Self Healing Concrete Properties and Applications

This assignment provides an overview of self-healing concrete, its development, and various research studies on its microstructure. It also explores the potential of bacterial resistance in self-healing materials. The assignment references articles from reputable sources such as Wind-Watch and ResearchGate, highlighting the importance of sustainable infrastructure solutions like self-healing concrete for the construction industry.

Dissertation - “Self-Healing
Concrete”

ABSTRACT
The research work proposed herewith aims at evaluating future of self-healing concrete as a
construction material & its impact on reducing long-term maintenance cost. In order to achieve
overall aim & conduct research with high efficiency, a sequential procedure is adopted. First of
all, the importance of using self-healing concrete in construction industry is evaluated. Also,
different approaches and mechanism of using self-healing concrete as per each of the approach is
analysed in detail. The research also throws light on cost-benefit analysis of using self-healing
concrete as a construction material into practice.
All relevant secondary information is accumulated for conducting an in-depth research. It is
through critical evaluation of published literatures that a valid outcome is generated. Distinct sets
of keywords such as: biological self-healing concrete, vascular self-healing concrete, chemical
self-healing concrete, etc. are used to search the relevant information. The information
accumulated is aggregated together and evaluated deeply so as to arrive at valid conclusion.
Also, a case analysis for construction projects in which self-healing concrete is used is presented.
It can be analysed that SHC is a cost-effective and sustainable element that is more beneficial
than the normal concrete. It has been analysed that SHC being a less permeable material restricts
the entry of foreign substances that increase the strength and thus, a durability of the structure.
SHC uses biological constituents for healing and thus, it does not affect the environment by
emitting CO2. The use of SHC reinforcement should be prevented in health care homes and
school’s due to the hazards that are caused by bacteria. It is observed that the production cost of
SHC was obtained comparatively higher which impacts upon its productivity.
It is seen that the initial outlay for using self-healing concrete in construction project is
comparatively higher. However, in long run, lower amount of maintenance cost is required.
Further, it is found that in present scenario, there is very limited application of the self-healing
concrete. However, in future, there will be more areas where development can be made.
Researchers are trying to find the effectiveness of the process under different environmental
conditions and area.
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ACKNOLODGEMWENT
I am so thankful to all those persons who have given me provision, guidance as well as
much needed motivation so as to complete the current research study. Firstly, I owe my thanks to
guide who gave me chance to undertake this dissertation. Furthermore, I am thankful to my team
members, family and friends who helped me in all possible accords. This led to successful
completion of dissertation and achievement of relevant results.
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contents
Chapter 1 - Introduction...................................................................................................................1
1.1 Background of the research..............................................................................................1
1.2 Rationale...........................................................................................................................5
1.3 Significance......................................................................................................................6
1.4 Aim and Objectives..........................................................................................................7
1.5 Research Questions..........................................................................................................8
1.6 Methods, tools and techniques.........................................................................................8
Chapter 2: Self-Healing Concrete..................................................................................................10
2.1 Cracks in concrete..........................................................................................................10
2.2 The healing process........................................................................................................13
2.3 Advantages and disadvantages of self- healing methods...............................................18
Chapter 3-Self-Healing concrete- Mechanism and advances........................................................20
3.1 Role of self-healing concrete..........................................................................................20
3.2 Mechanism of self-healing concrete...............................................................................20
3.3 Advancements associated with self-healing concrete....................................................22
3.4 Factors affecting efficiency of microbially induced carbonate precipitation.................25
Chapter 4- Field application of self healing concrete....................................................................27
4.1 Cruzsacha Canal in Ecuador...........................................................................................27
4.2 Lifeguard station on a lake in Netherlands.....................................................................28
4.3 Summary.........................................................................................................................29
Chapter 5- Effectiveness of the self-healing process.....................................................................30
5.1 Self-healing Attributes....................................................................................................30
5.2 Robustness Criteria.........................................................................................................30
5.3 Robustness in its approaches..........................................................................................31
Chapter 6-Cost-Benefit Analysis and sustainability of self-healing concrete...............................33
Chapter 7: Data Analysis...............................................................................................................36
7.1 Introduction....................................................................................................................36
7.2 Thematic analysis...........................................................................................................36
Chapter – 8 Conclusion And Recommendation.............................................................................47
8.1 Conclusion......................................................................................................................47
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8.1.1 Achievement of Aims........................................................................................47
8.2 Recommendations..........................................................................................................49
Chapter 9: References....................................................................................................................50
Books and Journals...............................................................................................................50
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Table of Figures
Figure 1: Cracks or gaps that occur in concretes.............................................................................2
Figure 2: Mechanism of Biological-based self-healing concrete....................................................3
Figure 3: Types of Cracks in Concrete..........................................................................................11
Figure 4: Types of Cracks in Concrete..........................................................................................11
Figure 5: Self-healing approaches.................................................................................................14
Figure 6: Mechanism of biological self-healing concrete.............................................................16
Figure 7: Illustration showing cracks fill through self-healing concrete.......................................16
Figure 8: Self-healing features of concrete with mineral admixtures............................................17
Figure 9: Bacterial fixing of cracks in concrete.............................................................................17
Figure 10: Mechanism of healing process.....................................................................................21
Figure 11: Self-healing mechanism (PVA engineered cementitious composite)..........................23
Figure 12: Self-healing process.....................................................................................................24
Figure 13: Bacillus sphaericus under microscope.........................................................................25
Figure 14: Lifeguard station on a lake in Netherlands..................................................................28
Figure 15: Biocement applied........................................................................................................29
Figure 16: Comparison of cost......................................................................................................33
Figure 17: Crack analysis..............................................................................................................37
Figure 18: Use of Non-pathogenic bacteria in self-concrete.........................................................38
Figure 19: Self-healing admixture.................................................................................................41
Figure 20: Permeability of cracked specimens..............................................................................44
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List of Table
Table 1: Keyword search.................................................................................................................9
List of Equations
Equation 1: Chemical equation of Calcium lactate.........................................................................2
Equation 2: Chemical Equation for Exothermic............................................................................21
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List of Chemical Symbols
CO2 Carbon Dioxide
Ca Calcium
H2O Water
CaCo3 Calcium Carbonate
pH potential of hydrogen
List of Abbreviations
GDP Gross Domestic Product
PVA Poly Vinyl Alcohol
ECC Engineering Cementitious Composites
SAP Super-absorbent polymers
MICP Microbially induced carbonate precipitation
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CHAPTER 1 - INTRODUCTION
1.1 Background of the research
The success of civil engineers is determined by durability of structural designs that are
created by them. A well- developed infrastructure owes its worth to its characteristic or
ability of being long-lasting in nature (Khaliq and Ehsan, 2016). Moreover, endurance of
roads, bridges, canals, dams, buildings and other structural designs depends upon distinctive
features of the material used. In today’s world of development, demand of concrete (material
for construction) is increasing at rapid pace. As per the report published by WBCSD,
material that is required to build infrastructure has the second highest production and
consumption after water.
In present world, cement is a widely used concrete that is formed through
combination of following substances: water, hydraulic powder material and mixture of
aggregates. On one hand, demand of concrete is expanding across the globe with
infrastructural growth. On other, civil engineers do face the biggest question of life span that
a concrete can survive for (Perez and et.al, 2015). With a view to multiply lifespan of
construction material, researchers and scientist have started developing a concrete that has
self-healing capacity. This implies that self-healing concrete would have a power to heal
itself by producing lime on surface area after coming into contact with water and air. The
research conducted herewith emphasizes on evaluating the future perspective of self-healing
concrete. It throws light on mechanism through which self-healing concrete helps in
increasing durability of the infrastructure constructed. Further, the research work studies
cost-benefit analysis of using self-healing concrete as a construction material.
Concrete as a mixture has its own set of advantages and disadvantages when it is used in
construction work. The main disadvantage that spoils proper functioning of this material is its
tendency of getting cracked quite easily when tension is applied (Roig-Flores and et.al., 2016).
The cracks developed into structures need to be repaired from time-to-time. It can be said that
cracks developed into concrete or material used for construction reduces its durability and
increases maintenance cost in long run. Some of the pictures are presented below to show the
manner in which cracks are developed into concrete slabs.
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Figure 1: Cracks or gaps that occur in concretes
Now, considering a situation in which cracks developed in a concrete slab are not
sustained; but self-repaired by itself (Van Tittelboom and De Belie, 2013). It was way back in
1877 when Ferdinand Cohn brought forward the fact that bacteria named as “Genus Becillus”
could heal the concrete. With the passage of time, it has been found that production of lime on
surface area of structure would help in self-healing concrete. The chemical equation presented
below further clears the point:
Ca ( C3 H5 O2 ) 2+7 O2 CaCO3 +5 CO2+ 5 H2 O
Equation 1: Chemical equation of Calcium lactate
Where,
Ca (C 3 H 5 O 2 ) 2 isCalcium lactate
CaCO 3 is Lime
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The equation presented above indicates that when Calcium lactate when comes into
contact with oxygen; it produces lime, carbon-di-oxide & water. The production of lime on
surface of concrete in turn would help in bridging the gaps created. In order to create self-
healing concrete, a bacterium named “Genus Becillus” with calcium-containing nutrients
such as calcium lactate, nitrogen & phosphorous are mixed with ingredients through which
the concrete is created. The diagram presented below gives a clear picture of way in which
bacteria produces healing substance and fills the crack into slabs.
Figure 2: Mechanism of Biological-based self-healing concrete
(Source: Li, 2012)
The diagram presented above indicates that bacteria comes to surface of crack; and it
gets multiplied with exposure to water and oxygen. Finally, the bacteria generate healing
substance that fills up the cracks or gaps into concrete slabs. This in turn indicates that self-
healing mechanism of concrete not only helps in bridging the gap; but also strengthen the
building capacity to last for long.
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It can be said that self-healing concrete is expected to prove highly valuable in
developing a robust future infrastructure. The process of recovery which involves direct
intervention by the subject which itself has experienced defects or faults is self-healing. The
discovery of self-healing concrete is expected to transform the world of civil engineering.
Intrinsic characteristics of concrete that can heal itself has largely influenced civil
engineering companies to use this distinct range of concrete in building new structures.
However, scientific researchers have enlightened the fact that long term use of concrete is less
favourable in the non-ideal environment. Cracks are expected to develop; when concrete is
subject to the continuous pressure in harsh environments (Šavija and et. al., 2016). For instance;
rains, earthquakes and heavy flow of winds are expected to damage or weaken the developed
structure. Before using any new substance or technique as a step of advancement; it is important
to check reliability and effectiveness of the concerned material.
There is about 4.3 billion tons of production of cement every year (Bacterial Concrete or
Self-Healing Concrete for Repair of Cracks in Structures, 2017). This figure is increasing
annually; due to growing demands of infrastructure development in recent past. An overall
development of infrastructure is considered to be a key to success of economy. The construction
industry is growing at rapid pace within the United Kingdom. As per the estimates of 2014,
construction industry has contributed around £ 103 billion in economic output that is equivalent
to 6.5% of total output of United Kingdom (The construction industry: statistics and policy,
2015). The construction industry in United Kingdom accounts for around 6% of country’s GDP.
Further, the country’s government allocates budget of around 1% to 1.2% of GDP towards
infrastructure development. Since, it is with overall advancement in country’s set up that more
business opportunities are created; and stronger and better economy is developed. In present
world of infrastructure development; it is significant to develop novel technology or substances
that can preserve our infrastructure during harsh environments and build-up conditions. Mainly,
the requirement of an advanced concrete that possesses higher durability and resistance to cracks
was realized a few decades ago. After introduction of bacteria in 1877; the self-healing concrete
was developed by Hendrik Jonkers in 2006 (Nishiwaki and et. al., 2014). This particular
invention had opened doors for various innovations into area of civil engineering.
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Concrete slabs or structures built upon in different times are always exposed to risk of
getting cracked. One of the major causes behind breaking of concrete has been identified as
undue leakage of water from different parts of structure built. The cracks that are developed due
to certain uncertain conditions are found to be grown into much deeper pathways for breakdown
because of water leakage. The water that flows because of leakage or rains causes the cracks to
widen and reach the steel reinforcements that accounts for skeletal structure of the building
(Williams, Kirisits and Ferron, 2017). This means that chemical reactions and oxidations take
place which deteriorates the material qualities and causing the concrete to break. However, bio-
concrete or Self-Healing concrete is a safe and effective technique which helps in resolving such
major civil engineering issues.
1.2 Rationale
It is since traditional times; construction industry is facing the issue of increasing
durability of buildings, bridges, canals, dams or any other structures developed.
Infrastructure development within an economy has evolved as a key to achieve long term
growth. The demand for concrete is continuously rising in recent past. However,
construction materials and concrete that is used possess tendency of getting cracked. The
future of construction industry is dependent upon scientific ways to increase lifespan of the
concrete. The research proposed herewith emphasizes on evaluating the effectiveness of
“Self-healing concrete” to increase durability of the construction materials. An investigation
is carried out herewith to understand; if self-healing concrete would help in reducing
maintenance cost & increasing life span of infrastructure built over a period of time. It also
emphasizes on understanding the future growth of the industry; if self-healing concrete is
used as a construction material. The rationale behind carrying research is to bring forward
different scientific mechanisms of developing self-healing concrete. Also, to understand the
factors that limits the practical use of this concrete in construction industry.
The present research on "Self-healing concrete" is intended to dissolve the literature
gaps which have been prevalent in this area. The emerging researchers were not able to
completely substantiate; whether the use of self-healing concrete is sustainable way to
develop large scale civil engineering projects. Through this research study, there are certain
recommendations provided to enlighten this area. Additionally, this study on "Self-healing
concrete and its future is conducted to contribute to the academic and professional
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development of presenter (researcher). The information gathered and structuring of a
dissertation adds valuable knowledge to the researcher's experience. Further, it shows the
importance of self-healing concrete and how it can reduce the cost of maintenance and repair
cost.
1.3 Significance
In present era of growth; whereby continuous development in infrastructure is
necessary to substantiate long-term progress; the technological enhancement in construction
methods seem to be an essential element. Developed countries like United Kingdom has
started to develop new construction materials that help in increasing life span of
infrastructure built. The construction material that has been traditionally used is highly
exposed to risk of deterioration. Henceforth, the repair and maintenance cost for the same
tends to continuously increase. In United Kingdom, majority of infrastructure requires repair
and maintenance. It has been estimated that repair and maintenance accounts for around
45% in the construction and building industry on which expenditure of the more than £40
Billion is made (Talaiekhozan and et.al, 2014).
Along with this, the same conditions can be seen in the other countries. For example,
in the US there were more than $5.2 billion of the amount that was spent in the areas of
reconstructing or modifying the bridges. In Asia, expenditure on maintenance and repair
have accounted for more than $2 trillion for making their infrastructure stronger and better
for the longer duration.
As per the research works published in past, self-healing concrete can reduce the repair-
cost in the civil construction areas by 50%. It has been found that initial cost for construction in
when self-healing concrete is used is comparatively higher. However, in long run, the cost tends
to get controlled in comparison to ordinary healing process. Further, the self-healing concrete
possesses higher strength and durability; which results in increasing the strength of the overall
civil structure (Van Tittelboom and De Belie, 2013). Additionally, advancement in this technique
can be seen as they can self-detect the cracks and repair them autonomously without the
interference of the humans. Following points of consideration help in determining the
significance of this study on “the importance of Self-healing concrete”:
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 The study provides valuable insights in relation to application of self – healing concrete
as a construction material.
 It will provide guidance to the civil engineers about the proper usage of self-healing
concrete and the effectiveness of using this concrete for infrastructure development in
future
 The information of this research is helpful in developing pathways for innovative
scientists when modernized civil engineering structures are considered.
 The study brings forth various approaches to self-healing mechanism such as: biological
based, chemical based & intrinsic healing. The mechanism through which self-healing
concrete in three of approaches is also highlighted.
 It also throws light on the way overall construction cost and maintenance cost is impacted
through application of self –healing concrete.
 It also portrays the future of civil engineering through usage of novel construction
methodologies and material such as self-healing concrete.
1.4 Aim and Objectives
Research Title:
“Is self-healing concrete a feasible option to reduce long-term maintenance cost? An
evaluation of future self-healing concrete.”
Research Aim:
“To assess the future of self-healing concrete through its impact on reduction in long-
term maintenance cost.”
Research objectives:
In order to achieve the long-term aim of the research, it has been categorised into list of
short term objectives as follows:
 To evaluate the mechanism of self-healing concrete & its importance.
 To identify the impact of self-healing concrete on reducing long term maintenance cost.
 To assess the application of self-healing concrete in future of civil engineering.
 To recommend ways to help self-concrete mechanism emerge as cost-effective and
sustainable technique in future.
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1.5 Research Questions
The research work presented herewith emphasizes on conducting an in-depth
investigation to answer the following research questions:
 What are different approaches through which self-healing concrete is formed?
 How does self-healing concrete processes to heal the cracks that arises in concrete slabs
in long run? (Mechanism of self-healing concrete)
 What are the advantages and limitations of using self-healing concrete as a construction
material?
 Do self-healing concrete promises a sustainable growth of construction industry in
future? How can self-healing concrete be made cost-effective and sustainable by
overcoming all limiting factors?
1.6 Methods, tools and techniques
The application of appropriate research methodologies and techniques is considered to
be necessary to derive valuable outcomes through the research work. For conducting any
research, it is required to have accurate approach in order to obtain required results. In this
context, inductive and deductive are two sets of approach from which either can be applied
(Rajesh and Venugopal, 2017). In this respect, inductive approach is applied whereby
researcher went from reviewing of literature and past study in order to ascertain the future of
self-healing concrete. Through this, researcher is able to shed light on feasibility of using
this concrete in buildings along with showcasing its strength and power.
Besides approach, data collection is of key importance in any study. In this context,
secondary mode of data collection is done where data is collected from multiple e-libraries
to collect relevant data related to self-healing concrete. Also, different databases are
considered to collect journal articles namely Science Direct, Emerald Insight, Jstor,
ProQuest Science Journals and Google scholar. In addition to it, multiple search engine is
used to obtain relevant information related to self-healing concrete. This mechanism of data
collection is applied because ample of data can be retrieved from internet easily which
assisted in gaining different aspect of self-healing concrete. In addition to it, snowball
sampling is applied whereby references of one articles has assisted in identifying more
relevant information regarding the subject matter (Kalhori and Bagherpour, 2017).
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Furthermore, keywords and search strategy has been used to obtain relevant
information related to self-healing concrete and its long-term consequences. In this respect
following keywords were used along with its significance in search strategy:
Table 1: Keyword search
Significance Keywords
High Self-healing concrete, crack healing, bioconcrete, feasibility of self-healing
concrete, vascular, capsule healing, biological self-healing.
Moderate Fixing the crack, Intrinsic self-healing, chemical self-healing, repair-system
Low calcium lactate, issues in self-healing, infrastructure development,
technological changes in construction industry
These keywords assisted in identifying different articles which were then categorised
in order to gain relevant information. Based on collected data, qualitative analysis is
conducted whereby thematic analysis is conducted. Considering resources, themes were
developed to ascertain the long-term consequences of self-healing concrete (Hanna, 2017).
This assisted in conducting systematic analysis whereby relevant information in highlighted
and concluded.
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CHAPTER 2: SELF-HEALING CONCRETE
2.1 Cracks in concrete
According to Alhalabi and Dopudja (2017), concrete has played a major role in
construction since past Roman Empire. It was later modified into Portland cement. It is most
versatile used material for the construction purpose. It has provided many advantages in the civil
branch. In this, the major contribution was made by François Coignet in the year 1853. He was
French industrialist who wanted to construct a building with the help of concrete (Qian and et.
al., 2015). It began to be considered as the most effective, versatile and economical material.
This increased its utilization in the field of construction. However, as mentioned by the Fre and
et. al. (2013), cracks have mostly affected the utilization of concrete. They decrease its strength
and holding capacity. Though the tensile strength of concrete is 10% more than compressive
strength, but during steel reinforcement, cracks are developed. Further, there are other reasons as
well which generate cracks in concrete. The figure below will clearly help to understand
different types of cracks which affect the strength of concrete.
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As shown in the figure above, cracks develop at two phases and hence are categorized as
those developing before hardening and after hardening. Cracks that develop after hardening are
further classified into four types. These are physical, chemical, structural and thermal cracks.
Before hardening, three types of cracks may develop. These include early frost, plastic and
constructional movement cracks. There are various reasons due to which cracks develop after
hardening. These consist of drying shrinkage, accidental overload, design load, thaw cycles etc.
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Figure 3: Types of Cracks in Concrete
(Source: Francesco, 2014)

in contrast to this, cracks developing before hardening may be due to plastic shrinkage, plastic
settlement, form- work movement and sub-grade movement.
As stated by Ramadan, Suleiman and Nehdi (2017), cracks developing in concrete
may of two different types. These are intrinsic and structural cracks. The former one is
caused due to chemical action and changes made in the physical state while the latter is
concerned with the changes that are caused by the direct loading. When concrete is affected
by the chemical action the main reasons behind it is the plastic settlement, cement
carbonation, and thermal movements. There are various standards and codes made so that
cracks can be prevented. Despite all these, the cracks appear in the material in the
development stage (Victor and Emily, 2012). Cracks affect the concrete by reducing its
strength and making it vulnerable in forming a structure. They also decrease its durability.
Another reason which causes cracks is the corrosion caused in the Iron. Due to the presence
of alkalinity, the material (Iron) gets degraded and corrosion is caused. Moreover, if there is
the presence of oxygen and moisture, it affects the material adversely. All these are the
reasons which make concrete weak and affect its durability.
Wang and et. al., (2014) asserted that the only solution that can help the concrete to
regain its strength and durability was to make it self-healing so that it can maintain and repair
itself. For this purpose, many researches are being undertaken on concrete performance. Based
on the research findings, different chemicals, bacteria, and elements are added in the structure so
that cracks prevention can be done. Various approaches are adopted by the scientists to improve
the performance and strength of the cement (Van Tittelboom and et. al, 2015). One such
technique is Self-healing Concrete.
In the earlier period, civil construction was made through the specified and fixed values/
specification which were mentioned in the standards. If the material deteriorated, then repair and
maintenance were considered as effective solutions. But, until 1962, the engineers were unable to
find an effective solution which could prevent the damage (VQureshi, Kanellopoulos and Al-
Tabbaa, 2016). The development that was made was not based on the concrete, but on the
polymers. Later in the same field, many researches were made and advanced technologies were
developed related to the self-healing properties of thermoplastic and cross linkage polymer (Van
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Tittelboom and De Belie, 2013). In late 1990, Dr. Carolyn Dry conducted a research, in which he
applied the polymer concept to concrete. However, the research was not successful.
Esser-Kahn, A. P. and et.al., (2010)carried out a research about " Programmable
microcapsules from self-immolative polymers". This was another step towards the concept of
autonomous repair. Healing can be defined as repairing or curing. Self-Healing is the ability by
which self-cure or repair can be done. In concrete, these damages can be self-healed through the
similar changes as seen in the human biological system. All living beings have the ability to self-
heal and their damaged parts get regenerated. The same technology can be used in the concrete
to make it self-healing. In the beginning, the damages are viewed. This is followed by adopting a
three stage procedure (Gilabert, and et.al., 2017). These stages are Damage perception, healing
mechanism and transport system which completes the healing mechanism.
2.2 The healing process
There are various approaches through which healing mechanism can be applied. Broadly,
there are two categories in which the self-healing processes of cement based material can be
classified. These are Autogenic self-healing and autonomic self-healing. Autogenic healing is the
process in which cracks are healed by material through its own generic constituents. In contrast
to his, autonomic self-healing is concerned with use of engineered additions into the
cementitious material. A figure of self-healing techniques for the reinforced concrete is
mentioned below.
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Figure 5: Self-healing approaches
The above figure provides a clear classification of techniques of self-healing. It
shows three broad categories namely intrinsic, biological based and chemical based.
The healing process is classified in three categories namely, Intrinsic, Biological
based and chemical based. Under the intrinsic methods, healing agents are not used and
changes are made in the cementitious material. Biological Based is the process in which
micro- organisms such as bacteria are used which help in making the desired changes. These
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Self-healing concrete
Intrinsic Self-healing concrete
Autogenous Healing
Improved autogenous healing
Healing in polymer modified
concrete
Biological Based self-healing
concrete
Aerobic bacteria
Anaerobic bacteria
Chemical Based self-healing
concrete
Capsule based self healing
concrete
Vascular based self-healing
concrete

micro- organisms are added in the form of a paste which releases the precipitates that help to
recover the blockage and cracks (Wang, 2013). It is considered as a more eco- friendly
approach. Under chemical based method, healing or repairing is done through the
application of the artificial healing chemicals. Encapsulation is another method through
which properties of construction material can be enhanced. It is regarded as a versatile and
effective strategy for self-healing. This comprises of using capsules for providing
mechanical protection to the healing agent. The capsules release the healing agents only
when they are triggered by the cracks (through diffusion or rupture) (Gupta and Kua, 2016).
Biological based self-healing concrete
Bio-mimicry is used by the engineers in the civil construction so that cracks can be
repaired naturally. It is more environmentally friendly and cost effective method. Bio- concrete
is an invention mimics the principle on the basis of which cracks in bones are healed in human
body. In Bio- concrete, the healing agent comprises of bacteria which are mixed into the
concrete. Various aerobic and anaerobic bacteria are used as healing agent. They have special
properties that they can make the minerals into their precipitates form after coming in contact
with water and oxygen. These minerals act as remediate to the cracks. In mid-1990, the ideas
were introduced by the Gollapudi et. al. As per his research precipitation can be caused by the
proteolytic bacteria when they are injected in the Concrete (Wang and et. al., 2014). It is
dependent on multiple factors such as pH levels, growth environment and concentration in which
they are injected. They can effectively survive through the presence of alkaline medium,
inorganic carbon and calcium ions concentration. It is based on the simple chemistry where
negative charge is attracted from the positive charge ions and precipitation is formed.
As discussed in above section, the biological mechanism of self-healing concrete is again
presented underneath. Also, some of the illustrations are shown to generate clear picture of way
in which bacterial composition helps in developing self-healing feature into concrete.
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Figure 6: Mechanism of biological self-healing concrete
(Source: Li, 2012)
Figure 7: Illustration showing cracks fill through self-healing concrete
(Source: Li, 2012)
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Figure 8: Self-healing features of concrete with mineral admixtures
(Source: Li, 2012)
Figure 9: Bacterial fixing of cracks in concrete
(Source: BacillaFilla: Fixing Cracks in Concrete, 2017)
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When a crack develops, the bacteria come into contact of oxygen and water.
Multiplication and germination of bacteria occurs in calcium based nutrient, calcium lactate.
The bacteria feed on lactate and combine calcium with carbonate ions. This leads to the
formation of limestone which performs the function of sealing the cracks (Formia, and et.al.,
2016, Van Belleghem and et.al., 2016). Thus, a reaction is formed and the concrete gets self-
repaired (Williams, Kirisits and Ferron, 2017).
Bacteria used in bio-concrete: the concrete mix is added with the bacteria in
suspension state. The concrete is basically alkaline in nature. It is due to this reason that
some special qualities must be possessed by the bacteria. They should be capable of
surviving in extreme environmental conditions. This implies that they should withstand dry
state and must survive in such alkaline nature. If anaerobic bacteria's are used for the process
there is increase in the compressive strength 30 times. When aerobic bacteria is to be used,
then Bacillus pasteurii, Bacillus sphaericus, Bacillus cohnii Escherichia coli, Bacillus
subtilis, etc. are added to the concrete.
2.3 Advantages and disadvantages of self- healing methods
There are various advantages and disadvantages of this process. Through the bacteria
insertion, the healing process can be started. Moreover, it is a more environmentally friendly
method as it does not cause any pollution. Along with this, the process is based on use of
advanced and innovative methods of utilizing micro-organisms and biological processes in
healing procedure of concrete. They can easily be present for the longer duration in the dry state
(up to 50 years). This method provides more viability and reduces the concern over the issue
(Šavija and et. al., 2016). In order to maintain the longevity of the bacteria, porous expanded clay
particles are used while preparing the solution for the concrete. The biological based method can
also be used to fill those gaps which have larger size and width. It is the easiest treatment which
can be provided to the civil process and has lowest maintenance cost (Gilabert, and et. al., 2017,
Seifan, Samani and Berenjian, 2016). The self-healing process using bio- concrete is more
effective and efficient and has great resistance to freeze-thaw attacks. It also reduces the chances
of corrosion.
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However, there are certain disadvantages of this method as it is complex and costly.
Embedding the micro-organisms can prove to be a difficult task. Bio- concrete is costly as
compared to conventional concrete. Further, the bacteria that are added to grow in concrete
are not considered good for human health. Moreover, calcite preparation involves
investigations which may prove to be costly can be used to recover the cracks generated.
(Van Belleghemand et. al., 2016). There is requirement of special environment for making
the precipitate. Though there are other methods which can be used in comparison to the
microorganisms such as Intrinsic and Chemical Based self-healing methods, but these have
certain disadvantages as well.
Intrinsic healing method is less complex. Also, this method does not require
sequestration of healing agent. However, its healing capacity to narrow cracks is limited. As
compared to this, chemical based self-healing method has an advantage of facilitated release
of healing agents. This method is capable of responding to multiple cracks simultaneously.
Furthermore, multiple healing of repeated damage events can be obtained by using chemical
base self-healing method. However, use of vascular system in this method requires difficult
installation of vascular network and concrete casting. This method has limited healing
capacity. When capsule based procedure is used, it may be a matter of concerned if
appropriate bind is not formed between capsule and matrix.
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CHAPTER 3-SELF-HEALING CONCRETE- MECHANISM AND
ADVANCES
3.1 Role of self-healing concrete
Self-healing concrete plays an important role in solving the problems of concrete
structures that sometimes deteriorate much before their service life. Many countries face the
challenges of the changing environment. They have concerns regarding the infrastructures
that develop cracks due to different weather conditions over time. Self-healing concrete can
act as a significant solution for preventing serious damages to buildings that are caused due
to appearance of cracks. Moreover, it is helpful for the developing countries as their civil
structure can be maintained for the longer duration (Van Tittelboom and et. al., 2016).
Moreover, there has been an increasing demand for buildings and infrastructures
owing to the rapid growth in world population and booming economies. This also implies
that adequate steps need to be taken for ensuring proper maintenance of these structures.
Furthermore, premature failure of concrete structures causes huge financial losses. Self-
healing concrete can help in damage prevention thus avoiding the situation of damage
control. It will help in preventing further widening of cracks thus assisting in averting the
danger of deterioration of buildings and other structures.
3.2 Mechanism of self-healing concrete.
The mechanism by which self-healing concrete works varies depending upon the repair
agent present in the mix. The process of repair can be considered as self-healing only if there is
no human intervention. There are different methods of self-healing of concrete are investigated
by different professionals. These mechanisms can be divided into three categories and they are
intrinsic, chemical and biological. Concrete can be healed by using its auto-genesis capacity of
the dried cement that is present in the mixture. With respect to this property of concrete, when
water molecules come into contact, rehydration process takes place. In this process, CO2 reacts
with ions of Ca and form the crystals of calcium carbonate. But there is a limitation of this
method as they can only heal the small cracks present in the structure.
This mechanism was first observed in water retaining structures. Besides this, a
systematic study on the self-sealing was made by (Van Tittelboom and et.al, 2016), which
reflects four different processes which help in the healing of concrete and they are
20

dissolution, deposition and crystallization; physical clogging; continuing hydration and
swelling of cement mix. Perez and et.al., (2015) observed the cracks in the bridges and
evaluated that concrete performs self-healing as some specimens are exposed to the freeze-
thaw cycles. The reaction followed under this mechanism is:
Equation 2: Chemical Equation for Exothermic
The image depicts the mechanism of healing process that taken place in concrete
when a crack develops. The first part shows the crack that has developed in the concrete.
The second part shows a version of calcite material that fills the crack. Thus, concrete is able
to heal itself.
Fly ash which is generated as a waste from thermal power plants and slags generated
from metallurgical industries has been utilized for improving the performance of cement.
Fly ash- cement system is found to possess self-healing ability for cracks due to shrinkage.
Figure 10: Mechanism of healing process
(Source: Goyal, 2015)
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Perez and et.al, (2015) explored the mechanism of self-healing by fly-ash and blast-
furnace slag. Both these constituents have self-healing properties because of the low
hydration degree of the slag and particles of fly ash. When cracking takes place, the
unreacted particles have the capability to be activated again and thus close the crack. The
self-healing ability of fly ash is found to increase with the increase in replacement ratio.
Pozzolanic and latent hydraulic reactions are other reasons behind the self-healing ability of
fly ash and blast furnace slag. A different approach of self-healing of concrete is proposed
by Tziviloglou and et.al, (2016), through a different route which is based on the metabolic
conversion of nutrients. This is one of the many pathways through which calcium carbonate
precipitation is induced. In contrary to these methods, chemical mechanism of self-healing
was also observed to be effectual. The main chemical based methods are the adhesive agents
that are stored in capsules. These capsules help in connecting two faces of a crack together.
The commonly used adhesive agents for this method are epoxy, methylmethacrylate,
cyanoacrylate, etc.
According to Van Belleghem, and et.al, (2016), vascular based self-healing method
employs the concept of bleeding via a network of capillaries or hollow channels. This
method can be implemented in two ways, either single channel systems or multiple channel
systems. Single channel systems involve the use of only one component healing agent. In
contrast to this, when a reaction of two healing agents is to be used for healing the cracks,
then multiple channel approach is used. Although it is an effective approach to supply
healing agent externally, but it cannot be regarded as self-healing as it requires external
intervention (Lucas, and et. al., 2016).
3.3 Advancements associated with self-healing concrete
A number of studies have been made to gain better understanding on this. Improvising
this method, some advances have been made which determine the self-healing method of
concrete. The major among them is Crack width control in which a new material, ECC-
engineering cementitious composites are used to provide better support to the traditional
auto-genesis method of healing.
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Figure 11: Self-healing mechanism (PVA engineered cementitious composite)
(Source: Yu and et.al., 2010)
The above image shows microstructure of self-healing phenomenon in PVA (Poly
vinyl alcohol) engineered cementitious composite. The self-healing sequence shows that
large crystal structures of carbonate have fully occupied a crack of 100 μm.
23

Previously, polythene was used in self-healing concrete but nowadays, it has been
replaced with Polyvinyl Alcohol. Moreover, it was investigated by many researchers that
water supply to the concrete helps in the further hydration of the un-reacted cement (Huang
and et. al., 2016, Roig-Flores, and et. al., 2016, Feiteira, and et. al., 2017). In addition to
this, by adding microfibres, the process of healing can be amplified.
Besides this, Sangadji, Wiktor and Schlangen, (2017) explained the importance of
hydrogels or super-absorbent polymers (SAP) as these are the products which can absorb
large quantity of water. Further, these molecules then retain the absorbed water into the
structure without any dissolution. The swelling due to the absorption seals the crack partly,
which later heals completely by desorption of SAP. This provides the fluid to the
surrounding structure for internal curing. Afterwards, rehydration takes place and the
precipitation of calcium carbonate takes place. Thus, this method has the capability to repair
the cracks completely. As per the views of Irico and et.al. (2017), autonomous self-healing
property of concrete is the most effective. In contrary to the auto-genesis mechanism which
is inherent feature of the concrete, autonomous method is a purposely designed self-healing
mechanism.
Figure 12: Self-healing process
(Source: Goyal, 2015)
The above image shows healing of concrete gaps by bacteria through mineral formations.
Van Tittelboom and et.al, (2015) suggested the best way to study self-healing
mechanism of autonomous method. It involves dispersing the capsules filled with a
24

cementite or synthetic healing agent. These agents absorb the water and result in healing
process. In order to overcome the limitation of penetration of water into a crack from
external sources Schlangen and Sangadji, S., (2013) suggested the use of water-saturated
porous particles. According to Talaiekhozan, and et.al, (2014), cracks can be healed by
using calcium carbonate precipitating micro-organisms. This is referred to as Microbially
induced carbonate precipitation (MICP) which includes using microbial cells and
biochemical activities to form calcium carbonate. This is a bio-based self healing method.
The bacteria used in this process should be effective enough to heal the cracks for the long
period of time. In order to increase the durability of these bacteria Dong, and et.al, (2015)
proposed the method of encapsulation. In this method, bacteria are implemented in the mix
with an outer covering that helps them in surviving in the concrete matrix for a long span of
time to achieve the effectiveness of the mechanism.
Figure 13: Bacillus sphaericus under microscope
(Source: Goyal, 2015)
The above image shows a microscopic view of Bacillus sphaericus. It is a urease
producing bacteria. Urease plays a major role in the process of microbially induced
carbonate precipitation.
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3.4 Factors affecting efficiency of microbially induced carbonate precipitation
Van Belleghem and et. al., (2016) concluded four major factors that govern the CaCo3
precipitation. These are pH, the concentration of calcium ions and urea, temperature, and
nucleation sites. The precipitation of calcite is influenced by pH due to the reason that the
activity of urease enzyme can only take place at pH values that are suitable for urea
hydrolysis. For the production of ammonia, there is requirement of high pH. Carbon dioxide
is released by aerobic bacteria during cell respiration. Parallel to this, there is an increase in
the pH due to production of ammonia. If the levels of pH are low, carbonate dissolves rather
than precipitating. Hence, alkaline conditions are required for enabling precipitation of
carbonate.
Concentration of Ca+ ions is another factor that is important for precipitation. The cell
surfaces of microbes are negatively charged. Hence, they get attracted towards cations. This
makes the microorganisms ideal crystal nucleation sites. Therefore, for CaCO3 precipitation,
ideal concentration of calcium is important. Similar to other enzymatic reactions, the process
of catalysis of urea by urease enzyme depends on temperature. 20 to 37 °C is found to be the
optimum temperature for urease. Increase in temperature upto 20 °C increases the urease
activity. Thus, temperature is an important factor for carbonate precipitation to take place.
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27

CHAPTER 4- FIELD APPLICATION OF SELF HEALING CONCRETE
In various fields, there is important application of self-healing concrete. It has provided
a greater solution to the civil engineers who are working in the extreme climatic conditions.
Moreover, its application can be used to improve the different structural system by the use
of modern technologies. There is certain limitation, but its application can be increased in
future.
4.1 Cruzsacha Canal in Ecuador
In Ecaudor, irrigation channels are there for the supply of water for drinking and farming
purpose. Due to changing environmental conditions and high turbulent pressure, there are cracks
generated in the canal which cause leakage and water penetration. These have adversely
impacted the stricture of the anal leading to reduced water supply at the utilization areas such as
farming.
Before releasing the application of self- healing concrete, an experiment was performed
at Cruzsacha canal. This comprised of five steps:
 Making two types of concrete discs
 Breaking concrete
 Measuring leakage
 Placing concrete in the canal
 Measurement of leakage after curing period.
Two types of concrete were used at Cruzsacha canal. One was presently used concrete
and the other was self-healing concrete in which nutrient calcium lactate and psychrophilic
bacteria were used as the healing agent. To develop the self-healing ability capsule method
and natural fibers were used. The bacteria were saved from the extreme environmental
conditions through the use of capsule. (Seifan, Samani and Berenjian, 2016). . The cost
which included in the process was based only on the bacteria's and employees and
community training. The price of 1 kg of self-healing agent was € 2.11. The other costs were
totally based on the employee training. Though the initial cost for the product was little
28

expensive it is expected to provide long term benefits. As estimated, it will increased the
durability and strength of the canal in the long run which will benefit the farmers.
4.2 Lifeguard station on a lake in Netherlands
After certain period or years, there are cracks formed within walls. Two of the scientist
Henk Jonkers and Eric Schlangen have developed concrete that can heal its own cracks with the
help of biological cement. This biocement make use of bacteria that is hard wired in order to eat
calcium lactate (Tziviloglou. and et. al., 2016). When this happens, then it produces calcite
which is an ingredient of limestone. This is helpful enough to fill up the space between cracks.
The scientist made of this mixture in real building through which lifeguard station was
developed. The procedure is compared with skin as bacteria produce limestone that are filled
between the gaps.
Figure 14: Lifeguard station on a lake in Netherlands
(Source: Self-healing concrete solves, 2015)
The scientists have worked over years and have also focused in the limitations in
concrete. More specifically, they have also focused on creating separations among spans and
avoiding sharp corners which break and cracks.
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Figure 15: Biocement applied
(Source: Self-healing concrete solves, 2015)
This type of technology can support to open up different possibilities for infrastructure
and in designing buildings (Gilabert and et. al., 2017). In addition to this, it can also impact
walls, sidewalks to skyscraper foundations and parking structures. Apart from this, there are
similar developments that are taking place in which sunlight is used for activation
mechanism rather than moisture. However, self-healing material is considered to be the first
full scale application.
4.3 Summary
From the above conducted two case studies, it is identified that self-healing of concrete is
highly benefits for the future. The results are still in progress. There are few years of time that
30

will take in order to come up with appropriate results. In both these studies the research are
carried out currently and it will take few years’ time to know the actual results.
CHAPTER 5- EFFECTIVENESS OF THE SELF-HEALING PROCESS
In terms of the effectiveness, there are various advantages of self-healing concrete.
However, there is restriction in the process as the healing can only be possible to a certain limit
(De Nardi and et. al., 2017). Further, its ability for being applied for the longer period and
strength recovery is less. It can be changed if capsules and vascular system are used in the
traditional concrete.
5.1 Self-healing Attributes
The process is majorly based on the system property and not on the material composition.
So the process has the disadvantage that it cannot be applied to the universal system (all kinds of
application). Nevertheless, there are chances that it can be implemented to recover such losses.
Scientists and researchers are identifying the areas which can help them to make the relevant
self-healing concrete that possess all the features required for self-repair. They have to make
considerable expenditure on researching this topic and identifying some of the techniques related
to it. Implementation of various technologies can make the system of self-healing more effective
and efficacious (Kanellopoulos, and et. al., 2017).
Use of self-healing concrete may cause certain issues to the health of the humans and
environment. So the process needs to be designed in such a way that these risk factors can be
eliminated and the essential properties of self-healing can be successfully accomplished (Feiteira
and et. al., 2017). The system must work similar to the principles of human body and. Whenever
there is need, the system of self-healing should be capable enough to initiate the process and
fulfil the crack. The self-healing process must also be more compatible and reliable so that the
structural performance or bonding is least affected.
5.2 Robustness Criteria
There are 6 criteria which are used to evaluate the robustness of the process. These are: Shelf Life: In the civil construction, as the services last for the 100 years at least so at any
duration there can be cracks in the concrete (Wang, and et. al., 2016). Thus, the process
31

must serve its assigned time period and should preserve the long shelf life of the building
or structure. Pervasiveness: In the civil structure, there are various ways through which cracks can
appear. These can be due to load and or complexity in the structure. So as per the location
and orientation they must be recovered and should be self-predicted (Al-Ansari and et.
al., 2017). It should not be based on the orientation, however, the structural integrity must
be maintained. Quality: For any type of the self-healing concrete, its effectiveness can be governed
through its ability to regain. This also includes the ability to mechanical properties,
permeability and diffusivity, of the crack, developed. Thus, for maintaining the quality,
the healing mechanism must be effective and capable of sealing the crack as soon as it is
identified. Moreover, it must develop the mechanical strength which can keep the civil
structure in its place.
 Reliability: When self-healing concrete is applied, it should perform consistent manner.
Further, the outcomes must be accurate and should be based on measurement and
specification which were used to make the self-healing concrete. As declared by Sangadji
and et. al., (2017), if there is the lack of consistency in the solution then the relatability of
using that mechanism decreases.
 Versatility: Versatility can be defined as the ability to perform different functions or
activities. As stated by Gruyaert and et. al., (2016) self-healing concrete is required to
possess the ability of being versatile. This indicates that the advancement to recover and
regain must be fulfilled as soon as the cracks are identified. Moreover, it must not get
affected by any other factor and should retain its property for the longer duration.
 Repeatability: over the time, a civil structure may lose its strength. Hence, cracks may
develop as the time passes due to continuous loading of the structure (Mignon and et. al.,
2017). Therefore repeatability of such concrete can be maintained through its multiple
properties. The concrete must be able to self-repair the cracks, must identify it and should
regain to its previous position when not in use.
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5.3 Robustness in its approaches
For the following section, the effectiveness of self-healing process is evaluated with
respect to the biological process. In the biological process, the bacteria are added and concrete
effectiveness is observed for several periods of time.
In terms of the criteria, in the mentioned process the expanded clay particles are used.
The spores developed after applying these can be uniformly distributed in the concrete matrix.
When discussing about the quality, the healing properties are excellent while mechanical
strength is considerably low. Regarding the aspects of reliability and versatility, no research has
been done. Further, sufficient data are not available regarding the aspect of Repeatability.
As per Sharma and et.al., (2017), the versatility and reliability were seen in the other
approaches of self-healing, it was lacking in the Biological process. Further, it was also found to
be less effective.
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CHAPTER 6-COST-BENEFIT ANALYSIS AND SUSTAINABILITY OF
SELF-HEALING CONCRETE
There is need of the maintenance, durability, and self-repair in the traditional concrete
which can otherwise adversely affect civil structures. Further, various civil structures are
required to be repaired after a specified time period. Considering these problems, self-healing
concrete provides a promising solution as it helps in increasing the durability and strength of the
structures. Though it has higher initial cost, but considering the long term stability and economic
utility, it is a more effective method. It brings reduction in the cost of maintenance and repair.
Khitab and et. al., (2016), identified that the cost for the maintenance and repair is huge and
time-consuming. As mentioned in the above study that the cost of the reconstructing and re-
development that are used in the other areas like the UK, US, and Asia comes to be over billions
and trillions of dollar. The cost of using self-healing concrete is much lower in comparison to it
(Han, and Xing, 2016). Along with this, the sustainability can be gained through the aspects
which are mentioned below: Safety: With the help of the self-healing concrete the general safety of the structure rises.
In addition to this, healing procedure helps concrete in gaining around 25% more
stability. Cost: Self-healing concrete helps in elimination of extra cost associated with the
maintenance of the structure (Abbas, Nehdi and Saleem, 2016). Further, the durability of
this type of concrete structure also makes it a cost-efficient option to prefer.
Figure 16: Comparison of cost
34

(Source: Li, C.V., 2012)
From the above figure, it can be stated that A is the normal expenditure that is incurred when
construction is to be done. On B is the bio cement, this shows the total cost initially is high.
However, in the long run, the cost reduces. It can be therefore said that when using self-
healing concrete, an initial outlay would be higher. However, in long run the expenditure
would reduce due to lower amount of maintenance cost. Durability: From the various researches that have been conducted on the durability of the
self-healing concrete, it was observed that bacteria assisted self-healing concrete is more
durable than concrete. Availability: Self-healing concrete lacks this aspect. Unlike regular concrete, it is less
available. The limitation of this section is the obstacles that are faced in its production
and a number of the constituents that are added in it.
 Effects on Architecture & Design: Whenever self-healing concrete is used in the civil
construction, engineers need to reconsider the design structure (Alghamri and et. al.,
2016). For any structure which is standing for the longer duration, architectures must
consider two main aspects in these:
(i) The expected purpose within a specific construction
(ii) The upcoming role of location encompassing a definite building.
Therefore, civil engineers and architectures have one more role that they must foresee the
future demands that are required by the construction and current requirements which are
necessary for that construction. Moreover, it must be more aesthetic and possess significantly
greater flexibility so that its functionality can be easily changed. Environmental impact: There was greater impact caused by the cement plants and when
the building is reconstructed. Further, there is more generation of the CO2 level due to
such construction. These were making more impact to the environment which can be
reduced by the application of self-healing concrete. Moreover, it reduces the resources
utilization and serves as environmentally friendly.
 Strength: When the strength is discussed related to traditional concrete, there is the rise
in its level. Further, it increases to more than 25% and duration for holding the structure
35

also increases. Moreover, the sustainability can be seen in this process as the concrete
based on the biological aspects as they are better and have the effective crack sealing
process (Nosouhian and Mostofinejad, 2016). They have the better approach to fulfil the
pores and the gaps which are generated through the cracks.
36

CHAPTER 7: DATA ANALYSIS
7.1 Introduction
After research methodologies, the next section of the research project is data analysis. It
is the process in which the accessed data is being investigated by together assessing the logical
reasoning in an effective manner. Along with this, it also evaluates the aims and objectives of the
study. This part of the chapter contains the details with whose assistance, relevant set of
information can be gathered as well as analysed for a refined interpretation at the end. After a
successful completion of this unit, another chapter of conclusion and recommendation is being
framed on the basis of the above carried discussion. The subdivisions in this study comprises
data analysis of the findings regarding 'Self-healing concrete and its application’. For whose
analysis, secondary method has been used over here for the generation of thematic outcomes.
7.2 Thematic analysis
Theme 1: Self-healing concrete help in recovering the cracks and maintaining the strength
level.
Findings: Being one of the most durable building material, self-healing concrete is
famously known for its several healing properties with a foremost role in improving cracks
in the buildings. This is basically to maintain the strengthening level of buildings.
Considering the same, self-healing concrete is itself known as a living concrete that tends to
repair the cracks themselves. It is on considering the secondary sources of data, one can
easily look into the healing properties of self-healing concrete where it is widely used in
construction work. Despite being a very old age theory used since Classical times of Roman,
it is more popular these days. It is however preferred to be the outcome of an intense
research carried out by a well-known microbiologist named Hendrik Jonker (Šavija and et.
al., 2016).
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Figure 17: Crack analysis
(Source: Zhu, Y., Zhang, Z, C., Yao, Y., Guan, X, M. and Yang, Y. Z., 2016)
It is mainly with reference to the most common concrete material that is largely used
for the purpose of construction all over the globe. However, it does not provide any
sustaining results and leads to crack and worsen at the end. It is therefore in order to find out
sustainable outcomes, a new generation of self-healing concrete has taken place where it
presented as a solution to such unsupportive consequences. This, in turn, reflected an
important agenda of resolving the aforesaid issue where there existed a prime requirement of
inventing such effective substance that in turn results in a better application of concrete.
This, in turn, resulted in an active existence of self-healing concrete made up by using
various bacterial contents in it. From the biological perspective, it is proven to be one of the
eco-friendliest approaches where self-concrete is essentially made up of an effective
material called bio-concrete.
38

Theme 2: Elements that can increase the mechanism of self-concrete and reduce its ill-
impact on humans.
Findings: It is mainly in context to an increased mechanism of self-concrete where it
is created using mineral producing bacteria that is in turn evident to assist in fixing the
minute cracks in the building. It is in accordance to the studies based on the secondary
sources of data where self-concrete formula is apparent to resolve the issues existing from
the corrosion of concrete structures that are supposed to sustain for a longer time period
(Karbhari and Seible, 2000). It is mainly with reference to a superior use of concrete in the
field of construction where deterioration of structures before their guaranteed service life is
proving to be an intense issue. This is also on considering the fact where concrete is
extensively used for the establishment of buildings to the structuring of underground parking
lots to the formation of bridges.
Figure 18: Use of Non-pathogenic bacteria in self-concrete
(Source: How does Bacterial Resistance happen? 2017)
It is therefore to maintain a sustainable position of these construction work; use of self-
concrete healing is known to play a major role. This is due to yet another considerate fact where
a minute ignorance can also lead to worsening the entire situation by directly affecting the lives
of many people. It is therefore important to such healing agent that in turn provides an assurance
of sustainability to a greater period of time. It is thus on comparing the traditional way of
construction where the concrete used in that process leads to crack when exposed to strain or
pressure. It is however on considering the fact related to the usage of self-concrete healing that is
also exposed to several numbers of ill impacts on the human.
It is the foremost concern of bearing the cost related to an effective use of self-concrete
healing. Herein, studies have revealed the reason behind an increasing cost of self-healing
39

concrete where it is basically due to a raised price of calcium lactate. Apart from this, the use of
bio concrete together has some leading ill effects on the physical and psychological well-being of
individuals. It is mainly in context of the use of various bacterial contents that could lead to the
release of ureases. This, in turn, can lead to the evolution of a disease called Proteus mirabilis.
Though, there exist some non-harmful microorganisms that can be used to reduce such ill impact
of bio concrete on humans (Pamulapati, and et. al., 2017). This involves the use of Bacillus
pasteurise as a proteolytic that is not harmful in comparison to the previously specified bacteria.
Being a non-pathogenic bacterium, it is widely used in the formation of self-healing concrete.
However, there still exists a matter of concern regarding its expensive price range that often
restricts the individuals to use it on an often basis. Instead, it is important for the construction
industry to take a serious consideration about its effective use for saving the future concern of
costs in repairing and restoration of bridges, buildings and parking lots, etc.
Theme 3: Possible threats from such methods to the civil structures and environment.
Findings: From the above carried analysis of the overall study, it has been found that
there exists certain negative outcomes of this entire procedure. 20% volume of the concrete
comprises of clay pellets that grasp the SH agent. This percentage indicates more
composition of the gravel. Hence, clay acts act as a weakening agent and reduces the
compressive strength of the concrete by 25% (Li, 2017). Though the compressive strength is
barely required for many structures at the time when there is some special application that
will in turn higher the risk. There is a problem related to the addition of the materials or
constituents in the self-healing concrete. It is where the use of any additive material should
be more specific or otherwise other problems can be generated. Moreover, such factors
cannot be ignored. As per the research of Henk M. Jonkers & Erik Schlangen, they have
carried out a study that was based upon the identification of the strength level.
Along with this, it has also been found that the cost of traditional concrete is just half of
the SHC. The current price of the self-healing concrete is up to €160 euros per cubic meter.
Despite of being more advantageous, people are preferring to use the most cost-effective
methods. Nevertheless, the areas where safety is majorly required, SHC is being used with a very
low percentage. For example, while constructing civil structures such as bridges, highways,
tunnel linings and marine structures, etc., it is mostly being used, as in these type of structures,
40

safety is a huge matter of concern. Moreover, these are the areas having limited access for
repairing and maintenance system. Adding self-healing concrete in such areas regardless of its
cost must be considered. Other than this, its specified cost can be reduced where this will require
large scale production.
Among the three aforesaid methods, it has been found that biological based self-healing
methods have very less ill-impact on the environment and humans. Using micro-organism can
help in preventing damage and is a pollution free approach (Khaliq and Ehsan, 2016). They are
having the greater life span of around 50 years and has the ability to themselves identify any
cracks or damages. Along with this, they can easily sustain in dry concrete for a longer time
period. When reconstruction of civil structure is taken into account, more release of CO2 has
been reported with more utilization of resources. This finding has led to further investigation to
find out a procedure to reduce its impact on humans and environment. Though the biological
process is found to be less strong but more versatile than the other two methods. There is another
important thing required to be taken into consideration for the biological process. This specifies
special climatic conditions for its survival that in turn impacts upon civil construction.
Theme 4: Effectiveness in using the self-healing concrete
Findings: This is from the carried analysis to determine the effectiveness of self-
healing concrete, it is known to have some greater advantages in comparison to the
traditional use of concrete. The effectiveness of this mechanism can be ensured through the
robustness of these procedures. Many researchers have approved greater advantages of self-
healing concrete for industrial applications. Here, this discussion has mainly concentrated on
self-healing process through biological method. The criteria used was by means of the
methods in internally expanded clay particles. They have an estimated life expectancy of 6
months and can be uniformly distributed on the surface. Its reliability is still to be studied by
the scientists. However, the use of different types of bacteria's can help the structure to
survive in different environmental conditions. By this, an increased strength with an
increased level of transportation has been found.
41

Figure 19: Self-healing admixture
(Source: Jonkers, 2012)
This examination was held in different conditions such as in application areas where
environment, place and effectiveness was evaluated. As mentioned, several positive outcomes
have been gathered by the researchers. Along with this, findings gathered by considering the
studied articles related to the use of self-healing concrete in UK, Scotland, and Ecuador, it was
found that these methods have provided greater advantages. The cost that is required to be spend
for the purpose of repair, maintenance and reconstruction can also be saved by together using it
in other areas as well. Further, the amount that was saved accounted more than 100 Billion
dollars. However, as per the findings, the initial cost of the concrete was found to be double than
the traditional. Though on considering the requirement of sustainability, use of self-healing
concrete is referred to be one of the best methods by agreeing to long term investment. The test
results from the study conducted by Bhattacharyya, Pelletier and Bose has shown increment in
strength and other affirmative features in the use of self-healing concrete. However, it together
indicated some concerning factors such as the environmental conditions of those areas where the
solution has been applied. Temperature, thickness, pH level and crack size are the main aspects
that are needed to be focused while the application of this solution onto the considered areas.
As per this research, in the past 10 years, several improvements have been seen in the use
of self-healing concrete. Earlier, this type of concrete was used in small structures with defined
cracks, shapes and sizes. This necessitated the investigation of its efficiency which is done after
the exposure of capsules. Whenever any such crack occurs, the casting process begins with the
help of those capsules. Non-destructive testing can also be done by using acoustic emission
analysis or X-ray radiography. They are used to find out the survivability of the capsules when
they are mixed up in the concrete. These methods are also used to know about the braking ability
42

of the capsules whenever the crack is formed. Herein, the evaluation was done by performing a
water permeability test. On whose basis, it has been found that as soon as the crack occurs, the
capsules gets activated. They start expanding and replacing other particles with the help of
bacteria to further heal the crack. Such type of techniques in turn enabled to identify the
effectiveness of self-healing concrete.
Theme 5: Cost-effectiveness and sustainability can be maintained in such process.
Findings: The factors that highly contributes in the reliance of self-healing concrete
are its cost-effectiveness and sustainability. It has been evaluated from the secondary data
collection that irrespective of its high production cost, the use of SHC in infrastructure is
highly recommended. It is because of its self-healing properties which helps in diminishing
the extra charges associated with the maintenance of structures. The investigation conducted
to assess the strength of infrastructure prepared from self-healing concrete was found to be
sustainable and has revealed the durability of the material used for its construction. The
deterioration of traditional concrete structures causes economic consequences such as
maintenance where more damage directly leads to reconstruction. In contrary to which, the
auto-healing capability of SHC is apparent to give several economic advantages.
Besides this, on scrutinizing the constituents of SHC such as bacteria assists in obtaining
positive outcomes which reflect the advantages of using self-healing concrete over traditional
concrete. It is thus on analysing this fact based on the secondary sources of data, it has been
found that SHC is much cost-effective in nature and is a sustainable element which is more
beneficial in comparison to normal concrete. In addition to its cost-effective nature, this research
also helped in analyzing the sustainability of SHC in different context. Contradictory to which,
using SHC in construction can significantly reduce several environmental impacts leading to
negative outcomes. The use of ordinary concrete releases CO2 which becomes hazardous by
together resulting in global warming. However, the auto-healing property of SHC makes it a
"smart material" and using SHC in the construction of infrastructure possesses an assured quality
of durability where there will be less emission of CO2 and hence, less damage to the environment
will occur.
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In contrary to the above stated facts, the investigation on the self-healing concrete has
revealed several problems of availability that directly impacts upon its use. As a result, to which,
it is not being used to a great extent. Also, on relating to this finding with that to the secondary
source of information, it has been observed that the production cost of SHC is comparatively
higher that in turn impacts upon its productivity. This generated a contradictory result where less
availability and high cost of production are the two major point of consideration. In addition to
this, there together exists such environmental factors that restricts the growth of bacteria and
results in the failure of structures formed with the use of SHC. However, the success factor of
this material lies in its numerous qualities that are being accessed while the construction of
structures with the use of SHC.
Theme 6: Verification of SH ability on fabricated SHC.
Findings: Self-healing is the term used in the construction industry which is related
to the concrete source for constructing buildings. Under this, several kind of methods are
included where the present study is based on its biological procedure. In the current theme,
experimental method is referred to be highly supportive for fabricating self-healing concrete.
It is one of the significant methods through which, self-healing process can be taken into
proper direction. With the help of biological process, the engineers become more capable in
using self-healing concrete for the purpose of constructing buildings. Those engineers who
are working in the construction industry are trying to utilize bio-mimicry that includes
various related mechanisms. Along with this, they are also able to develop bio-based
concrete with the help of selected self-healing process. It is one of the highly effective
methods that support the contractors for completing the method of an eco- friendly self-
healing.
Theme 7: Potential usage of the biological self-healing concrete.
Findings: It is on the basis of the carried secondary analysis, several number of
advantages has been found from the use of biological method of self-healing concrete rather
than choosing the intrinsic chemical methods. It is from the information that has been
gathered from secondary sources, it can be said that biological SHC are much more effective
to a greater extent (Tittelboom and Belie, 2013). It has been scrutinized that there exists
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some adverse effect on the environment from the use of chemical methods. In contrary to
which, the biological processes are degradable in nature and does not cause any harm to the
ecosystem that reveals environmental sustainability from the use of biological self-healing
concrete. Further, the structures formed by the use of chemical substances have become the
victim of chemicals due to the reaction that directly impacts upon its strength in a negative
manner.
The secondary data has proven a fact where biological concrete mix validates flexural
and compressive strength. In addition to this, it has together been found that some studies have
claimed that polymers are better than bacterial concrete that necessitated further examination.
This in turn have explained that these polymers release some liquid monomers that decreases the
shelf life of such type of concrete.
Figure 20: Permeability of cracked specimens
(Source: Jonkers, 2012)
It is on considering the above illustrated diagram that has represented the permeability of
cracked specimen after four weeks of immersion in tap water at room temperature. After which,
45

2 specimens out of all 6 control specimens have appeared to be sealed entirely. With the help of
the secondary sources, it has together been evaluated that biological self-healing concrete is more
durable in nature and provides more strength to the infrastructure. It is due to its inactive nature
and capsule diffusion which leads to zero possibility of chemical change and assures no
deterioration of the construction (Jonkers, 2012). By making an examination on the permeability
of conventional and biological concrete, it has been analyzed that the structure which has
bacteria based concrete have low permeability which makes it more durable than the formulaic
concrete infrastructures. This type of concrete mix is potentially used due to its high level of
resistance towards the freeze-thaw attacks that in turn reduces the chance of corrosion in
reinforcement.
It has been examined from the secondary sources that excessive use of concrete structures
should be limited to some extent where there exist some adverse effects of these bacteria used in
such infrastructures on human health and atmosphere. This is on analysing the data that has been
collected from alternative sources, it has been found that the use of such reinforcement should be
prevented in health care homes and schools. Such factor results in comparatively higher rates of
this concrete which cannot be afforded by everyone and is also limited to its use. Some other
factor that limits its use is weather and opposing environmental conditions where bacteria are
living organism and their sprouting are not suitable in some conditions. Despite of this fact,
biological SHC is significant in context to the field of construction at several places that do not
involves any suspected areas.
Theme 8: Major difference between the self-healing concrete and traditional concrete.
Findings: It is on the basis of secondary sources, it has been assessed that traditional
concrete lacks in pursuing environmental sustainability. This is mainly due to the particles
that are being released by it and involves CO2 that in turn creates some hazardous issues like
greenhouse effect and global warming, etc. In contrary to this, it has been examined that
SHC uses biological constituents for healing and thus, it does not lead to any bad impact
upon the environment by emitting CO2. Further, the inactive nature of biological concrete
structure possesses no or less deterioration as compared to the structures made up from the
use of traditional concrete which is highly reactive. Herein, the diffusion of bacteria in the
form of capsules leads to an upright strengthening (Herbert and Li, 2013).
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This is on considering the information gathered from secondary sources, it has been
found that one of the biggest advantage of using SHC over the conventional concrete
measures is its cost-effectiveness. The permeability segment of the concrete has together
been analysed where SHC is found to be less permeable. It is mainly due to its material that
restricts the entry of any foreign substances that in turn increases its strength by together
enhancing the durability of the structures made up from its use. Whereas, the traditional
concrete is found to be more permeable in nature and thus there are high chances of
corrosion based on the reinforcement of this mix. In chemical SHC, the capsules containing
the calcium mix fill in the cracks that occurs due to excessive pressure of water, unlike
tradition concrete structures that cannot withstand in such situation. Thus, SHC is a
revolutionary tool that can be used in the construction of dams, bridges and boat hulls, etc.
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CHAPTER – 8 CONCLUSION AND RECOMMENDATION
8.1 Conclusion
There is wide application of SHC in the civil structure and in development of the
traditional concrete buildings. It has been carried out in more effective and efficacious ways so
that recommendation can be made on the study. The researcher has made use of qualitative
survey that is focused on self-healing approaches. More specifically, it includes their robustness
and applications and also considering the cost effectiveness of the technology.
8.1.1 Achievement of Aims
The study is carried out within the field of civil engineering in which self-healing is
considered. There are various other aspects that are focused which includes chemical based,
biological based and examined intrinsic for self-healing methods. There are two different type of
case studies on which the research is focused on. These are on Lifeguard Station in Netherlands
and Cruzsacha Canal in Ecuador. These cases were selected as these were built by making use of
the self-healing concrete in successful manner. Apart from this, the aim of the research topic is
divided into four different objectives that are focused on. Each of the objectives are covered and
they are as follows:
Objective: 1 To study the importance of self-healing concrete.
From the above study, it can be concluded that self-healing concrete has changed the
ways civil construction were made. There are greater scope through this application and to other
industries. It has been inferred that it saves a lot of money that is being invested in repair and
maintenance. Further, conditions were cracks orlarge gaps are found, generally people use to
reconstruct them and this incurs high cost. This cost is easily reduced as the cost for repair or
maintenance is eliminated. . Every year, UK, US, and many other countries spend more than 100
billion dollars for reconstruction, repair and maintenance. When self-healing was applied in,
Ecuador, Scotland, and UK, effective outcomes were identified. The data gathered from
secondary information, it has been accessed that there are increase in strength, flexibility and
time durability of the concrete. Other than this, it has been seen that they can identify the cracks
themselves, repair them and come back to its original position. All this task are completed own
their own without the involvement of the humans. Biocement for self-healing is added at the time
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when concrete is formed and this way, it enables to raise the durability of the concrete. It has
been determined that the application of the self-healing has proved to be advantageous for the
people that have applied it in practice.
Objective: 2 To understand the mechanism and application of self-healing concrete.
From the present report, the mechanism and application of self-healing concrete has been
effectively evaluated, here details about the biological process, chemical, intrinsic methods have
been mentioned. It can be evaluated that in the process of self-healing, bacterias are used which
are helpful in producing limestone to fill up the gapes or cracks and this can be compared to skin.
The process is faster and affected areas can be healed within few weeks’ time. In this process,
one of the main challenges is that it requires high initial cost and specific standards of elements
need to be added. The mechanisms that are available in the current studies are mentioned but it is
also minimum as there are further study and researchers to be organized in the process.
Objective: 3 To analyze the applications of self-healing concrete in future of civil
engineering.
From the application areas, it can be concluded that people will get highly benefited
through this application. Generally, people prefer to make use of traditional concrete as it is less
expensive. The government of Scotland and UK have recognized the advantages of the self-
healing concrete. Further, there are more advantages compared to the disadvantage of the self-
healing concrete. People in different countries have started using it and are getting themselves
protected from the repair and maintenance cost. This shows that there are vast scope of self-
healing concrete in the future of civil engineering.
Objective: 4 To recommend ways by which these methods can become cost-effective and
sustainable in future
It has been explored from the study that stated methods are highly cost-effective and
sustainable in the present conditions. There will be more scope in the future for the same. As per
the research, new ways and elements are found by the scientists so that data improvement and
advancement both can be implemented in the study. Moreover, it has been concluded that if the
price of the concrete is less, then it will be more utilized and preferred. Further, if the bacteria
have increased the process, then it will also hike up and it’s efficiency will also be boosted. Life
49

expansion of the concrete can be seen and they the ways it recover themselves makes them more
sustainable for the future application.
8.2 Recommendations
There are several recommendations that can be made on the self-healing concrete, its
cost-effectiveness, and sustainability. The effectiveness of the process can be increased in more
significant manner. It can be suggested from the aim that civil constructions require these types
of technologies so that they can reduce the extra cost that are adding in the repair and
maintenance of the buildings. Moreover, in the countries like the UK, US and part of Asia where
the people are considering the reconstruction are benefited when they implement self-healing
concrete. This can be done through popularizing the details regarding the benefits which are
gained by applying or using the self-healing concrete.
Further, it required to make use of multidisciplinary research in comparing economists,
biologists, structural engineers and material researchers in order to produce more holistic and
robust results. Contract should be made with the suppliers of concrete, engineering firms,
contractors and research institutions so that they contribute in the future research.
When construction process of new building are made, then there CO2 is released in the
environment which causes harm to humans and nature. These can be stopped through the
application of the self-healing concrete. As the cost of the product is more so government must
support and should promote the use of such technologies.
It is suggested that in order to improve the effectiveness and to reduce the cost, other
similar elements can be used in the process. Further, the technology development in these areas
of the research where main focus must be made on the application areas, climatic conditions, and
constituents. If cost and its application areas are identified then more people will adopt this
technology for their civil construction.
50

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