Ijciet 10 02_023

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International Journal of Civil Engineering and Technology (IJCIET)
Volume 10, Issue 02, February 2019, pp. 202-210, Article ID: IJCIET_10_02_023
Available online at http://www.iaeme.com/ijciet/issues.asp?JType=IJCIET&VType=10&IType=02
ISSN Print: 0976-6308 and ISSN Online: 0976-6316
© IAEME Publication Scopus Indexed
RECOVERY OF MECHANICAL PROPERTIES
OF SELF HEALING CONCRETE USING SUPER
ABSORBENT POLYMER (SAP)
Manoj Kumaar. C
Research Scholar, Department of Civil Engineering,
Sathyabama Institute of Science and Technology, Chennai, India
Dr. Mageswari. M
Professor and Head, Department of Civil Engineering,
Panimalar Engineering College, Chennai, India
ABSTRACT -
This project is study of Self-healing behaviour of concrete which deals with
mechanical properties of concrete is widely used to improve the durability of the
concrete. Self-healing concrete is a product that will chemically produce hydrates to
heal the cracks that appear on the surface of concrete structures. In self-healing
process healing agent absorbs the moisture content present in atmosphere to heal.
This process enhanced mechanical properties of concrete. Superabsorbent polymers
(SAPs) are materials that have the ability to absorb and retain large volumes of water
and aqueous solutions. SAP is now a mature product that has quickly progressed from
specialty chemical to special commodity. Sodium silicate is used as SAP chemical
admixtures as well as self-healing agent for concrete. Sodium silicate in liquid form at
2% is mixed with concrete based on previous work. As per IS 10262 : 2009, M40
grade concrete mix design is derived for both control and SAP concrete and
specimens are prepared for compressive strength, split tensile strength and flexural
strength. At age of 7, 14, and 28 and 56 days, tests are conducted to determine the
compressive, split tensile and flexural strengths. The specimen are also pre-cracked
on 28th
day and re-cured for 28 days to undergo rapid self-healing process. On 56th
day, they are tested for determining the recovery of strengths. The effect of 2%
sodium silicate on the strength and the healing property of concrete is studied by
determining the self-healing efficiency.

Manoj Kumaar. C and Dr. Mageswari. M
Keywords: self-healing, super absorbent polymer, sodium silicate, crack, mechanical
properties.
Cite this Article: Manoj Kumaar. C and Dr. Mageswari. M, Recovery of Mechanical
Properties of Self-Healing Concrete Using Super Absorbent Polymer (Sap),
International Journal of Civil Engineering and Technology, 10(02), 2019, pp. 202–
210
http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=10&IType=02
1. INTRODUCTION
Concrete is a basic material which most commonly used building material in the world. It is
available in various features and properties. It is durable and recyclable product and also
inexpensive material. Unfortunately, concrete is susceptible to many source of damage. Crack
is mostly considered as damage to the concrete. Crack can be formed interior which cannot
be seen and also exterior at any stage of their life span. Cracks is caused by extreme loads,
present other particles, present of air and water voids, improper method, placing and curing
of concrete, corrosion and other environmental conditions. Cracks can form at any stage of its
life and most begin internally where they cannot be seen for years until major repairs are
needed.
Now a day’s life span of concrete is very low. The lower sustainability of concrete is the
worldwide problem. The production of concrete is an energy-intensive process where mining,
transportation and processing is considered. To avoid concrete failure damage, deterioration,
structural integrity, replacement and repair are conventionally monitored through routine
inspection.
Self-healing has been observed in traditional, fibrous and self-compacting concrete. The
self-healing concrete now possesses the quality to repair itself and thus increases the
sustainability of concrete. Consequently, this concept will save a lot of money, keeping in
mind the 80 years future prospectus. The technique is well experimented and is also called
Bio concrete. Self-healing cracks in one of phenomenon also acting positively in durability
problem of cracks.
The major steps involved in the process of healing are
 The hydration of unhydrated cement particles.
 The precipitation of calcium carbonate hydrates in cracks.
SAPs are polymeric materials that have the ability to absorb a large amount of liquid from
the surroundings and retain it within their structure. SAPs are mainly developed for
absorption of aqueous solutions and, in extreme cases, they may have a water uptake of 5000
times their own weight. Standard, industrial-quality SAPs typically have water absorption
and they can be produced in almost any size and shape. SAPs belong to the group of so-called
smart materials that, in a controlled way, significantly change their properties in response to
an external stimulus. When SAPs are exposed to water, they swell, and when subsequently
subjected to drying, they reversibly shrink. These key properties can actively be used in
relation to concrete.
Based on the volume fraction, the particle size distribution and the expansion model of
unhydrated cement nuclei, a model was proposed to determine the self-healing efficiency of
cracks created by two different modes – splitting crack mode and dome like crack mode1
.
Engineered Cementitious Composite Beams with 4% SAP are deflected up to 3mm to form
the parallel cracks. These cracks were observed to selfheal completely with the healing

Recovery of Mechanical Properties of Self-Healing Concrete Using Super Absorbent Polymer
(Sap)
products like calcium carbonate and calcium hydroxides2
. Glass tubes of 16 mm diameter and
125 mm length, filled with aqueous sodium silicate are embedded in concrete. During the
formation of cracks, these tubes break and release the sodium silicate, which reacts with
calcium hydroxide to form the CSH gel3
. The self-healing mechanism can be achieved by
three different systems, namely – capsule based healing system, vascular healing system and
intrinsic healing system. The capsule based healing system seizes after healing of cracks in a
single damage event. Vascular healing system heals the cracks over multiple damage events
but integrating it with the existing material system is difficult. Intrinsic healing systems are
simple and heal the cracks formed during small damage events4
. The self-healing engineered
cementitous composites ECC could reduce the maintenance costs and allow for more
sustainable development in the future by decreasing the amount of resources and energy
required for manufacturing cement. ECC specimens were monitored using resonant
frequency and mechanical reloading after subsequent damages. The rate and extent of self-
healing in the natural environment were determined. The recovery of strength and stiffness
was more than 100% after exposing the self-healing concrete to the natural environment for 6
months5
. A self-repairable concrete of M30 grade was prepared using 2% of capsules with
sodium silicate by weight of cement. The cracks in cube specimens are healed after 28 days
of re-curing. The capsules did not cause any change in the compressive strength. Thus, the
concrete can have very long life span as the reinforcement bars are protected from corrosion
by healing the cracks6
. The effect of cementitious hollow tubes filled with sodium silicate and
rhodamine B as colouring agent were used in a proportion of 1.6% by volume. It didn’t
influence the compressive strength. Potassium silicate solution was also used as healing agent
but not effective as sodium silicate. The extent of self-healing was measured by determining
the load recovery index and stiffness recovery index7
. A polymer composite material was
developed with micro-capsules which have the ability to recover up to 90% of its virgin
fracture toughness. The concentration of micro-capsules filled with DPCD monomer was
10wt%8
. The healing rate of concrete beams with 5% double walled microcapsules was
higher than those with 2.5% microcapsules. The healing process was monitored and
quantified using portable ultrasonic non-destructive digital indicating tester9
. The healing
agent particles were protected in concrete, from getting soluble in water during mixing and
leaching, by coating them with geolpolymers like metakaolin, sodium silicate and sodium
aluminate10
. The optimum use of sodium polyacrylates as super absorbent polymers has
improved the properties in both fresh and hardened stage. The gels act as cushion for large
aggregates and prevent them from segregation. It has also improved the frost resistance of
hardened concrete. The SAP has reported to increase the workability of fresh concrete mix11
.
2. METHOD
The M40 grade concrete for Control mix and SAP concrete are designed as per IS 10262:
2009. The ratio for control concrete is 1:1.80:2.93 and SAP concrete is 1:1.76:2.91. The
water cement ratio is 0.43. Aqueous sodium silicate of 2% by weight of cement is adopted.
Casting of control and SAP concrete each 15 no. of cubes of size 150 x 150 x 150 mm, 15 no.
of cylinders of size 150 x 300 mm and 15 no. of prisms of size 150 x 150 x 700 mm are
carried out and cured. The compression, split tensile and flexural strength for both control
and SAP specimens are determined on 7, 14, 28 and 56th
days. The pre- cracks are induced
for both control and SAP specimens on 28th
day by applying load gradually.
Re-curing is done for the cracked specimen for 28 days for triggering the self-healing process for
both control and SAP concrete. Self-healed specimens are tested for determining the recovery of
mechanical properties on 56th
day

2.1. Materials
The materials used in the experimental work are
2.1.1. Cement
Ordinary Portland cement of 53 grade and specific gravity of 3.15 is used.
2.1.2. Fine aggregate
Fine aggregate of specific gravity 2.65 and size 1.76 mm is used.
2.1.3. Coarse aggregate
Coarse aggregate of specific gravity 2.61 and size 20 mm and 12.5 mm.
2.1.4. Sodium silicate
Sodium silicate is used whose density is 1.6 g/cm3
and pH should in the range of 8-13. The
industrial beginnings of sodium silicate start in 1818 but references to making sodium silicate
like products can be traced back as far as the ancient Phoenicians. One reason for the early
development of soluble silicate was the relatively simple process for manufacturing it.
Sodium silicates are manufactured by fusing sand (SiO2) with sodium carbonate (Na2CO3) at
1100-1200°C. The resulting glass can be dissolved with high pressure steam to form a clear,
slightly viscous liquid known as “water glass”. The liquids can also be spray-dried to form
quick dissolving, hydrous powders. Dissolved or liquid silicates are the most popular
commercial form of sodium silicate for agglomeration applications, although there are
occasions when hydrous powders or ground glass are better suited. Sodium silicate acts as
super absorbent polymer as well as self-healing agent. Based on the previous work, SAP is
added at 2% by weight of cement.
2.1.5. Water
Water used in concrete whose pH value less than 6, and potable is used.
3. STANDARD TESTS
3.1. Workability test
The slump cone test is used to measure the workability. According to IS 7320: 1974 the
slump cone test is conducted. The decrease in height of concrete to that of mould is noted
with measuring scale.
For control concrete (CC) Slump = 300 - 295 = 5 mm.
For SAP concrete (SAPC) Slump = 300 - 293 = 7 mm.
The type of slump is true slump for both control and SAP concrete. The SAPC is more
workable compared to CC.
3.2. Compression strength test
Compressive strength is the capacity of a material or structure to withstand loads tending to
reduce size, as opposed to tensile strength, which withstands loads tending to elongate. In
other words, compressive strength resists compression (being pushed together), whereas
tensile strength resists tension (being pulled apart). By reference of IS 516: 1959 compression
strength test is conducted in cubes.

(Sap)
3.3. Split tensile strength test
The resistance of a material to longitudinal stress, measured by the minimum amount of
longitudinal stress required to rupture the material. By reference of IS 516: 1959 split tensile
strength test is conducted in cylinder.
3.4. Flexural strength test
Flexural tests are generally used to determine the flexural modulus or flexural strength of a
material. A flexural test is more affordable than a tensile test and test results are slightly
different. The material is laid horizontally over two points of contact (lower support span)
and then a force is applied to the top of the material through either one or two points of
contact (upper loading span) until the sample fails. The maximum recorded force is used in
calculating the flexural strength of that particular sample. In this test, two point loading is
preferred. By reference of IS 9399 : 1979 and IS 516 : 1959 flexural strength test is
conducted in prism.
4. RESULTS AND DISCUSSION
The test results for compressive, split tensile and flexural strengths at the age of 7th
, 14th
, 28th
and 56th
days, Stress applied to induce cracks on 28th
day and Strengths of healed specimens
on 56th
day are displayed in table 1 and also graphically represented in fig 1, 2 and 3. The %
difference in strength of SAPC specimens with respect to CC specimens are also shown in
the table 1. The compressive, split tensile and flexural strengths of SAPC are slightly lesser
than that of CC on 7th
, 14th
and 28th
days due to decreased rate of hydration and more voids
caused by sodium silicate in SAPC. As a result of decreased rate of hydration, the presence of
unhydrated cement particles is relative more compared to CC. The strengths are found to be
enhanced in SAPC specimen compared to CC on 56th
day. It signifies that the hydration
process has been continued between the unhydrated cement particles and the water in SAPC
unlike CC. The strengths are found to be enhanced in SAPC pre-cracked specimen compared
to CC on 56th
day. This is because of precipitation of more calcium hydroxide in the cracked
portions in SAPC specimens compared to that of CC specimens.
Figure 1 Compressive strength of cube specimens

Figure 2 Split tensile strength of cylinders
Figure 3 Flexural strength of prisms
Table 1 :
Results of
Compressive,
Split tensile
and Flexural
StrengthsStres
s level
Age
(days)
Compressive strength
(MPa)
Split tensile strength
(MPa)
Flexural strength
(MPa)
CC SAPC
%
difference
wrt CC
CC SAPC
%
difference
wrt CC
CC SAPC
%
difference
wrt CC
Ultimate 7 32.55 29.13 -10.5 1.85 1.71 -7.6 4.82 4.35 -9.8
Ultimate 14 36.45 34.24 -6.1 2.35 2.2 -6.4 5.14 4.96 -3.5
Ultimate 28 41.18 40.29 -2.2 2.62 2.53 -3.4 5.86 5.75 -1.9
Ultimate 56 42.65 43.46 1.9 2.8 2.86 2.1 6.13 6.22 1.5
Pre-cracking 28 22.37 21.29 -4.8 2.19 2.07 -5.5 2.92 2.44 -16.4
Ultimate
(after
Healing)
56 40.85 42.51 4.1 2.74 2.83 3.3 5.21 5.82 11.7
The self-healing efficiencies of cubes, cylinders and prisms in closing their cracks due to
compression, tension and bending respectively are calculated using the equation2
mentioned
below
Self-Healing Efficiency, η = x 100

(Sap)
Table 2 : Self
Healing
efficiency of
CC and SAPC
samplesType of
cracks
Mix
Strength
of virgin
specimen
(MPa)
Strength
of healed
specimen
(MPa)
Pre-
cracking
Stress
(MPa)
Self-
healing
Efficiency
η
% η
difference
with
respect to
CC
Compression
CC 42.65 40.85 22.37 91.1243
SAPC 43.46 42.51 21.29 95.7149 5.0
Tension
CC 2.8 2.74 2.19 90.1639
SAPC 2.86 2.83 2.07 96.2025 6.7
Bending
CC 6.13 5.21 2.92 71.3396
SAPC 6.22 5.82 2.44 89.418 25.3
The self-healing efficiencies of SAPC are higher than that of CC. It can be observed that
the cracks due to compression and tension in cubes and cylinders are healed much better than
those due to bending in prisms.
Figure 4 Cracks developed in CC sample on 28th
day
Figure 5 Poorly healed cracks in CC sample

Figure 6 Cracks developed in SAPC sample on 28th
day
Figure 7 Well healed cracks in SAPC sample – showing the deposits of healing products.
However, the SAPC prisms have healed its cracks exceptionally than the CC prisms did.
The pre-cracks induced in CC and SAPC samples on 28th
day are shown in fig 4 and 6
respectively.
In order to maintain the severity of damage, cubes and prisms are stressed around 50 % of
their ultimate strengths and cylinders are tensioned around 80% of its ultimate tensile
strength on 28th
day. The extent of cracks healed after 28 days of pre-cracking in CC and
SAP samples are shown in fig 5 and 7 respectively.
5. CONCLUSION
 The mechanical properties are found to be enhanced in SAP concrete specimen
compared to control concrete after self-healing period of 28 days i.e., at the age of
56th
day.
 It is evident that the self-healing has been advanced in SAP concrete specimen
compared to control concrete specimen as observed from the self-healing
efficiency of mechanical properties.

(Sap)
 It signifies that the usage of sodium silicate as SAP has triggered the self-healing
mechanism in SAP concrete.
ACKNOWLEDGEMENT
The authors would like to thank Sathyabama Institute of Science and Technology, Chennai
and National Test House, Chennai for helping to conduct the experimental work and
testing.
REFERENCES
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[7] Alessandra Formia, Sara Irico, Federica Bertola, FulvioCanonico, Paola Antonaci, Nicola
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