A short description of Self Healing Concrete and its Mechanisms.

1. By
Shubham Arora

2. Introduction
 Self-healing concrete is an artificial or synthetically-
created substance that has the built-in ability to
automatically repair the damage to itself without any
external diagnosis or human intervention.
 The invention comes in three forms:
 a spray that can be applied to existing construction for
small cracks that need repairing,
 a repair mortar for structural repair of large damage and
 self-healing concrete itself, which can be mixed in
quantities as needed.

3. Why Needed?
 Crack formation in concrete structures is inevitable
due to deterioration throughout its service life due to
various load and non-load factors. Therefore, repair
and maintenance operations are needed to prevent
cracks from propagating and decrease the structures’
service life.
 Accessibility to cracked zone may be difficult and one
may need to re-build things.
 It is an eco-friendly technique which can be used to
save metals also from deteriorating.

4. Mechanism
 Even after complete hydration, 20%-30% of cement
remains un-hydrated and can be used by healing agents as
its food.
 The cracks provide a pathway and space for healing
materials, moisture, chlorides, etc. to react and form a
stabilized end product.
 There are mainly 2 ways in which self healing is possible-
 The crack openings let oxygen penetrate inside concrete and
bacteria along cracked surfaces convert calcium lactate into calcium
carbonate and carbon dioxide. The bacteria may be added directly
or encapsulated.
 The second method of making the self healing concrete is a
chemical method .The healing chemicals are inserted in the capsule
which breaks when cracks occurs and hence re-joins the micro
cracks.

5. Literature Review
S. No Title Publisher Year Author Results/Findings
1. Autonomous
healing in
concrete by
bio-based
healing agents
– A review
Construction
and Building
Materials 146
(2017) 419–428
2014 Gupta
Souradeep
Pang
Sze Dai ,
Kua Harn
Wei a
1. The initial cost of
incorporating
bacteria is quite high.
2. If infrastructures are
built with self-healing
concrete that is
designed to function
under multiple
damages, very
minimal cost may be
accumulated over the
lifetime.

6. Literature Review
S. No Title Publisher Year Author Results/Findings
2. Self Healing
Concrete
International
journal of
Recent
Scientific
Research.
2015 Rishabh
Lala,
Aslam
Hussain,
Salim
Akhtar
1. While most healing
agents are chemically
based, more recently the
possible application of
bacteria as self-healing
agent has also been
considered.
2. Metabolically active
bacteria consume oxygen;
the healing agent may act
as an oxygen diffusion
barrier protecting the
steel reinforcement
against corrosion.

7. Literature Review
S. No Title Publisher Year Author Results/Findings
3. Key roles of
pH and
calcium
metabolism
in
microbial
carbonate
precipitation.
Rev. Environ.
Sci. Biotechnol
1 (1) (2002) 3–
7.
2002 F.
Hammes,
W.
Verstraete.
1. The precipitation of calcium
carbonate in natural environment
is ideally influenced by
concentration of calcium ions,
pH of the solution, concentration
of dissolved inorganic carbon and
availability of nucleation sites.
2. The self-healing by bacteria
may be accomplished by any of
these mechanisms but the
efficiency of healing in
concrete would depend on a
number of other factors
availability of moisture, crack
area or width to be healed, age of
concrete and survival of bacteria
in long term.

8. Literature Review
S.No. Title Publisher Year Author Results/Findings
4. Factors
affecting
crack
repairing
capacity of
bacteria-
based self-
healing
concrete.
Construction
Building
Material 87
(2015) 1–7.
2014 M. Luo,
C.x. Qian,
R.-y. Li,
1. It was observed that under
immersion in water condition
crack width up to 0.3 mm were
completely healed and healing
ratio of cracks between 0.1 and
0.3 mm were about 85%.
2. Water curing and wet-dry
cycles showed best healing
performance although the repair
rate was slower for wet-dry cycle
condition.
3. Better healing in terms of
recovery of flexural strength
was obtained in samples
containing calcium glutamate.
Crack widths varied from 0.1 to
0.4 mm and were partially sealed
by mineral precipitates which are
formed by bacterial metabolism.
4. Specimens with bacterial
spores displayed superior healing
to control samples but its
effectiveness was less than that of
external healing.

9. Literature Review
S. No Title Publisher Year Author Results/Findings
5. Use of silica
gel or
polyurethane
immobilized
bacteria for
self-healing
concrete.
Construction
Building
Materials
26 (1) (2012)
532–540.
2012 J. Wang, K.
Van
Tittelboom
N. De
Belie, W.
Verstraete
1. Reduction in water
permeability may be
significantly influenced
by capsule material or
immobilization medium
used.
2. In case of
immobilization by silica
gel, reduction of
permeability by two
orders of magnitude was
observed.
3.Bacterial activity
was higher in silica gel
and therefore precipitate
formed blocked the pores
and reduced permeability.

10. Mechanism 1- Chemical Method
 Two substances methacryloxypropyle terminated
polydimethylsiloxane and benzoyl isobutyl-ether are mixed
in the presence of sunlight, they transform into water-
proof polymer that sticks to concrete.
 Now this balm is put inside tiny capsules made of Urea and
formaldehyde, which keeps the chemical mixture isolated
from sunlight.
 When due to external conditions the cracks occur, the
capsule breaks and the balm comes out.
 The mixture is mixed with liquid polymer and sprayed the
mixture on to some concrete blocks and allowed the
resulting film to solidify.

11. Chemical Method
 The cracks in the concrete propagated into the
polymer film containing the capsules, and cracked
some of the capsules open too, releasing their
contents.
 These then set, on exposure to the sun, into a
waterproof layer after 24 hours immersion in water,
the blocks are weighted, to see how much water they
had soaked up.

12. Mechanism 2- Biological Method
 The bacteria are added to the concrete mixture as spores.
Spores are inactive cells with a high survival rate. They are
proof against unfavourable circumstances like temperature
fluctuation and moisture.
 The spores become active when getting into contact with
water. When the alkali‐bacteria grow active, they can make
limestone out of calcium lactate ( a form of limestone).
 Limestone will fill the cracks and there is no possibility for
water to leak into the concrete anymore.
 These bacteria are able to heal cracks of a width of 0.80
mm within circa 100 days. After filling the cracks, the
circumstances turns unfavourable again so the bacteria will
form spores again.

13. Reactions Involved
• Ca(C3H5O2)2 + 7O2  CaCO3 + 5CO2 + 5H2O
Calcium Lacate + Oxygen  Calcium Carbonate +Water
• 5CO2 + 5Ca(OH)2  5 CaCO3 + 5H2O

14. Types of Bacteria available
 There are certain bacteria can utilize urea present in the
material by the production of enzyme urease. This enzyme
hydrolysis urea to ammonia and carbon dioxide. Ammonia
increases the pH of the surrounding and carbon dioxide
combines with calcium ions resulting in formation of
calcite( a form of CaCo3). Broadly, they can be-
 Bacillus,
 Klebsiella,
 Psychrophilic bacterium,
 Staphylococcus and
 Proteus.

15. Types of Bacillus Bacteria
 Bacillus alkalinitrulicus
 Bacillus pasterurii
 Bacillus sphaericus
 Bacillus subtilis
 Bacillus cohnii
 Bacillus balodurans
 Bacillus pseudofirmus
 Escherichia coli

16. Cost Comparison
S.No. Things
Required
Quantity Cost/Unit Concrete
(M20)
SH-Concrete
(M20)
1. Cement Bag 8 400/- 3200/- 3200/-
2. Self Healing
Agent
5 500/- ---------- 2500/-
3. Grit & Sand ---------- 1500/- 1500/- 1500/-
Total 4700/- 7200/-

17. Advantages of SHC
 The Self Healing Concrete has comparatively very less
permeability, more durability and strain bearing capacity than
the conventional concrete.
 This can be applied to existing buildings in the form of spray
which can reduce the overall repair and maintenance cost of
buildings.
 It is an eco-friendly technique as the carbon dioxide produced is
curbed due to reduced use of concrete.
 SHC is more effective shock absorbent making it safer during
earthquakes because of the polymer membrane on its surface.
 It can work at internal levels which means smallest of cracks can
be reached.
 Un-hydrated Cement which does not contribute to the strength
involvement can be used.

18. Disadvantages of SHC
 A potential drawback of this reaction mechanism is
that for each carbonate ion two Ammonium ions are
simultaneously produced which may result in
excessive environmental nitrogen loading.
 The matrix of concrete changes and reduces the
amount of mixture which reduces the strength of
concrete.
 Skilled Labour is required for the usage of this
concrete as it is costly.
 Strength increase is quite slow process.
 Bacterial use, for now is costly.

19. Applications of SHC
 It can be actively used in case of roads to mitigate the
traffic jams.
 It can be used by oil and gas industries, which can stop
small cracks frim becoming spillways.
 It can be used to strengthen any kind of Structural
building, both existing and new.
 It can be effective in the regions where buildings
undergo freezing and thawing frequently.
 It can prove to be economical in case of irrigation
works, dams etc. which are directly in contact with
water.

20. Viability & Feasibility
 This technique has proved to be better because of its
increased durability and eco-friendly nature.
 There has been large amount of reduction in permeability
of concrete, hence improving the life of structure.
 This has opened a new dimension of research, calling the
focus on application of bio-technology in the field of
building materials.
 The cost of applying the bacteria and other types of
bacteria need more consideration for finding out viable
type of concrete, both technically and economically.