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MECHANICAL PROPERTIES AND DURABILITY
OF MAE MOH-FLY ASH MORTAR
B Chatveera
S Thasanakosol
Thammasat University
Thaiiand
A B S T R A C T . The objective of this paper was to investigate the depth of carbonation,
autogenous shrinkage, drying shrinkage and compressive strength of mortar containing
lignite fly ash from Mae Moh. The water-cementitious materials ratio was kept constant.
The main parameter was the percentage replacement of fly ash, 30% and 60%. For
carbonation, autogenous shrinkage and drying shrinkage tests, the specimens were made with
the replacement of only one type of fly ash whereas for compressive strength test, 3 types of
fly ash were used. The test results were indicated that when pertentage of fly ash
replacement increased all types of shrinkage decreased. However, fly ash did not improve
the carbonation resistance. For the compressive strength result, the strength of fly ash mortar
can be predicted when the CaO-Equivalent in mortar was known.
Keywords: Autogenous shrinkage, Carbonation, Compressive strength, Drying shrinkage.
D r B u r a c h a t C h a t v e e r a is an assistant professor in the Department of Civil Engineering at
Thammasat University, Rangsit Campus, Pathum Thani 12121, Thailand. He received his
D.Eng. from Asian Institute of Technology, Thailand.
M r Sayan Thasanakosol is a graduate student in the Department of Civil Engineering at
Thammasat University, Rangsit Campus, Pathum Thani 12121, Thailand. He received his
B.Eng. from Chiang Mai University, Thailand.
Downloaded by [ Griffith University] on [25/10/17]. Copyright © ICE Publishing, all rights reserved.
152 Chatveera, Thasanakosol
INTRODUCTION
It is known that fly ash is one of pozzolanic materials, which has great potential to be used to
improve concrete quality in construction. In recent years, energy consumption in Thailand
rises appreciably due to the industry expansion and economic growth, causing the increase of
coal consumed to produce electricity, therefore increasing the amount of fly ash which is
waste product. Mae Moh electricity generating plants use 3 million tons of lignite coal each
year to produce the electricity. It generates a lot of amount of coal ash but a little amount is
used. The remained amount may harmful to the environment in term of dispersing in the air
if keeping condition is unsuitable. If the using of fly ash increases, environmental problem
will be solved.
This paper presents some advantages of using fly ash as a constituent in mix in term of
mechanical properties and durability.
EXPERIMENTAL DETAILS
Materials
Portland cement: Ordinary Portland cement type 1 was used. The properties and composition
are shown in Table 1.
Fly ash: Three type of fly ash from Mae Moh electricity generating plant were used. The
properties and composition are shown in Table 1.
Fine aggregate: Natural river sand passing ASTM sieve number 4 was used. It was prepared
in accordance with ASTM CI28.
Mixing water: Ordinary tap water was used.
Table 1 Composition and properties of cement and fly ash
COMPOSITION/PROPERTIES
OPC
FH
FM
FL
Si0 , %
A1 0 , %
Fe 0 , %
CaO, %
MgO, %
K 0, %
Na 0, %
S0 , %
MnO, %
Specific Gravity
Bulk Density, gm/L
Fineness Passing 45 um sieve, %
Moisture content, %
21.45
5.35
3.01
67.33
1.52
0.33
0.11
2.31
26.23
13.72
9.99
29.97
3.16
1.7
0.21
6.01
0.139
2.65
1.13
30.22
0.08
30.39
15.9
10.53
23.12
3.26
2
0.19
4.17
0.132
2.23
1.00
35.68
0.14
42.86
23.05
8.75
10.13
2.93
2.55
0.2
1.17
0.087
1.94
1.00
42.68
0.07
2
2
3
2
3
2
2
3
FH, high S 0 fly ash
3
3.15
1.02
8.6
0.11
FM, medium S 0 fly ash
3
FL, low S 0 fly ash
3
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M a e Moh-FIy A s h M o r t a r
153
Mix P r o p o r t i o n s
The mix proportions are summarized in Tables 2 and 3
Table 2 Mix proportion for shrinkage and carbonation tests
% FLY A S H
W/(C+F)
F/(F+C)
(F+C)/S
O(OPC)
30
60
0.5
0.5
0.5
0
0.3
0.6
0.36
0.36
0.36
TYPE OF F L Y
ASH
FL
FL
Table 3 Mix proportion for strength test
MORTAR
OPC(W)
OPC(W-D)
FH-30(W)
FH-30(W-D)
FH-60(W)
FH-60(W-D)
FM-30(W)
FM-30(W-D)
FM-60(W)
FM-60(W-D)
FL-30(W)
FL-30(W-D)
FL-60(W)
FL-60(W-D)
W/(C+F)
F/(F+C)
(F+C)/S
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0
0
0.3
0.3
0.6
0.6
0.3
0.3
0.6
0.6
0.3
0.3
0.6
0.6
0.36
0.36
0.36
0.36
0.36
0.36
0.36
0.36
0.36
0.36
0.36
0.36
0.36
0.36
TYPE OF
FLY A S H
CURING
CONDITION
-
W
W-D
W
W-D
W
W-D
W
W-D
W
W-D
W
W-D
W
W-D
FH
FH
FH
FH
FM
FM
FM
FM
FL
FL
FL
FL
Curing Environments
For strength test, two curing conditions were used. These were : (W) water curing, (W-D)
cyclic wetting and drying condition. One cycle consists of 1-week wetting and 1-week
drying period. For wetting, the specimens were submerged in water. For drying, the
specimens were put into the specimen curing unit having temperature of 25±2°c and 6 0 ± 5 %
relative humidity.
For drying shrinkage test, water curing for 28-day after demolding. Then, the specimens
were put into the specimen curing unit having temperature of 25±2°c and 6 0 ± 5 % relative
humidity.
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154
Chatveera, Thasanakosol
For autogenous shrinkage test, after demolding, the specimens were wrapped with plastic
sheet and put into the specimen curing unit having temperature of 25±2°c and 60±5% relative
humidity.
For carbonation test, water curing for 28-day after demolding. Then, the specimens were
placed in the location containing CO2.
RESULTS AND DISCUSSION
S t r e n g t h of M o r t a r
It was obviously observed from Figures 1 and 2 that strength of mortar having 30 and 60
percent replacement of fly ash to ordinary Portland cement are lower than the control in early
age. In long term, mortar having 30 percent replacement of fly ash to ordinary Portland
cement have nearly value of strength due to the pozzolanic reaction which occurred in longterm. Furthermore, the value of strength varied by the amount of SO3 in material
compositions. It was found that high SO3 fly ash has a tendency that strength will higher
because fly ash in this study has the amount of CaO regarding to the amount of SO3. The
higher amount of CaO in material composition implied that the strength of mortar is
higher [1].
100
AGE (DAYS)
Figure 1 Compressive strength of mortar having varied amount of SO3 and percent
replacement of fly ash to cement in water curing condition
D r y i n g S h r i n k a g e of M o r t a r
Figure 3 showed that the mortar with fly ash display smaller drying shrinkage than the
control especially when the percentage of replacement is larger because the water
requirement of mortar with fly ash is smaller. So, it can be noticed that the water to
cementitious materials ratio of the mixture with fly ash can be reduced in practice, therefore,
drying shrinkage is reduced [2].
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M a e Moh-Fly Ash M o r t a r
70
155
r
0
20
40
60
80
100
AGE (DAYS)
Figure 2 Compressive strength of mortar having varied amount of SO3 and percent
replacement of fly ash to cement in cyclic wetting and drying curing condition
Figure 3 Drying shrinkage of mortar containing fly ash
Autogenous s h r i n k a g e of m o r t a r
Figure 4 showed the comparison of length change of specimens containing fly ash 30 and 60
percent to the control. It was shown that all specimens with fly ash exhibit smaller
autogenous shrinkage than the control, especially when the replacement percentage is higher.
It can be seen that the higher content of fly ash is the more reduction of autogenous
shrinkage. It can be explained that it is the result of spherical shape of fly ash resulting in
less retained water than the cement particles [2]. This result is larger free water content in the
mixture with fly ash than the mixture without fly ash when prepared with the same water to
binders ratio. As the autogenous shrinkage is a result of water consumption in hydration
process.
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156 C h a t v e e r a , T h a s a n a k o s o l
Figure 4 Autogenous shrinkage of mortar containing fly ash
C a r b o n a t i o n of m o r t a r
Figure 5 illustrated that carbonation of mortar containing fly ash is larger than the control and
higher when the amount of fly ash is increased [1].
1 MONTH
2 MONTH
3 MONTH
Figure 5 Carbonation depth of mortar
A m o d e l for s t r e n g t h p r e d i c t i o n of m o r t a r containing M a e Moh-fly ash
The parameters affecting the strength of mortar are type of fly ash and percent replacement of
fly ash to cement. When the affecting parameter are changed, strength of mortar will be
changed. Generally, the crucial portion of chemical composition affecting to the strength of
mix is CaO and Si02 in cementitious materials contents, as known in the hydration reaction.
Refer to Table 1, the control compound affecting the strength of mix is CaO. The CaO
affecting the strength of mix is called as CaOEquivaient comprising CaO from cement powder
and fly ash.
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Mae Moh-Fly Ash Mortar
157
In this study, the strength of mortar having the water to cementitious materials ratio equal to
0.5 can be predicted by linear regression analysis from strength data, percent replacement of
fly ash to cementitious materials and CaOEquivaient in fly ash.
5
1 day
0
-\
.
1
0
10
20
.
o
.—•
1
30
o
40
1
1
1
50
60
70
80
CaO EQUIVALENT, %
Figure 6 Relationship between compressive strength of mortar and CaOEquivaient
From Figure 6, strength of mortar can be predicted by the following equations.
STi = 0.4399(CaO vaient)-14.658
ST
=0.5261(CaO
>10.442
ST, = 0.5982(CaO ,ent)-9.4456
ST = 0.9094(CaO ,ent)-14.989
ST = 0.7466(CaO
t)-3.241
Equi
7
Equivalent
4
Equiva
28
Equiva
90
Where
Equivalen
CaO aient = (1 -r)(CaO )+(r)(CaO )
CaO is percent by weight of CaO in cement powder
CaOf is percent by weight of CaO in fly ash
r is the weight ratio of fly ash by cementitious materials [F / (F+C)]
Equiv
c
f
c
CONCLUSIONS
1. By replacing the fly ash to some parts of cement at 30 percent, early age strength is lower
whereas long-term strength is the same as the control. However, at the percentage of fly
ash replacement equal to 60 percent, strength is reduced.
2. At the same percentage replacement of fly ash, the compressive strength of mortar is
regarding to the content of CaO in fly ash. That is the more content of CaO in fly ash, the
more strength in mortar.
3. Under saturated and cyclic wetting-drying curing conditions of mortar containing fly ash
at 30 or 60 percent by weight, strength is slightly different.
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158 Chatveera, Thasanakosol
4. The autogenous shrinkage and drying shrinkage can be reduced by increasing the content
of fly ash in mixture.
5. The carbonation of mortar containing fly ash is larger than the control and higher when
the amount of fly ash in mixture is increased.
6. The strength of mortar can be predicted when the
CaOE ivaient
qu
was known.
REFERENCES
1. DECHNANTARAT, T, TANTIWAT, S AND YOTHMAT, S, Mechanical Properties and
Durability of Mae Moh-Fly Ash Mortar. B.Eng. Civil Engineering Project, Thammasat
University, Bangkok, Thailand, 1995.
2. TANGTERMSIRIKUL, S, Durability of Concrete using Pozzolans. Seminar of Advance
in Concrete Technology, ACI (Thailand Chapter) and Engineering Institute of Thailand,
Bangkok, 1996.
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