Implementing self
healing bacterial medium in concrete to heal cracks in monumental buildings.
- Introduction
This report is prepared to propose to
Building Construction Authority (BCA) on the adoption of self-healing concrete
to be incorporated into the historical buildings to prolong the longevity of
the building structure. This prevents the formation of cracks in monumental and
historical buildings.
1.1 Background
Information
Preserving our heritage through
buildings is essential to our future generations. Some of the heritage and
cultures were represented in buildings such as the Old Parliament House, which
was built in 1827. These buildings were constructed using mainly concrete
consisting of Ordinary Portland Cement (OPC), which is known to deteriorate
over a long period of time. 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 the concrete over time. This results in
shrinkage of concrete due to the volumetric change.
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 such as
bacteria, it aids in healing cracks effectively in structures. The bacteria
embedded in this self healing concrete behave in a way such that when triggered
by contact with water and air, it produces limestone, and in doing so they
repair the crack by filling the air and water voids. From an interview
conducted with Professor Fei Jin from Singapore Institute of Technology, he
stated that there are two methods to incorporate this self healing bacteria.
First method is incorporating the dormant bacteria into the design mix which
will be activated when cracks are formed. Second method is incorporating live
bacteria into grout for healing purposes as the grout will be injected into
cracks to fill up the cracks.
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 with self healing bacterial admixture.
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
|
Fig
1 -
Comparison of compressive concrete strength (What is Bacterial Concrete or Self
Healing Concrete?, 2019).
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 Portland Cement (PC) does not contain
self-healing properties and tends to deteriorate over a certain time span,
which makes it susceptible to cracks. With the introduction of bacteria as a
self-healing medium, 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), the adoption of self-healing concrete to be incorporated into
the historical buildings to prolong the longevity of that monumental building
structurally.
2.
Proposed Solution
The team proposes a solution to prolong the longevity of monumental
buildings by incorporating self healing bacteria into a concrete mix design. There are two types of methods which are the injection
of self-healing bacteria into existing concrete structures and recasting of
concrete structures using concrete mix containing self-healing bacteria. 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 with shophouses will be selected for inspection of cracks
on concrete structures. 2-3 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 in the surface. The
proposed grout consists of a mixture of Portland Cement (PC), sand, aggregates,
self healing bacteria, nutrient (calcium lactate) and water. 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.
Add a picture of
grouting
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 the period of 2-3 years. (Shall add the parameter
we are going to record as results)
The accumulation of the results can be
used to determine whether it is feasible and viable for the self-healing
concrete to be incorporated in the maintenance of the concrete structures of
monumental buildings.
2.2 Recasting of
damaged concrete structure using Self-healing Concrete Mix
A concrete mix containing dormant self-healing
agent (bacteria) and nutrients (calcium lactate) shall be used to recast the
existing damaged concrete structure. If the similar type of damage occurs the
dormant self-healing agent will be activated. The reaction between the bacteria,
nutrients and water will produce limestones which 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.
2.2.2 Application
This method shall be applied to damaged concrete
structures which are carrying critical load (eg. Beams and slabs). The damages
occurring at these concrete structures can be detrimental to the overall
building. Therefore, they shall be fully replaced with a recasted concrete
structure.
3.
Benefits
3.1 Less Human
Intervention
As the self healing bacteria will only be activated when cracks are
formed, visual cracks can be seen when the bacteria are all used up. This
reduces the maintenance frequency needed for each monumental building. In
addition, building management may reduce manpower or even divert their manpower
elsewhere.
3.2 Less Cost of
Maintenance
With lesser human intervention, it will
mean that there will be a reduction of maintenance needed which will lead to a
decrease in manpower and materials. This will lead to a lower maintenance cost
as the frequency will be lower.
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 agent into grout injection and concrete design
mix to restore old concrete structures is feasible. From an interview with Dr
Fei Jin, he mentioned that there are alot of studies regarding this self
healing agent being incorporated in concrete design mix to achieve the self
healing properties. He also states that it is possible as there was research that
found success in using this self healing agent.
4.1 Limitation
In order to
incorporate this self healing agent, there are several challenges that will
surface.
The social stigma of
using bacteria as our main healing agent will not be supported. Bacteria are
associated with infection, virus and decomposition of living organisms. In
addition, bacteria produce a pungent smell which may lead to additional
challenges in future.
(to be continued)
5.
Methodology and Procedure
5.1 Primary
Research
Primary research in the form of an interview was
conducted with Dr Fei Jin, who is an Assistant Professor in University of
Glasgow Singapore. Dr 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 historical buildings in Singapore. However, he also mentioned that the
initial investment of utilising 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 Ingenia Inc
(2011). The magazine issue published by Ingenia Inc, documented comprehensive
information on the topic of self healing agents being incorporated into
concrete. It covered the need of these in today’s world, including how these
agents specifically work and the advantages and disadvantages of the agent.
Other sources of secondary research include online publications and websites.
(Not complete)
6.
Conclusion
The National Heritage Board states that 73 buildings and structures in
Singapore is national monuments. This is a small number of national monuments
compared to other countries. Conserving these timeless buildings in Singapore
is crucial for our future generations. Most of these buildings were built with
concrete which is known to deteriorate over time. The frequency of the
maintenance for these buildings is high and costly. With the incorporation of
self-healing concrete into the maintenance process of the concrete structures
of the historic buildings, we will be able to bring down the maintenance cost
in the long run. (Not complete)
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