 4.028 million in the year 2000 to 5.612 million in the year 2017, the amount of waste produced has been increasing at an alarming rate. In the year 2016, 7.81 million tonnes of waste were produced compared to 7.67 million tonnes in 2015. Our only remaining landfill Semakau landfill is expected to be fully filled by the year 2035. With the pressure of our landfill filling up, NEA has been encouraging the local construction industry to incorporate more recycled and waste materials as building materials. (Eco-business, 2011)

The construction industry in Singapore has been using waste materials such as Recycled Concrete Aggregates (RCA), Washed Copper Slag (WCS) and Ground-granulated blast-furnace slag (GGBS) as the partial substitution for coarse aggregates (stones), fine aggregates (sand) and cement respectively. When part of the conventional materials is replaced with recycled or waste materials, it is termed as Green Concrete. Plastic waste can be converted into carbon nanotubes and it can be used as an additive in concrete. (Goy,2016) The project team sees the potential of using plastic waste as a material substitution in concrete and is going to focus on pitching the idea of incorporating plastic waste into concrete to BCA.

1.2 Problem Statement

To achieve sustainable construction in Singapore, local construction industry should be incorporating 30-40% of plastic waste into concrete as it is environmentally friendly and provides a new purpose for plastic waste. However, this approach has not been fully investigated in Singapore. By adopting this method in the concrete design in Singapore, Building and Construction Authority can reduce the amount of waste being released into the environment. Incorporating plastic waste into concrete would be environmentally friendly, cost-effective, reduce the weight of concrete and enhances concrete properties. This would be beneficial to the construction companies and the building users.

1.3 Purpose Statement

The purpose of this report is to propose to the management of Building and Construction Industry to adopt the idea of partially incorporating plastic waste as aggregates replacement in concrete, and to highlight the advantages of plastic as aggregates in concrete and the applications of it in building constructions.  

2.0 Proposed solution

Green concrete refers to concrete that has a partial or complete replacement of either cement, fine (sand) or coarse aggregates (granite stones) with waste or residual products. When the substitution materials are less dense than the conventional materials, lightweight concrete is produced.

The team’s proposed solution is to incorporate plastic waste as partial substitution of stones and sand in forms of moulded and shredded plastic while carbon nanotubes can be implemented as an additive of cement. Carbon nanotubes are used as a cement composite to reinforce the concrete making the concrete much more stable. Carbon nanotubes (CNTs) can be used concurrently with the shredded plastics as a supplementary material to improve certain properties of the concrete. CNTs are composed of tiny carbon atoms linked in hexagonal shapes that formed a cylinder nanostructure and they are being used as a cement composite to reinforce the concrete, making the concrete much stronger.

There are two common types of CNTs, they are the single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs). MWCNTs are commonly used as they are cheaper to make and have a better reinforcement in concrete.

With our proposed design of concrete mix, the concrete can be used as concrete in non-structural design.

2.1 Case Studies

In a research done in the United Kingdom, University of Bath has collaborated with Indian researchers in a two-year project using plastic waste as a partial replacement for fine aggregates in concrete. Their main purpose of the research is to determine how the properties of concrete will be affected when 10% of fine aggregates is replaced with waste plastic. It was concluded that the results were often lower than conventional concrete and further investigations are required to consider the use in the application of structural concrete.

In addition, a case study in Bangladesh has proved that by using carbon nanotubes, it helps to strengthen the concrete making the concrete more durable. A technological company called BlueRen believes that more plastic waste can be recycled and the use of cement to make concrete reduced, as carbon can be used as an additive in concrete instead.

2.2 Benefits

2.2.1 Improving Concrete Properties

Plastic waste has been increasingly used as a partial substitute for aggregates due to the versatility of plastics that can be customised to meet specific technical requirements. Plastics are non-biodegradable, extremely durable and have great resistance against chemical, water, and impact. (Jaivignesh and Sofi, 2017) These factors improve the properties of concrete and to some extent, acts as a solution to the disposal of plastic.

Plastic aggregates have been identified to improve properties such as abrasion resistance, impact resistance, ductility, shock absorption, and thermal conductivity. (Jaivignesh and Sofi, 2017) Ductility is one of the main properties that are very important for the safety of the building. Ductility helps the concrete to stretch well. High ductility is useful in harsh conditions as it will expand and contract well, as well as having freeze-thaw resistance. (Kumar and Kumar, 2016)

Application of carbon nanotubes has high thermal conductivity preventing cracks in concrete (refer to Appendix B Figure 11) and have tensile strength 100 times stronger than steel. (Goy, 2016) Concrete has very low tensile strength, by adding carbon nanotubes, it enhances concrete to be stronger, more stable and durable in a long term.  This is due to interlocking carbon-to-carbon covalent bonds.  (Refer to Appendix B Figure 7 & Table 10 for the comparison between carbon nanotubes and other cement composites).

2.2.2 Reduction of concrete weight

The usage of plastic waste as aggregates can also greatly reduce the weight of the concrete, producing lightweight concrete. (Kumar and Kumar, 2016) Lightweight concrete is very useful in urban areas as it can be installed on the top floors of high rise buildings. This is extremely applicable to structural buildings as it can be used in the construction of top floors in high rise buildings as the lightweight property eases the transportation to the top floors. The application of lightweight concrete in high rise buildings can reduce building cost, this will be further explained in 2.2.4.  (Jin, Jay, Yoon & Dong, 2015)

Utilizing lightweight concrete will be the future of Singapore construction industry as it will allow companies to build more iconic structures in Singapore, such as the Marina Bay Sands.

2.2.3 Environmental Sustainability

The utilization of plastic waste is environmentally sustainable as the plastic waste is being reused, hence, extending the lifespan of the plastic. Apart from this, utilizing plastic waste can help to reduce the dependence of importing construction raw materials from neighbouring countries. In addition, this can reduce the amount of plastic waste being released into the environment and landfill.

2.2.4 Cost Effectiveness

Using plastic waste is an effective way to save cost as plastics are relatively cheaper than aggregates. It is possible to utilize the vast amount of existing plastic waste accumulated in Singapore to replace a significant amount of aggregates in concrete production. This can help companies to reduce the overall cost of the construction project as they would not need to rely on our neighbouring countries such as Indonesia, to import raw materials and aggregates for construction purposes. Incorporating plastic waste into concrete can save a significant amount of cost as compared to traditional concrete production.

2.3 Evaluation

There are a few challenges when it comes to incorporating plastic waste into concrete (refer to Appendix A).

2.3.1 Low Strength

The addition of plastic waste does not bond well with cement paste. Hence, it causes the compressive, tensile and flexural strength of the concrete to reduce. The addition of steel fibres can help to restore some of the strength in concrete. (Jaivignesh and Sofi, 2017) Even with the addition of steel fibres, the concrete might not be strong enough to be used as a foundation concrete or load-bearing beam. This can be overcome by placing the concrete on the higher floor of the building. Alternatively, they can be used for aesthetic purposes on the interior and exterior of the building.

2.3.2 Operational cost

Plastic waste must be cleaned condition before being added to the concrete mixture as aggregates. Therefore, it is a hassle and an additional cost to ensure that plastics are unsullied. The overall cost would also increase when equipment might be required to monitor the gas emission and the presence of toxic and polluting elements. However, this only applies when heating is required to mould the plastic.

Companies deter from the use of carbon nanotubes due to the processing cost (refer to Appendix 2 Figure 8). The cost of carbon nanotubes is much steeper than other materials such as steel and carbon fibres. However, the cost of carbon nanotubes has decreased vastly in the year 2016 compared to the year 2001.

2.3.3 Size of Carbon Nanotubes

Incorporating carbon nanotubes in concrete can be a challenge due to the size of carbon nanotubes, refer to Appendix B Figure 9 to see the size of carbon nanotubes. It requires new technology like Dynamic Light Scattering (DLS) in order to process carbon nanotube.  DLS is a technology that has the ability to readily characterize a statistically significant number of particles. Although, it can even measure the size of carbon nanotube and the results but DLS do not clearly correspond to a single dimension (length or diameter) of the tube, rather to a combined value. Therefore, it is a challenge to incorporate carbon nanotube in concrete due to its estimation and not the exact value.

3.0 Methodology

This project team performed primary and secondary research that includes a site visit and obtaining online material from various sources and government organizations.

3.1 Primary Research

The project team had the opportunity to visit Samwoh Research and Development Centre as one of our module site visit. The project team talked to the lab manager, Mr. Teo Yong Boon regarding incorporation of plastic into concrete and there is researches on lightweight aggregates and adding of carbon fibres into concrete (refer to Appendix C). However, there was no information regarding the recycling of plastic waste for concrete.

3.2 Secondary Research

A range of secondary data was obtained from official websites, news articles and research journals. This project team gathered statistics regarding Singapore’s waste generation and recycling rate from National Environment Agency (NEA)’s website. A news article has been published quoting NEA promoting Singapore’s construction industries to incorporate more recycled and waste materials as building materials were used as a motivation to promote our idea to Samwoh Corporation.

4.0 Conclusion

With the National Environment Agency urging local construction industry to use more of recycled and waste materials. Our team’s proposal of incorporating plastic aggregates and carbon nanotubes in concrete provides various benefits. Even though there will challenges to be resolved, in the long run, the benefits will outweigh the challenges.

In conclusion, we hope that BCA will take into consideration of our proposal and promote the implementation of plastic waste into concrete to Singapore’s construction industry.

References

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