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.
