Brad Blackstone
Assistant Professor
Singapore Institute of Technology
(SIT)
10 Dover Drive
Singapore 138683
Dear Professor Blackstone,
Re: Proposal to Implement
Self-Healing Bacteria Agent into Concrete
Enclosed for your
kind consideration is a response to the request for a proposal on developing
solutions for an engineering problem in Singapore. The enclosed report has been
prepared with the objective of implementing a self-healing bacteria agent into today’s
concrete mix practices to heal cracks in monumental buildings.
This proposal
explores the lack of self-healing properties in the concrete structures of
monumental buildings located in Singapore and discusses the mechanism of a
self-healing agent named Bacillus. The benefits and limitations of the proposed
the solution is provided as well.
In conjunction with
Singapore’s efforts to preserve its heritage and implementing a self-healing
bacteria agent into concrete mix practices to heal cracks in monumental
buildings are of high importance. This increases the longevity of the building
for the future generation to appreciate the art and history of our national
monuments.
Thank you for your
time and consideration of the proposal.
Yours sincerely,
Wai Yan
On behalf of Apollo
Concrete
CVE1281 Effective
Communication
Singapore Institute
of Technology
COVER PAGE
Implementing self-healing bacteria
agents in concrete to heal cracks in monumental buildings.
Table of Content
Biodata
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Moe Wai Yan Tun
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Moe Wai Yan Tun graduated with a diploma in civil engineering with
business from Singapore Polytechnic and is currently an SIT student pursuing a bachelor's degree in civil engineering. His familiarity with structural engineering and civil engineering materials has helped him understand the properties of concrete structures during the primary research stage. His contribution to the report includes…...
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Thoufeek Mohammed
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Thoufeek Ansari graduated with a diploma in civil engineering with
business from Singapore Polytechnic and is currently an SIT student pursuing a degree in civil engineering. He is well-versed in concrete mix designs,
having taken a relevant module in his current undergraduate study. His contributions to the report include….
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Nurliwani Ardini
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Nurliwani Ardini graduated with a diploma in civil engineering with
business from Singapore Polytechnic and is currently a student in SIT
pursuing a degree in civil engineering. Her working experience as an
assistant engineer in a geotechnical firm [INCOMPLETE]
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Justin Chong
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Executive Summary
This proposal was
prepared in response to the request for proposals on developing solutions for
an engineering problem. In this proposal, the team has identified that
self-healing bacteria agents have not been introduced as an admixture into
concrete mix design for repair works. As a result, frequent maintenance and
repair works are required for buildings. Targeting Singapore’s national
monuments, it is important to preserve the architecture and heritage. As the
usage of bacteria agents in large scale construction has not been adopted in
the world, our team proposed a trial in Chinatown, Singapore, to gather data
for further improvisation of our proposed solution.
In the interest of
preserving Singapore’s national monuments aesthetic and history, the team’s
the proposal is to implement self-healing bacteria agent into concrete mix design
for the purpose to heal cracks, which consists of grout injections and
recasting by adding bacteria agents into the concrete mix. The proposed solution,
when implemented, it will allow cracks to heal itself without human intervention.
Besides, considering the proposed solution as a green technology, it
increases sustainability as it reduces maintenance and material costs. The
limitation of the proposed solution includes the social stigma towards
bacteria, alkalinity of concrete and its high initial cost. Both primary and
secondary research, including creating survey questionnaires and reading
professional publications, were used to support the team’s proposal and have
been included.
1.Introduction
This report has been
developed in response to the request for proposals on developing solutions for
engineering problems.
1.1 Background Information
Preserving our
heritage through buildings is essential for our future generations. Buildings
such as the Old Parliament House, which was built in 1827, are rich in the
culture and heritage of Singapore. These buildings were constructed mainly with
concrete, which consists of Ordinary Portland Cement (OPC), which is known to
deteriorate over a long period. The deterioration of the concrete in
Singapore is mainly due to the shrinkage caused by high temperatures and the
acidity of rain. According to Hu,
Balasubramanian, and Wu (2003), Singapore’s rainwater is “typically acidic” due
to impurities from the atmosphere such as carbon dioxide. According to “Types and Causes of Concrete
Deterioration”, it is stated that concrete has poor resilience against acid.
Therefore this will lead to the deterioration of concrete which may result in
the formation of cracks.
According to “Types and Causes of
Concrete Deterioration”, it is also stated that the formation of cracks in
concrete is imminent due to the “drying shrinkage” phenomenon. This phenomenon
is due to the evaporation of moisture in concrete over time. This results
in the shrinkage of concrete due to the volumetric change in the
material.
Due to these cracks, water could seep in and as a result, corrode the
steel reinforcements inside the concrete. According to Arnold (2011), steel-reinforced
bars are added into concrete structures as it improves the concrete strength.
The corrosion of these reinforcements could be detrimental to the concrete
structure as the overall weight-bearing capacity of the concrete structure
would be greatly reduced. Under such circumstances, the concrete structure,
thus, becomes unsafe for the building occupants and will be required to
be restored immediately.
By introducing a self-healing agent consisting of
bacteria, aids in healing cracks in structures effectively. The bacteria
embedded in this self-healing agent behave in a
way such that when triggered by contact with water and air, it produces
limestone, and in doing so it repairs the crack by filling the air and water
voids. From an interview conducted with Professor Fei Jin from the Singapore
Institute of Technology (SIT), he informed us that the usage of self-healing
agents, especially with the use of bacteria, is popular among current-day
researchers. He supported our two proposed methods of incorporating this self-healing
bacteria agent into concrete mix designs either
by incorporating dormant bacteria into the concrete design mix or live bacteria
into grout mixture. Dormant bacteria will be activated when cracks are formed
while live bacteria will be injected into cracks for healing purposes.
By incorporating this into existing buildings, we will ultimately be
able to heal concrete without any external actions, increase the structural
strength, and also reduce the corrosion of the inner steel reinforcements. Even
though self-healing concrete costs more
than normal concrete, when looking toward the long term, one can expect to save
much more on maintenance and refurbishment works.
The table below shows the comparison of strength
between a typical concrete mix used today and a concrete mix with self-healing
bacteria agent as an admixture.
Table 1 - Comparison of compressive concrete
strength
|
S/N
|
Days
|
Normal Concrete
Strength
(N/mm^2) |
Self-Healing
Concrete Strength
(N/mm^2) |
|
1
|
7
|
20.35
|
26.90
|
|
2
|
28
|
30.50
|
37.97
|
Ideally, structural concrete in monumental
buildings should have self-healing properties so the formation of cracks can be
alleviated. Without such self-healing mechanisms, these cracks could
lead to a structural failure, thus reducing concrete longevity of the
structure.
1.2 Problem Statement
Traditional concrete such as OPC does not contain self-healing
properties and tends to deteriorate over a certain time, which makes it
susceptible to cracks. With the introduction of bacteria as a self-healing
agent, we aim to preserve structural monuments thus prolonging the longevity
and maintaining its structural integrity.
1.3 Purpose Statement
The purpose of this report is to propose to Building Construction
Authority (BCA) and the National Heritage Board on the adoption of self-healing
concrete to be incorporated into the national monumental buildings to prolong
the longevity of the building structure.
2.
Proposed
Solution
The team proposes a solution to prolong the longevity of monumental
buildings by incorporating self-healing
bacteria agents into a concrete mix design. There are two types of methods which are the injection of self-healing
bacteria agents into existing concrete structures and recasting of concrete
structures using concrete mix containing self-healing bacteria agents.
Before implementing it into high profile monumental buildings, a trial
application of the concrete mix to be used in historical shophouses in
Chinatown, Singapore. A street in Chinatown consisting of shophouses will be
selected for inspection of cracks on concrete structures. About 2 to 3
shophouses in the selected street with numerous minor cracks on their concrete
structures will be shortlisted for the application of grout injection.
2.1 Grout Injection
Grout, by definition,
refers to a composite material used to fill in voids and openings on the
surface. The proposed grout consists of a mixture of OPC, sand, aggregates,
water and the self-healing agent consisting of
bacteria and nutrients such as calcium lactate. With a proper mix design
of grout injection, cracks with thickness as slim as 0.08mm and as large as
12mm could be filled. Grout injection could be carried out with little
disturbance to the surrounding structures. Therefore, it is a preferred method
for minor cracks that do not jeopardize the integrity of concrete structures.
2.1.2 Application
The grout injection
mix containing self-healing agents and traditional grout injection mix will be
prepared according to the sizes of the cracks. The mixes will be applied to
separate concrete structures with minor cracks in the shophouse. After the
application of the grout injection into the cracks, the results between the
mixes will be monitored and compared over 3 to 5 years.
The feasibility and
viability of the self-healing concrete in the concrete structures of the
monumental buildings could be evaluated from the results collected over the
years.
2.2 Recasting of Damaged Concrete Structure using Self-healing
Concrete Mix
A concrete mix containing dormant self-healing
agents, bacteria and nutrients such as calcium lactate, shall be used to recast
the existing damaged concrete structure. If a similar type of damage resurfaces
the dormant self-healing agent will be activated. The reaction between the
bacteria, nutrients, and water will produce limestones that will fill the gaps
of the cracks. This method is suitable for cracks which are so large that the
reinforcements within the concrete are being exposed. An example of this process
can be seen in the images below.
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Fig 1 - Test sample of self-healing
concrete
that has just been cracked (CNN, 2016).
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Fig 2 - Limestone filling the crack (CNN, 2016).
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2.2.2 Application
This method shall be applied to damaged concrete
structures which are carrying a critical load such as beams and slabs. The
damages occurring at these concrete structures can be detrimental to the
overall building. Therefore, they shall be fully replaced by recasting the
concrete structure to assure they have satisfied full structural
integrity.
During the duration of our proposed trial, critical
structures will be identified and recast using a concrete mix with the
self-healing bacteria agent. Similar to grout injections, the concrete will be
monitored over 3 to 5 years. The feasibility and viability of the
self-healing concrete in the concrete structures of the monumental buildings
could be evaluated from the results collected over the years.
2.3 Summary of Proposed Solution
The table below shows a summary of the two proposed
methods.
Table 2 - Summary of Proposed Solution
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Type of Application
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Grout Injection
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Recasting of Damaged
Concrete
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Crack Diameter
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0.08mm to 12mm
|
> 40mm and/or
Depending on the
severity of cracks
|
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Example of
Cracks
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Fig 3 - Minor Cracks due to aging of concrete
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Fig 4 - Structural Cracks from 1900 building
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Concrete Mixture
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Ordinary Portland
Cement + Fine & Coarse Aggregates + Self Healing Agent (Bacteria) +
Nutrient (Calcium Lactate) + Water
|
|
3.
Benefits
The injection of self-healing bacteria into
existing concrete structures and recasting of concrete structures using
a concrete mix containing self-healing bacteria will produce long term benefits
such as less human intervention, less cost of maintenance and increase in
sustainability.
3.1 Less Human Intervention
The self-healing bacteria agent will
only be activated when cracks are detected and cracks can only be visible to
the naked eye when all self-healing bacteria agents are used up. Due to such
characteristics, the maintenance frequency needed for each monumental building
can be reduced. With lesser cracks, lesser manpower needed for maintenance and
inspection thus allowing the building management department to divert their
manpower elsewhere.
According to The Straits Time (2017), chief executive from EM Services
claims that half of its 1,500 staff are facility managers. With the
implementation of our proposed solutions, facility managers can be reduced
where the excess manpower can be diverted to other major or crucial departments
such as the project planning department.
3.2 Less Cost of Maintenance
With lesser human intervention, it will mean that there will be a
reduction of maintenance needed which leads to a decrease in manpower and
materials. This leads to a lower maintenance cost as the frequency will be
lower.
According to Channel
News Asia (2019), S$2.61 million from the national monument funds will be set
aside to fund 15 national monuments restoration and repair works while
S$115,000 of the amount will co-fund its maintenance. With the implementation
of our proposed solutions, funds used for maintenance will be reduced where the
excess funds can be kept or used for other purposes such as enhancing programs
for educational purposes.
3.3 Increase Sustainability
Due to its small size, having a sustainable construction in Singapore is
crucial especially with the limited natural resources the country has. Nearly
all construction materials have to be imported which includes cement,
aggregates, and water. With the implementation of our proposed solutions,
material imports can be greatly reduced.
As Singapore progresses towards having a sustainable construction
industry, our proposed solutions can be mentioned as one of the green
technologies. By optimizing the use of materials, concrete structures will have
a longer lifespan. The introduction of the self-healing agents such as bacteria
enables the concrete structure to repair itself thus resulting in lesser human
intervention and maintenance cost.
3.4 Key Stakeholders Action Plan
Potential key stakeholders and action plans
required are summed up in the table below.
Table 3 - Action Plan for Respective Key
Stakeholders
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Key stakeholders
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Roles and Responsibilities
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Action Plan
|
|
Build Construction Authority
(BCA)
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Role: Regulators
Responsibility: Oversee all the construction works in Singapore
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Ensure the building and facility management adopt the technology
correctly.
|
|
National Heritage Board
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Role: Owner
Responsibility: Preserve and protect national monuments
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Supports the idea of self-healing bacteria agents in the concrete mix to
be incorporated in their buildings.
|
|
Building / Facility Management
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Role: Client
Responsibility: Maintain the operation of the facilities
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Promotes the usage of self-healing bacteria agents in the concrete mix via
grouting injection or recasting of concrete to its maintenance contractor.
|
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General public
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Role: Consumers
Responsibility: Rights to comfortability, security, and safety
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Ensure the concrete is safe and secure for public use.
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4.
Evaluation
In this section, the feasibility and challenges of the proposed solution
will be evaluated and discussed.
The proposed solution of incorporating self-healing
agents into grout injection and concrete design mix to restore old
concrete structures are feasible. From an interview with Professor Fei Jin, he
informed of multiple studies on incorporating self-healing agents in the concrete
mix to achieve self-healing properties. He mentioned the feasibility of the
proposed solutions as successful research with regards to the incorporation of
self-healing agents into concrete designs can be found.
4.1 Limitations
There are a few limitations to using bacteria as a self-healing agent
such as the social stigma of bacteria, alkalinity of concrete, high initial
cost and pungent smell produced by bacteria.
4.1.1 Social Stigma of Bacteria
The social stigma of society towards bacteria is more towards the
negative aspects. As bacteria are frequently associated with diseases such as
pneumonia, decompositions of living organisms, etc, the society is currently
not open to the idea of using bacteria as a main healing agent. This obstacle
can be overcome by educating society on the advantages of non-pathogenic
bacteria and how the proposed solution benefits Singapore.
4.1.2 Alkalinity of Concrete
Most of the bacteria do not thrive in high alkaline places such as
concrete as it hinders its livelihood. There is a need to cultivate a type of
bacteria strain which is capable of surviving in such high alkaline
places.
Bacteria such as Bacillus are proven to have a high survival rate in
alkaline places. These bacteria will be used as the main healing agent in the
proposed solution. However, in-depth research will be conducted to widen the
list of such bacteria to avoid shortage in the future.
4.1.3 High Initial Cost
The cultivation of bacteria for large scale quantities is not available
in Singapore as there are no demands currently. Besides, the adoption of
green technology has a higher initial cost due to the lack of demands.
Industrial players are still skeptical about investing in the production of
bacteria as they do not foresee any market or demand in the near future. To
combat this issue, business meetings and presentations are needed to attract
potential industry players. Successful results from the proposed trial will
ensure industry players on the foreseeable demand and market.
According to The Straits Time(2019), S$20 million of the national fund
set aside for developers and building owners to introduce green and
technological innovations. Industry players may request funds to cover the
initial cost of the cultivation of bacteria.
4.1.4 Pungent Smell Produced by Bacteria
As bacteria is a form of a living organism, it will feed on nutrients
which will produce waste together with its pungent smell. The society,
inclusive of the National Heritage Board, may raise up concerns about the smell
as it will repel patrons from entering the national monuments.
Bacteria will only be activated when cracks are formed as it is in
contact with water. The quantity during the healing period is small-scaled and
a strong smell will not be produced. As the National Heritage Board
fearful of the decrease in visitors, data from the proposed trial can be
presented to tackle this issue. Programs or interesting facts can be displayed
to educate and indirectly attract support from the public.
5.
Methodology and
Procedure
In this section, the method of research and resources that we have
utilized will be explained.
5.1 Primary Research
Primary research in the form of an interview was
conducted with Professor Fei Jin, who is an Assistant Professor at the University
of Glasgow Singapore. Professor Fei Jin specializes in Civil Engineering with a
Doctor of Philosophy (Ph.D.) from the University of Cambridge.
He mentioned that our two proposed methods were
feasible and could be incorporated into concrete mix designs to maintain and
conserve monumental and historical buildings in Singapore. However, he also
mentioned that the initial investment of utilizing such self-healing agents
into concrete structures would be at least twice as high compared to the
typical ones being used today. The benefits would rather play out in the long
run when the cost of maintaining the concrete structure would be greatly
reduced which could lead to every company’s goal of cost-saving.
5.2 Secondary Research
The main source of secondary research is Ingenia
Inc (2011). The magazine issue published by Ingenia Inc, documented
comprehensive information on the topic of self-healing bacteria
agents being incorporated into concrete. It covered the
need in today’s world, including how these agents specifically work and the
benefits and limitations of the agent. Other sources of secondary research
include online publications and websites which supports this technical report
such as The NewPaper (2018), Cardiff University (2018), Giatec (2017), CNN
Business (2016), Straits Times (2019), Ingenia Online (2011), the constructor
(n.d.), Cardiff University (2018).
6.
Conclusion
According to the National Heritage Board, there are 73 national
monumental buildings and structures in Singapore. It is a small number
compared to other countries. Thus making it important to conserve these
timeless buildings for the future generation as it is rich in culture and
history.
The implementation of self-healing bacteria agents into concrete mix
design enables buildings, especially national monuments, to prolong the
deterioration period. Two applications of the mix will be made available for
different purposes. The proposed trial in an identified street of shophouses in
Chinatown, Singapore, stimulates gathering large scale live construction
data for future improvements. By tackling limitations on the social
stigma of bacteria, the alkalinity of concrete and high initial cost, it
provides the long term benefits in the reduction of frequency and cost of
maintenance that benefit all stakeholders. As Singapore opens to the adoption
of automation from self-driven trains to self check out systems, the idea of
implementing self-healing bacteria in the concrete mix to heal cracks will soon be
accepted by the country.
7.
References
Interview with professor Fei Jin.
Appendix A
Appendix B: Interview with
Professor Fei Jin
Professor Fei Jin is an Assistant Professor in
The University of Glasgow Singapore which specializes in Civil Engineering with a
Doctor of Philosophy (Ph.D.) from the University of Cambridge.
Typically, self-healing mechanisms such as bacteria, mineral (concrete
clinker) and the external injection method can be used to heal concrete cracks.
Ordinary Portland Cement (OPC) has autogenous self-healing properties as it
contains Calcium Silicate (CaSi) and will heal hairline cracks by itself.
Alternatively, the addition of healing agents is considered as autonomous
self-healing agents associated with large cracks.
Professor Fei Jin emphasis the difference in self-healing and
self-restoration concept. With the focus of national monuments, the main goal
of incorporating self-healing properties is to improve durability and ensure
the aesthetic value of the buildings remains the same. With improved
technologies and regulations over time, OPC used in the 80s has different
properties from the current OPC. As Singapore uses purely Type 1 OPC, it
narrows the focus of concrete for the proposed solution.
The limitation of using bacteria as a self-healing agent is the social
stigma of bacteria and the production of pungent smell as bacteria are living
organisms that constantly feed on minerals. Excess in bacteria may losses
its functions in terms of aesthetics. Although there are many successful
experiments using bacteria as a self-healing agent, there are currently no high
scaled experiments. All the available data are from lab-based
experiments.
Despite its limitation, the proposed solution is feasible and will
produce effective long term benefits such as the decrease in human intervention
and maintenance cost. Professor Fei Jin discourages the usage of self-healing
bacteria agents in the concrete mix to the whole building due to its high cost and
divert the team to focus on maintenance aspects.
Alternatively, Professor Fei Jin encourages research on minerals as a
self-healing agent as they are highly reactive and have no smell. However, the
usage of minerals also leads to a high initial cost and it requires additional
agents to control its activation to serve the needs of the proposed
applications. Also, he suggested a research paper by MICP which will
help with our research as they use magnesium as a self-healing mineral on the
usage of ground concrete.
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