Session A9
Paper 184
Disclaimer—This paper partially fulfills a writing requirement for first year (freshman) engineering students at the University
of Pittsburgh Swanson School of Engineering. This paper is a student, not a professional, paper. This paper is based on publicly
available information and may not provide complete analyses of all relevant data. If this paper is used for any purpose other
than these authors’ partial fulfillment of a writing requirement for first year (freshman) engineering students at the University
of Pittsburgh Swanson School of Engineering, the user does so at his or her own risk.
SELF-HEALING CONCRETE: USING BACTERIA TO EXTEND
THE LIFE OF CONCRETE
Ivan Menz, [email protected], Mena 1:00, Duncan Clear, [email protected], Sanchez 5:00
Abstract—Concrete is the backbone of our nation’s
infrastructure and is the most widely used construction
material in the world. However, this highly versatile material
has a major weakness: it is very brittle in tension and will
inevitably crack. Rebar is added to increase the tensile
strength of concrete, but when these micro-cracks form, water
and other harmful substances corrode the reinforcement bars.
Concrete infused with a limestone-producing bacterium, from
the genus Bacillus, can fix these small fissures, sealing off the
concrete and extending its life by decades. The bacteria, which
are contained in small clay pellets with calcium lactate, can
seal cracks up to 0.8 mm wide with limestone in just three
weeks. They are also very hardy and are able to lie dormant
for up to 200 years. This additive will greatly improve the
sustainability of general concrete by increasing its strength
and lifespan significantly, lessening its need for repair, and
reducing both its financial and environmental costs. The
sustainability discussed in this paper is defined as, reducing
both the environmental and life cycle costs of a product by
extending its service life, thus, improving the lives of future
generations. This paper will research and evaluate the
effectiveness and sustainability of Bacillus-based, self-healing
concrete using sources primarily from scholarly articles and
studies done on this topic by other engineers and scientists in
the field. These resources will be used to discuss the future of
this product, including its economic practicality and its
potential for mass production.
Key Words—Bacillus, Bacteria,
Encapsulation, Repair, Self-Healing.
Concrete,
has a massive range of applications from building houses to
skyscrapers, sidewalks to superhighways, and swimming
pools to hydroelectric dams. Other reasons include that
concrete has a high thermal capacity, which makes it especially
good for building houses. It can be produced almost anywhere
in the world. Also, it is durable and has a high compressive
strength. In fact, even when subjected to adverse conditions
such as “carbonation or chloride ingress, concrete structures
can reach a service life of 50 years or longer if properly
maintained” [4]. However, traditional concrete has a major
imperfection that significantly decreases its overall lifespan.
In tension, concrete is extremely brittle and cracks easily.
Thus, steel reinforcement is added to supply the necessary
tensile strength for the concrete when cracks begin to form. As
seen in the picture, when a reinforced concrete beam is
subjected to excessive loading, microcracks begin to form.
This particular beam is undergoing a load test, so the cracks
formed in a very short amount of time. Usually, the cracks
would form over a much longer period of time and initially
look more like the ones branching out towards the end of the
beam. As shown, most of the cracks tend to form on the
underside of the beam, which is the side subjected to the tensile
stress.
Cracks,
A SUSTAINABLE SOLUTION TO THE
PROBLEMS WITH CONVENTIONAL
CONCRETE
Concrete is the most widely used construction material in
the world because of its remarkable structural qualities and
affordable price [1]. In 2016, 4.2 billion metric tons of cement
were produced globally, which translates to roughly between
28 and 42 billion metric tons of concrete, as the average mix
of concrete contains 10 to 15 percent cement [2][3]. One
reason concrete is such a popular building material is that it
University of Pittsburgh Swanson School of Engineering 1
03.31.2017
FIGURE 1 [5]
Reinforced concrete beam undergoing a load test
In the next picture, the underside of a bridge is shown that
has had excessive cracking without repair. These cracks have
allowed pieces of concrete to break off and expose the rebar
reinforcements. This consequently leads to the corrosion of the
rebar.
Ivan Menz
Duncan Clear
is heated to 2,600 degrees Fahrenheit along with other
feedstock materials that contain silicates, such as clay [9] [10].
At this temperature, the two compounds break down and then
recombine to produce clinker (calcium silicate), and carbon
dioxide (CO2). Finally, gypsum is added to the clinker (to
prevent flash setting) and ground into a fine dust to make
cement [9]. This final product is what provides concrete with
its strength and durability.
The cement is then mixed together with water and
aggregates such as sand and gravel to form a slurry. The water
and cement then undergo a hydration reaction that “releases
highly alkaline hydroxyl ions which help form calcium silicate
hydrates that bind the aggregates together” [8]. This reaction
fuses the materials together in a bond that is very strong under
compression and continues to grow stronger as the concrete
ages. The fact that concrete can be produced so easily on-site
and can cure in nearly any set of conditions, makes it an
extremely valuable and convenient material that is used on
nearly every construction project.
FIGURE 2 [6]
Formation of cracks in concrete
According to H. M. Jonkers, a professor at Delft
University of Technology in the Netherlands, the “cracking of
concrete structures is triggered by temperature and humidity
fluctuations, mainly at an early age, and by external loading,
mainly at a later age” [7]. This is because when concrete is
curing, the chance of it cracking is increased when it is
subjected to external stresses caused by fluctuations in
humidity and temperature. Furthermore, when a structure ages,
it becomes more brittle due to its low moisture content and is
damaged more easily by tensile and flextural forces. Microcracks are necessary so that the tension in the concrete can be
passed on to the reinforcement, but damage occurs when they
provide a pathway for corrosive substances that can “lead to
the premature corrosion of the reinforcements and early failure
of the structure” [4]. Cracking also causes several other
problems including frost damage and leakage of water. Frost
damage occurs when a crack, filled with water, freezes and is
forced open further by the expansion of the water as it freezes.
Water leakage is the most severe for structures built to retain
water, such as dams and some foundations.
This results in concrete structures needing continual
maintenance, as Prachi Patel writes in an article for Chemical
and Engineering News, “Our seemingly resilient infrastructure
would crumble without routine, and costly, patching” [8].
However, there is a sustainable solution to this problem: selfhealing concrete. Concrete can be made self-healing by adding
an agent that uses bacteria to seal off the cracks as soon as they
form, preventing these cracks from growing and weakening
the structure. This agent can effectively make general concrete
more sustainable by reducing both its environmental and life
cycle costs by extending its service life, thus, improving the
lives of future generations.
OVERVIEW OF SELF-HEALING
CONCRETE
The idea of self-healing concrete was first researched by
Carolyn Dry, an architecture professor at the University of
Illinois, Urbana-Champaign, in the early 1990s [8]. Dry tried
embedding glass capsules in the concrete that would break
when the concrete cracked, releasing methyl methacrylate
glues. Two major problems that prevented this technology
from being successful were: the glues were too viscous to flow
out of the capsules once they were broken and the capsules
were not strong enough to survive the concrete mixing process
[8]. Nevertheless, despite the failure of Dry’s idea, the concept
of a self-healing concrete was born.
Since then, numerous scientists have worked on this
elusive material that poses two major obstacles. The first is that
the amount of healing agent that can be put into the concrete is
limited as the concrete needs to be able to maintain its density
and strength [8]. The second is that encapsulating the healing
agent has proven to be very tricky because the capsules need
to be flexible during the mixing process to avoid breaking, but
then as the concrete hardens they need to become brittle so that
they crack with the concrete and release the healing agent [8].
According to Prachi Patel, many effective healing agents have
been produced, including “minerals, polymers, resins, and
even bacteria,” but “making the capsule itself has been a
stumbling block says Kevin A. Paine, a professor of civil
engineering at the University of Bath” [8]. However, within
the last decade, tremendous progress has been made using
bacteria as the healing agent.
Starting in 2006, H. M. Jonkers pioneered a bacteriabased self-healing agent [11]. It took several years to perfect
the product because the bacteria used needed to be able to
survive the alkaline environment of concrete for decades [11].
Eventually, H. M. Jonkers found a limestone-producing
OVERVIEW OF CONCRETE
According to the Portland Cement Association, a typical
mix of concrete is made up of “10 to 15 percent cement, 60 to
75 percent aggregate and 15 to 20 percent water” [3]. Cement
is the most important ingredient in the mixture and is what
binds the aggregates together. To produce cement, limestone
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Ivan Menz
Duncan Clear
the limestone that eventually repairs the cracks” [13]. The fact
that the healing process occurs under the conditions that are
the most harmful to concrete is the reason that this technology
is so effective. As soon as the crack forms, the bacteria are
activated and begin to seal it with limestone while it is still
small and easy to repair. This ingenious technology has
tremendous potential in the construction industry and provides
many economic and environmental benefits.
bacterium that is found in extremely alkaline lakes near
volcanoes and is “able to lie dormant for up to 200 years” [12].
The bacteria are contained in small clay pellets with calcium
lactate, and “when the pellets crack with the concrete, moisture
in the air triggers the spores to germinate” [8]. In the space of
just three weeks, the bacteria, feeding on the calcium lactate,
can seal up cracks up to 0.8 mm wide with limestone [8].
Shown in the pictures below is a crack in a piece of self-healing
concrete, before and after the healing process.
SCIENCE OF BACILLUS BASED SELFHEALING CONCRETE
The Chemistry of the Healing Process
When concrete is subjected to fluctuations in temperature
and humidity or experiences excessive tensile stresses, it
develops microscopic fissures that lead to larger cracks and
greater structural damage. It is inside these tiny cracks that the
self-healing process takes place. This self-healing process is
made possible by microbial-induced carbonate precipitation
(MICP) [4]. MICP is the process in which limestone (calcium
carbonate, CaCO3) is produced as the result of the metabolic
activity of bacteria. This MICP process is relatively
complicated and involves multiple metabolic pathways to
produce the sealant: limestone. The most commonly used
system, according to H. M. Jonkers, is the enzymatic
hydrolysis of urea (CO(NH2)2) to form carbonate (CO2−
3 ). This
whole process occurs within the bacterium. The following set
of chemical equations represents this pathway:
FIGURE 3 [8]
Before the healing process. Capsules containing the
bacteria are the black circles.
System of equations:
CO(NH2)2 +H2O → NH2COOH + NH3
NH2COOH + H2O → NH3 + H2CO3
−
2NH3 + 2H2O → 2NH+
4 + 2OH
−
+
H2CO3 + H2O → HCO3 + H3O
2−
+
HCO−
3 + H2O → CO3 + H3O
−
+
2H3O + 2OH → 4H2 O
Net reaction:
+
CO(NH2)2 +2H2O → CO2−
3 + 2NH4
FIGURE 5 [14]
Equations for the first pathway
During the reactions shown above, the cell wall of the
bacterium is negatively charged, causing cations to be attracted
from the surroundings [14]. In a calcium rich environment,
calcium ions (Ca2+) are deposited on the cell’s surface. This
leads to a subsequent reaction between the carbonate and the
calcium ions, resulting in a precipitation of limestone on the
cell’s surface [14]. Unfortunately, after the crack has been
filled, the surface of the bacterium is coated with limestone,
resulting in the death of the microorganism [6]. The following
chemical equation shows this final step of this process:
FIGURE 4 [8]
After the healing process. Cracks and holes are sealed
with limestone.
R. Spinks, in an article for the Guardian, comments on
the interesting nature of this healing process: “It is only with
the arrival of concrete’s nemesis – rainwater or atmospheric
moisture seeping into cracks – that the bacteria start to produce
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Ivan Menz
Duncan Clear
Ca2+ + CO2−
3 → CaCO3
Jonkers explains what bacteria spores are, and why they are so
effective:
FIGURE 6 [14]
Final equation for the first pathway
Spores are dormant bacterial cells with
characteristic compact round shape, typically in the
size range of 0.8–1 μm. Spores can remain viable
up to 200 years. When environmental conditions are
favorable (presence of water, nutrients, and oxygen)
these spores germinate and grow into vegetative
active bacterial cells [4].
However, the first pathway has shown evidence of
causing problems as it produces ammonium ( NH+
4 ) as a
byproduct which can have negative effects on the concrete [4].
Fortunately, the pathway used by H. M. Jonkers’ bacteriabased healing agent does not have this negative side effect.
This system uses the carbon dioxide that is produced through
bacterial respiration, to form carbonate ions. In a reaction
identical to the one explained above, the carbonate ions
limestone carbonate precipitate. The second pathway is
represented by the following equations:
The fact that these spores stay viable for so long and are so
well suited to the environment of concrete made this bacterium
the obvious choice for the agent. The alkali-resistant sporeforming bacteria that H. M. Jonkers eventually chose are in the
genus Bacillus. Several of the species from this genus were
found to be “able to convert organic calcium salt to calciumbased mineral upon activation of crack ingress water in
hydrated cement paste specimens” [4]. With these bacteria in
the healing agent, the one thing left was to provide it with the
necessary nutrients and calcium salt to undergo the reaction
when activated.
CO2(g) ↔CO2(aq)
CO2(aq) + H2O ↔ H2CO3
H2CO3 + H2O ↔ HCO3− + H3O+
2−
+
HCO−
3 + H2O ↔ CO3 + H3O
2−
Ca2+ + CO3 → CaCO3
FIGURE 7 [4]
Equations for the second pathway
Selection of the Nutrients
For the MICP process to take place there must be proper
sustenance for the bacteria. Choosing the correct food source
was difficult because it must not negatively affect the strength
of the concrete when mixed. H. M. Jonkers tried many
different organic compounds and tested their effect on the
strength of the produced concrete. Most of the compounds
resulted in a decrease in strength development; calcium lactate,
however, resulted in an increase in compressive strength [4].
For this reason, along with the fact that the calcium lactate
provides the necessary calcium ions to precipitate with the
carbonate ions, it is a great choice for a food source for the
bacteria. The chemical process of metabolic conversion by the
bacteria of calcium lactate results in the formation of limestone
through the following equation:
This specific set of reactions must take place in a calcium
rich environment with an alkaline pH [4]. The reason an
alkaline environment is necessary is because the first four
reactions are in equilibrium. This means that once there is a
certain amount of product present in the solution, the forward
reaction will stop. The only way to continue the forward
reaction is by removing some of the product. As a weak acid,
carbonic acid (H2CO3) produces hydronium (H3O+) when it
disassociates. Thus, in order for the forward reaction to occur,
the hydronium must be removed by reacting with hydroxide
(OH-) to form water. In an acidic solution, this will not occur
because of the high levels of hydronium already present.
However, an alkaline solution has high levels of hydroxide that
will react with the hydronium, making the forward reaction
spontaneous. This will make the whole system of equations
spontaneous because each reaction consumes the products of
the previous one. The result is a reduction in the pH of the
concrete and the production of limestone. Therefore, concrete
is an excellent environment for this reaction because of its high
pH.
Ca(C3H4O3)2 + 6O2 → CaCO3 + 5CO2 + 5H2O
FIGURE 8 [4]
Equations for the formation of limestone.
H. M. Jonkers goes on to state that because concrete is a
calcium rich environment, the CO2 resulting from the bacterial
respiration can react with the portlandite(Ca(OH) 2) present in
the cement, producing even more limestone [4]. This can be
seen with the following chemical equation:
Selection of the Bacteria
The most important factor that allows this reaction to take
place is the presence of a bacteria that will activate it. The
selection of this bacteria was no easy matter, as they had to be
able to survive the extremely alkaline pH (~12.8) of concrete
and had to be viable as a healing agent for a long time [6]. The
spore-forming alkaline-resistant bacteria H. M. Jonkers
eventually used had both of these characteristics [4]. H. M.
5CO2 + 5Ca(OH)2 → 5 CaCO3 + 5H2O
FIGURE 9 [4]
Equations for the second formation of limestone.
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Duncan Clear
These two equations show that for each mole of calcium
lactate reacted, one mole of limestone can be produced and that
for every 5 moles of carbon dioxide reacted with the
portlandite in the concrete, another 5 moles of limestone can
be produced. Because of the large amount of possible
limestone product, the healing process of small cracks is quite
effective.
times their own weight [6]. This encapsulating method has
several beneficial properties as described in an article from
Ghent University:
When cracks occur, SAP are exposed to the humid
environment and swell. This swelling reaction
partly seals the crack from intruding potentially
harmful substances. After swelling, SAP particles
desorb and provide the fluid to the surrounding
matrix for internal curing, further hydration and the
precipitation of CaCO3. In this way, cracks may
close completely [6].
Encapsulating the Bacteria
For the healing process to take place, however, the
bacteria and calcium lactate must first be safely implanted into
the concrete mix and be evenly distributed throughout. To keep
the bacteria safe in the rigorous cement mixing process, the
capsules in which the bacteria are stored must have certain
qualities. First, the capsule must be strong enough to survive
the mixing process and then become brittle so that they break
when a crack forms. Next, the capsule must have a good bond
with the surrounding hydrated cement paste. Lastly, the
capsule must be able to release the bacteria and nutrients into
the crack when broken.
H. M. Jonkers has found that the resolution of these
requirements is to immobilize the bacterial spores and calcium
lactate in clay particles before adding them to the concrete
mixture. According to H.M. Jonkers, these clay particles not
only represent an internal reservoir but also constitute both a
structural element of concrete as well as a protective matrix for
the self-healing agent [4]. These clay particles are a
lightweight, expanded clay aggregate, typically less than 2 mm
across. They are created by heating clay to over 1000˚C in a
rotary kiln. This process causes the clay to expand, and form
many small bubbles in it. These small bubbles are the
reservoirs that H. M. Jonkers spoke of because they are a great
location for the bacteria and calcium lactate to be implanted.
Breakage of the capsule while mixing the cement is not a
problem because the bacteria and nutrients are enclosed in the
tiny bubbles in the clay and will not be damaged or lost if the
capsule breaks. The capsules are also very small which ensures
an even distribution throughout the mix. When the clay
particles get wet during the production of the cement, the
bacterium spores do not prematurely germinate and die. This
is because the bacterium spores need water as well as oxygen
over an extended period of time in order to germinate, which
the mixing process does not provide. A few other beneficial
characteristics of these expanded clay particles are: they have
good thermal insulation, a low conductivity, are moisture
impermeable, fire resistant, and have a nearly neutral pH.
Because of these factors, these expanded clay particles are a
great material to encapsulate the bacteria in for the self-healing
concrete. Though this clay encapsulation process is being used
by H. M. Jonkers and his team, there have been multiple other
propositions as to how the bacteria could be safely stored in
the concrete.
A second container being proposed is a superabsorbent
polymer (SAP), also known as hydrogel. These hydrogels are
capable of holding large quantities of fluid, even up to 500
Like the clay particles, the bacterium and nutrients are
encapsulated in the SAP and only germinate when they come
in contact with water and oxygen. This method adds the unique
ability for particles to immediately seal the crack off from the
ingress of water and then slowly release the stored water for
the use of the bacterium. The article continues to state that
these polymers could even be created to only absorb water
when there is a change in pH. This could be very useful
because the when a crack occurs, there is a drop-in pH from
12.8 to between 9 and 10 [6]. This could potentially be a new
way to trigger the healing process because the SAP capsules
would only swell when a crack occurs. Unlike the clay particle
method which is in production, the SAP method is still being
tested and designed so not as much is known about its
effectiveness and cost.
THE PRODUCT AND ITS APPLICATIONS
The technology has come far enough that this healing
agent is already being produced for commercial consumption
in the Netherlands. Basilisk Self-Healing Concrete, a spinoff
company of TU Delft, sells three distinct products that enable
concrete to become self-healing and thus, more sustainable.
They include a self-healing repair mortar, a spray on selfhealing solution and a self-healing agent for mixing into
concrete [15]. The first two products use the same bacterial
technology (described in this paper), but the last one is what
could really change the construction industry because it is
added into the concrete mix, pre-construction. This healing
agent uses both the bacterial and the encapsulating processes
invented by H. M. Jonkers (described above) and “can be
applied in ready mixes, prefabricated applications, or added
directly to the truck mixer on site” [15]. The recommended
application calls for 5 kilograms of expanded clay healing
agent per cubic meter of concrete. This ensures a sufficient
density of agent throughout the mixture, allowing for the
concrete to crack in more than once in the same location [15].
A sample of the clay pellets embedded with the bacterium and
nutrients is shown in the picture below.
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Ivan Menz
Duncan Clear
roughly 9.5% of global carbon emissions, according to a recent
European Commission report,” second only to coal-powered
electricity [8][9]. Furthermore, the fossil fuels used during the
production of US cement, account for 2.4% of US energy
consumption, according to the US Department of Energy [10].
Each ton of cement produced “requires 4.7 million BTUs of
energy, equivalent to about 400 pounds of coal” [17]. Clearly,
something must be done to lessen the environmental impact of
the production of cement. One major way to make cement
more sustainable, and consequently concrete, is to extend the
life of concrete, reducing the need for cement and improving
its overall impact on the environment. Self-healing concrete
would do just that, by preventing the concrete from
deteriorating nearly as fast as traditional concrete.
Although no conclusive testing has been done to
determine exactly how much longer self-healing concrete will
last than traditional concrete, evidence from H. M. Jonkers’
experiments show that it will greatly decrease the need for
repair and consequently extend its life by decades. Most cracks
in concrete start extremely small and can be easily healed by
the bacteria. This is sufficient to protect the concrete from
nearly all cracking except for where the structure is especially
weak and cracks form too fast. When this occurs, there is most
likely a design flaw causing the excessive cracking that is
beyond the capability of the self-healing agent to fix. Also, the
bacteria spores remain viable long enough that if the structure
is built right, it could have a lifespan of up to two centuries
without the need for extensive repair done on the concrete [8].
When compared to traditional concrete that needs maintenance
to be able to last 50 years, this is a substantial increase in the
service life of a concrete structure. With an increased lifespan
of anywhere up to 150 years depending on the stress the
structure undergoes, self-healing concrete would be
significantly better for the environment and greatly improve
the sustainability general concrete. This would not only reduce
CO2 emissions from the production of cement, but it would
also greatly reduce the energy and material needed to maintain
the structures. It would also significantly reduce the need to
demolish buildings because they were deemed structurally
unsafe. This, in turn, would decrease the cement and aggregate
needed to replace old buildings, which would positively affect
the environment. Overall, self-healing concrete is more
environmentally friendly and thus more sustainable than
traditional concrete.
FIGURE 10 [15]
The expanded clay self-healing agent
Because this agent is most effective in wet environments,
the recommended applications include, “tunnel elements,
liquid-containing reservoirs, basement walls, subsurface
constructions, marine constructions, and bridges and parking
decks” [15]. Not only can water easily damage all these
structures, but they are all very costly to repair. Construction
life cycle costs are the major reasons that lead companies to
add this agent to their concrete even though it increases the
initial cost of the structure. One reason that makes some of
these structures especially expensive to repair is that they are
heavily depended on and can’t be taken out of commission for
long periods of time. For instance, tunnels, bridges, and
reservoirs are depended on daily. Others are expensive to
repair because of their inaccessible locations, like basement
walls, tunnels, and marine structures. As this agent becomes
more affordable, it will become easier to justify including it in
the concrete mixes for structures with large estimated life cycle
costs.
THE SUSTAINABILITY OF SELF-HEALING
CONCRETE
Environmental
While concrete is a great construction material, one of its
most significant downfalls is its negative impact on the
environment. Two of its biggest environmental problems occur
during the production of cement (detailed in a previous
section). The problems with this process are that it releases
carbon dioxide (CO2, the primary greenhouse gas contributing
to global warming) and uses a massive amount of energy [16].
For every ton of cement produced, one ton of CO 2 is released
into the atmosphere [9]. The chemical reaction during the
process is responsible for 70% of the CO2 and the fossil fuels
burned produce the other 30% [9]. This industry alone “creates
Economic
The deterioration of concrete structures caused by microcracking has many economic consequences, causing
traditional concrete to not be very sustainable. According to H.
M. Jonkers, “The average annual costs for maintenance and
repair accounts for 30%–50% of the money spent in the
building industry” [4]. This is because so much of our
infrastructure is made of concrete and most of it is getting old
and needs repair. This is a major problem in the United States,
made evident in the last infrastructure report card issued by the
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American Society of Civil Engineers this year, in which our
country earned a D+ [18]. Two of the areas that received the
worst scores were our nation’s roads and bridges, both of
which are made predominantly out of concrete [18]. The report
says that over 56,000 American bridges are structurally
deficient with that number only increasing as the bridges get
older, as depicted in the graph below [18].
service life of a tunnel, then the higher price would definitely
be justified. For structures that are very costly to repair, like
dams, even just a reduction in the number of repairs needed
over its life cycle, would make self-healing concrete a more
economically sustainable material than general concrete. Once
H. M. Jonkers and his team are able to develop a less expensive
nutrient for the bacteria, the material would become
sustainable for a much wider segment of the infrastructure.
When strictly looking at the costs of self-healing concrete over
its life time it is hard to justify it as a sustainable alternative to
general concrete across the industry. However, there are
certain structures that are more prone to deterioration or are
costlier to fix for which self-healing concrete is an
economically sustainable alternative.
OVERALL SUSTAINABILITY AND FUTURE
OF THE TECHNOLOGY
When looking at the overall sustainability of self-healing
concrete compared to general concrete, the only thing against
it is its initial price. Bacillus-based self-healing concrete has
definite potential for future mass production and use in the
construction industry. The process uses bacteria to seal up
cracks in concrete structures with limestone as soon as they
form. The bacteria are very compatible with the alkaline
environment of concrete because they create spores that can
survive for centuries. The major benefit of this is that it
prevents the ingress of harmful substances into the concrete,
increasing its sustainability by extending the life of the
structure by decades.
Environmentally, bacillus-based self-healing concrete
has many superior qualities compared to traditional concrete,
including lower overall carbon emissions and lower energy
consumption. These two assets make this concrete increasingly
attractive as environmental issues become more of a concern
in the construction industry. Also, when buildings last longer
because of the self-healing concrete, the demand for aggregate
should be less than what it would have been because fewer
buildings will need to be demolished for structural reasons.
This would also be beneficial to the environment because it
would reduce the mining of aggregate. From an environmental
point of view, the sustainability of concrete is greatly increased
by adding a self-healing agent.
Economically, bacillus-based self-healing concrete does
not have as strong a case because it is still roughly twice as
expensive to produce as traditional concrete. However, it is
reasonable to assume that the price of this self-healing agent
will drop in the future as more technological breakthroughs
occur in the field. One big step to reducing its cost would be to
invent a cheaper food source for the bacteria, which H. M.
Jonkers and his team seem close to achieving. Still, in many
cases, the high initial cost is justified considering the
structure’s estimated life cycle. Thus, for certain projects, selfhealing concrete can prove to be economically sustainable.
FIGURE 11 [18]
Age of bridges in the US
Roads are in similar disrepair and the estimated backlog
of highway and bridge capital needs is $836 billion. It is clear
from these reports that traditional concrete is a very costly
material to maintain for the service life of any structure, but
does self-healing concrete provide a more sustainable and
cheaper alternative even with its initially higher price tag?
The main hurdle that the producers of self-healing
concrete have yet to overcome is the materials price. For H. M.
Jonker’s method, which is the closest to production,
The production cost is still twice the cost of regular
concrete manufacture (€80/m3). A large part of the
cost is the expensive calcium lactate nutrient for the
bacteria, but Jonkers and his team are well
underway to creating a sugar-based nutrient, which
would reduce the cost to a level far closer to that for
regular concrete (e.g. between €85/m3 and
€100/m3), making it a viable additive and
sustainable prevention method [12].
The fact that the current price of the self-healing agent doubles
the cost of traditional concrete definitely weakens its financial
sustainability. Without the advanced testing that would tell us
exactly how much money self-healing concrete would save
over its lifespan, it would be more difficult to justify its initial
cost for its future savings. However, the higher price might be
justified if building something that has a high life cycle cost.
For instance, if the self-healing concrete would double the
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Ivan Menz
Duncan Clear
When considering both factors, self-healing concrete is
sustainable when used for structures that are prone to crack and
for companies that place a high value on green products.
Concerning the future of the technology itself, it seems likely
that it will continue to get more advanced and effective. This
technology began in the early 1990s with simple glass capsules
containing glue. Today, this technology has advanced to an
entirely new level. Currently, the glass capsule has been
replaced with expanded clay particles or innovative polymer
and hydrogel technology, and the healing agent has been
upgraded to limestone producing bacterium. Adding a
bacillus-based self-healing agent to general concrete is a
sustainable method of preventing the cracks that form in
concrete from damaging the whole structure. By extending the
service life of structures, reducing the money spent on
maintaining them, and lessening their negative environmental
impact, this product will improve the lives of future
generations.
_Netherlands/links/54ee2e4b0cf2e55866f231e2.pdf#page=67
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[8] P. Patel. “Helping Concrete Heal Itself.” Chemical and
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[11] A. Stewart. “The 'Living Concrete' That Can Heal Itself.”
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[13] R. Spinks. “The Self-Healing Concrete that can Fix its
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[16] “Emissions from the Cement Industry.” State of the
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[17] “Can Concrete be Eco Friendly?” Green Living Ideas.
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[18] “Infrastructure Report Card.” American Society of Civil
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[1] P. Abigail. “Does the Future of Sustainable Construction
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[7] H. M. Jonkers, E. Schlangen, E. Tziviloglou. “BacteriaBased Self-Healing Concrete to Increase Liquid Tightness of
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P. Lopez, K. Reynolds, S. Sedgwick, J. Wilkening. “Industrial
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56. p.6
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Duncan Clear
ACKNOWLEDGMENTS
Thank you to our co-chair, Emily Adelsohn, for
encouraging us to get working on this paper, even though we
didn’t want to start. Getting started was the hardest part and
once we did, things started to fly.
Many thanks to Michael Cornelius, our writing
instructor, for the helpful revising tips on our draft.
Thanks also to our two chairs, Louis Gualtieri and
Nicholle Piper, for their expert advice on our outline and first
draft and how best to write this paper professionally.
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