Akif Perwez presented on self-healing concrete at a technical seminar. Bacteria-based self-healing concrete contains bacterial spores and nutrients that become activated when cracks form, allowing the bacteria to consume the nutrients and seal the cracks with limestone. Laboratory tests showed this concrete could self-heal cracks up to 0.8mm wide. Using this concrete could reduce costs by decreasing steel reinforcement needed and improve sustainability by reducing steel usage in waterproof applications. The presentation discussed how the bacteria-based self-healing process works, finding suitable bacteria that can survive in concrete, and full-scale testing of cracked concrete samples.

1. DEPARTMENT OF CIVIL ENGINEERING
TECHNICAL SEMINAR PRESENTATION
ON
SELF HEALING CONCRETE
PRESENTED BY:
AKIF PERWEZ
1DA19CSE01
Under the Guidance of :-
Dr. VIJAYA.S
Professor and Head, Department of Civil Engineering

2. SUBJECT OF TECHNICAL SEMINAR
SELF HEALING CONCRETE

3. ABSTRACT
BACTERIA-BASED SELF-HEALING CONCRETE IS AN INNOVATIVE CONCRETE THAT CONTAINS
A SELF-HEALING AGENT THAT PROVIDES THE MATERIAL WITH ENHANCED AUTONOMOUS
CRACK-SEALING PERFORMANCE. A SPECIFIC TYPE OF THIS CONCRETE, BASED ON A
HEALING AGENT COMPOSED OF BACTERIAL SPORES AND LACTATE AS CARBON SOURCE,
HAS BEEN DEVELOPED AND APPLIED BY THE DELFT UNIVERSITY OF TECHNOLOGY FOR OVER
TEN YEARS. UNDER LABORATORY CONDITIONS IT WAS PROVEN THAT, DEPENDING ON THE
DOSAGE OF HEALING AGENT, SELF-HEALING OF CRACKS UP TO 0.8 MM WIDTHS OCCURS.
AS SUCH THE MATERIAL POTENTIALLY ALLOWS REDUCTION OF STEEL REINFORCEMENT
USED FOR CRACK WIDTH LIMITATION IN WATERTIGHT CONSTRUCTIONS. APPLICATION
OF SELF-HEALING CONCRETE WOULD THEREFORE NOT ONLY RESULT IN A REDUCTION OF
COSTS BUT ALSO IN IMPROVEMENT OF ENVIRONMENTAL PERFORMANCE AND EASE OF IN
SITU CASTING DUE TO REDUCTION OF USE OF STEEL IN WATERPROOF APPLICATIONS

4. CONTENT
• INTRODUCTION
• AUTONOMOUS HEALING
• WHY THE NEED
• HOW DOES BIOCONCRETE WORKS
• FINDING THE RIGHT BACTERIA
• FULL SCALE TESTING
• BIOCONCRETE MECHANISM
• ADVANTAGES
• DISADVANTAGES
• CURRENT RESEARCH
• REFERENCES

5. INTRODUCTION
• Crack formation is a typical phenomenon related to durability.
• Percolation of crack may lead to leakage problems, causing deterioration of the
concrete matrix or corrosion of embeddedsteel reinforcement.
• In recent years a bacteria –based self healing concrete is being developed in order to
extend the service life.
• Atwo component healing agent is added to the concrete mixture.
• The agent consist of bacteria and an organic mineral precursor compound.

6. Self-healing concrete could solve the problem of concrete structures deteriorating well
before the end of their service life. CONCRETE IS STILL ONE OF THR MAIN MATERIALS USED
IN THE CONSTRUCTION n industry, from the foundation of buildings to the structure of
bridges and underground parking lots. Traditional concrete has a flaw, it tends to crack
when subjected to tension.
When bacteria embedded in the concrete convert nutrients into limestone has been under
development at the civil engineering and geosciences faculty in delft since 2016. The
project is part of a wide programme to study the self-healing potential of plastics,
polymers, composites, asphalt and metals as well as concrete.

7. Schematic of self-healing process in bacterial concrete. In A, water
enters from the left into a micro crack activating the embedded
bacterial spores. In B, the active bacteria seals the cracks with the
production of limestone, protecting the embedded steel
reinforcement (brown bar) from attack and erosion

8. AUTONOMOUS HEALING
Concrete constructions are currently designed according to set norms that allow cracks to form up to
0.2mm wide. Such micro cracks are generally considered acceptable, as these do not directly impair
the safety and strength of a construction. Moreover, micro cracks sometimes heal themselves as many
types of concrete feature a certain crack-healing capacity.
Research has shown that this so called ‘autonomous’ healing capacity is largely related to the number
of non-reacted cement particles present in the concrete matrix. On crack formation, ingress water
reacts with these particles, resulting in closure of micro cracks. However, because of the variability of
autonomous crack healing of concrete constructions, water leakage as a result of micro crack
formation in tunnel and underground structures can occur.
The autonomous self-healing of control samples and compared that to the self-healing capacity of
concrete with an inbuilt bacteria-based self-healing agent. While self-healing of 0.2mm wide cracks
occurred in 30% of the control samples, complete closure of all cracks was obtained in all bacteria-
based samples. Moreover, the crack sealing capacity of the latter group was found to be extended to
0.5mm cracks

9. WHY THE NEED
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

10. HOW DOES BIOCONCRETE WORKS
Self-healing concrete is a product that will biologically produce limestone to heal cracks that appear on the
surface of concrete structures. Specially selected types of the bacteria genus bacillus, along with a calcium-
based nutrient known as calcium lactate, and nitrogen and phosphorus, are added to the ingredients of the
concrete when it is being mixed. These self-healing agents can lie dormant within the concrete for up to 200
years. However, 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. 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. It mimics the process by which bone fractures in the human body are naturally
healed by osteoblast cells that mineralize to re-form the bone. The consumption of oxygen during the
bacterial conversion of calcium lactate to limestone has an additional advantage. 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. The two self healing agent parts (the bacterial
spores and the calcium lactate-based nutrients) are introduced to the concrete within separate expanded clay
pellets 2-4mm wide, which ensure that the agents will not be activated during the cement-mixing process.
Only when cracks open up the pellets and incoming water brings the calcium lactate into contact with the
bacteria do these become activated. Testing has shown that when water seeps into the concrete, the bacteria
germinate and multiply quickly. They convert the nutrients into limestone within seven days in the laboratory.
Outside, in lower temperatures, the process takes several weeks.

11. FINDING THE RIGHT BACTERIA
The starting point of the research was to find bacteria capable of surviving in an extreme alkaline
environment. 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. The search
concentrated on microbes that thrive in alkaline environments which 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. Samples
of endolithic bacteria (bacteria that can live inside stones) were collected along with bacteria found in
sediments in the lakes. Strains of the bacteria genus bacillus were found to thrive in this high-alkaline
environment. Back at delft university the bacteria from the samples 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 pulverised 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. 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. Finding a
suitable food source for the bacteria that could survive in the concrete took a long time and many different
nutrients were tried until it was discovered that calcium lactate was a carbon source that provides biomass. If
it starts to dissolve during the mixing process, calcium lactate does not interfere with the setting time of the
concrete.

13. FULL SCALE TESTING
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. 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.

14. 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 .

16. 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. 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.

17. 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.

18. 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.

19. CURRENT RESEARCH
• 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

20. REFERENCES
• ANTONOPOULOU, S. SELF HEALING IN ECC MATERIALS WITH HIGH CONTENT OF DIFFERENT MICROFIBERS AND MICRO
PARTICLES, MSC THESIS, DELFT UNIVERSITY OF TECHNOLOGY, 2018
• DE MUYNCK, W., DEBROUWER, D., DE BELIE, N., VERSTRAETE, W., 2018. BACTERIAL CARBONATE PRECIPITATION
IMPROVES THE DURABILITY OF CEMENTATIONS MATERIALS. CEMENT & CONCRETE RES. 38, 1005–1014.
• BANG, S.S., GALINAT, J.K., RAMAKRISHNAN, V., 2019. CALCITE PRECIPITATIOINDUCED BY POLYURETHANE-
IMMOBILIZED BACILLUS PASTEURII. ENZYME MICROB. TECHNOL. 28, 404-409
• MINERAL-PRODUCING BACTERIA HAVE BEEN FOUND THAT COULD HELP MEND MICRO-CRACKING IN CONCRETE. DR
HENK JONKERS, A MICROBIOLOGIST AT DELFT UNIVERSITY, TALKED TO INGENIA ABOUT RESEARCH DEVELOPMENTS IN
PRODUCING BIOCONCRETE THAT COULD BRING BENEFITS FOR CIVIL ENGINEERING PROJECTS.

21. THANK YOU