The aim of this study is analyzing the self-healing capability of high strength concrete (M70) with nano silica and crystalline admixture in three types of environmental exposures i.e. water immersion, wet/dry cycles and water contact. The percentage replacements of cement with nano silica were 1%, 2%, 3% with addition of 1.1% crystalline admixture. The specimens were pre-cracked at 28 days in the range of 0.10-0.40mm and the time set for healing was 42 days. The result shows that all the mixes have considerable amount of closing ability and strength regaining capacity for all exposure conditions. The concrete with 2% nano silica and 1.1% crystalline admixture (CA) has complete crack closing ability and strength regaining capacity for water immersion and wet/dry cycle conditions.

1. http://www.iaeme.com/IJCIET/index.asp 69 editor@iaeme.com
International Journal of Civil Engineering and Technology (IJCIET)
Volume 10, Issue 05, May 2019, pp. 69-74. Article ID: IJCIET_10_05_008
Available online at http://www.iaeme.com/ijciet/issues.asp?JType=IJCIET&VType=10&IType=05
ISSN Print: 0976-6308 and ISSN Online: 0976-6316
© IAEME Publication
STUDY OF THE EFFECT OF NANO SILICA ON
THE SELF HEALING ABILITY OF HIGH
STRENGTH CONCRETE WITH CRYSTALLINE
ADMIXTURE
S. Sirajuddin
M. Tech. Student, Department of Civil Engineering, GPREC, Kurnool, AP, India
Dr. T. Chandra Sekhara Reddy
Professor, Department of Civil Engineering, GPREC, Kurnool, AP, India.
T. Bhuvana Vijaya
Assistant Professor, Department of Civil Engineering, GPREC, Kurnool, AP, India.
K Ramamohan Reddy
Assistant Professor, Department of Civil Engineering, GPREC, Kurnool, AP, India
ABSTRACT
The aim of this study is analyzing the self-healing capability of high strength
concrete (M70) with nano silica and crystalline admixture in three types of
environmental exposures i.e. water immersion, wet/dry cycles and water contact. The
percentage replacements of cement with nano silica were 1%, 2%, 3% with addition of
1.1% crystalline admixture. The specimens were pre-cracked at 28 days in the range of
0.10-0.40mm and the time set for healing was 42 days. The result shows that all the
mixes have considerable amount of closing ability and strength regaining capacity for
all exposure conditions. The concrete with 2% nano silica and 1.1% crystalline
admixture (CA) has complete crack closing ability and strength regaining capacity for
water immersion and wet/dry cycle conditions.
Keywords: Crystalline admixture, Self-healing, High strength concrete, Nanosilica
Cite this Article: S. Sirajuddin, Dr. T. Chandra Sekhara Reddy, T. Bhuvana Vijaya and
K Ramamohan Reddy, Study of the Effect of Nano Silica on the Self-Healing Ability
of High Strength Concrete with Crystalline Admixture, International Journal of Civil
Engineering and Technology, 10(5), 2019, pp. 69-74.
http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=10&IType=05

2. Study of the Effect of Nano Silica on the Self-Healing Ability of High Strength Concrete with
Crystalline Admixture
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1. INTRODUCTION
Cracks inevitably exist in concrete due to chemical shrinkage, dry shrinkage, autogenous
shrinkage. If micro cracks grow and reach the reinforcement, not only the concrete itself may
be attacked, but also the reinforcing steel bars will be corroded. Therefore, it is important to
control the crack width and to heal the cracks as soon as possible. Self-healing concrete also
called as self-repairing concrete, is mostly defined as the ability of concrete to repair it cracks
autogenously or autonomously. Self-healing concrete can be categorized in two types:
autogenous and autonomous self-healing concrete. The autogenous self-healing mainly
depends on further hydration of cement/ other binders and carbonation of Ca (OH)2. However,
the autonomous self-healing concrete depends on manual methods. Such as the use of super
absorbent polymers (SAP's), bacterial concrete, microencapsulated healing agents, and the use
of crystalline admixtures. Crystalline admixture is a waterproofing admixture and it reduces
the size of capillary pores, their numbers and continuity inside the concrete structure. There are
many products in the market now a days to protect the concrete structure from damage due to
water penetration. For example, coatings, sealers, membranes etc. are used to prevent water
penetration.
Abram's [1] suggested that the healed strength of concrete is caused by the retarded or the
interrupted hydration of the cement. Edvardsen [2] conducted some experiments in order to
verify the water flow in different crack width, under different pressure conditions. She found
that, after 7 weeks exposure for lower pressure of the water, the cracks were closed completely
whereas the same one for higher pressure had just 25% of closure. Sahraman et al [3]
investigated the recovery of compressive strength after the induction of cracks marked by
different cracking modes. Ferrara et al. [5] a methodology has been proposed and validated to
assess and quantify the effects of self-healing on the recovery of mechanical properties of
normal strength concrete, with and without crystalline admixtures under different exposure
conditions. M. Roig-Flores et al. [6] analyzing the self-healing effect of a crystalline admixture
in four types of environmental exposure comparing with a reference concrete. The studied
crack openings were under 300µm and the time set for healing was 42 days. Specimens cast
with concrete containing crystalline admixture and stored under water immersion achieved the
highest self-healing rate. M. Roig-Flores et al [7] studied on the self-healing capacity of early-
age fiber-reinforced concrete and the effectiveness of a crystalline admixture as self-healing
agent in different exposure conditions. The results show the best healing under exposure
condition of water immersion at 30º c with the crystalline admixture. The presence of
crystalline additive in concrete improves its self-healing properties. Immersion in water
improves the higher self-healing properties, for higher crack widths especially, as expected [8-
12].
The main objective of this project is to determine the self-healing ability of high strength
concrete (M70) with nano silica and crystalline admixture in different exposure conditions.
2. EXPERMENTAL PROGRAM AND METHODOLOGY
2.1. Materials and mix proportions
The materials used for this research were cement, coarse aggregate, fine aggregate, water, nano
silica, crystalline admixture, super plasticizer and steel fibers.
The type of cement was OPC 53 grade for plain concrete, concrete with nano silica,
concrete with crystalline admixture and concrete with both nano silica and crystalline
admixture. For better results, locally available portable water conforming to IS 456-2000 is
used for making concrete. Aggregates of size (12-10mm) were selected as coarse aggregate,

3. S. Sirajuddin, Dr. T. Chandra Sekhara Reddy, T. Bhuvana Vijaya and K Ramamohan Reddy
http://www.iaeme.com/IJCIET/index.asp 71 editor@iaeme.com
and river sand was used as fine aggregate. The quantity of steel fibers was fixes at 40 kg/m³
according to the criterion of making the crack opening easily controllable while avoiding
excessive branching of cracks. A dosage of 1.1% of crystalline admixture was introduced in
the concrete by partial replacement of cement. Two types of admixtures namely, nano silica as
partial replacement of cement and super plasticizer for increasing workability of the fresh
concrete, were incorporated in the concrete mixture. The mix proportions used in various mixes
are mentioned below.
Table 1 Mix proportions
Mixes
Nano
Silica
(%)
Cement
(kg/m³)
Fine
aggregate
(kg/m³)
Coarse
aggregate
(kg/m³)
Nano
Silica
(kg/m³)
Water
(lit/m³)
Super
plasticizer
(lit/m³)
Crystalline
admixture
(kg/m³)
Steel
Fibers
(kg/m³)
Plain concrete (PC) 0 490 722 1044.88 0 145 4.84 0 9.88
Concrete with 1.1%
crystaline admixture (CCA)
0 490 722 1044.88 0 145 4.84 5.39 9.88
Concrete with 1%nano
silica& 1.1% crystalline
admixture (CNS1)
1% 485.1 722 1044.88 4.9 145 4.84 5.39 9.88
Concrete with 2%nano
silica& 1.1% crystalline
admixture (CNS2)
2% 480.2 722 1044.88 9.8 145 4.84 5.39 9.88
Concrete with 3%nano
silica& 1.1% crystalline
admixture (CNS3)
3% 475.2 722 1044.88 14.7 145 4.84 5.39 9.88
2.2. Methodology
In study to evaluate the effects of s1elf healing consists of four stages given below
1. Determination of compressive strength of plain concrete (PC) and concrete with
crystalline admixture (CCA), and concrete with crystalline admixture and nano silica
(CNS1, CNS2&CNS3) at 28 days.
2. Creation of controlled damage in the specimens.
3. Simulation of the various environmental exposures needed to achieve better healing
results.
4. Determination of regained compressive strength of specimens subjected to controlled
cracking and self-healing for 28 and 42 days under three different exposure conditions.
A total five group of specimens were cast, each group consists 3 cubes. Four groups are
used for improvement of strength characteristics. They are concrete with nano silica and
crystalline admixture (CNS1, CNS2 & CNS3), concrete with crystalline admixture (CCA). Five
groups are used for structural cracks self-healing study under three exposure conditions
respectively.
1. Cube specimens of 100X100X100mm were prepared to determine compressive
strength of plain concrete (PC), Concrete with crystalline admixture (CCA)and
concrete with crystalline admixture and nano silica (CNS).
2. Creation of damage (pre- cracking process); cube specimens (100X100X100mm) were
pre- cracked at the age of 28 days for structural cracks by means of a compression test.
Controlled damage; this was meant as the width of the crack, which was set to reach a
target value by controlled loading.

4. Study of the Effect of Nano Silica on the Self-Healing Ability of High Strength Concrete with
Crystalline Admixture
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3. Exposure simulation; three environmental exposure conditions were considered in
order to determine the influence of water availability and its temperature on the self-
healing capability of the tested specimens, comparing reference concrete with nano
silica and crystalline admixture concrete. All specimens were left to heal for 28 and 42
days.
4. Determine the regained compressive strength of concrete after healing cracks in
concrete specimens under three different environment exposure conditions at 28 and 42
days.
3. RESULTS AND DISCUSSIONS
3.1. Compressive strength
Compressive strength of M70 concrete with partial replacement of cement by nano silica is
increases up to 2% replacement and with further increase in nano silica the compressive
strength decreases. The maximum compressive strength of 96 N/mm² is achieved for the
concrete mix with 2% replacement of cement by nano silica which is 14 % more than that of
plain concrete (PC) for 28 days curing. At the age of 28 days, specimens were pre-cracked to
introduce a structural crack width of 0.1-0.4mm. Thereafter, pre-cracked specimens are tested
after self-healing of cracks, the regained mechanical properties after healing of structural cracks
under water immersion, Wet /Dry and Water contact. The regained compressive strength of
concrete values is shown in following figures.
Figure 1 Variation of regained compressive strength under Water Immersion after 28 and 42 days
self-healing.
0
20
40
60
80
100
120
140
PC CCA CNS1 CNS2 CNS3
Regainedcompresivestrength(MPa)
Mixes
water immersion condition
Regained compressive
strength @ 28days self
healing
Regained compressive
strength @ 42days self
healing

5. S. Sirajuddin, Dr. T. Chandra Sekhara Reddy, T. Bhuvana Vijaya and K Ramamohan Reddy
http://www.iaeme.com/IJCIET/index.asp 73 editor@iaeme.com
Figure 2 Variation of regained compressive strength under Wet/dry after 28 and 42 days self-healing.
Figure 3 Variation of regained compressive strength under Water contact after 28 and 42 days self-
healing.
4. CONCLUSIONS
This study investigates the Self-healing behavior of high strength concrete with nano silica and
crystalline admixture. After 28 days of curing, the specimens were pre-cracked with subsequent
healing in three different exposure conditions. The recovery of mechanical properties was
investigated.
1. Maximum compressive strength attained for plain concrete at 28days of curing is 82.5
N/mm2
2. Maximum compressive strength of 85.94N/mm² is obtained for concrete mix with 1.1%
of crystalline admixture (CA) for 28 days curing.
0
20
40
60
80
100
120
140
PC CCA CNS1 CNS2 CNS3
Regainedcompresivestrength(MPa)
Mixes
wet/dry cycle condition
Regained compressive
strength @ 28days self
healing
Regained compressive
strength @ 42 days self
healing
0
20
40
60
80
100
120
140
PC CCA CNS1 CNS2 CNS3
Regainedcompressivestrength(MPa)
Mixes
water contact condition
Regained compressive
strength @ 28days self
healing
Regained compressive
strength @ 42 days self
healing

6. Study of the Effect of Nano Silica on the Self-Healing Ability of High Strength Concrete with
Crystalline Admixture
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3. The maximum compressive strength of 96 N/mm2
is achieved for 2% replacement of
Cement by nano silica which is 14 % more than that of plain concrete (PC) at 28 days
curing.
4. The best healing exposure condition is water immersion. The maximum regained
compressive strength attained for concrete with 2% nano silica and 1.1% crystalline
admixture is 132 N/mm² after 42 days healing under water immersion.
5. The concrete specimen with 2% of nano silica and1.1% of crystalline admixture (CNS2)
has complete crack closing ability and strength regaining capacity for all exposure
condition.
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