Cardiff University: Self-Healing Concrete Efficiency Variables Report

This report, based on experimental work conducted at Cardiff University, investigates the efficiency of self-healing concrete, focusing on the application of shape memory polymers (SMP) for crack closure and the enhancement of autogenous healing. The literature review covers both autogenic and autonomic healing techniques, including the use of SMP tendons activated by electrical heating, and the report outlines methods for measuring self-healing efficiency. The study delves into the properties of concrete, the mechanisms of self-healing, and the factors influencing it, such as crack size and age. The methodology involves theoretical analysis of PET tendons and experimental procedures, including the testing of concrete specimens with varying SMP configurations. The findings aim to evaluate the effectiveness of SMP in improving the durability and reducing the life cycle costs of concrete structures, addressing the increasing need for sustainable construction practices and reducing environmental impact.

Running head: EFFICIENCY OF SELF HEALING IN CONCRETE
Variables affecting the efficiency of Shape Memory Polymers healing in Concrete
Name of the student:
Name of the university:
Author note:

1
EFFICIENCY OF SELF HEALING IN CONCRETE
2. Literature review:
2.1 Introduction:
The report is based on the experimental work that is undertaken so as to create a brief
study based on the scheduled testing of shape memory polymers on crack closure arrangement
and also to identify the structural elements of concrete. A detailed review of the self-healing
polymers is thus carried out in Chapter 2 while focusing on the Autogenic as well as autonomic
healing techniques. Besides these techniques, the literature review also talks about the passive
and active process of self-healing techniques. The chapter also discusses about the trying of the
shape memory polymers including the PET tendons. The detailed procedure of the Shape
Memory Polymers concrete crack closure arrangement is determined with the help of activated
heating mechanism. In this context, the activation methods used are described in details. Besides
all these, the self-healing efficiency measuring tests are also identified and discussed within the
chapter 2 of the literature review while outlining the justification for choosing the types of tests.
2.2 Concrete:
Concrete is defined as a combination of cements along with water, and other sand courses
that are been used in different forms from the past time. The Romans were known especially for
their concrete based structures. In present days concrete is determined to be one of the
extensively used material for structure around the world. It is assessed that about 11 billion of
concretes are being produced all over the world on an annual basis. Concrete has its several uses
starting from constructing of tall structures to constructing of the longest and deepest tunnels for
passing railways around the world. It is estimated that about one cubic meter of concrete
typically costs between $65 - $85 and is relatively cheaper than any other materials that are

2
EFFICIENCY OF SELF HEALING IN CONCRETE
getting used within the construction sites. Concrete structures used within the construction
industries are mainly two different types. One is the unreinforced concrete structures and the
reinforced concrete structures. Unreinforced concrete s which has directed to the combination of
the reinforced steel into modern concretes. While the reinforced concrete constructions are used
within the construction industry since 1850s and are determined as materials having wide variety
of applications while having a high tensile strength.
2.3 Self-Healing:
Self-Healing in the concrete resources is one of the widely researched topics within the
arena of self-healing material. The mechanism of self-healing is defined as the procedure by
means of which the cracks present within concrete structures gets blocked with the help of
transportation of fluid materials. During this time the crack between two surfaces connects with
the chemical reaction that takes place within the process of SHC.
The progression of self-healing is also defined by the way where materials gets involved
within the recovery of concrete based structures while improving the performance of the
concrete action. The cracks that gets sealed via the action that takes place between concrete
structures results in the decrease of the penetrability of the concrete and hence is determined to
be self-healed while reducing the penetrability of the concrete while accepting the improvement
of the performance of the concrete. In direction to proceed with self-healing process, either the
autogenic way of healing or the autonomic way of healing is introduced with the help of specific
constituents causing repairment of the concrete leading to self-healing of the materials (Qureshi
2016).
2.3.1 Autogenic healing:

3
EFFICIENCY OF SELF HEALING IN CONCRETE
In direction to group the process of self-healing within concrete, the development
includes the Autogenic way of healing as well as Autonomic way of healing.
The Autogenous way of self-healing technique also known as self-generated healing
makes use of material components that gets used within the design process of self-healing
technique. The mechanism of Self-Healing technique in concrete proceeds with the continuous
hydration of cement materials along with precipitation of calcium carbonate that are faced inside
the crack of the concretes.
The entire thesis is carried out is based on the concept of shape memory polymers where
the closing of the cracks is improved via the process of autogenous self-healing mechanism. As
per RILEM technical Committee the use of autogenous self-healing technique is devoted to
single self-healing techniques that are mainly used within the onsite purpose within the
application of self-healing concrete. It is agreed between various researchers that there exist two
main processes that contributes to the self-healing of the cement based resources and that
includes the precipitation of calcium carbonate within the cracked parts and the other is by
continuously hydrating the cement within the concrete materials. However, another type of
technique that is proposed in this context is the effective method of autogenous self-healing that
mainly rest on the durability of the concrete during the period of cracking. The hydration process
that goes on within this mechanism consists of availability of dehydrated cement which gets
precipitated with the CaCo3 which becomes more effective along with the increase in the age of
the concrete. The dominant nature of self-healing also depends on the size of the crack that needs
to be cured. Here the ongoing mechanism of self-healing mainly depends on the size of the rack
that needs to be healed. The process of clogging of paths via physical methods which includes
the movement of the fragments gets suspended within the liquid serving as one of the factors but

4
EFFICIENCY OF SELF HEALING IN CONCRETE
not a dominant one in the self-healing method of cementitious materials. Various types of
experiments are also carried out where the water gets replaced by propanol 2 ol as one of the
permeants. Here the viscosity of the liquid remains close to water helping in the transport of
external materials within the cracks while enabling the ability to heal the cracks.
While initiating the process of autogenous healing procedure of concrete several
conditions are required within the entire process which are described as follows:
Presence of water: All the mechanism that are used within the process of autogenous self-
healing of polymers, requires the presence of water that needs to be supplied through continuous
process of submersion leading to continuous wet and dry cycles through the cracks. Water is a
vital constituent of the autogenous self-healing process without which the autogenous process
cannot be done.
Crack size: Another factor that is responsible for initiating the autogenous way of self healing is
the size of the crack. From numerous researches that has been carried out previously it is agreed
generally that about maximum of the autogenic self-healing process takes place with the
presence of a certain width of cracks which can not be below 0.25 mm. However, the concept of
healing the cracks fully varies from different studies as in some cases, the self-healing is well-
defined as the reduction of the size of the cracks whereas in some studies it is denoted by
reducing the permeability of the crack (Davies et al. 2016). The procedure of self-healing of the
crack is noted to those cases where the flow of water completely stops through the cracks present
within the sample while in some cases it is denoted when the resonance frequency of the samples
gets recovered whose values gets associated with the undamaged specimens. However, the
researches that depicts these cases fails to provide any indication reflecting the equivalency of
the two measurements.

5
EFFICIENCY OF SELF HEALING IN CONCRETE
Hence while reviewing the process of autogenous technique of self-healing process, it is
seen that the cracks having width of 0.25 mm gets sealed autogenously and are usually measured
by the characteristics of strengths of cracks having width of less than 0.05 mm.
Age at first cracking:
Among various factors that are required for the development of autogenous healing of
crack, the age of the crack serves as a subsequent healing character for the process of hydration
curing. While performing this process, a subsequent decrease in the recovery strength of the
cracks are noticed along with the aging of the crack and the it is attributed to the hydration
process of the sample that gets cracked within 72 hours after the method of casting.
While reviewing various researches it is seen that the process of autogenous self-healing
progression is much more effective to samples where the damages are 6 months older that than
damages that are 3 days older.

6
EFFICIENCY OF SELF HEALING IN CONCRETE
2.3.2 Autonomic healing:
In case where the autogenous self-healing procedure is considered to be one of the
inherent features of cement based systems, the autonomic self-healing process is also described
as one of the efficiently designed method of self-healing. The autonomic way of curing of
concrete which is also known as involuntary healing involves the inclusion of specific materials
that are used within the expansion of self-healing. The Autonomic technique of self-healing
makes use of adhesive repairing agents that are embedded within the Cementous mixture
forming a protective micro capsule through the previously formed network of vascular flow
(Feiteira, Gruyaert and De Belie 2016). The autonomous way of self-healing can be labeled by
the process of dispersing the capsules containing cementitious healing agent that are used within
the process of self-healing. This process of encapsulation within self-healing polymers is
determined to be one of the significant process where the capsules may get ruptured on cracking
while causes releasing of self-healing negotiators into the crack. The self-healing property of
concrete can be observed in several old structures standing for a longer period of time and have
limited maintenance process (Qureshi 2016). Here it is observed that the cracks that are present
within the concrete structures self-heals themselves while interacting with the surrounding

7
EFFICIENCY OF SELF HEALING IN CONCRETE
moisture along with non-hydrated cements within the cracks that are present within the concrete
structures. In present days the construction of the cement is lowered down as a process of
modern construction methods as a result of which the property of non-hydrated cement remains
less within the concrete structures and hence the natural property of self-healing gets reduced by
times (Feiteira, Gruyaert and De Belie 2016). The property of self-healing consists of some
principle phases including inflammation and hydration of the cement paste which is also
followed by the precipitation method of calcium carbonate or CaCo3 as well as the method of
obstacle of the flow tracks formed due to the admission of impurities of water or due to the
movement of concrete bits that gets detached through the entire process of cracking (Huang et
al. 2016). There are various other factors that are considered in the process of naturally curing
the cracks in the concrete structures which includes temperature, the freeze thaw cycles, degree
of impairment, average age of the concrete structure, and also the state of the mortar (Gruyaert et
al. 2016). The previous method that is the artificial way of healing the cracks was done by using
a healing agent which is a type of adhesive encapsulated within a micro capsule. In case when a
crack is formed within the concrete structure, the micro capsule inserted within it breaks while
releasing the healing agent and as a result the cracks starts healing (Roig-Flores et al. 2016). The
adhesive that is used within the entire process of healing the crack can also be used or stored in
short fibers or in any long tubes (Hu et al. 2018). However rather than the manmade initiated
healing process, the most effective process or method is considered to be the self-healing power
of concrete which includes several processes or approaches that are dedicated to it (Khaliq and
Ehsan 2016). These approaches include-
Bacteria based Healing Process: which is also recognized as the Bio-concrete process to
seal the formed cracks within concrete structures. Here the entire mechanism consists of mixing

8
EFFICIENCY OF SELF HEALING IN CONCRETE
up of the concrete with other constituents such as precursor of calcium lactate, micro capsules
planted with bacteria which gets germinated once the water flows through the cracks (Dong et
al. 2015). As soon as the germination takes place, the production of limestone is caused due to
the multiplication of the bacteria leading to addition of a double layer shield so as to prevent to
corrosion within the steel (Muhammad et al. 2016). The process includes incorporation of
oxygen that helps in benefiting the corrosion process of the steel. With the incorporation of this
kind of mechanism, the crack inside a concrete can be recovered up to 90 percent causing to
increase its initial strength (Luo, Qian and Li 2015).
2.3.3 Passive and active self-healing:
Alternative technique of self-healing that is reflected within the research is the healing of
cracks while filling the voids using the active and passive mode of activation technique (Seifan,
Samani and Berenjian 2016). In the passive way of self-healing polymers, porous particles
containing the rejuvenator are used at the starting of the course whereas, in instance of active
self-healing process, the case steel wool fibers get assorted over the bitumen which then gets
animated with the help of an initiation machine (Pamulapati et al. 2017). This internal heating is
defined as the active self-healing process under the autonomic healing method. A passive mode
of self-healing the cracks includes the ability to get reacted with the help of an external stimulus
where no other human interventions are required whereas in active method of self-healing
concretes, a strong intervention is required for the structures so as to complete the self-healing
procedure.
2.4 Shape Memory Polymers

9
EFFICIENCY OF SELF HEALING IN CONCRETE
Shape memory polymers are defined as the resources that are used to respond to exterior
stimuli while changing the physical outlines of the samples (Pilate et al. 2017). The most
common type of stimulus that gets provoked within the shape memory polymers is the direct
heating of polymers causing to change the temperature of the polymer.
2.4.1 Polyethene Terephthalate, PET Tendons:
Polyethene Terephthalate is one of the most common thermoplastic polyester which is
characterized by clear, lightweight and strong polymer which is usually used for packing foods
and beverages. PET is casted-off in case of shape memory polymers for closing the concrete
cracks. PET is usually formed from ethylene glycol or from terephthalic acid. With the help of
both the methods the excess EG gets removed to form the PET. The PET strands that gets
formed are then chilled and cut into minor parts known as PET resin which is then heated into a
molten liquid and hence can be molded into the desired shape.
2.4.2 SMP concrete crack closure system triggered by heating:
The Shape memory polymers are considered to be a semi crystalline polymers having a
predefined form that are remembered within their construction that helps them in later process to
go back to their unique state.
Whenever a crack occurs within a concrete structure, the systems gets itself triggered up
and the shape memory polymers present within the cracks gets activated by, means of heat which
can be in any form like in the form of direct heat or by means of any kind of heat generated due
to electrical current. As soon as the polymers gets activated, the effect of shape memory or the
shrinkage process takes place as a result of the restraining nature of the tendons and a tensile
force gets generated during the process (Xiao et al. 2015).

10
EFFICIENCY OF SELF HEALING IN CONCRETE
2.4.3 Activation methods:
The different types of heating activation methodsin case of Shape memory ploymers that
helps in closing the cracks in concrete system includes Dry heat activation methods, steam heat
activationmethod and water heat activation method. The detailed description of the different
methods are described within the table as mentioned below:
2.5 Investigation on the competence of Shape Memory Polymers healing in Concrete
Shape Memory PET Filament Tendons: Crack Closure based Experiments
While proceeding with the investigation of the efficiency of the Shape Memory Polymer
in the curative process of concrete, the tendons were first verified that are present outside the
concrete beams so as to control the restrained shrinkage stress. The tendons are then placed
within the unreinforced and also with the reinforced concrete beams that gets triggered using the
electrical arrangement that are used to examine the capability to cure the cracks. Within the
entire experiment, the samples measuring between 500x100x100mm area casted using the steel
casts. Here individually each of the assessment beams contains one PET tendon having length
of 400mm and covering about 200 threads. The armor-plated sample consists of 6mm diameter
of high ductile steel bars.

11
EFFICIENCY OF SELF HEALING IN CONCRETE
In this experiment, the tendons are being encumbered to a pre-stress of 2Mpa while cumulative
the aloofness among the steel grasps. From the experiment conducted, results shows that the
manufacture process produces a repeatable peak of 3.2 % while manufacturing a final stress of
the tendons.
2.5.1 Self-Healing Efficiency measuring methods:
Compressive strength tests:
The strength of three combinations that are used within this test consists of
microcapsules, control and bacteria that gets assessed while taking 100x100x100mm cube
samples and then gets tested in agreement to the BS EN 12390-2.
The results of the test are shown below:
Three-point bending test:
The three-point bending test is the most simple type of test that is adopted so as to obtain
the tension of the concrete. The deflection that gets measured during the test while maoing use of
the referenced beam gets attached to the top f the beam by means of three steel blocks that are
glued to the beam surface (Teall et al. 2018). The idealized loading of the cracks that are noticed
with the three-point bending tests includes the following:
Load Pinitial
Initial loading
Papparent Final loading
Pfinal
Final loading for
PET specimens

12
EFFICIENCY OF SELF HEALING IN CONCRETE
Crack measuring by microscope:
Another method that is used within the closing of crack includes the crack measuring
mechanism with the help of USB microscope within a graduated scale. Here for each image, the
crack having the measurement of width as 0.75 mm were done perpendicular to the cracked face
while making use of the Image J software.
2.6 Conclusion:
From the above study it can be determined that since the use of Self-Healing concretes is
a promising one hence its it is important to understand its effect on the architectural designs.
There are various other researches that are still going on based on the different approaches that
helps in ensuring the closure of the cracks with the help of minimum interventions while keeping
the costs at a reasonable rate. The study shows that Self-healing concretes is one of the most
effective method of closing up the cracks in concrete in comparison to other methods. As a result
Presidual
CMOD
Bottom of the
notch
Three crack
measurements
0.75mm apart
Graduated scale
8mm long
Crack

13
EFFICIENCY OF SELF HEALING IN CONCRETE
of its increased popularity, the general safety of the architectural buildings also increases while
increasing their strengths. Hence from the present study, it can be examined and associated
regarding the several tests and approaches that are used to measure the competence of the self-
healing concretes.

14
EFFICIENCY OF SELF HEALING IN CONCRETE
References:
Davies, R., Pilegis, M., Kanellopoulos, A., Sharma, T., Teall, O., Gardner, D., Jefferson, A. and
Lark, R., 2016. Multi-scale cementitious self-healing systems and their application in concrete
structures.
De Belie, N., Gruyaert, E., Al‐Tabbaa, A., Antonaci, P., Baera, C., Bajare, D., Darquennes, A.,
Davies, R., Ferrara, L., Jefferson, T. and Litina, C., 2018. A review of self‐healing concrete for
damage management of structures. Advanced Materials Interfaces, 5(17), p.1800074.
Dong, B., Wang, Y., Fang, G., Han, N., Xing, F. and Lu, Y., 2015. Smart releasing behavior of a
chemical self-healing microcapsule in the stimulated concrete pore solution. Cement and
Concrete Composites, 56, pp.46-50.
Feiteira, J., Gruyaert, E. and De Belie, N., 2016. Self-healing of moving cracks in concrete by
means of encapsulated polymer precursors. Construction and Building Materials, 102, pp.671-
678.
Gruyaert, E., Debbaut, B., Snoeck, D., Díaz, P., Arizo, A., Tziviloglou, E., Schlangen, E. and De
Belie, N., 2016. Self-healing mortar with pH-sensitive superabsorbent polymers: testing of the
sealing efficiency by water flow tests. Smart Materials and Structures, 25(8), p.084007.
Hager, M.D., Bode, S., Weber, C. and Schubert, U.S., 2015. Shape memory polymers: Past,
present and future developments. Progress in Polymer Science, 49, pp.3-33.
Hu, Z.X., Hu, X.M., Cheng, W.M., Zhao, Y.Y. and Wu, M.Y., 2018. Performance optimization
of one-component polyurethane healing agent for self-healing concrete. Construction and
Building Materials, 179, pp.151-159.

15
EFFICIENCY OF SELF HEALING IN CONCRETE
Huang, H., Ye, G., Qian, C. and Schlangen, E., 2016. Self-healing in cementitious materials:
Materials, methods and service conditions. Materials & Design, 92, pp.499-511.
Khaliq, W. and Ehsan, M.B., 2016. Crack healing in concrete using various bio influenced self-
healing techniques. Construction and Building Materials, 102, pp.349-357.
Luo, M., Qian, C.X. and Li, R.Y., 2015. Factors affecting crack repairing capacity of bacteria-
based self-healing concrete. Construction and building materials, 87, pp.1-7.
Pamulapati, Y., Elseifi, M.A., Cooper III, S.B., Mohammad, L.N. and Elbagalati, O., 2017.
Evaluation of self-healing of asphalt concrete through induction heating and metallic
fibers. Construction and Building Materials, 146, pp.66-75.
Pilate, F., Toncheva, A., Dubois, P. and Raquez, J.M., 2016. Shape-memory polymers for
multiple applications in the materials world. European Polymer Journal, 80, pp.268-294.
Qureshi, T.S., 2016. The Role of Expansive Minerals in the Autogenous and Autonomic Self-
healing of Cement Based Materials. University of Cambridge.
Roig-Flores, M., Pirritano, F., Serna, P. and Ferrara, L., 2016. Effect of crystalline admixtures on
the self-healing capability of early-age concrete studied by means of permeability and crack
closing tests. Construction and Building Materials, 114, pp.447-457.
Seifan, M., Samani, A.K. and Berenjian, A., 2016. Bioconcrete: next generation of self-healing
concrete. Applied microbiology and biotechnology, 100(6), pp.2591-2602.
Teall, O., Pilegis, M., Davies, R., Sweeney, J., Jefferson, T., Lark, R. and Gardner, D., 2018. A
shape memory polymer concrete crack closure system activated by electrical current. Smart
Materials and Structures, 27(7), p.075016.

16
EFFICIENCY OF SELF HEALING IN CONCRETE
Van Stappen, J., Bultreys, T., Gilabert, F.A., Hillewaere, X.K., Gómez, D.G., Van Tittelboom,
K., Dhaene, J., De Belie, N., Van Paepegem, W., Du Prez, F.E. and Cnudde, V., 2016. The
microstructure of capsule containing self-healing materials: A micro-computed tomography
study. Materials Characterization, 119, pp.99-109.
Van Tittelboom, K., Wang, J., Araújo, M., Snoeck, D., Gruyaert, E., Debbaut, B., Derluyn, H.,
Cnudde, V., Tsangouri, E., Van Hemelrijck, D. and De Belie, N., 2016. Comparison of different
approaches for self-healing concrete in a large-scale lab test. Construction and building
materials, 107, pp.125-137.
Xiao, X., Kong, D., Qiu, X., Zhang, W., Liu, Y., Zhang, S., Zhang, F., Hu, Y. and Leng, J., 2015.
Shape memory polymers with high and low temperature resistant properties. Scientific reports, 5,
p.14137.