1. Next Generation Self-Healing Concrete:
Infusing Bacteria into Engineered Cementitious Composite
Benjamin Kaplan
Newmark Civil Engineering Laboratory
&
Byram Hills High School, Armonk, New York
Mentor: Paramita Mondal
Department of Civil and Environmental Engineering
University of Illinois at Urbana-Champaign

2. i
TABLE OF CONTENTS
ACKNOLEDGEMENTS ………………………………………………………………… iii
LIST OF FIGURES………………………………………………………………………. v
SECTION
I. ABSTRACT……………………………………………………… 1
II. INTRODUCTION………………………………………………... 2
III. REVIEW OF LITERATURE …………………………………….
Robust Self-Healing
Autonomous Self-Healing and its Limitations
Bacterial Concrete: A Novel Approach to Self-Healing
Engineered Cementitious Composite: The Leading Approach
to Self-healing
Self-Healing in the Field
Combining the Approaches: A Novel Solution
2
2
3
4
5
6
6
IV. HYPOTHESIS………………………………………………….. 7
VI. OBJECTIVES…………………………………………………... 8
VII. METHODS & MATERIALS…………………………………...
My Role in the Study
Mix Amount and Raw Materials
Nutrient Medium and Bacteria Culturing
Specimen Preparation
Resonant Frequency Testing and Tensile Damaging
Environments
Sorptivity Testing
Compressive Strength Testing
Statistical Testing
8
8
9
9
10
11
11
12
13
13

3. ii
VIII. RESULTS & DISCUSSION……………………………………
Self-Healing in Beams
Differences amongst ECC types
Environmental Tests
Laboratory
Exposed
Underground
General healing trends
Sorptivity Testing
Compressive Strength Testing
13
13
14
15
15
15
16
16
17
19
IX. CONCLUSION…………………………………………………. 20
REFERENCES………………………………………………………………………….. a

4. iii
Acknowledgements
I would like to thank my mentor, Dr. Paramita Mondal, her doctoral candidates: Pete
Stynoski and Bin Zhang along with graduate student Jeevaka Somaratna, my science research
advisors: Mr. David Keith, Mr. Ken Kaplan, and Ms. Stephanie Greenwald, and lastly my
parents: Dr. Howard Kaplan and Ms. Jennifer Lacks Kaplan, my stepmother: Janet Shimer, and
my grandfather: Dr. Sanford Lacks.

5. iv
LIST OF FIGURES
Figures Page
1. Ben Kaplan testing the flowability of an ECC mix……………….…….. 8
2. ECC mixture in midst of flowability test………………………………... 9
3. Petri dishes with mature Sporosarcina pasteurii culture………………... 10
4. Set up all mold fixtures used in experiment……………………………... 10
5. Instrom 4502 applying tensile damage to ECC practice beam………….. 11
6. Concrete in the laboratory, exposed, and underground environments…... 11
7. Comparison of self-healing amongst all experimental groups…………... 13
8. Comparison of self-healing amongst ECC types………………………... 14
9. Comparison of self-healing amongst environmental groups…………….. 15
10. Correlation between resonant frequency damage and subsequent
increase…………………………………………………………………... 17
11. Increase in mass (by %) due to water absorption………………………... 17
12. Comparison of exponential rates of absorption………………………….. 18
13. Comparison of compressive strength……………………………………. 19
14. OPC cube post compressive strength failure…………………………….. 19

6. 1
Abstract
Concrete is vulnerable to a variety of aggressive environmental agents; yet, our
dependence on it has never been greater. Such aggressors can cause concrete to crack and lose
strength, accelerating the degradation process until the concrete is ineffectual. Self-healing stops
this by remediating initial micro-cracks. Two of the leading approaches of self-healing are
Engineered Cementitious Composite (ECC) and bacterial concrete. My study combined both and
assessed the resulting hybrid in multiple environments. Resonant frequency values were
measured for concrete beams before and immediately after application of tensile damage, and
again after each beam was allowed to heal in its environment for 28 days. Additionally,
absorption and compressive strength tests were performed on ECC, Ordinary Portland Cement
(OPC), and bacterial-ECC cubes in order to measure compatibility between ECC and bacteria.
Results showed that ECC infused with Sporosarcina pasteurii showed statistically greater
healing (p = 0.042) than normal ECC. Furthermore, there was no significant difference for
healing in an underground environment versus optimal laboratory conditions (p = 0.44), a find
previously unreported in literature. In the exposed environment, self-healing was negligible.
Underground concrete foundations are found in nearly all infrastructure and residential projects,
so underground self-healing is incredibly practical, and the success of bacterial-ECC in this
environment lays the foundation for further field studies.

7. 2
Introduction
The Tappan Zee Bridge, a vital lifeline for New York State crossed by 50 million
vehicles annually, is crumbling; chunks of concrete are falling from the bridge deck and into the
Hudson River (Rice, 2013). Such decrepitude is emblematic of The United States’ infrastructure
as a whole, which the American Society of Civil Engineers rated a D+ in need of over $2.2
trillion for repairs and retrofits (ASCE, 2013; Li, 2012). At the center of these problems is
concrete. American construction relies heavily on concrete for nearly all infrastructure projects,
yet it is vulnerable to degradation from harmful chemicals (e.g., chlorides and sulfates), freeze
thawing, tensile stressing, and shrinkage (DeMyunck, 2008; Jonkers, 2008). Concrete is often
difficult to repair because the damage can be hard to locate as well as access, and only half of
repairs are even permanently successful (Li, 2012; Mather and Warner, 2003). Furthermore,
concrete production produces over 7% of humanity’s carbon footprint, creating an environmental
impetus for longer lasting concrete (James, 2013). Because of these economic and environmental
concerns, there is a need for more durable concrete, leading to the aim of my study: To explore a
never before created combination that will help make the next generation of concrete possible.
Review of Literature
Robust Self-Healing
Recently, self-healing concrete has emerged as a potential solution for infrastructure
inadequacies, but to become a practical solution, it must first meet the criteria of robustness:
defined as self-healing that realizes ever-readiness, high quality restoration, pervasiveness,
reliability, versatility, and repeatability (Li, 2012). Ever-readiness means that the self-healing

8. 3
mechanism lasts and is fully functional for the entirety of an infrastructure’s service life
(typically 50-100 years). Pervasiveness ensures that the mechanism is omnipresent in the
concrete, so that any crack may be healed wherever they occur. High quality restoration requires
that self-healing not only seal cracks but restores former mechanical and transport properties by
forming new chemical bonds within the concrete matrix. Versatility ensures that self-healing can
take place in whatever environment or conditions the concrete is exposed to. Finally,
repeatability guarantees that the self-healing process can be repeated ad infinitum in any one
area; a must since damage is often applied cyclically in the same locale. If all criteria are met,
then concrete can continuously maintain peak performance and save significant allocations of
money and manpower over time.
Autonomous Self-Healing and its Limitations
First noticed in 1863 by the French Academy of Science, autonomous concrete self-
healing usually occurs when calcium carbonate crystallizes in the concrete matrix, filling cracks
and forming a new support structure (Wu, 2012). This happens when water liberates calcium
hydroxide and disperses it into cracks where new calcium carbonate crystals take root, grow, and
heal the concrete. However, as Jonkers & Schlangen (2008) point out, this process is limited
because the healing agents are consumed in the process, and cracks larger than 100-200 µm are
too large to be remediated this way. As a result, researchers have begun looking for ways to
enhance concrete’s intrinsic self-healing and add new mending mechanisms in order to obtain
robust self-healing.

9. 4
Bacterial Concrete: A Novel Approach to Self-Healing
Concrete researchers have turned towards biomineralizing bacteria in their quest to
achieve robust self-healing. Bacterial concrete consists of urelytic bacteria mixed in, sprayed on,
or encapsulated within the concrete and capable of utilizing microbial induced calcium carbonate
precipitation to seal cracks and pores. The enzyme urease catalyzes urea (CO(NH2)2) into
ammonium (NH4
+
) and, most importantly, carbonate (CO3
2–
). Carbonate is then attracted to
metal cations on the bacterial cell wall and begins to nucleate into calcium carbonate crystals,
which strengthens the cement matrix and seal cracks (Wu, 2012).
Researchers have identified bacteria found in the Bacillus genus, and other closely related
genera, as ideal for bacterial concrete (Prabhakara, 2013). Found naturally within soil, sewage,
and even urinal incrustations. Bacilli are capable of producing endospores: nearly invulnerable
stripped down bacteria cells capable of surviving for possibly millions of years and able to
tolerate intense heat, extreme freezing, desiccation, light radiation, and most chemical
disinfectants. Consequently, Baccili can not only handle the harsh alkaline environment of
concrete but also remain present and prepared for activation within the infrastructure’s long
lifespan.
Bacteria have been found to heal cracks capable of up to 460 µm and restore all transport
properties, theoretically extending a structure’s lifespan by 30% (Jonker’s 2011). Furthermore,
laboratory studies have shown that adding bacteria enhances many additional properties of
concrete. Studies mixing bacteria into the mortar have obtained a six-fold decrease in water
absorption (sorptivity) and an increase in compressive strength of 36.15% (Achal, 2010).
Similarly, it was found that merely applying bacteria plus nutrients to the surfaces of mortar
cubes increases resistance to gas permeability by 50%, carbonation/degradation by 25-30%,

10. 5
chloride migration by 10-40%, as well as freeze thawing (Demuynck, 2008). Unfortunately,
there are still a few drawbacks to the bacterial approach. Bacteria can only remediate cracks
when moisture is present and bacterial self-healing does not lead to a significant regain of
mechanical strength (Li, 2012; Wang, 2012). In addition, there exists a dearth of literature due to
the novelty of bacterial concrete; for example there appear to be no published tests of bacterial
concrete in field environments. Hence, this study combines bacterial concrete with ECC in order
to address the aforementioned pitfalls; an approach heretofore unreported in the literature.
Engineered Cementitious Composite: The Leading Approach to Self-healing
ECC is micromechanically-designed: a material for which the mechanical interactions
between fibers, matrix and interface are taken into account by micromechanical models (Li,
1993; Mechtcherine, 2006). In other words, ECC is “tailored” so that every component is
selected to minimize crack growth and ensure an abnormally high ductility, 500 times that of
OPC. Consequently, when tensile strain is applied to the point of first cracking, the fibers bridge
the crack and engage in strain hardening: the strengthening of a metal (or in the case of ECC, a
substance that acts like a metal) by plastic deformation. This transfers the tensile stain across the
surface and thereby limits crack size to a predetermined amount, causing a new micro crack to
form at the material’s next weakest point. This progression perpetuates so that the mortar’s
matrix is permeated with mostly harmless microcracks instead of being marred by one crippling
crack.
Consequently, ECC possesses remarkable durability alongside greatly enhanced
autonomous self-healing. Because ECC limits its cracks to a manageable size (determined by the
mix designer), autonomous self-healing is almost always able to take place. Crack healing of up

11. 6
to 150 µm has been documented (Li, 2012; Yang, 2009). Furthermore, ECC’s controlled
cracking confers additional resistance against high temperatures and humidity, water permeation,
shrinkage (drying out), chloride attacks, alkaline attacks, freeze thaw attacks, and tensile strain.
Remarkably, even under these adverse conditions, ECC can still self-heal (Sahmaran, 2010).
However, ECC still suffers from a high initial material cost, approximately twice that of regular
concrete. Nevertheless, field testing shows that ECC’s arsenal of benefits more than overcomes
this pitfall.
Self-Healing in the Field
In 2011, Herbert and Li conducted a study in which ECC was allowed to self-heal outside
from late winter to spring in Michigan. Upon its completion, crack healing for the majority of
cracks under 20 µm was documented, and up to 90% of initial resonant frequency values were
recovered; however, this underperformed lab studies where cracks of up to 150 µm were healed
and 100% of resonant frequency value recovered. It appears that there is a discrepancy between
self-healing in laboratory and field conditions. As for bacterial concrete, no field studies have
been published yet, something this paper’s study addresses.
Combining the Approaches: A Novel Solution
Uniting the healing power of bacteria with the intrinsic crack-controlled healing of ECC
should yield a more robust hybrid with greater self-healing than either of its parent approaches.
The greatest weakness of all forms of self-healing is large crack widths, but this is counteracted
by ECC; thereby bolstering bacterial self-healing. As Jonkers & Schlangen (2008) have called
attention to, autonomous self-healing (which is augmented and utilized by ECC) is checked by

12. 7
the limited materials available for calcification; however, this is ameliorated by microbial
induced calcium carbonate precipitation. Combined together, ECC and bacterial concrete form a
two-pronged synergistic approach that in theory minimizes each method’s weaknesses while
maximizing their respective benefits. Prior to my study, this approach had not been tried or
tested in either laboratory or field conditions.
Hypotheses
H01: Bacterial-ECC (ECCbacteria) will not show additional self-healing capabilities compared with
the control groups, which are regular ECC (ECCregular) and ECC infused with bacterial medium
but not bacteria (ECCmedium).
H1: ECCbacteria will show greater self-healing capabilities than the control groups as measured by
the average increase of resonance frequency (RF) following a 28-day healing period.
H02: There will be no difference in self-healing capabilities of both the field environment,
underground as well as exposed, compared with the laboratory setting.
H2: Self-healing in laboratory conditions will be greater than self-healing in an underground
environment and that will in turn be greater than self-healing in the exposed environment, the
last of which will show little if any self-healing.
H03: There will be no difference in compressive strength or sorptivity (rate of water absorption)
amongst all groups.
H3: The addition of bacteria to ECC will yield a boost in compressive strength and a decrease in
water absorption, demonstrating the compatibility between ECC and bacteria.

13. 8
Objective
The purpose of this study was to infuse bacteria into Engineered Cementitious Composite
and investigate the resulting hybrid. Specifically:
1. To evaluate the hybrid’s self-healing capabilities against the control groups’.
2. To assess self-healing in field environments as well as in the laboratory.
3. To assess the effectiveness of the combined the approach with benchmark compressive
and sorptivity testing.
Methods & Materials
My Role in the Study
I independently conceived of my study and presented the
idea to my mentor, Dr. Paramita Mondal, in mid-spring 2013.
Over the course of nine weeks during the summer, I conducted
my study at the Newmark Civil Engineering Laboratory. There,
my mentor’s doctoral candidates trained me to mix, cast, and de-
mold all concrete samples on my own. One of the doctoral
candidate and I prepared the bacterial medium, during which I
mainly provided assistance measuring and mixing the needed
constituents. I had help preparing a heated curing chamber/water
bath, but I solely set up the underground environment. Later, I
coordinated with two other students for resonant frequency
testing, tensile damaging and compressive strength testing.
Lastly, I alone performed all statistical testing.
Fig. 1. Ben Kaplan testing the
flowability of an ECC mix (photo
by author).

14. 9
Mix Amount and Raw Materials
The ECC mix as well as equivalent OPC mix was derived from ECC R0 (Li, 2004).
However, the proportion of superplasticizer used was changed following several mix trials and
the PVA fibers were unable to be coated in oil due to the unavailability and patenting of the
treatment. All mixes used 446.39 g of cement, 446.05 g of F-110 silica sand, 11.90 grams of
PVA fibers, and 178.90 g of water, nutrient medium, or bacteria suspended in nutrient medium.
For ECC mixes, 1.60 g of ADVA Cast 575 (Grace Construction Products, Columbia, MD) was
incorporated into the water, suspension, or medium and contributed towards the total mass of
178.90 g. The W/c was 0.395.
Nutrient Medium and Bacteria Culturing
The liquid nutrient medium incorporated 20.00 g of yeast within 400 mL of distilled
water, 10g of Ammonium Sulfate (NH4)2SO4 within 300 mL of distilled water, and 15.73 g of
tris ((HOCH2)3CNH2) within 300 mL of distilled water. All constituents were autoclaved in the
aforementioned amounts and then mixed together in sterile conditions. Solid medium for
Fig. 2. ECC mixture in midst of flowability test (photo by author).

15. 10
bacterial culturing was prepared consisting of 40 mL of yeast (2.00 g), 20.00 mL of Ammonium
Sulfate (NH4)2SO4 (1.00 g), 20.00 mL of tris (1.57 g), and 20 ml of Agar (2 g).
Sporosarcina pasteurii (formerly known as Bacillus pasteurii), designation ATCC 11859,
was acquired from the American Type Culture Collection (ATCC) bacterial bank at Manassas,
VA in January 2011. Specimens were cultivated at 30°C on a shaking table for 24 hours, as
recommended by the supplier, and placed in petri dishes for future use. 24 hours prior to mixing,
the bacteria were allowed to propagate in nutrient media and at 30°C on a shaking table.
Specimen Preparation
All constituents were mixed using a Hobert mixer.
Following this, specimens were cast in 30.48 x 2.54 x 2.54 cm
(12 x 1 x 1 inch) molds for beam specimens and 5.08 x 5.08 x
5.08 cm (2 x 2 x 2 inch) molds for cube specimens. All beams
samples were cured for one week before being bisected and
trimmed into two 12.7 x 2.54 x 2.54 cm (5 x 1 x 1 inch) beams.
Fig. 3. Petri dishes with mature Sporosarcina pasteurii culture (photo by author).
Fig. 4. Set up all mold fixtures
used in experiment (photo by
author).

16. 11
Resonant Frequency Testing and Tensile Damaging
After allowing seven days of curing, each
beam specimen was tested for resonant frequency
according to ASTM C 215 standard procedures
using a LeCroy Waverunner LT344 digital
oscilloscope. Subsequently, each beam was placed
into an Instrom 4502 load frame with a three-point
test apparatus and damaged until first crack.
Immediately thereafter, each sample was again
tested to measure the drop in resonant frequency
value. Finally, the specimens were placed in their
proper environment for 28 days after which they
were again tested for resonant frequency values.
Environments
Fig 5. Instrom 4502 applying tensile damage to
ECC practice beam (photo by author).
Fig. 6. Concrete in the laboratory, exposed, and underground environments, from left to right respectively
(photo by author).

17. 12
Each environment was selected to convey conditions concrete experiences on a day-to-
day basis in the field. The control environment consisted of optimal conditions for self-healing in
a laboratory: an enclosed water bath heated to 30°C (86° Fahrenheit) with samples curing in
limewater. The first experimental environment was the exposed environment. In it, specimens
were placed outside on a ledge by the laboratory’s north side, exposed to the summer sun, air,
winds, and (infrequent) rain. This was chosen to represent more exposed placements of concrete
found above a building’s foundation. The other experimental environment was underground, also
by the building’s north side. Samples in this environment were given a day to re-saturate before
being buried at an approximate depth of 21.6 cm (8.5 inches). Following burial, soil was re-
compacted. Each environmental group consisted of twelve 12.7 x 2.54 x 2.54 cm (5 x 1 x 1 inch)
beams with four ECCregular beams, four ECCmedium beams, and four ECCbacteria beams. Outdoor
temperatures during this time were typically within 16-26° Celsius (60-80° Fahrenheit) with
lows between 10-16°C (50-60° F) and highs between 26-32°C (80-90° F). Rainfall was
infrequent and thus conditions were dry (Angel, 2013).
Sorptivity Testing
Testing was conducted according to ASTM C642 standard procedures. All cubes were
dried for 48 hours in a Solitest L-72A oven at 110°C. Cubes were then allowed to cool overnight.
Next, the cubes were weighed and then fully immersed in water. At the time intervals of 0.25,
0.5, 1, 1.5 hours, 2, 3, 6, 24, 48, and 52.5 hours, cubes were removed from the water, towel dried,
and weighed again.

18. 13
Compressive Strength Testing
Following sorptivity testing, each cube was then oven dried for another 48 hours and
cooled overnight in order to minimize any differences due to differing water content.
Compressive strength tests were then conducted using a Forney QC-0410-D3 point load frame.
Statistical Testing
The analysis of all tests except sorptivity was conducted using Microsoft Excel software.
Groups of beams were compared using independent, paired, one-tailed Student’s T-tests, and
alpha was set at 0.05 for the entire study. The correlation between damage done and subsequent
healing was measured using Pearson’s R tests. Finally, for sorptiviy testing, the software
Mathematica was used to calculate each sample’s saturation curve to the fit A(1 - e(-k *t)
), where A
is the amplitude, k the rate determining exponent, and t time in hours.
Results&&&Discussion&
Self-Healing in Beams
Fig. 7. Comparison of self-healing amongst all experimental groups. Control = laboratory environment.

19. 14
Note that resonant frequency (RF) increases as a sample continues to undergo the curing
process, so RF gains due to self-healing may be exaggerated in an absolute sense, but this will
have little impact on the relative results that this study centers on.
Differences amongst ECC types. Self-healing for ECCbacteria significantly exceeded that
of ECCregular (p = 0.042) and ECCmedium (p = 0.007) samples. Bacterial specimens showed the
greatest self-healing, augmenting Resonant Frequency (RF) by an average of 9.69% under all
conditions. Specifically, RF for the laboratory environment increased 13.20%, the exposed
2.62% and the underground 13.26%. The average resonant frequency gain for ECCregular samples
was 7.97%, such that the laboratory, exposed, and underground environments increased 11.37%,
1.74%, and 10.81% respectively. For the ECCmedium samples, there was no significant difference
in self-healing when compared to the ECCregular groups (p = 0.392). ECCmedium averaged a 7.61%
RF increase whereby RF for the laboratory, exposed, and underground environments grew
11.70%, 0.60%, and 10.55% respectively.
Fig. 8. Comparison of self-healing amongst ECC types

20. 15
Environmental Tests. Notable self-healing occurred within both the laboratory and
underground environments, but not the exposed environment. Markedly, in contrast to the
hypothesis, specimens within the underground environment exhibited statistically equivalent
rates of self-healing (p = 0.44). Therefore, both the laboratory and underground environment
were equally conductive towards self-healing. While conditions between the underground and
laboratory environments were not equal per se, both environments were equally sufficient for
self-healing to proceed at its full potential.
Laboratory. All samples fully recovered and exceeded resonant frequency values prior to
damage. RF increased by an average of 12.09%, with the regular, medium, and bacteria groups
gaining 11.37%, 11.70%, and 13.20% respectively. Laboratory samples showed no loss of mass,
and demonstrated slight calcium deposits on their surface from the limewater solution.
Exposed. Samples failed to fully recover RF during the 28-day healing interval, on
average yielding only a 1.65% increase (13.81% recovery) with the regular, medium, and
bacteria groups gaining 1.74%, 0.60%, and 2.62% respectively. On average, mass decreased
Fig. 9. Comparison of self-healing amongst environmental groups

21. 16
2.59% due to dehydration resulting from exposure to the dry atmosphere for four weeks. Hence,
samples appeared dry and brittle, and the lack of water arrested the self-healing process. In
contrast, Li and Herbert found 90% R.F recovery (2011). However, that study was conducted in
Michigan between February and May—a far moister climate than central Illinois between July
and August. Additionally, the discrepancy might also be merely a matter of the samples’ sizes;
Li et al. used larger beams less likely to suffer from detrimental dehydration, but even larger
samples will eventually dry out. This raises the question of whether self-healing is viable for arid
environments.
Underground. All samples fully recovered and exceeded resonant frequency values prior
to damage. RF increased by an average of 11.54%, with the regular, medium, and bacteria
groups gaining 10.81%, 10.55%, and 13.26% respectively. Underground samples showed no loss
of mass, and the surfaces appear to have remained moist for the duration of the four-week period.
Evidently, despite the laboratory environment samples’ immersion in limewater and curing at a
higher temperature, gains in RF where equal, suggesting that concrete is capable of full
underground self-healing.
General healing trends. For each environment, RF regains showed a statistically
significant positive correlation with the level of damage induced into the beam (r = 0.90 & p =
0.000036, r = 0.55 & p = 0.033, and r = 0.86 & p = 0.00014 for the laboratory, exposed, and
underground environments respectively). Theoretically, both bacterial healing and autonomous
healing (enhanced by ECC) should achieve these correlations. In ECC, strain hardening becomes
more widespread with more cracks, and in bacteria, widespread cracking allows more oxygen

22. 17
and water to enter the matrix. Interestingly, one beam specimen was accidently damaged beyond
first cracking, achieving only 16.79 % healing despite an initial RF decrease of 39.9%). This
serendipitous sample demonstrated the limitation of self-healing and reaffirmed results from
other studies that have shown a maximum crack size after which ECC self-healing ceases to be
effective.
Sorptivity Testing
Fig. 11. Increase in mass (by %) due to water absorption.
0.00%$
2.00%$
4.00%$
6.00%$
8.00%$
10.00%$
12.00%$
0$ 10$ 20$ 30$ 40$ 50$ 60$
%&Water&Uptake&
Time&[hrs]&
OPC/R/A$
OPC/R/B$
OPC/R/C$
OPC/M/A$
OPC/M/B$
OPC/M/C$
OPC/B/A$
OPC/B/B$
OPC/B/C$
Fig. 10. Correlation between % decrease due to tensile damaging and subsequent increase due to self-healing.

23. 18
Results for Sorptivity testing demonstrated little inherent difference between final
absorption for each cube, and though notable differences in the rate of absorption were recorded,
the results proved inconclusive. Using the fit A(1 - e(-k*t)
), all groups demonstrated a similar
amplitude (A) of 10.58 ± 0.59, but the exponent (k) of absorption (which determined the rate)
varied considerably.
• OPC-R: k = 0.72
• OPC-M: k = 0.28
• OPC-B: k = 0.35
• ECC-R: k = 0.46
• ECC-M: k = 0.40
• ECC-B: k = 0.38
Despite the bacteria cubes having the highest air entrapment of all the groups (as
evidenced by their slight but notably lower mass per size), they demonstrated lower than average
absorption, but not to the extent of previous literature. One possible explanation for this
(supported by the compressive strength data below) is that the heating treatment may have over-
dried the cube and resulted in a proliferation of micro cracks capable of bypassing any sealing
that resulted from microbial
induced calcium carbonate precipitation. Though each sample was dried at the proper
temperature and time according to the standard, the cubes were under the recommended size and
mass. Consequently, micro cracking appears have been severe enough to allow a notable ingress
of water.
Fig. 12. Comparison of exponential rates of absorption

24. 19
Compressive Strength Testing
Data from compressive strength testing also supports the notion that widespread micro
cracking was present within the cube specimens. OPC cubes exhibited inconsistent strength
characteristic of random defects within the concrete being exacerbated by micro cracking, so
compressive strength testing was deemed inconclusive for OPC cubes. However, the ECC cubes
showed consistent points of failure due to ECC’s inherent resistance to heat damage and ability
to heal micro cracks. Contrary to expectations, ECCbacteria samples demonstrated 13.59% lower
compressive strength; while the ECCmedium samples were on par with ECCregular (medium samples
were only 1.39% less). At first glance, this conflicts with most existing literature; however
Ramachandran et al. (2001) have found an explanation for this phenomena: dead bacterial
biomass created by premature cell death will weaken the mortar over time, and the high pH of
limewater plus oven heating likely killed the bacteria before endosporulation could occur.
Conclusion
Bacterial healing complements ECC’s enhanced autonomous self-healing, notably
increasing remediation rates and thus confirming H1. Outside of the laboratory, rates of self-
healing depended upon the environmental conditions. As anticipated, samples performed poorly
Fig. 13.Comparision of compressive strength amongst all ECC
samples (blue) and group averages (red).
Fig. 14. OPC cube post compressive strength failure.
(photo by author)

25. 20
in exposed environments, but showed serendipitous success underground; hence, H2 has been
confirmed in part.
Bacterial-ECC’s proof of concept paves the way for future inquiries into the possibility of
bacteria becoming a component of robust self-healing concrete. More sophisticated bacterial
self-healing methods, such as encapsulation, should be explored with ECC; such a combination
may likely satisfy Li’s criteria for robustness (Li, 2012). Further, the success of underground
healing warrants additional investigation. Follow up studies should be done to determine the
effectiveness of underground self-healing in dissimilar soils (differing in pH and/or moisture
content) and to investigate additional environments, such as underwater conditions (e.g., flowing
rivers, still ponds, tidally exposed levees). Preferably, studies should also look for differing
results in various seasons and climates. They should also utilize alternative methods of
measuring self-healing in order to fully ascertain both self-healing and self-sealing of cracks.
Underground foundations are paramount to nearly every construction project from a streetlight to
a stadium, and endowing robust self-healing onto these structures will go a long way towards
solving humanity’s concrete conundrum. Self-healing concrete in its current stage has not yet
reached the level of practicality needed for commercialization. Saving our crumbling bridges,
highways and buildings will require new methods of concrete composition. By combining
bacteria and ECC, and evaluating this hybrid’s robustness in real field environments, my study
validated a new approach for creating a durable, safe, and environmentally friendly infrastructure.

26. a
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