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

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

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

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.

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

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.

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

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.

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%,

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

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

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.

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).

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).

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).

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).

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.

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.

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

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

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

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.

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

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)

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.

a

References

Achal, V., Mukherjee, A., & Reddy, M. S. (2010). Microbial Concrete: A Way to Enhance the

Durability of Building Structures. Journal of Materials in Civil Engineering, 23(6). doi:

10.1061/(ASCE)MT.1943-5533.0000159

Angel, J. (2013, August 31). Climate Observations for Champaign-Urbana, IL (Rep.). Retrieved

October/November, from University of Illinois, Urbana Champaign website:

http://www.isws.illinois.edu/atmos/statecli/cuweather/

Cocks, J. (2013, June 7). Roman concrete provides the secret for modern advances. Archaeology

News from Past Horizons RSS. Retrieved from

http://www.pasthorizonspr.com/index.php/archives/06/2013/roman-concrete-provides-

the-secret-for-modern-advances

Demuynck, W., Debrouwer, D., Debelie, N., & Verstraete, W. (2008). Bacterial carbonate

precipitation improves the durability of cementitious materials. Cement and Concrete

Research, 38(7), 1005-1014. doi: 10.1016/j.cemconres.2008.03.005

Herbert, E. N. and Li, V. C., (2011). “Self-healing of engineered cementitious composites in the

natural environment.” In: High Performance Fiber Reinforced Cement Composites 6,

Ann Arbor, MI, USA, June 20-22.

Jonkers, H. M., (2011). “Bacteria-based self-healing concrete.” Heron, 56(1/2), 1-12.

Jonkers, H. M., & Schlangen, E. (2008). Development of a bacteria-based self healing concrete.

Tailor Made Concrete Structures.

Li, V. C.; Fischer, G.; Lepech, M.(2004). "Crack Resistant Concrete Material

b

for Transportation Construction" Transportation Research Board 83rd Annual Meeting,

Transportation Research Board 83rd Annual Meeting, Washington, D.C., Compendium

of Papers CD ROM, Paper 04-4680, 2004. <http://hdl.handle.net/2027.42/84828>

Li, V.C., & Herbert, E. (2012). Robust Self-Healing Concrete for Sustainable Infrastructure.

Journal

of Advanced Concrete Technology, 10, 207-218.

Li, V. C., Stang, H. and Krenchel, H. (1993). “Micromechanics of crack bridging in fiber

reinforced concrete.” J. of Materials and Structures, 26, 486-494.

Mather, B. and Warner, J., (2003). “Why do concrete repairs fail.” Interview held at Univ. of

Wisconsin, Dept. of Eng. Professional Development, MD, WI,

<http://aec.engr.wisc.edu/resources/rsrc07.html>. Accessed, Nov., 2013.

Mechtcherine, V. (2006). “Testing the behavior of strain hardening cementitious composites in

tension” 1–8. Retrieved from

http://tchfc.engin.umich.edu/doc/HawaiiPapers/A/Mechtcherine-Testing.pdf

Prabhakara, R. (2013). “Bio Mineralisation Of Calcium Carbonate By Different Bacterial Strains

And Their Application In Concrete Crack Remediation.” International Journal of Advances

in Engineering & Technology, 6(1), 202–213.

Ramachandran, S. K., Ramakrishnan, V., & Bang, S. S. (2001). “Remediation of concrete using

micro-organisms.” Materials Journal, (98), 3–9. Retrieved from

http://sphinx.murdoch.edu.au/units/extern/BIO301/teach/download/Chemostat/B. pasteuri

literature examples/Concrete remediation with B. pasteurii.pdf

c

Rice, A. (2013, January 27). New York Magazine. NYMag.com. Retrieved from

http://nymag.com/news/features/tappan-zee-bridge-2013-2/

Sahmaran, M. and Li, V. C., (2008). “Durability of mechanically loaded engineered cementitious

composites under highly alkaline environments.” Cement and Concrete Composites, 30,

72-81.

Wu, M., Johannesson, B. and Geiker, M., (2012). “A review: Self-healing in cementitious

materials and engineered cementitious composite as a self-healing material.”

Construction and Building Materials, 28, 571-583.

Yang, Y., Lepech, M. D., Yang, E. and Li, V. C., (2009). “Autogenous healing of engineered

cementitious composites under wet-dry cycles.” Cement and Concrete Research, 39, 382-

390.