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ICEAS-1707
Influence of Fly Ash on Self-healing Performance in Cracked Concrete
Mohamed Zakaria*
Muroran Institute of Technology, Muroran 050-8585, Japan
Faculty of Engineering, Aswan University, Aswan 81542, Egypt
eng_zakaria@yahoo.com
Na Seung Hyun
Muroran Institute of Technology, Muroran 050-8585, Japan
10091504@mmm.muroran-it.ac.jp
Yukio Hama
Muroran Institute of Technology, Muroran 050-8585, Japan
hama@mmm.muroran-it.ac.jp
Abstract
This paper investigates the self-healing ability in cracked concrete specimens, with or without
air entraining agents, incorporating by-products fly ash that is a kind of coal ash. Concrete
specimens are cracked by accelerated environmental action that is repeating cycles of
low/high temperatures or freezing/thawing process. The experiments examined the change of
relative dynamic modulus of elasticity, compression strength and carbonation coefficient as
index of self-healing properties in concrete specimens before cracking, after cracking, after
healing due to curing in water. The results revealed that incorporating fly ash in concrete
showed a positive effect on compressive strength, and it continues to increase even after 28
days due to its pozzolanic reaction and attributed to densification of concrete matrix.
Moreover, it was observed that self-healing effect is related to curing age before deterioration,
when curing age increases, for long-term curing age case, the healing ability decreases due to
decrease of un-reacted cement and fly ash in investigated concrete samples. Finally, it is
recommended to add air entraining agent in fly ash concrete specimens to increase the air
content and consequently the frost resistance of concrete.
Keyword: Concrete, Self-healing ability, Fly ash, Compressive strength, Carbonation
coefficient, Micro-cracks, Mineral admixture
1. Introduction
Concrete material has been widely used for a long time in civil engineering and construction
field all over the world for its wide application, as many benefits such as low cost, extremely
strong compression, etc. It is quite needed to maintain the structural performance of concrete
structures, such as serviceability and durability, in order to prolong their service life.
However, the deterioration of concrete is inevitable since there are many deterioration
mechanisms, such as carbonation, alkali-aggregate expansion reaction, freeze-thaw expansion,
salt scaling by deicing salts, autogenous and drying shrinkage, surface attack on exposure to
ground waters containing surface ions, sea water attack, and corrosion that caused by salts,
can harm adversely the performance of concrete structures due to its exposure to severe
weather conditions [1, 2]. This adverse harm can be increased greatly in case of cracked
concrete which has internal or external micro cracks, due to the rapid mass transport through
those micro cracks induced in mortar or concrete. Due to the deterioration more cracks occur
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into the concrete, leading to the reduction of service life time of concrete structure. Further,
when cracks are introduced into concrete, the cost and amount of labor required for diagnosis
and repair work should be considered in order to restore its original performance. Therefore,
to solve this problem, it is necessary to have smart technique to fill the micro-cracks to
extend the service life of the concrete structures. Mineral admixtures as by-products, which
are fly ash, ground granulate blast furnace slag and silica fume, etc, have been widely used to
improve the mechanical properties of concrete. However, the effect of such materials on selfhealing
ability have not been fully explored since the effect of environmental conditions as
deterioration mechanisms is complicated and can result in variable widths and locations of
micro-cracks inside the concrete matrix.
To date, research on self-healing ability has been widely performed all over the world. The
ability is unique and promising solution to recover the damaged concrete that caused by
various deteriorations such as carbonation, autonomous and drying shrinkage and frost
damage and so on. In 2007, JCI Technical Committee (JCI-TC075B 2007) was established
and the task of this committee was to investigate the self-healing ability in cementitious
materials as shown in Fig. 1.
Many researches have been carried out about self-healing ability in concrete through many
techniques [1, 4, 5, 6, 7]. However, those methods have many disadvantages such as cost
efficiency, difficulty of casting and limited amount of healing agent. Fly ash and ground
granulate blast furnace slag are a promising solution, due to the fact that the materials have
good pozzolanic and latent hydraulic activities in comparison with normal cement, thus,
improved workability, long-term strength, reduced alkali silica reactivity, lower porosity and
moreover reduce CO2 emissions considering it as eco-friendly solution to the environment.
Pipat et al. [4] have investigated the self-healing ability in cracked fly ash blended cement
systems for autogenous and drying shrinkage after 28 days, they pointed out that when
cement was replaced by fly ash, the compressive strength decreased. This problem may be
overcome if fine aggregate instead of cement is replaced by fly ash. The fly ash reacts with
calcium hydroxide and water then produces C-S-H gel, which called pozzolanic reaction. The
amount of cement reduction will vary depending on the reactivity of the pozzolan.
Engineered healing
Activated
repairing
Autogenous
healing
Natural
healing
Autonomic
healing
Fig. 1 Definition of self-healing [3]
The objective of this paper is to investigate experimentally the self-healing performance of
cracked concrete incorporating fly ash (FA) with or without air-entraining agent. Concrete
specimens are cracked by accelerated environmental action that is repeating cycles of
low/high temperatures or freezing/thawing process. The experiments discussed how the
change of relative dynamic modulus of elasticity, compression strength and carbonation
coefficient as index of self-healing properties in concrete specimens before cracking, after
cracking, after healing due to curing in water can be. The obtained findings are useful
information for concrete material field.
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2. Experimental Work
2.1 Experimental materials
Chemical and physical properties of used cement, fly ash, fine aggregate and coarse
aggregate are given in Tables 1, 2 and 3. Ordinary Portland cement (OPC) was used in
preparation of concrete specimens. All cylindrical concrete specimens (100Ø×200 mm) were
casted using water to cement ratio of 0.51 and sand to coarse aggregate ratio around 0.46 to
reach acceptable degree of workability and slump values around 180 mm, as shown in Table
4 for the mix proportions and fresh properties of examined mixtures. Four mixtures, which
included two types of normal concrete (N, F) without air-entraining agent and two types of
air-entrained concrete (NA, FA), were tested to evaluate the self-healing ability of concrete
samples w/o fly ash and w/o air-entraining agent. In Table 4, N and NA refer to OPC
concrete samples without adding fly ash, while F and FA refer to fly ash concrete samples
incorporating fly ash with 15% replacement ratio of fine aggregate by volume. All of the
investigated concrete samples were mixed in accordance with JIS A-1138 and were designed
to ensure the required slump and air contents. The slump was set 180±20 mm. After casting,
concrete samples were sealed and cured in laboratory for 1 day, then, placed in water
container at 20±3 degree until required test ages.
2.2 Test Methods
Compression tests of examined fly ash concrete samples were carried out according to JIS A-
1108 at age of 7, 28 and 91 days to know how fly ash can contribute into the development of
the strength.
Table 1 Characteristics of used cement
Cement
type
Density
(g/cm3)
Blain
(cm2/g)
Chemical composition (%) Mineral composition (%)
SiO2 Al2O3 Fe2O3 CaO MgO SO3 C3S C2S C3A C4AF
N 3.16 3250 21.5 5.4 2.9 64.3 1.9 1.8 52 23 10 9
Table 2 Properties of fly ash
Fly
Ash
Density
(g/cm3)
Blain
(cm2/g)
Chemical composition (%)
SiO2 Al2O3 Fe2O3 CaO MgO Na2O K2O SO3 TiO2 MnO
FA 2.11 3900 73.1 16.9 3.0 1.6 1.2 0.3 1.0 0.2 0.7 0.0
Table 3 Physical properties of used aggregate materials
Types of aggregates
Surface dried density
(g/cm3)
Absolute dried
density (g/cm3)
Water absorption
ratio (%)
Coarse
grain ratio
(%)
Fine aggregate 2.65 2.64 0.42 2.66
Coarse aggregate 2.67 2.62 1.93 6.64
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Table 4 Mix proportions of concrete samples and fresh characteristic
Note: s/a=fine aggregate/coarse aggregate, Ad1) = high performance water reducing agent, Ad2) = airentraining
agent and fly ash air entraining agent added only to FA mixture. W/C = water-to-cement
ratio
For self-healing evaluation, after curing concrete samples at 28 days, the relative dynamic
modulus of elasticity (RDM) was measured (recorded as initial value of RDM). Then, in
order to introduce the micro cracks in the fly ash concrete sample, the freeze and thaw test
was performed until 30 cycles of freezing/thawing in accordance with JIS A-1127. After
deterioration of concrete samples, curing conditions of concrete samples were considered in
water at 40􀉗 for 2 weeks as one cycle of deterioration/healing in order to investigate the
self-healing potential in designed fly ash concrete samples. Further, accelerated carbonation
test (phenolphthalein method) was performed to calculate the carbonation depth and
coefficient before/after deterioration of fly ash concrete occurred and after curing-based selfhealing
of fly ash concrete samples, in accordance with JIS A-1153.
3. Results and Discussion
3.1 Compressive Strength
Figure 2 shows the results of compressive strength for four mixtures of concrete samples at
the ages of 3, 7, 28, 91 and 365 days. The compressive strength for N and NA concrete
samples showed a significant increase in compressive strength until 7 days of curing age, and
then exhibited a slight increase at 28 days of curing age. While, the compressive strength of
concrete samples (F and FA) produced with fly ash as replacement of fine aggregate
continued to increase significantly after 28 days, particularly increase of compressive strength
for F sample increase was remarkable. Therefore, in the comparison to normal concrete
without fly ash (N and NA), fly ash concrete samples (F and FA) exhibited greater
compressive strength, this increase in compressive strength can be related to different pore
structure in concrete samples. Hence, the fly ash replacement of fine aggregate can improve
the compressive strength due to its pozzolanic effect and attributed to densification of
concrete matrix.
Mixture
W/C
(%)
s/a
(%)
Unit weight􃸦kg/m3􃸧
Slump
(mm)
Air
content
Water Cement (%)
Fly
ash
Fine
aggregate
Coarse
aggregate
Ad1) Ad2)
N
51.1
47 151 296 􃸫 955 1084 3.85 􃸫 165 4.0
NA 46 151 296 􃸫 880 1038 3.26 0.067 175 5.5
F 48 151 296 44.4 930 1065 3.85 􃸫 180 2.6
FA 46 151 296 44.4 836 1038 3.26 0.2893) 190 5.1
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0
10
20
30
40
50
60
70
0 100 200 300 400
Compressive strength(MPa)
Curing age (days)
N NA
F FA
Fig. 2 Compressive strength development with curing ages until 365 days
3.2 Frost Resistance
Figure 3 presented the results of freeze/thaw test for concrete samples with different curing
ages at 28 and 365 days according to the ASTM C 666 standards. The relative dynamic
modulus of elasticity is a non-damaged test method to evaluate the deteriorated concrete. For
example, RDM reached 60% at 42 cycles in case of F fly ash concrete sample cured at 28
days, as shown in Fig. 3. However, in the case of FA concrete sample RDM was similar to
NA concrete sample, which is the case of concrete with air-entraining agents. For the case of
curing at 365 days, RDM values of all concrete samples were rapidly decreased before 30
cycles. In addition, the variation of RDM for N, NA and FA concrete samples showed a
similar trend.
3.3 Self-healing Ability in AE Fly Ash Concrete
The results of relative dynamic modulus of elasticity for fly ash concrete samples which
include 15 % by volume fly ash replacement ratio w/o air entrained agent, F and FA samples
respectively, and normal concrete samples w/o air entrained agent, N and NA samples,
respectively, at different curing ages, considering the three studies cases which are No
cracking case (initial value), deterioration case (micro-cracking) and water-based-healing
case at 40􀉗 for 4 weeks in water, are shown in Fig. 4. In the case of 28 days, after
deterioration, it can be seen from the figure that most of the investigated concrete samples
decreased until 80-90 of RDM. Then, after healing case, they were healed almost until No
cracking case (initial value) in all concrete samples. It can be revealed that most of the
investigated concrete samples were partially recovered after healing case to initial values of
RDM for the case of 28 days initial curing. While samples with initial curing of 365 days did
not show the same behavior due to the fact that self-healing ability can be decreased with
increasing initial curing ages due to decrease of un-reacted cement and fly ash in concrete
samples.
Relative dynamic modulus of elasticity(%)
Number of cycles
Fig. 4 Self-healing ability based on change of RDM in concrete samples with different curing
age (a) initial water curing at 28 days (b) initial water curing at 365 days
Figure 5 shows the results of accelerated carbonation test for concrete samples after two
initial water curing conditions (before deterioration), including four cases which consist of
No cracking case, after deterioration case, after healing case and repetition of deterioration
and healing case. The carbonation coefficient in all investigated concrete samples was
calculated by measured carbonation depth value until 26 weeks.
It can be confirmed from the figure that in both two curing ages at 28 and 91 days a
significant decrease of carbonation coefficient for F and FA concrete samples obtained,
which involve 15 % by mass of fly ash replacement ratio, implying that incorporating fly ash
into fine aggregate exhibits high self-healing performance after curing in water at 40􀉗 for 4
weeks, and hence can delaying carbonation process after deterioration.
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No cracking after deterioration after healing repetition of deterioration and healing