BACTERIAL CONCRETE - A SOLUTION TO CRACK FORMATION

International Journal of Innovative Research in Advanced Engineering (IJIRAE) ISSN: 2349-2163
Issue 10, Volume 4 (October 2017) www.ijirae.com
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IJIRAE: Impact Factor Value – SJIF: Innospace, Morocco (2016): 3.916 | PIF: 2.469 | Jour Info: 4.085 |
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IJIRAE © 2014- 17, All Rights Reserved Page –1
BACTERIAL CONCRETE - A SOLUTION TO CRACK
FORMATION
Gaurav Agarwal, Rahul Kadam
Civil, Mumbai University, INDIA
Manuscript History
Number: IJIRAE/RS/Vol.04/Issue10/OCAE10080
DOI: 10.26562/IJIRAE.2017.OCAE10080
Received: 22, September 2017
Final Correction: 30, September 2017
Final Accepted: 05, October 2017
Published: October 2017
Editor: Dr.A.Arul L.S, Chief Editor, IJIRAE, AM Publications, India
Copyright: ©2017 This is an open access article distributed under the terms of the Creative Commons Attribution
License, Which Permits unrestricted use, distribution, and reproduction in any medium, provided the original author
and source are credited.
Abstract—Concrete is a homogenous mixture and cracks in concrete are inevitable so there is a need for repair
which affects the economic life of any structure. To overcome this problem an inherent biomaterial is developed, a
self-repairing material which can remediate the cracks in concrete. Bacterial concrete is a technique which is
highly desirable because the calcium precipitation is induced as a result of microbial activities. This helps in
increasing the strength and durability of concrete. As per the results, it is clearly observed that there is increase in
compressive strength, tensile strength and durability in bacterial concrete as compared with normal concrete. This
is the main objective of the bacterial concrete for which it was introduced. Various tests which are carried out to
study these properties of concrete are compressive strength test, Split tensile test. Scanning Electron Microscope
(S.E.M) is used to study the growth of bacteria in the concrete. It is observed that for bacterial proportion 105 cells
(24 ml of bacteria in 1000ml), there is significant increase in compressive strength of the bacterial concrete i.e.
around 25% increase in strength as compared with normal concrete. For this purpose bacteria used is Bacillus
Subtilis.
Keywords—Introduction, Mechanism of self-healing using bacteria, Working Principle, Test results, Conclusion,
References
I. INTRODUCTION
We can also define bacterial concrete as self-healing concrete. Now, as the name suggests a self-healing concrete is
one that can sense its crack formation and can react to cure itself without any kind of human intervention. It is a type
of concrete that can biologically produce calcium precipitate (limestone) to heal the cracks that appear on the surface
of any concrete structure. The process of self-healing can be carried out by adding specially selected types of bacteria
which are added to the ingredients of the concrete when it is being mixed. Bacillus Sphaericus is a type of soil
bacterium which can continuously precipitate a new highly impermeable calcite layer over the surface of an already
existing concrete layer. Underfavorable conditions Bacillus Pasteurii when used in concrete can continuously
precipitate a new highly impermeable calcite layer over the surface of the already existing concrete layer. Calcite has
a coarse crystalline structure that readily adheres to surfaces in the form of scales. In addition to the ability to
continuously grow upon itself it is highly insoluble in water. Cracks in concrete significantly influence the durability
characteristics of the structure. The bacterial remediation technique can be used for repairing structures of historical
importance to preserve the aesthetics value, as conventional technique, such as epoxy injection cannot be used to
remediate cracks in those structures The favorable conditions do not directly exist in a concrete but have to be
created.

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Tests are conducted to study the mechanical properties of the above concrete with various percentages of Bacteria.
The tests carried out are Compressive strength test, Split Tensile strength test, Flexural test, two point load test,
Soundness Test, Ductility test etc.
II. MECHANISM OF SELF-HEALING USING BACTERIA
The main mechanism for bacterial healing is that it should transform the soluble organic matter or nutrients into
insoluble inorganic matter, which further seals the cracks. Both bacteria and nutrients should work together for
better and effective results. Various bacteria survive in high pH conditions. If we mix the bacteria directly into the
concrete, two main problems occurs, first is the continuous cement hydration, which further results in the reduction
of cement sand matrix pore diameter. Secondly, insufficient amount of nutrients to precipitate calcite crystals. Both
bacteria and nutrients should not disturb the integrity or working of the concrete. Further it should not reverse the
working of fresh and hardened concrete.
III. VARIOUS TYPES OF BACTERIA USED IN CONCRETE
There are various types of bacteria which were used in construction area, from literature review it is as shown in
Fig.1
Figure 1
IV. WORKING PRINCIPLE OF SELF-HEALING CONCRETE
The cracks up to size 0.2 mm occurring in concrete are healed autogenously. These cracks are acceptable as they do
not hamper the strength and durability of the concrete. Research has shown that autogenously, healing happens due
to hydration of non-reacted cement particles present in the concrete matrix when comes in contact with ingress
water resulting in closure of micro cracks. Still, due to the variability of crack healing the possibility of micro cracks
occurrence is higher. In spite of all the possibility the inbuilt bacteria based self-healing process was found to heal
cracks up to 0.5 mm width. On the surface of control concrete, calcium carbonate will be formed due to the reaction
of CO2 present with calcium hydroxide present in the concrete matrix according to the following reaction:
CO2 + Ca(OH)2 CaCO3 + H2O.
The calcium carbonate production in this case is due to limited amount of CO2 present. As Ca(OH)2 is a soluble
mineral it gets easily dissolved in water and diffuses out of the crack in form of leaching. The self-healing process in
bacteria incorporated concrete is much more efficient due to the active metabolic conversion of calcium nutrients by
the bacteria present in concrete:
Ca(C3H5O2)2 + 7O2 CaCO3 + 5CO2 + 5H2O.
In the above process calcium carbonate is not produced directly due to microbial process but also indirectly due to
autogenously healing process. This result into efficient crack sealing technique which is bio based. Now, an ureolytic
bacterium such as Bacteria Subtilis JC3 is able to precipitate CaCO3 in a high alkaline environment by converting urea
into ammonium & carbonate. The ammonia degradation of urea locally increases the pH and promotes the microbial
deposition of carbonate as calcite crystals in a calcium rich environment along with maintaining the pH of concrete.
These precipitated crystals can thus seal the cracks. The enhancement of strength and durability properties of
concrete due to bacteria induction is studied in this research by conducting water permeability tests, ultrasound
transmission measurements and visual examination. The microbial precipitation of calcite crystals is determined by
factors such as the pH of the environment, availability of calcium ions and the presence of nucleation sites,
concentration of dissolved inorganic carbon in the form of available nutrients.

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The first three factors are based on the metabolic process of the bacteria species added while the last factor is based
on the cell membrane of the bacteria. The bacteria’s which are used for the study exhibits which catalyzes the
hydrolysis of urea (CO(NH2)2) into ammonium (NH4+) and carbonate (CO3). Firstly, urea is hydrolyzed to carbonate
and ammonia. Carbonate then hydrolyses to form additional carbonic acid and ammonia. These products
subsequently form bicarbonate and ammonium and hydroxide ions. The ammonia is responsible for pH increase,
which in turn shifts the bicarbonate equilibrium, resulting in the formation of calcium carbonate ions. Since, the cell
membrane of the bacteria is negatively charged, the bacteria draw cations from the environment including, Ca2+ to
deposit on their cell surface. The Ca2+ ions subsequently react with the CO3
2− ions, leading to the precipitation of
CaCO3 at the cell surface that serves as a nucleation site.
Ca2
+ + Cell Cell- Ca2+ Cell- Ca2
+ + CO3
2-Cell- CaCO3
V. CHARACTERISTICS OF BACTERIA’S
The bacteria which are to be used should have following characteristics:
1. Bacteria should react only when aerobic conditions prevail.(Since these bacteria only react in presence of O2,
otherwise anaerobic bacteria, if used would start reacting in absence of O2).
2. Bacteria should form spores.(For reproductive purposes. Because these spores formation, bacteria can
remain dormant in place for almost 100 years).
3. They should not evolve hydrogen sulphide (H2S) gas.(Because such gas can corrode reinforcement inside)
4. They should not evolve carbon-dioxide (CO2) gas.
5. They should form calcite precipitate after reacting with water.
Various tests are carried out to find the characteristics of bacteria. Some of them are Indole production, Methyl red
test, Vogesproskauer test, Starch hydrolysis, Lipid hydrolysis etc. (1)(3)(4)
VI. TESTS TO BE CARRIED OUT
A. Tests to be carried out on uncracked cubes
a) Compressive Strength of Concrete:
b) Flexural Strength of Concrete:
c) Split Tensile Test.
B. Sustainability tests (tests to be carried out on cracked cubes)
a) Scanning Electron Microscope [S.E.M]:
The scanning electron microscope (SEM) uses a focused beam of high-energy electrons to generate a variety of
signals at the surface of solid specimens.
Figure 2 shows the compressive testing machine.
Figure 3 shows Flexural Strength Test Arrangement
The signals that derive from electron-sample interactions reveal information about the sample including external
morphology (texture), chemical composition, and crystalline structure and orientation of materials making up the
sample.

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In most applications, data are collected over a selected area of the surface of the sample, and a 2-dimensional image is
generated that displays spatial variations in these properties. Areas ranging from approximately 1 cm to 5 microns in
width can be imaged in a scanning mode using conventional SEM techniques (magnification ranging from 20X to
approximately 30,000X, spatial resolution of 50 to 100 nm). The SEM is also capable of performing analyses of
selected point locations on the sample; this approach is especially useful in qualitatively or semi-quantitatively
determining chemical compositions (using EDS), crystalline structure, and crystal orientations (using EBSD). The
design and function of the SEM is very similar to the EPMA and considerable overlap in capabilities exists between
the two instruments.
Working of SEM:
The SEM is an instrument that produces a largely magnified image by using electrons instead of light to form an
image. A beam of electrons is produced at the top of the microscope by an electron gun. The electron beam follows a
vertical path through the microscope, which is held within a vacuum. The beam travels through electromagnetic
fields and lenses, which focus the beam down toward the sample. Once the beam hits the sample, electrons and X-
rays are ejected from the sample. Detectors collect these X-rays, backscattered electrons, and secondary electrons
and convert them into a signal that is sent to a screen similar to a television screen. This produces the final image.
Figure 4 shows working of SEM Figure 5 shows the electron rays from the SEM
Preparation of sample:
Because the SEM utilizes vacuum conditions and uses electrons to form an image, special preparations must be done
to the sample.
Figure 6 shows the arrangement of SEM.

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All water must be removed from the samples because the water would vaporize in the vacuum. All metals are
conductive and require no preparation before being used. All non-metals need to be made conductive by covering the
sample with a thin layer of conductive material. This is done by using a device called a "sputter coater."The sputter
coater uses an electric field and argon gas. The sample is placed in a small chamber that is at a vacuum. Argon gas and
an electric field cause an electron to be removed from the argon, making the atoms positively charged. The argon ions
then become attracted to a negatively charged gold foil. The argon ions knock gold atoms from the surface of the gold
foil. These gold atoms fall and settle onto the surface of the sample producing a thin gold coating.
VII. TESTS RESULTS
COMPARISON OF COMPRESSIVE STRENGTH BETWEEN NORMAL CONCRETE AND BACTERIAL CONCRETE
Days Normal Concrete Bacterial Concrete % Increased
7 20.63 25.55 23.85
28 25.92 30.54 17.82
56 37.94 44.23 16.57
Average Percentage increase in Compressive strength of bacterial concrete in comparison with normal concrete is
19.41%.
COMPARISON OF FLEXURAL STRENGTH TEST BETWEEN NORMAL CONCRETE AND BACTERIAL CONCRETE
Days Normal Concrete Bacterial Concrete % Increased
28 2.10 2.48 18.09
56 2.46 3.10 26.06
Average Percentage increase in Flexural strength of bacterial concrete in comparison with normal concrete is 22.07
%.
SCANNING ELECTRON MICROSCOPE (S.E.M)
Results from S.E.M:-
VIII. CONCLUSION
 Bacterial Concrete also known as microbial concrete technology has proved to be better than many
conventional technologies because of its eco- friendly nature, self-healing abilities and increase in
durability of various building materials.

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 Average Percentage increase in Compressive strength of bacterial concrete in comparison with normal
concrete is 19.41%.
 Average Percentage increase in Flexural strength of bacterial concrete in comparison with normal
concrete is 22.07 %.
 Work of various researchers has improved our understanding on the possibilities and limitations of
biotechnological applications such as bacteria on building material.
 Enhancement of compressive strength, reduction in permeability, water absorption, are some of the high
points of Bacterial Concrete.
 This will soon provide the basis for high quality structures that will be cost effective and environmentally
safe.
 Due to bacterial activity a calcium precipitate layer is deposited on the crack surface, sealing and blocking
entrance to deteriorating substance.
 Bacterial spores and a suitable organic bio chemical precursor compound using porous expanded clay
particles as a reservoir is a promising bio-based and thus sustainable alternative to strictly chemical or
cement based healing agents.
 It is observed that for bacterial proportion 105 cells (24 ml of bacteria in 1000ml) gives optimum results.
 Bacteria can live in concrete for over 100 years in form of spores.
REFERENCE
1. ‘Performance of standard grade bacteria (Bacillus subtillis) Concrete’-Asian journal of civil engineering 43-
55.
2. ‘Study of the effect of bacteria on cement composites’:- Kashyap, Vijeth N and Radhakrishnan Bangalore:
International journal of research in Engineering & Technology, Nov 2013.
3. ‘Bacterial based self-healing concrete’- Jonkers, Henk M and Mors, Renee M. Netherland: Delft University.
4. ‘Bio-engineered concrete-A sustainable self-healing construction material’-Rao, Seshagiri M and Reddy,
Shrinivasa V, Hyderabad: Research journal of engineering science, 2013.
5. ‘Bioremediation of concrete’- Parnnika, HimthaniHarshal, Das Amruta, Thailand: International Conference
on Emerging Trends in engineering and technology, Dec-2013.
6. ‘Microbial concrete- A way to enhance durability of building structures’- Achalvarenyam, Mukherjee Abhijit,
Reddy, Sudhakara M, Patiala : Thapar University.
7. ‘Overview of factors affecting M.I.C.P and its potential applications in soil improvements’- Wei-Soon Ng, Lee
Minn –Lee, HieSiew-Ling: Malaysia: World academy of science, engineering and technology 62, 2012.
8. ‘Self-Healing of Cracked concrete’-A bacterial approach’- Jonkers, H.M, Schlagen E. Netherland:Delft
University. ‘Concrete Technology’-MS Shetty.
9. ‘Microbiology’-Pelzar.

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