SELF HEALING BACTERIAL CONCRETE

A SEMINAR REPORT

Submitted by,

SAHEENA BEEVI ABDUL VAHAB

11428054

BACHELOR OF TECHNOLOGY

IN

CIVIL ENGINEERING

RAJADHANI INSTITUTE OF ENGINEERING AND TECHNOLOGYJULY 2014

DEPARTMENT OF CIVIL ENGINEERING,RAJADHANI INSTITUTE OF ENGINEERING AND

TECHNOLOGY,ATTINGAL, THIRUVANANTHAPURAM

2014

CERTIFICATE

This is to certify that the Seminar Report entitled ‘SELF HEALING BACTERIAL

CONCRETE’ is a bonafide record of the seminar done by SAHEENA BEEVI ABDUL

VAHAB, Reg. No: 11428054, S7 Civil Engineering, Rajadhani Institute Of

Engineering And Technology during the year 2014 for the partial fulfillment of the

requirements for the award of the degree of Bachelor Of Technology by the

University of Kerala.

Prof.V.Janardhana Iyer

HOD Asst.Prof

Gayathri U.V GUIDE

ACKNOWLEDGEMENT

First and foremost I concede the surviving presence and the flourishing

refinement of almighty God for his concealed hand yet substantial supervision all

through the seminar.

I would like to thank our seminar coordinator Smt. Biji.B.J and my guide

Smt.Gayathri U.V for their valuable guidance and assistance.

I sincerely thank Sri.Janardhana Iyer, Head of Department, civil engineering

for his kind co-operation and technical support rendered by him in making my

seminar a success.

I extend my sincere gratitude to our respected principal Sri.R.Sathikumar

For his countenance towards the successful accomplishment of the course.

I sincerely thank all staff of the Civil Engineering Department for providing

their valuable guidance and support

Above all I would like to express my sincere gratitude and thanks to all friends

for their valuable comments and suggestions for making this work a success.

SAHEENA BEEVI ABDUL VAHAB

ABSTRACT

Cracks in concrete are inevitable and are one of the inherent weaknesses

of concrete. Water and other salts seep through these cracks, corrosion

initiates, and thus reduces the life of concrete. So there was a need to

develop an inherent biomaterial, a self-repairing material which can

remediate the cracks and fissures in concrete. Bacterial concrete is a

material, which can successfully remediate cracks in concrete. This

technique is highly desirable because the mineral precipitation induced

as a result of microbial activities is pollution free and natural. As the

cell wall of bacteria is anionic, metal accumulation (calcite) on the

surface of the wall is substantial, thus the entire cell becomes

crystalline and they eventually plug the pores and cracks in concrete.

This paper discusses the plugging of artificially cracked cement mortar

using Bacillus Pasteurii and Sporosarcina bacteria combined with sand

as a filling material in artificially made cuts in cement mortar which

was cured in urea and CaCl2 medium. The effect on the compressive

strength and stiffness of the cement mortar cubes due to the mixing of

bacteria is also discussed in this paper. It was found that use of bacteria

improves the stiffness and compressive strength of concrete. Scanning

electron microscope (SEM) is used to document the role of bacteria in

microbiologically induced mineral precipitation. Rod like impressions

were found on the face of calcite crystals indicating the presence of

bacteria in those places. Energy- dispersive X-ray (EDX) spectra of the

microbial precipitation on the surface of the crack indicated the

abundance of calcium and the precipitation was inferred to be calcite

(CaCO3).

CHAPTER 1

INTRODUCTION

Concrete is a vital building material that is an

absolutely essential component of public infrastructure and most

buildings. It is most effective when reinforced by steel rebar, mainly

because its tensile strength without reinforcement is considerably low

relative to its compressive strength. It is also a very brittle material

with low tolerance for strain, so it is commonly expected to crack with

time. These cracks, while not compromising structural integrity

immediately, do expose the steel reinforcement to the elements, leading

to corrosion which heightens maintenance costs and compromises

structural integrity over long periods of time. That being said, concrete

is a high maintenance material. It cracks and suffers serious wear and

tear over the decades of its expected term of service. It is not flexible

and cannot handle significant amounts of strain. Self-healing concrete

in general seeks to rectify these flaws in order to extend the service life

of any given concrete structure.

There is a material in the realm of self-healing

concrete in development, now, that can solve many of the problems

commonly associated with standard concrete. This material is bacterial

self-healing concrete. Self-healing concrete consists of a mix with

bacteria incorporated into the concrete and calcium lactate food to

support those bacteria when they become active. The bacteria, feeding

on the provided food source, heal the damage done and can also reduce

the amount of damage sustained by the concrete structure in place.

CHAPTER 2

SELF BACTERIAL HEALING CONCRETE

Fig 2.1 Self healing bacterial concrete

Autogenously crack-healing capacity of concrete has been recognized in several

recent studies. Mainly micro cracks with widths typically in the range of 0.05 to 0.1

mm have been observed to become completely sealed particularly under repetitive

dry/wet cycles. The mechanism of this autogenously healing is chiefly due to

secondary hydration of non- or partially reacted cement particles present in the

concrete matrix. Due to capillary forces water is repeatedly drawn into micro cracks

under changing wet and dry cycles, resulting in expansion of hydrated cement

particles due to the formation of calcium silicate hydrates and calcium hydroxide.

These reaction products are able to completely seal cracks provided that crack widths

are small. Larger sized cracks can only be partially filled due to the limited amount of

non-reacted cement particles present, thus resulting in only a thin layer of hydration

products on the crack surface. With respect to crack-sealing capacity, a process

homologous to secondary hydration of cement particles is the process of carbonation.

This reaction is also expansive as ingress atmospheric carbon dioxide (CO2) reacts

with calcium hydroxide particles present in the concrete matrix to various calcium

carbonate minerals. From the perspective of durability, rapid sealing of particularly

freshly formed surface cracks is important as this hampers the ingress of water and

other aggressive chemicals into the concrete matrix.

Although bacteria, and particularly acid-producing bacteria, have been traditionally

considered as harmful organisms for concrete, recent research has shown that specific

species such as ureolytic and other bacteria can actually be useful as a tool to repair

cracks or clean the surface of concrete. In the latter studies bacteria were externally

and manually applied on the concrete surface, while for autogenously repair an

intrinsic healing agent is needed.. Species from Bacillus group appear promising

intrinsic agents as their spores, specialized thick-walled dormant cells, have been

shown to be viable for over 200 years under dry conditions. Such bacteria would

comprise one of the two components needed for an autogenously healing system. For

crack repair filler material is needed, and bacteria can act as catalyst for the metabolic

conversion of a suitable organic or inorganic component, the second component, to

produce this. The nature of metabolically produced filler materials could be bio-

minerals such as calcite (calcium carbonate) or apatite (calcium phosphate). These

minerals are relatively dense and can block cracks, and thus hamper ingress of water

efficiently. The development of a self-healing mechanism in concrete that is based on

a potentially cheaper and more sustainable material then cement could thus be

beneficial for both economy and environment.

CHAPTER 3

USE OF SELF HEALING BACTERIAL CONCRETE

Concrete will continue to be the most important building material for infrastructure

but most concrete structures are prone to cracking. Tiny cracks on the surface of the

concrete make the whole structure vulnerable because water seeps in to degrade the

concrete and corrode the steel reinforcement, greatly reducing the lifespan of a

structure. Concrete can withstand compressive forces very well but not tensile forces.

When it is subjected to tension it starts to crack, which is why it is reinforced with

steel to withstand the tensile forces.

Structures built in a high water environment, such as underground basements and

marine structures, are particularly vulnerable to corrosion of steel reinforcement.

Motorway bridges are also vulnerable because salts used to de-ice the roads penetrate

into the cracks in the structures and can accelerate the corrosion of steel

reinforcement. In many civil engineering structures tensile forces can lead to cracks

and these can occur relatively soon after the structure is built. Repair of conventional

concrete structures usually involves applying a concrete mortar which is bonded to the

damaged surface. Sometimes, the mortar needs to be keyed into the existing structure

with metal pins to ensure that it does not fall away. Repairs can be particularly time

consuming and expensive because it is often very difficult to gain access to the

structure to make repairs, especially if they are underground or at a great height.

CHAPTER 4

BACTERIAS USED

Cement and water have a pH value of up to 13 when mixed together, usually a hostile

environment for life, most organisms die in an environment with a pH value of 10 or

above.

In order to find the right microbes that thrive in alkaline environments can be found in

natural environments, such as alkali lakes in Russia, carbonate-rich soils in desert

areas of Spain and soda lakes in Egypt. Strains of endolithic bacteria of genus

Bacillus were found to thrive in this high-alkaline environment. These bacteria were

grown in a flask of water that would then be used as the part of the water mix for the

concrete. Different types of bacteria were incorporated into a small block of concrete.

Each concrete block would be left for two months to set hard. Then the block would

be pulverized and the remains tested to see whether the bacteria had survived. It was

found that the only group of bacteria that were able to survive were the ones that

produced spores comparable to plant seeds. They are namely bacillus pasturii, bacillus

filla and bacillus cohnii.

Fig 4.1.Bacillus cohnii Fig 4.2.Bacillus filla Fig 4.3.Bacillus parturii

Such spores have extremely thick cell walls that enable them to remain intact for up

to 200 years while waiting for a better environment to germinate. They would become

activated when the concrete starts to crack, food is available, and water seeps into the

structure. This process lowers the pH of the highly alkaline concrete to values in the

range (pH 10 to 11.5) where the bacterial spores become activated.

CHAPTER 5

PREPERATION OF BACTERIAL CONCRETE

Self healing bacterial concrete can be prepared in two ways.

By direct application

By encapsulation in light weight concrete.

By the method of direct application bacterial spores and calcium lactate are added

directly while making the concrete and mixed. Here when the crack occurs in the

concrete bacterial spores broke and bacteria comes to life and feed on the calcium

lactate and limestone is produced which fill the cracks.

By encapsulation method the bacteria and its food, calcium lactate, are placed inside

treated clay pellets and concrete is made. About 6% of the clay pellets are added for

making bacterial concrete. When concrete structures are made with bacterial concrete,

when the crack occurs in the structure and clay pellets are broken and bacterial

treatment occurs and hence the concrete is healed. Minor cracks about 0.5mm width

can be treated by using bacterial concrete

Among theses two methods encapsulation method is commonly used, even though

it’s costlier than direct application. Bacillus bacteria are harmless to human life and

hence it can be used effectively.

CHAPTER 6

TESTING OF BACTERIAL CONCRETE AND RESULT

Concrete disks are prepared containing the porous aggregates filled with food only

and with food and bacteria. The specimens are cured for 56 days and then tested in a

deformation controlled tensile splitting loading to crack them partially. After this

cracking the specimens are placed in a permeability test setup in which water is

applied at one side of the specimen for 24 hours. After the healing the cracks are

examined under the microscope and the results were observed.

Fig 6.1 Test samples Fig 6.2 Test setup

Also the permeability of the healed specimens was determined. The outcome of this

study shows that crack healing in bacterial concrete is much more efficient than in

concrete of the same composition but without added biochemical healing agent. The

reason for this can be explained by the strictly chemical processes in the control and

additional biological processes in the bacterial concrete. On the crack surface of

control concrete some calcium carbonate will be formed due to the reaction of CO2

present in the crack ingress water with Portlandite (calcium hydroxide) present in the

concrete mixture according to the following reaction:

CO2 + Ca(OH)2 → CaCO3 + H2O

The amount of calcium carbonate production in this case in only minor due to the

limited amount of CO2 present. As Portlandite is a rather soluble mineral in fact most

of it present on the crack surface will dissolve and diffuse out of the crack into the

overlying water mass. Subsequently, as more CO2 is present in the overlying water,

dissolved Portlandite will as yet precipitate in the form of calcium carbonate but

somewhat away from the crack itself, as can be seen. The self healing process in

bacterial concrete is much more efficient due to the active metabolic conversion of

calcium lactate by the present bacteria:

Ca(C3H5O2)2 + 7O2 → CaCO3 + 5CO2 + 5H2O

This process does not only produce calcium carbonate directly but also indirectly via

the reaction of on site produced CO2 with Portlandite present on the crack surface. In

the latter case, Portlandite does not dissolve and diffuse away from the crack surface,

but instead reacts directly on the spot with local bacterially produced CO2 to

additional calcium carbonate. This process results in efficient crack sealing as

can be seen .

Fig 6.3 Controlled and uncontrolled specimen

The conclusion of the test is that the proposed two component biochemical healing

agent composed of bacterial spores and a suitable organic bio-cement precursor

compound, both immobilized in reservoir porous expanded clay particles, represents a

promising bio-based and thus sustainable alternative to strictly chemical or cement

based healing agents.

CHAPTER 7

BIOCONCRETE MECHANISM

When the concrete is mixed with bacteria (bacillus subtilus), the

bacteria go into a dormant state, a lot like seeds. All the bacteria need

is exposure to the air to activate their functions. Any cracks that should

occur provide the necessary exposure. When the cracks form, bacteria

very close proximity to the crack, starts precipitating calcite crystals.

When a concrete structure is damaged and water starts to seep through

the cracks that appear in the concrete, the spores of the bacteria

germinate on contact with the water and nutrients. Having been

activated, the bacteria start to feed on the calcium lactate nutrient. Such

spores have extremely thick cell walls that enable them to remain intact

for up to 200 years while waiting for a better environment to germinate.

Fig 7.1 Bacterial self healing process

As the bacteria feeds oxygen is consumed and the

soluble calcium lactate is converted to insoluble limestone. The

limestone solidifies on the cracked surface, thereby sealing it up.

Oxygen is an essential element in the process of corrosion of steel and

when the bacterial activity has consumed it all it increases the

durability of steel reinforced concrete constructions. Tests all show that

bacteria embedded concrete has lower water and chloride permeability

and higher strength regain than the surface application of bacteria. The

last, but certainly not least, key component of the self-healing concrete

formula is the bacteria themselves. The most promising bacteria to use

for self-healing purposes are alkaliphilic (alkali- resistant) spore-

forming bacteria. The bacteria, from the genus Bacillus Subtilus is

adopted for present study. It is of great concern to the construction

industry whether or not these bacteria are “smart” enough to know when

their task is complete because of safety concerns. Bacillus Subtilus

which is a soil bacterium is harmless to humans as it is non-pathogenic

microorganism.

CHAPTER 8

ADVANTAGES

Incorporation of the agent in the concrete will be relatively cheap as well as

easy when the aggregate is immobilized in porous light weight aggregate prior

to addition to the concrete mixture.

The self healing bacterial concrete helps in reduced maintenance and repair

costs of steel reinforced concrete structures.

Oxygen is an agent that can induce corrosion, as bacteria feeds on oxygen

tendency for the corrosion of reinforcement can be reduced.

Self healing bacteria can be used in places where humans find it difficult to

reach for the maintenance of the structures. Hence it reduces risking of human

life in dangerous areas and also increases the durability of the structure.

Formation of crack will be healed in the initial stage itself thereby increasing

the service life of the structure than expected life.

CHAPTER 9

DISADVANTAGES

If the volume of self healing agents (bacteria and calcium lactate) mixed

becomes greater than 20%, the strength of the concrete is reduced.

Preparation of self healing concrete needs the requirement of bacteria and

calcium lactate. Preparation of calcium lactate from milk is costlier. Hence

preparation of self healing concrete costs double than conventional concrete.

CHAPTER 10

CURRENT RESERCHES

There will be full-scale outdoor testing of self-healing concrete

structures. A small structure or part of a structure will be built with the self-healing

material and observed over two to four years. Structures will be fitted with some

panels of self-healing concrete and others with conventional concrete so that the

behavior of the two can be compared. Cracks will be made in the concrete that are

much larger than the ones that have healed up in the laboratory to determine how well

and fast they heal over time.

The research will test two systems. The first technique will see

bacteria and nutrients applied to the structure as a self-healing mortar, which can be

used to repair large-scale damage. The second technique will see the bacteria and food

Nutrients dissolved into a liquid that is sprayed onto the surface of the concrete from

where it can seep into the cracks. Laboratory tests are being carried out to accelerate

the ageing process of self-healing concrete. The tests will subject the concrete to

extreme environments to simulate changing seasons and extreme temperature cycles,

wetter periods and dryer periods

CHAPTER 11

APPLICATIONS

Self healing bacterial concrete can be used for sectors such as

tunnel-lining, structural basement walls, highway bridges, concrete floors and marine

structures.

Fig 10.1 Marine structure Fig 10.2 Base wall

Fig 10.3 Concrete flooring Fig 10.4 Tunnel lining

Fig 10.5 Highway bridge Fig 10.6 Underground retaining walls

CHAPTER 11

CONCLUSION

The bacteria which are known to be alkali-resistant, i.e. they grow in natural

environments characterized by a relatively high pH (10-11). In addition, these strains

can produce spores which are resting cells with sturdy cell walls that protect them

against extreme environmental mechanical- and chemical stresses. Therefore these

specific bacteria may have the potential to resist the high internal concrete pH values

(12-13 for Portland cement-based concrete), and remain viable for a long time as well,

as spore viability for up to 200 years is documented. We hypothesized that concrete-

immobilized spores of such bacteria may be able to seal cracks by bio mineral

formation after being revived by water and growth nutrients entering freshly formed

cracks.. Although the exact nature of the produced minerals still needs to be clarified,

they appear morphologically related to calcite precipitates.

The mechanism of bacterially-mediated calcite production likely proceeds via organic

carbon respiration with oxygen what results in carbonate ion production under

alkaline conditions. The produced carbonate ions which can locally reach high

concentrations at bacterially active 'hot spots' precipitate with excess calcium ions

leaking out of the concrete matrix. This microbial calcium carbonate precipitation

mechanism is well studied and occurs worldwide in natural systems such as oceans,

bio films, microbial mats and stromatolites. For an autonomous self-healing

mechanism all needed reaction components, or self-healing agents, must be present in

the material matrix to ensure minimal externally needed triggers. To conclude we can

state that the application of bacteria as a self-healing agent in concrete appears

promising

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carbonate precipitation improves the durability of cementations materials.

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Bang, S.S., Galinat, J.K., Ramakrishnan, V., 2001. Calcite precipitatioinduced

by polyurethane-immobilized Bacillus pasteurii. Enzyme Microb. Technol. 28,

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Jonkers, HM & Schlangen, E. (2009a). Bacteria-based self healing concrete.

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