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Physical and permeability properties of cementitious mortars having fly ash with optimized particle size distribution
Accepted Manuscript Physical and permeability properties of cementitious mortars having fly ash with optimized particle size distribution İlhami Demir, Özer Sevim PII:
S0958-9465(18)30697-8
DOI:
https://doi.org/10.1016/j.cemconcomp.2018.11.017
Reference:
CECO 3185
To appear in:
Cement and Concrete Composites
Received Date: 6 July 2018 Revised Date:
5 November 2018
Accepted Date: 26 November 2018
Please cite this article as: İ. Demir, Ö. Sevim, Physical and permeability properties of cementitious mortars having fly ash with optimized particle size distribution, Cement and Concrete Composites (2018), doi: https://doi.org/10.1016/j.cemconcomp.2018.11.017. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT 1
iPHYSICAL AND PERMEABILITY PROPERTIES OF CEMENTITIOUS MORTARS
2
HAVING FLY ASH WITH OPTIMIZED PARTICLE SIZE DISTRIBUTION
3 İlhami Demir1,2, Özer Sevim*1
4
Department of Civil Engineering, Kırıkkale University, Kırıkkale, Turkey. 2
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Department of Architecture, Amasya University, Amasya, Turkey.
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ABSTRACT
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Gradation of powder materials is often avoided in pozzolanic materials, such as fly
11
ash. Without good gradation, powder materials result in high void ratios similar to the case of
12
aggregates. The products obtained after hydration would still have voids.
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This study calculated the particle size distributions (PSDs) of fly ash using a vacuum
14
sieve in accordance with the Dinger–Funk PSD modulus. The optimal PSD was defined, and
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the compressive strength of fly-ash-blended cement mortars at 7, 28 and 90 days was
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explored. Properties such as water absorption capacity, dry density and rapid chloride
17
permeability of the optimised fly ash were analysed by varying the replacement levels. The
18
water absorption capacity of the optimised fly-ash-blended cement mortar was lower than that
19
of the blended cement mortar having non-optimised fly ash. Moreover, at 90 days, the
20
chloride permeability of the optimised fly-ash-blended cement mortar was improved by up to
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39.1% when compared to that of the blended cement mortar having non-optimised fly ash.
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Keywords: Binder System, Fly Ash, Particle Size Distribution, High Compactness,
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Water Absorption, Rapid Chloride Permeability.
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Corresponding author. Tel: +90-318-357-4242 (1263), E-mail: [email protected]. 1
ACCEPTED MANUSCRIPT 1. INTRODUCTION
32
Fly ash is commonly used as a cement additive, and replacement material. The
34
fineness of fly ash is the most important property that affects its performance in cement and
35
concrete. Previous studies have shown that the properties of fly-ash-blended concrete, such as
36
strength, abrasion resistance and freeze-thaw resistance, are a function of fineness of the used
37
fly ash [1-6].
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Previous studies have commonly focused on the effect of fineness and particle size
39
distribution (PSD) from a single point or multiple points of view. Fineness has been
40
emphasised in the literature on PSD. Slanicka [7] discussed the effects of the chemical and
41
mineralogical properties of fly ash, as well as its fineness, on the strength of concrete. The
42
aggregate was replaced with fly ash. Monzo et al. [8] investigated the compressive and
43
flexural strength of the cement mortar blended with Class F Spanish fly ash having varied
44
fineness levels at a replacement level of 30%. The increase in the fineness of fly ash also
45
increased the compressive strength. Erdoğdu and Türker [9] analysed the properties of fly-
46
ash-blended cement mortars having different PSDs. They argued that the use of fly ash having
47
different PSDs resulted in different cement properties. The compressive strength of the
48
samples was investigated, which were prepared using six fly ash groups having particle sizes
49
of 125, 90, 63 and 45 µm at a replacement level of 25%. The optimal strength results were
50
obtained from the sample substituted by fly ash of 45 µm or less in size. Lee et al. [10]
51
analysed the effects of fly ash PSD on the viscosity of the cement mortar. An increase in the
52
PSD increased the viscosity. Bentz et al. [11,12] prepared samples having five different
53
specific surface areas for cement and fly ash. The compressive strength of the samples was
54
then analysed at replacement ratios of 20%, 35%, 50% and 65%. The optimised compressive
55
strength was obtained from the sample having a fly ash replacement of 20%. The compressive
56
strength of the sample having a fly ash replacement of 35%, on the other hand, was close to
57
that of the reference Portland cement.
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To date, there is lack of research on the optimal designs aimed to obtain high
59
compactness using powder material gradation with pozzolans, such as fly ash. Particle size
60
has been used to obtain an economic concrete design. The selection of PSD requires focus on
61
the ability to fill in voids among particles. First, PSD was analysed for an economic concrete
62
design [13]. The Fuller–Thompson theory has been widely used in PSD optimisation to define
63
the replacement ratio of aggregates in concrete [14]. In many European countries, well-graded
64
ideal aggregate granulometry is optimised for concrete design. Therefore, Fuller’s curve is
65
still used by many authors in concrete mix design. However, this optimisation curve has not 2
ACCEPTED MANUSCRIPT been altered for the last century. In this context, the most important development was made by
67
Funk and Dinger by applying a minimum particle diameter. Furthermore, some researchers
68
have suggested different exponential values to determine the ideal curve for self-compacting
69
concrete or high-performance concrete [15]. In particular, owing to the introduction of new
70
superplasticisers, there is a need to renew the interest in PSD, high-performance concrete and
71
other types of concrete containing high amounts of additives. The concept of PSD
72
optimisation is also important for producing environment-friendly concrete. Cement mortar is
73
used to fill the voids available in aggregates to obtain the lowest void ratio. Using this
74
method, the optimised aggregate and cement mixtures can offer sufficient strength [16,17].
75
Many studies focusing on aggregate gradation recommended the use of an ideal aggregate
76
PSD curve for the concrete design [13-17]. It is possible to obtain high compactness levels in
77
aggregates using granulometry curves populated via the formulas developed and reported in
78
the literature. These methods were used to ensure the high compactness of pozzolanic
79
materials such as fly ash irrespective of the powder material gradation.
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On the basis of the aforementioned information, designs were made to obtain the
81
optimal fly ash PSD to achieve the highest compactness. It is possible to obtain a mixture of
82
materials at suitable percentages, which have low void ratio and high compactness. Properties
83
such as water absorption capacity, dry density and rapid chloride permeability of fly ash
84
having the optimised PSD were explored for varied replacement levels.
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The water absorption capacity of hardened concrete affects its durability and strength
86
in physical and chemical reactions that may exist throughout the service life of concrete [18-
87
20]. Water and other fluids permeate into concrete through voids in its structure, introducing
88
harmful substances into concrete [21]. Concrete having high water absorption capacity, i.e.
89
concrete having high permeability, loses its strength and durability in physical and chemical
90
phenomena. In addition to the water absorption capacity, dry or bulk density affects the
91
compressive strength, flexural strength and elasticity modulus of cement mortars. An increase
92
in dry density improves the mechanical properties, and a high dry density is a parameter of
93
high compactness. Concrete having high compactness offer minimal void ratio, i.e. porosity,
94
as well as higher strength [22].
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Another important parameter for the service life of concrete is how chloride ions
96
permeate into concrete [23-26]. Several mechanisms have been reported in this regard.
97
Additives in concrete, de-icer chemicals, aggregates obtained from the sea and sea water
98
result in a porous structure in concrete, deteriorating the passive protective layer created on
99
the reinforcing steel in the process of corrosion [27]. High chloride permeability in concrete 3
ACCEPTED MANUSCRIPT facilitates the infiltration of chloride ions into concrete, suggesting that the reinforcing steel is
101
easily subjected to these ions. Concrete having low chloride permeability is produced to
102
ensure the durability of concrete and to prevent the corrosion of reinforced concrete. It has
103
been reported that the use of a specific amount of pozzolans (fly ash, blast-furnace slag, silica
104
fume, etc.) as a binder in concrete production can give desirable results [28-34]. In the fly-
105
ash-replaced concrete, Ca(OH)2 in the concrete that was produced after hydration reacted with
106
SiO2 and Al2O3 compounds in fly ash and produced extra C-A-H and C-S-H compounds,
107
increasing the strength of concrete in alkali and chloride media [35–37].
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This study aims to find the optimal PSD of fly ash and analyse its effect on the
109
compressive strength of the fly-ash-blended cement mortar. The suitable PSD of fly ash was
110
obtained using a vacuum sieve. We analysed properties such as water absorption capacity, dry
111
density and rapid chloride permeability of fly-ash-blended cement mortars having different
112
replacement levels and calculated the distribution modulus to obtain the optimal design.
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2. EXPERIMENTAL DESIGN
114 115 116
2.1. Materials Used in this Study Portland Cement
Portland cement type CEM I 42.5 R (similar to ASTM Type I cement) that complied
118
with TS EN 197-1 standard was used in this study [38]. The physical and chemical properties
119
of the used cement are listed in Table 2.1.
Table 2.1. Chemical and physical properties of CEM I 42.5 R cement. Chemical composition (%) SiO2
Portland cement 21.02
Al2O3
5.38
Fe2O3
3.22
CaO
62.12
MgO
1.98
Na2O
0.39
K2O
0.81
SO3
3.11
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Physical properties
121 122
Specific gravity (unitless)
3.18
Blaine fineness (cm²/g)
3356
Loss on ignition (%)
2.37
4
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Fly Ash The fly ash used in this study was Class C fly ash (SiO2 + Al2O3 + Fe2O3 < 70% and
125
CaO > 10%) obtained from Çayırhan Coal Power Plant. The fly ash was used as received
126
without grinding. The reason for selecting the Class C fly ash was to illustrate the effects of
127
fillers having optimised PSDs. It would be possible to clearly observe the effect of fillers on
128
the strength rather than chemical effects of the optimised fly ash. The chemical and physical
129
properties of the fly ash are listed in Table 2.2.
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Table 2.2. Chemical and physical properties of fly ash. Chemical composition (%)
Fly ash
SiO2
46.59
Al2O3
12.42
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Fe2O3
9.74
14.50
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MgO
7.23
SO3
5.52
Na2O
1.01
K2O
2.28
Physical properties
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Density (g/cm )
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2.2. Method
135
PSD Optimisation
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Fly ash samples were sieved using an Alpine vacuum sieve that complied with TS EN
137
933-10 standard for the particle sizes ranging from 0 to 25, 25 to 50, 50 to 63, 63 to 75 and 75
138
to 90 µm to define their PSDs [39]. Sieve analyses were performed using the vacuum sieve
139
for each particle size. Here, the optimal PSD was found in accordance with Equation 1, as
140
suggested by Funk and Dinger [15]. When the minimum particle size is set to zero and the
141
distribution modulus is equal to 0.5, this equation is simplified to the Fuller–Thompson
142
model, which is used to optimise the aggregate distribution [14].
143
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P D =
144 145
where
146
P(D)
×100,
(1)
: Total percentage of the material smaller than the diameter 5
ACCEPTED MANUSCRIPT of pores on the sieve, D.
147 148
D
: Diameter of pores on the sieve.
149
Dmin
: Minimum particle diameter of fly ash.
150
Dmax
: Maximum particle diameter of fly ash.
151
q
: Distribution modulus.
152
The optimal PSD design was obtained from the 20% fly-ash-blended cement. The
154
replacement level of 20% was selected to facilitate the observation of the fly ash activity.
155
After the optimal distribution modulus (q) was obtained, samples were prepared for
156
replacement levels of 5%, 10%, 15%, 20% and 30% using the distribution modulus to
157
obtain the optimal design. The compressive strengths of cement mortars were observed for
158
defining the optimal particle size using the TS EN 196-1 standard. The results were
159
obtained by calculating the mean values for six prismatic cement mortar samples [40].
160
Materials and Mix Ratios
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CEM I 42.5 R Portland cement, Class C fly ash, standard sand and potable water
162
were used in this study. Cement mortars were prepared using replacement levels of fly ash
163
of 0% (control), 5%, 10%, 15%, 20% and 30%. The obtained cement mortars were stored
164
under humid conditions for 24 h and then cured in water for a defined period. The water–
165
binder (W/B) ratio of the fly-ash-blended cement mortars prepared in this study was 0.50.
166
Table 2.3 shows the mixture ratios of the materials used; FA stands for fly ash in this table.
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Table 2.3. Mix ratios of the cement mortar.
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0% FA
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Component (g)
10% FA
15% FA
20% FA
30% FA
Potable water (Total)
225
225
225
225
225
225
Portland cement
450
427.5
405
382.5
360
315
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168 169 170 171
5% FA
Fly ash
0
22.5
45
67.5
90
135
Standard sand
1350
1350
1350
1350
1350
1350
Water Absorption and Dry Density Properties
172
The water absorption and dry density properties of cement mortars blended with 5%,
173
10%, 15%, 20% and 30% fly ash, with and without the optimised PSD, were explored for 7, 28
174
and 90 days in accordance with ASTM C 642 [41]. Cubic cement mortar samples with a
175
dimension of 50 × 50 × 50 mm3 (width × height × length) were used. The results were obtained
176
by calculating the mean values of six prismatic cement mortar samples. In the experiment,
177
cement mortars were cured in potable water for specified periods and weighed (B) after being 6
ACCEPTED MANUSCRIPT dried using a dry cloth. After storage in an oven at 100 ± 5°C for 24 h, cement mortars were
179
then weighed again (A) at 20°C–25°C. Cubic cement mortar samples with dimensions of 50 ×
180
50 × 50 mm3 were boiled for 5 h and weighed again (C) at 20°C–25°C. Cubic cement mortar
181
samples with dimensions of 50 × 50 × 50 mm3 were weighed in water after immersion and
182
boiling (D). The water absorption percentage of cement mortars was calculated using Equation
183
2. The dry density of cement mortars was calculated using Equation 3.
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184 185
Water absorption percentage:
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Bulk density, dry:
× 100
× ρ =g .
188
(3)
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(2)
Rapid Chloride Permeability Test
The rapid chloride permeability tests of cement mortars blended with 5%, 10%, 15%,
190
20% and 30% fly ash, with and without optimised PSD, were explored for 7, 28 and 90 days in
191
accordance with ASTM C 1202 [42]. Cylindrical samples (diameter = 100 mm, length = 200
192
mm) of fly-ash-blended cement mortars were prepared in accordance with TS EN 196-1 [40].
193
Experimental samples (diameter = 100 mm, length = 50 mm) were cut out from the central part
194
of the prepared samples after being cured in water for 7, 28 and 90 days [40]. Four cylindrical
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samples of each mix were used for a rapid chloride permeability test. The mean values were
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achieved based on these four samples.
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The cement mortar was placed in the experimental cell. One end was in contact with
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0.30 M sodium hydroxide (NaOH) solution and the other with 3% sodium chloride (NaCl)
199
solution. The total amount of current flowing through each sample subjected to a voltage of
200
60.0 ± 0.1 V for 6 h was measured and reported in Coulombs. ASTM C1202 (2012) classify
201
rapid chloride permeability into five groups, from ‘Negligible’ to ‘High’, based on Coulomb
202
values [42].
204 205
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3. EXPERIMENTAL FINDINGS AND DISCUSSION
3.1. Fly Ash PSD Analyses
206
The optimal PSD of fly ash was calculated between q = 0 and q = 1 using Equation 1
207
with gradual increments of 0.1. The total passing percentage of the material was calculated
208
using sieves having mesh sizes of 25, 50, 63, 75 and 90 µm to measure the distribution
209
modulus. PSD curves were populated based on these materials, and the passing percentage for
210
each distribution modulus was obtained. These PSD curves are shown in Fig. 3.1. 7
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q=0.2
q=0.3
q=0.4
q=0.5
q=0.6
q=0.7
q=0.8
q=0.9
q=1.0
100
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Passing percentage (%)
70
40
30
10
0
213 214 215 216
20
30
40 50 Particle diameter (µm)
60
70
80
90
Fig. 3.1. PSD curves for different distribution moduli.
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3.2. Optimal Fly Ash PSD Analyses The effect of fly ash PSDs on the mechanical properties of the cement mortar was
217
analysed. The effect of the PSD of fly ash on the compressive strength of fly-ash-blended
218
cement mortar at 7, 28 and 90 days was explored.
219 220
Effect of PSD on Mechanical Properties
221
The effect of PSD on the mechanical properties was explored based on different
222
distribution moduli. The mechanical properties of 20% fly-ash-replaced cement mortar were 8
ACCEPTED MANUSCRIPT 223
analysed after PSD analysis to better observe the activity of fly ash for different distribution
224
modulus values. Fig. 3.2 shows the compressive strength of cement mortars blended with the
225
optimised 20% fly ash at 7, 28 and 90 days. 7 Days
28 Days
90 Days
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50 45
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40 35 30 25 0.0
0.1
0.2
0.3
0.4 0.5 0.6 0.7 Distribution Modulus
0.8
0.9
1.0
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227 228 229 230
Fig. 3.2. Compressive strength results obtained from the optimised 20% fly-ash-blended cement mortars at 7, 28 and 90 days.
231
of 0.1 to 0.4, before being gradually decreased from a distribution modulus of 0.4 to 1.0.
232
Thus, the best compressive strength was obtained from the distribution modulus of 0.4 among
233
others. In other words, the distribution modulus of q = 0.4 ensured a significant increase in the
234
compressive strength and provided the highest compactness. At 7, 28 and 90 days, the highest
235
compressive strengths for q = 0.4 were found to be 32.08, 42.91 and 54.39 MPa, respectively.
236
The compressive strengths for the distribution modulus of q = 0.4 at 7, 28 and 90 days were
237
increased by 9.08%, 11.22% and 2.82%, respectively, when compared to that of the control
238
sample. The highest standard deviation values for the compressive strength results were 1.12,
239
1.21 and 1.22 for 7, 28 and 90 days, respectively.
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As shown in Fig. 3.2, compressive strength was increased from a distribution modulus
240 241 242 243
Material Coding Table 3.1 lists the sample coding for the fly-ash-blended cement samples optimised for PSD (q = 0.4) and sample non-optimised for PSD. 9
ACCEPTED MANUSCRIPT Table 3.1. Code of fly-ash-blended cement samples for various replacement levels. Sample code
Control
FA0
5 Non-optimised
FA5
5 Optimised
0.4FA5
10 Non-optimised
FA10
10 Optimised
0.4FA10
15 Non-optimised
FA15
15 Optimised
0.4FA15
20 Non-optimised
FA20
20 Optimised
0.4FA20
30 Non-optimised
FA30
30 Optimised
0.4FA30
245 246
3.3. Water Absorption Capacity
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Additive ratio (%)
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The purpose of this experiment was to obtain general information about the void ratios
248
of cement mortar blends with both optimised and non-optimised fly ash, which had
249
replacement levels of 5%, 10%, 15%, 20% and 30%. Because the cement mortar having low
250
strength would have a great void ratio, the water absorption capacity can also be increased.
251
Water absorption percentages at 7, 28 and 90 days were calculated using Equation 2 and are
252
listed in Table 3.2.
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Table 3.2. Water absorption percentages calculated at 7, 28 and 90 days. Sample code 7 days (%) 28 days (%) 90 days (%) FA0
9.81
9.27
9.05
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FA5
9.84
9.34
9.25
0.4FA5
9.74
9.17
8.83
FA10
9.93
9.55
9.41
0.4FA10
9.92
9.25
9.17
FA15
9.99
9.83
9.76
0.4FA15
9.98
9.52
9.34
FA20
10.28
10.19
10.11
0.4FA20
10.26
10.06
9.99
FA30
10.68
10.47
10.34
0.4FA30
10.60
10.32
10.16
10
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Fig. 3.3 shows the change in water absorption percentage of optimised and non-
255
optimised fly-ash-blended cement mortars after 7 days of water curing. The change in the
256
percentage was calculated by setting the water absorption percentage of the control cement
257
mortar as 100%. Optimized
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Change in water absorption (%)
110 108 106 104
SC
102
98 96 0
5
10
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100
258 259
Non-optimized
15 20 Additive ratio (%)
25
30
Fig. 3.3. Change in water absorption percentage of fly-ash-blended cement mortars at 7 days. As shown in Table 3.2 and Fig. 3.3, the water absorption percentage was increased by
261
increasing the replacement level of fly ash. The use of the cement mortar blended with the
262
30% optimised fly ash increased the water absorption percentage by 8.9%. The use of
263
optimised 30% fly-ash-blended cement mortar increased the water absorption percentage by
264
8.1%. A comparison of cement mortars blended with the optimised and non-optimised fly ash
265
showed that the water absorption percentage of the optimised fly-ash-blended cement mortar
266
at 5% replacement level was 0.1% lower than that of the non-optimised fly-ash-blended
267
cement mortar. By increasing the replacement level, the difference was increased and finally
268
reached 0.8% at 30% replacement level. These results showed that the void ratio of the
269
optimised fly-ash-blended cement mortar was lower than that of the non-optimised fly-ash-
270
blended cement mortar at 7 days.
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Similarly, the changes in water absorption percentage of optimised and non-optimised
272
fly ash after water curing for 28 days are shown in Fig. 3.4. The change in percentage was
273
also calculated via taking the water absorption percentage of the control cement mortar as
274
100%.
275 11
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116 114 112 110 108 106 104 102 100 98 96 0
5
10
15 20 Additive ratio (%)
276
25
30
Fig. 3.4. Change in water absorption percentage of fly-ash-blended cement mortars at 28 days.
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Non-optimized
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Change in water absorption (%)
Optimized
278
The water absorption percentage was also increased by increasing the replacement
280
percentage of fly ash. In addition, the water absorption percentage was increased by 12.9%
281
and 11.3% at a replacement level of 30% using non-optimised and optimised fly ash,
282
respectively. The water absorption percentage of the optimised 5% fly-ash-blended cement
283
mortar was lower than that of the control cement mortar. The void ratio and permeability of
284
the concrete were increased by increasing the replacement level. By comparison, the water
285
absorption percentage of the optimised fly-ash-blended cement mortar at different
286
replacement levels was lower than that of the non-optimised fly-ash-blended cement mortar.
287
Thus, the void ratio of the optimised fly-ash-blended cement mortar was lower than that of the
288
non-optimised fly-ash-blended cement mortar at 28 days.
EP
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289
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279
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116 114 112 110 108 106 104 102 100 98 96 0
5
10
SC
Change in water absorption (%)
Optimized
15 Additive ratio (%)
291
25
30
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20
Fig. 3.5. Change in water absorption percentage of fly-ash-blended cement mortars at 90 days.
292
Similarly, as shown in Table 3.2 and Fig. 3.5, the water absorption percentage at 90
294
days was increased by increasing the replacement level of fly ash. A replacement level of 30%
295
using non-optimised and optimised fly ash increased the water absorption percentage by
296
14.3% and 12.3%, respectively. The water absorption percentage of optimised 5% fly-ash-
297
blended cement mortar was lower than that of the control cement mortar as well. Thus, the
298
void ratio of concrete was increased by increasing the replacement level. Similarly, the water
299
absorption percentage of optimised fly-ash-blended cement mortar was lower than that of non-
300
optimised fly-ash-blended cement mortar, indicating higher compactness.
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The increase in fly ash replacement level also increased the water absorption
302
percentages. The water absorption percentage of the optimised cement mortar was lower than
303
that of the non-optimised cement mortar. The highest water absorption percentage was
304
achieved from the non-optimised sample replaced by 30% fly ash at 7 days. The lowest water
305
absorption percentage was obtained from the optimised sample replaced by 5% fly ash at 90
306
days. The water absorption percentage results obtained at 90 days were consistently lower
307
than those of other days in cement mortars having both optimised and non-optimised fly ash
308
with different replacement levels.
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309
The fact that hydration products fill the voids in the concrete gradually as the concrete
310
matures accounts for these findings. The increase in void ratio and permeability increases the
311
water absorption percentage and decreases the mechanical properties. The highest 13
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compactness level that is achieved through fly ash PSD optimisation can reduce the water
313
absorption percentage and increase the strength of concrete.
314
319
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dry density values at 7, 28 and 90 days. Table 3.3. Dry density values calculated at 7, 28 and 90 days. Sample code 7 days (g/cm3) 28 days (g/cm3) 90 days (g/cm3) FA0
1.99
2.01
FA5
1.99
2.01
0.4FA5
1.99
2.01
FA10
1.99
2.01
2.01
0.4FA10
1.99
2.01
2.01
FA15
1.99
0.4FA15
1.99
FA20
1.98
0.4FA20
1.99
FA30
1.97
0.4FA30
1.98
SC
317
Dry density properties were calculated using Equation 3. Table 3.3 shows the calculated
M AN U
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3.4. Dry Density Properties
TE D
315
2.01 2.01
2.02
2.00
2.01
2.01
2.01
1.99
2.00
2.00
2.01
1.98
1.99
1.99
2.00
Fig. 3.6 shows the percentage change in dry density of optimised and non-optimised
321
fly-ash-blended cement mortars after water curing for 7 days. The change in percentage was
322
calculated by setting the dry density value of the control cement mortar as 100%.
AC C
323
EP
320
14
ACCEPTED MANUSCRIPT
101.0 100.5 100.0 99.5 99.0 98.5 98.0 5
10
15 20 Additive ratio (%)
25
30
SC
0 324
Fig. 3.6. Percentage change in dry density of fly-ash-blended cement mortars at 7 days.
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325
Non-optimized
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Change in dry density (%)
Optimized
326
As shown in Table 3.3 and Fig. 3.6, dry density was decreased by increasing the
328
replacement level of fly ash, indicating an increase in void ratio. Dry densities of the samples
329
did not change at 15% replacement level. The dry density of the optimised fly-ash-blended
330
cement mortar was decreased at replacement levels of 20% and 30%. These results showed that
331
the void ratio at 7 days of the optimised fly-ash-blended cement mortar was lower than that of
332
the non-optimised fly-ash-blended cement mortar. In addition, PSD allowed for high
333
compactness in optimised cement samples. The cement mortar blended with 30% non-
334
optimised fly ash resulted in the lowest dry density values.
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327
Similarly, Fig. 3.7 shows the percentage changes in dry density of optimised and non-
336
optimised fly-ash-blended cement mortars after 28 days of water curing. As shown in Table 3.3
337
and Fig. 3.7, dry density also increased as the replacement level of fly ash was increased,
338
indicating that the void ratio increased as the replacement level was increased. The change in
339
dry densities of the samples was neglected up to 10% replacement level. The dry density of the
340
optimised fly-ash-blended cement mortar was higher at high replacement levels than that of the
341
non-optimised fly-ash-blended cement mortar. This finding indicates that the optimised fly ash
342
offered low void ratios and allowed for higher compactness.
AC C
EP
335
343 344 345 346 347 15
ACCEPTED MANUSCRIPT Optimized
Non-optimized
100.5 100.0 99.5 99.0 98.5 98.0 5
10 15 20 Additive ratio (%)
348
30
Fig. 3.7. Percentage change in dry density of fly-ash-blended cement mortars at 28 days.
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25
SC
0
RI PT
Change in dry density (%)
101.0
350
As shown in Table 3.3 and Fig. 3.8, the dry density at 28 days was also decreased as the
352
replacement level of fly ash was increased. Similarly, the dry density of the optimised samples
353
was either identical or higher than that of the non-optimised cement mortars. At 90 days, the
354
void ratio of the optimised fly-ash-blended cement mortar was also lower than that of the non-
355
optimised fly-ash-blended cement mortar, indicating high compactness.
358 359 360 361 362 363 364
EP
357
AC C
356
TE D
351
16
ACCEPTED MANUSCRIPT Non-optimized
101.0 100.5 100.0 99.5 99.0 98.5 98.0 5
10
15 20 Additive ratio (%)
365
30
Fig. 3.8. Percentage change in dry density of fly-ash-blended cement mortars at 90 days.
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25
SC
0
RI PT
Change in dry density (%)
Optimized
367
In short, the dry densities of the optimised samples were either identical or higher than
369
those of the non-optimised cement mortars. The optimised 5% fly-ash-blended cement mortar
370
gave the highest value at 90 days, while the lowest value was obtained from non-optimised
371
30% fly-ash-blended cement mortar. The dry density values obtained at 90 days were higher
372
than the other experimental periods.
TE D
368
373
Table 3.4. Rapid chloride permeability values calculated at 7, 28 and 90 days. Sample code 7 days (C) 28 days (C) 90 days (C) FA0
EP
375
3.5. Rapid Chloride Permeability
4428
3125
2452
4560
3236
2720
AC C
374
0.4FA5
4214
2987
2056
FA10
5741
3579
2515
0.4FA10
5135
3109
1808
FA15
6157
3784
2216
0.4FA15
5863
3314
1726
FA20
7582
4158
1804
0.4FA20
6933
3446
1651
FA30
8423
4824
1376
0.4FA30
7418
3628
1232
FA5
376 377 17
ACCEPTED MANUSCRIPT Table 3.4 shows the rapid chloride permeability values calculated at 7, 28 and 90 days.
379
As shown in Table 3.4 and Fig. 3.9, rapid chloride permeability was increased by increasing
380
the replacement percentage of fly ash. All rapid chloride permeability values for 7 days were
381
above 4000 Coulombs. Thus, high rapid chloride permeability was achieved. A replacement
382
level of 30% using non-optimised and optimised fly ash increased the rapid chloride
383
permeability by 90.2% and 68.0%, respectively. The rapid chloride permeabilities of the
384
optimised samples were lower than those of the non-optimised samples at all replacement
385
levels. These results also indicate that the optimised fly-ash-blended cement mortar at 7 days
386
offered low void ratios and high compactness.
RI PT
378
SC
387
388
Non-optimized
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210 190 170 150
110 90 0
TE D
130
5
EP
Change in rapid chloride permeability (%)
Optimized
10 15 20 Additive ratio (%)
25
30
Fig. 3.9. Percentage change in rapid chloride permeability of fly-ash-blended cement mortars at
390
7 days.
391
AC C
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Similarly, Figs. 3.10 and 3.11 show the percentage changes in rapid chloride
392
permeability of optimised and non-optimised fly-ash-blended cement mortars after water
393
curing for 28 and 90 days, respectively. Optimised fly-ash-blended cement mortars at 28 and
394
90 days also offered high compactness. The pozzolanic effect was intensified as the
395
replacement level increased, improving the durability.
396
18
ACCEPTED MANUSCRIPT Non-optimized
160 150 140
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130 120 110 100
SC
Change in rapid chloride permeability (%)
Optimized
90 0
5
10
25
30
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15 20 Additive ratio (%)
398
Fig. 3.10. Percentage change in rapid chloride permeability of fly-ash-blended cement mortars
399
at 28 days.
400
Non-optimized
TE D
120 110 100
EP
90 80 70
AC C
Change in rapid chloride permeability (%)
Optimized
60 50 40
0
5
10
15 20 Additive ratio (%)
25
30
401 402 403 404
Fig. 3.11. Percentage change in rapid chloride permeability of fly-ash-blended cement mortars at 90 days.
405
A comparison of the rapid chloride permeability at 7 and 28 days showed that rapid
406
chloride permeability was improved at 28 days. This finding further showed that the durability
407
was improved at 28 days with the intensified pozzolanic effect. All of the rapid chloride 19
ACCEPTED MANUSCRIPT permeability results obtained from 7 days were above the 4,000 Coulombs level. In
409
comparison, only the results obtained from non-optimised 20% and 30% fly-ash-blended
410
cement mortars were above 4,000 Coulombs at 28 days. All other results were around the
411
medium level of rapid chloride permeability. A comparison of the rapid chloride permeability
412
calculated at 28 days and 90 days showed that the rapid chloride permeability was
413
consistently reduced at 90 days for every replacement level. Different from 7 days and 28
414
days, the rapid chloride permeability was reduced at 90 days as the replacement level was
415
increased. The best rapid chloride permeability results were obtained from 90 days.
416
4. CONCLUSION
SC
417
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408
The compressive strength properties of fly ash having particle sizes ranging between 0
419
and 25, 25 and 50, 50 and 63, 63 and 75 and 75 and 90 µm were explored with respect to their
420
optimal PSDs using distribution modulus between q = 0 and q = 1 with gradual increments of
421
0.1. Properties such as water absorption capacity, dry density and rapid chloride permeability
422
of optimised fly ash were explored for varied replacement levels. The findings are
423
summarised as follows:
424
•
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High compactness was ensured with the filler effect in the PSD optimisation of fly ash. The distribution modulus of q = 0.3, q = 0.4 and q = 0.5 offered high
426
compressive and flexural strength values at 7, 28 and 90 days. The distribution
427
modulus of q = 0.4 offered the highest compressive strength and provided the
428
highest increase in compactness. •
The changes in the compressive strength clearly reveal the importance of PSD
EP
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425
in the filler effect, which minimised the voids available in the distribution of
431
fly ash and resulted in high compactness.
432 433 434 435 436
AC C
430
•
The water absorption percentage of optimised cement mortar was lower than
that of the non-optimised cement mortar.
•
The dry density of the optimised samples was either identical or higher than
that of the non-optimised cement mortars.
•
Optimised fly-ash-blended cement samples consistently gave better rapid
437
chloride permeability than those obtained from non-optimised ones. These
438
findings showed that the void ratio was reduced and high compactness was
439
possible.
440
In conclusion, it was possible to improve the mechanical properties and rapid chloride
441
permeability of the cement using the optimised fly ash, ensuring the effect of high 20
ACCEPTED MANUSCRIPT compactness. With the PSD optimisation of fly ash, the necessary amount of cement can be
443
reduced for the target distribution and the use of fly ash can be widespread. Thus, the costs
444
involved in concrete production can be reduced. In addition, the use of waste materials could
445
be increased and carbon emissions could be reduced owing to the reduced amount of cement
446
used. The achievement of the best PSD for high compactness can allow for improved savings
447
in cement.
RI PT
442
448
It may also be of interest to explore the mechanical properties and durability of
449
mixtures having the optimised PSDs of different pozzolans such as blast-furnace slag and
450
silica fume. The future studies should explore the effects of cement of different types and
451
dosages on the optimal PSD.
454 455
Acknowledgement
The authors gratefully acknowledge the financial assistance of the Scientific and
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Technical Research Council of Turkey (TUBITAK) provided under Project: 215M081.
456
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Standard Institution, Ankara, 2016.
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S0958-9465(18)30697-8
DOI:
https://doi.org/10.1016/j.cemconcomp.2018.11.017
Reference:
CECO 3185
To appear in:
Cement and Concrete Composites
Received Date: 6 July 2018 Revised Date:
5 November 2018
Accepted Date: 26 November 2018
Please cite this article as: İ. Demir, Ö. Sevim, Physical and permeability properties of cementitious mortars having fly ash with optimized particle size distribution, Cement and Concrete Composites (2018), doi: https://doi.org/10.1016/j.cemconcomp.2018.11.017. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT 1
iPHYSICAL AND PERMEABILITY PROPERTIES OF CEMENTITIOUS MORTARS
2
HAVING FLY ASH WITH OPTIMIZED PARTICLE SIZE DISTRIBUTION
3 İlhami Demir1,2, Özer Sevim*1
4
Department of Civil Engineering, Kırıkkale University, Kırıkkale, Turkey. 2
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5 6 7
Department of Architecture, Amasya University, Amasya, Turkey.
8
ABSTRACT
9
Gradation of powder materials is often avoided in pozzolanic materials, such as fly
11
ash. Without good gradation, powder materials result in high void ratios similar to the case of
12
aggregates. The products obtained after hydration would still have voids.
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This study calculated the particle size distributions (PSDs) of fly ash using a vacuum
14
sieve in accordance with the Dinger–Funk PSD modulus. The optimal PSD was defined, and
15
the compressive strength of fly-ash-blended cement mortars at 7, 28 and 90 days was
16
explored. Properties such as water absorption capacity, dry density and rapid chloride
17
permeability of the optimised fly ash were analysed by varying the replacement levels. The
18
water absorption capacity of the optimised fly-ash-blended cement mortar was lower than that
19
of the blended cement mortar having non-optimised fly ash. Moreover, at 90 days, the
20
chloride permeability of the optimised fly-ash-blended cement mortar was improved by up to
21
39.1% when compared to that of the blended cement mortar having non-optimised fly ash.
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Keywords: Binder System, Fly Ash, Particle Size Distribution, High Compactness,
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Water Absorption, Rapid Chloride Permeability.
24 25 26 27 28 29 30 31 *
Corresponding author. Tel: +90-318-357-4242 (1263), E-mail: [email protected]. 1
ACCEPTED MANUSCRIPT 1. INTRODUCTION
32
Fly ash is commonly used as a cement additive, and replacement material. The
34
fineness of fly ash is the most important property that affects its performance in cement and
35
concrete. Previous studies have shown that the properties of fly-ash-blended concrete, such as
36
strength, abrasion resistance and freeze-thaw resistance, are a function of fineness of the used
37
fly ash [1-6].
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Previous studies have commonly focused on the effect of fineness and particle size
39
distribution (PSD) from a single point or multiple points of view. Fineness has been
40
emphasised in the literature on PSD. Slanicka [7] discussed the effects of the chemical and
41
mineralogical properties of fly ash, as well as its fineness, on the strength of concrete. The
42
aggregate was replaced with fly ash. Monzo et al. [8] investigated the compressive and
43
flexural strength of the cement mortar blended with Class F Spanish fly ash having varied
44
fineness levels at a replacement level of 30%. The increase in the fineness of fly ash also
45
increased the compressive strength. Erdoğdu and Türker [9] analysed the properties of fly-
46
ash-blended cement mortars having different PSDs. They argued that the use of fly ash having
47
different PSDs resulted in different cement properties. The compressive strength of the
48
samples was investigated, which were prepared using six fly ash groups having particle sizes
49
of 125, 90, 63 and 45 µm at a replacement level of 25%. The optimal strength results were
50
obtained from the sample substituted by fly ash of 45 µm or less in size. Lee et al. [10]
51
analysed the effects of fly ash PSD on the viscosity of the cement mortar. An increase in the
52
PSD increased the viscosity. Bentz et al. [11,12] prepared samples having five different
53
specific surface areas for cement and fly ash. The compressive strength of the samples was
54
then analysed at replacement ratios of 20%, 35%, 50% and 65%. The optimised compressive
55
strength was obtained from the sample having a fly ash replacement of 20%. The compressive
56
strength of the sample having a fly ash replacement of 35%, on the other hand, was close to
57
that of the reference Portland cement.
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To date, there is lack of research on the optimal designs aimed to obtain high
59
compactness using powder material gradation with pozzolans, such as fly ash. Particle size
60
has been used to obtain an economic concrete design. The selection of PSD requires focus on
61
the ability to fill in voids among particles. First, PSD was analysed for an economic concrete
62
design [13]. The Fuller–Thompson theory has been widely used in PSD optimisation to define
63
the replacement ratio of aggregates in concrete [14]. In many European countries, well-graded
64
ideal aggregate granulometry is optimised for concrete design. Therefore, Fuller’s curve is
65
still used by many authors in concrete mix design. However, this optimisation curve has not 2
ACCEPTED MANUSCRIPT been altered for the last century. In this context, the most important development was made by
67
Funk and Dinger by applying a minimum particle diameter. Furthermore, some researchers
68
have suggested different exponential values to determine the ideal curve for self-compacting
69
concrete or high-performance concrete [15]. In particular, owing to the introduction of new
70
superplasticisers, there is a need to renew the interest in PSD, high-performance concrete and
71
other types of concrete containing high amounts of additives. The concept of PSD
72
optimisation is also important for producing environment-friendly concrete. Cement mortar is
73
used to fill the voids available in aggregates to obtain the lowest void ratio. Using this
74
method, the optimised aggregate and cement mixtures can offer sufficient strength [16,17].
75
Many studies focusing on aggregate gradation recommended the use of an ideal aggregate
76
PSD curve for the concrete design [13-17]. It is possible to obtain high compactness levels in
77
aggregates using granulometry curves populated via the formulas developed and reported in
78
the literature. These methods were used to ensure the high compactness of pozzolanic
79
materials such as fly ash irrespective of the powder material gradation.
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On the basis of the aforementioned information, designs were made to obtain the
81
optimal fly ash PSD to achieve the highest compactness. It is possible to obtain a mixture of
82
materials at suitable percentages, which have low void ratio and high compactness. Properties
83
such as water absorption capacity, dry density and rapid chloride permeability of fly ash
84
having the optimised PSD were explored for varied replacement levels.
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The water absorption capacity of hardened concrete affects its durability and strength
86
in physical and chemical reactions that may exist throughout the service life of concrete [18-
87
20]. Water and other fluids permeate into concrete through voids in its structure, introducing
88
harmful substances into concrete [21]. Concrete having high water absorption capacity, i.e.
89
concrete having high permeability, loses its strength and durability in physical and chemical
90
phenomena. In addition to the water absorption capacity, dry or bulk density affects the
91
compressive strength, flexural strength and elasticity modulus of cement mortars. An increase
92
in dry density improves the mechanical properties, and a high dry density is a parameter of
93
high compactness. Concrete having high compactness offer minimal void ratio, i.e. porosity,
94
as well as higher strength [22].
AC C
EP
85
95
Another important parameter for the service life of concrete is how chloride ions
96
permeate into concrete [23-26]. Several mechanisms have been reported in this regard.
97
Additives in concrete, de-icer chemicals, aggregates obtained from the sea and sea water
98
result in a porous structure in concrete, deteriorating the passive protective layer created on
99
the reinforcing steel in the process of corrosion [27]. High chloride permeability in concrete 3
ACCEPTED MANUSCRIPT facilitates the infiltration of chloride ions into concrete, suggesting that the reinforcing steel is
101
easily subjected to these ions. Concrete having low chloride permeability is produced to
102
ensure the durability of concrete and to prevent the corrosion of reinforced concrete. It has
103
been reported that the use of a specific amount of pozzolans (fly ash, blast-furnace slag, silica
104
fume, etc.) as a binder in concrete production can give desirable results [28-34]. In the fly-
105
ash-replaced concrete, Ca(OH)2 in the concrete that was produced after hydration reacted with
106
SiO2 and Al2O3 compounds in fly ash and produced extra C-A-H and C-S-H compounds,
107
increasing the strength of concrete in alkali and chloride media [35–37].
RI PT
100
This study aims to find the optimal PSD of fly ash and analyse its effect on the
109
compressive strength of the fly-ash-blended cement mortar. The suitable PSD of fly ash was
110
obtained using a vacuum sieve. We analysed properties such as water absorption capacity, dry
111
density and rapid chloride permeability of fly-ash-blended cement mortars having different
112
replacement levels and calculated the distribution modulus to obtain the optimal design.
M AN U
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108
113
2. EXPERIMENTAL DESIGN
114 115 116
2.1. Materials Used in this Study Portland Cement
Portland cement type CEM I 42.5 R (similar to ASTM Type I cement) that complied
118
with TS EN 197-1 standard was used in this study [38]. The physical and chemical properties
119
of the used cement are listed in Table 2.1.
Table 2.1. Chemical and physical properties of CEM I 42.5 R cement. Chemical composition (%) SiO2
Portland cement 21.02
Al2O3
5.38
Fe2O3
3.22
CaO
62.12
MgO
1.98
Na2O
0.39
K2O
0.81
SO3
3.11
AC C
EP
120
TE D
117
Physical properties
121 122
Specific gravity (unitless)
3.18
Blaine fineness (cm²/g)
3356
Loss on ignition (%)
2.37
4
ACCEPTED MANUSCRIPT 123
Fly Ash The fly ash used in this study was Class C fly ash (SiO2 + Al2O3 + Fe2O3 < 70% and
125
CaO > 10%) obtained from Çayırhan Coal Power Plant. The fly ash was used as received
126
without grinding. The reason for selecting the Class C fly ash was to illustrate the effects of
127
fillers having optimised PSDs. It would be possible to clearly observe the effect of fillers on
128
the strength rather than chemical effects of the optimised fly ash. The chemical and physical
129
properties of the fly ash are listed in Table 2.2.
RI PT
124
Table 2.2. Chemical and physical properties of fly ash. Chemical composition (%)
Fly ash
SiO2
46.59
Al2O3
12.42
SC
130 131
Fe2O3
9.74
14.50
M AN U
CaO
MgO
7.23
SO3
5.52
Na2O
1.01
K2O
2.28
Physical properties
TE D
Blaine fineness (cm²/g) 3
Density (g/cm )
134
2.2. Method
135
PSD Optimisation
2.47
EP
132 133
2830
Fly ash samples were sieved using an Alpine vacuum sieve that complied with TS EN
137
933-10 standard for the particle sizes ranging from 0 to 25, 25 to 50, 50 to 63, 63 to 75 and 75
138
to 90 µm to define their PSDs [39]. Sieve analyses were performed using the vacuum sieve
139
for each particle size. Here, the optimal PSD was found in accordance with Equation 1, as
140
suggested by Funk and Dinger [15]. When the minimum particle size is set to zero and the
141
distribution modulus is equal to 0.5, this equation is simplified to the Fuller–Thompson
142
model, which is used to optimise the aggregate distribution [14].
143
AC C
136
P D =
144 145
where
146
P(D)
×100,
(1)
: Total percentage of the material smaller than the diameter 5
ACCEPTED MANUSCRIPT of pores on the sieve, D.
147 148
D
: Diameter of pores on the sieve.
149
Dmin
: Minimum particle diameter of fly ash.
150
Dmax
: Maximum particle diameter of fly ash.
151
q
: Distribution modulus.
152
The optimal PSD design was obtained from the 20% fly-ash-blended cement. The
154
replacement level of 20% was selected to facilitate the observation of the fly ash activity.
155
After the optimal distribution modulus (q) was obtained, samples were prepared for
156
replacement levels of 5%, 10%, 15%, 20% and 30% using the distribution modulus to
157
obtain the optimal design. The compressive strengths of cement mortars were observed for
158
defining the optimal particle size using the TS EN 196-1 standard. The results were
159
obtained by calculating the mean values for six prismatic cement mortar samples [40].
160
Materials and Mix Ratios
M AN U
SC
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153
CEM I 42.5 R Portland cement, Class C fly ash, standard sand and potable water
162
were used in this study. Cement mortars were prepared using replacement levels of fly ash
163
of 0% (control), 5%, 10%, 15%, 20% and 30%. The obtained cement mortars were stored
164
under humid conditions for 24 h and then cured in water for a defined period. The water–
165
binder (W/B) ratio of the fly-ash-blended cement mortars prepared in this study was 0.50.
166
Table 2.3 shows the mixture ratios of the materials used; FA stands for fly ash in this table.
TE D
161
Table 2.3. Mix ratios of the cement mortar.
167
0% FA
EP
Component (g)
10% FA
15% FA
20% FA
30% FA
Potable water (Total)
225
225
225
225
225
225
Portland cement
450
427.5
405
382.5
360
315
AC C
168 169 170 171
5% FA
Fly ash
0
22.5
45
67.5
90
135
Standard sand
1350
1350
1350
1350
1350
1350
Water Absorption and Dry Density Properties
172
The water absorption and dry density properties of cement mortars blended with 5%,
173
10%, 15%, 20% and 30% fly ash, with and without the optimised PSD, were explored for 7, 28
174
and 90 days in accordance with ASTM C 642 [41]. Cubic cement mortar samples with a
175
dimension of 50 × 50 × 50 mm3 (width × height × length) were used. The results were obtained
176
by calculating the mean values of six prismatic cement mortar samples. In the experiment,
177
cement mortars were cured in potable water for specified periods and weighed (B) after being 6
ACCEPTED MANUSCRIPT dried using a dry cloth. After storage in an oven at 100 ± 5°C for 24 h, cement mortars were
179
then weighed again (A) at 20°C–25°C. Cubic cement mortar samples with dimensions of 50 ×
180
50 × 50 mm3 were boiled for 5 h and weighed again (C) at 20°C–25°C. Cubic cement mortar
181
samples with dimensions of 50 × 50 × 50 mm3 were weighed in water after immersion and
182
boiling (D). The water absorption percentage of cement mortars was calculated using Equation
183
2. The dry density of cement mortars was calculated using Equation 3.
RI PT
178
184 185
Water absorption percentage:
186
Bulk density, dry:
× 100
× ρ =g .
188
(3)
SC
187
(2)
Rapid Chloride Permeability Test
The rapid chloride permeability tests of cement mortars blended with 5%, 10%, 15%,
190
20% and 30% fly ash, with and without optimised PSD, were explored for 7, 28 and 90 days in
191
accordance with ASTM C 1202 [42]. Cylindrical samples (diameter = 100 mm, length = 200
192
mm) of fly-ash-blended cement mortars were prepared in accordance with TS EN 196-1 [40].
193
Experimental samples (diameter = 100 mm, length = 50 mm) were cut out from the central part
194
of the prepared samples after being cured in water for 7, 28 and 90 days [40]. Four cylindrical
195
samples of each mix were used for a rapid chloride permeability test. The mean values were
196
achieved based on these four samples.
TE D
M AN U
189
The cement mortar was placed in the experimental cell. One end was in contact with
198
0.30 M sodium hydroxide (NaOH) solution and the other with 3% sodium chloride (NaCl)
199
solution. The total amount of current flowing through each sample subjected to a voltage of
200
60.0 ± 0.1 V for 6 h was measured and reported in Coulombs. ASTM C1202 (2012) classify
201
rapid chloride permeability into five groups, from ‘Negligible’ to ‘High’, based on Coulomb
202
values [42].
204 205
AC C
203
EP
197
3. EXPERIMENTAL FINDINGS AND DISCUSSION
3.1. Fly Ash PSD Analyses
206
The optimal PSD of fly ash was calculated between q = 0 and q = 1 using Equation 1
207
with gradual increments of 0.1. The total passing percentage of the material was calculated
208
using sieves having mesh sizes of 25, 50, 63, 75 and 90 µm to measure the distribution
209
modulus. PSD curves were populated based on these materials, and the passing percentage for
210
each distribution modulus was obtained. These PSD curves are shown in Fig. 3.1. 7
ACCEPTED MANUSCRIPT 211 q=0.1
q=0.2
q=0.3
q=0.4
q=0.5
q=0.6
q=0.7
q=0.8
q=0.9
q=1.0
100
RI PT
90
80
SC
60
50
M AN U
Passing percentage (%)
70
40
30
10
0
213 214 215 216
20
30
40 50 Particle diameter (µm)
60
70
80
90
Fig. 3.1. PSD curves for different distribution moduli.
AC C
212
10
EP
0
TE D
20
3.2. Optimal Fly Ash PSD Analyses The effect of fly ash PSDs on the mechanical properties of the cement mortar was
217
analysed. The effect of the PSD of fly ash on the compressive strength of fly-ash-blended
218
cement mortar at 7, 28 and 90 days was explored.
219 220
Effect of PSD on Mechanical Properties
221
The effect of PSD on the mechanical properties was explored based on different
222
distribution moduli. The mechanical properties of 20% fly-ash-replaced cement mortar were 8
ACCEPTED MANUSCRIPT 223
analysed after PSD analysis to better observe the activity of fly ash for different distribution
224
modulus values. Fig. 3.2 shows the compressive strength of cement mortars blended with the
225
optimised 20% fly ash at 7, 28 and 90 days. 7 Days
28 Days
90 Days
RI PT
50 45
SC
40 35 30 25 0.0
0.1
0.2
0.3
0.4 0.5 0.6 0.7 Distribution Modulus
0.8
0.9
1.0
TE D
226
M AN U
Compressive strength (MPa)
55
227 228 229 230
Fig. 3.2. Compressive strength results obtained from the optimised 20% fly-ash-blended cement mortars at 7, 28 and 90 days.
231
of 0.1 to 0.4, before being gradually decreased from a distribution modulus of 0.4 to 1.0.
232
Thus, the best compressive strength was obtained from the distribution modulus of 0.4 among
233
others. In other words, the distribution modulus of q = 0.4 ensured a significant increase in the
234
compressive strength and provided the highest compactness. At 7, 28 and 90 days, the highest
235
compressive strengths for q = 0.4 were found to be 32.08, 42.91 and 54.39 MPa, respectively.
236
The compressive strengths for the distribution modulus of q = 0.4 at 7, 28 and 90 days were
237
increased by 9.08%, 11.22% and 2.82%, respectively, when compared to that of the control
238
sample. The highest standard deviation values for the compressive strength results were 1.12,
239
1.21 and 1.22 for 7, 28 and 90 days, respectively.
AC C
EP
As shown in Fig. 3.2, compressive strength was increased from a distribution modulus
240 241 242 243
Material Coding Table 3.1 lists the sample coding for the fly-ash-blended cement samples optimised for PSD (q = 0.4) and sample non-optimised for PSD. 9
ACCEPTED MANUSCRIPT Table 3.1. Code of fly-ash-blended cement samples for various replacement levels. Sample code
Control
FA0
5 Non-optimised
FA5
5 Optimised
0.4FA5
10 Non-optimised
FA10
10 Optimised
0.4FA10
15 Non-optimised
FA15
15 Optimised
0.4FA15
20 Non-optimised
FA20
20 Optimised
0.4FA20
30 Non-optimised
FA30
30 Optimised
0.4FA30
245 246
3.3. Water Absorption Capacity
SC
RI PT
Additive ratio (%)
M AN U
244
The purpose of this experiment was to obtain general information about the void ratios
248
of cement mortar blends with both optimised and non-optimised fly ash, which had
249
replacement levels of 5%, 10%, 15%, 20% and 30%. Because the cement mortar having low
250
strength would have a great void ratio, the water absorption capacity can also be increased.
251
Water absorption percentages at 7, 28 and 90 days were calculated using Equation 2 and are
252
listed in Table 3.2.
EP
Table 3.2. Water absorption percentages calculated at 7, 28 and 90 days. Sample code 7 days (%) 28 days (%) 90 days (%) FA0
9.81
9.27
9.05
AC C
253
TE D
247
FA5
9.84
9.34
9.25
0.4FA5
9.74
9.17
8.83
FA10
9.93
9.55
9.41
0.4FA10
9.92
9.25
9.17
FA15
9.99
9.83
9.76
0.4FA15
9.98
9.52
9.34
FA20
10.28
10.19
10.11
0.4FA20
10.26
10.06
9.99
FA30
10.68
10.47
10.34
0.4FA30
10.60
10.32
10.16
10
ACCEPTED MANUSCRIPT 254
Fig. 3.3 shows the change in water absorption percentage of optimised and non-
255
optimised fly-ash-blended cement mortars after 7 days of water curing. The change in the
256
percentage was calculated by setting the water absorption percentage of the control cement
257
mortar as 100%. Optimized
RI PT
Change in water absorption (%)
110 108 106 104
SC
102
98 96 0
5
10
M AN U
100
258 259
Non-optimized
15 20 Additive ratio (%)
25
30
Fig. 3.3. Change in water absorption percentage of fly-ash-blended cement mortars at 7 days. As shown in Table 3.2 and Fig. 3.3, the water absorption percentage was increased by
261
increasing the replacement level of fly ash. The use of the cement mortar blended with the
262
30% optimised fly ash increased the water absorption percentage by 8.9%. The use of
263
optimised 30% fly-ash-blended cement mortar increased the water absorption percentage by
264
8.1%. A comparison of cement mortars blended with the optimised and non-optimised fly ash
265
showed that the water absorption percentage of the optimised fly-ash-blended cement mortar
266
at 5% replacement level was 0.1% lower than that of the non-optimised fly-ash-blended
267
cement mortar. By increasing the replacement level, the difference was increased and finally
268
reached 0.8% at 30% replacement level. These results showed that the void ratio of the
269
optimised fly-ash-blended cement mortar was lower than that of the non-optimised fly-ash-
270
blended cement mortar at 7 days.
AC C
EP
TE D
260
271
Similarly, the changes in water absorption percentage of optimised and non-optimised
272
fly ash after water curing for 28 days are shown in Fig. 3.4. The change in percentage was
273
also calculated via taking the water absorption percentage of the control cement mortar as
274
100%.
275 11
ACCEPTED MANUSCRIPT
116 114 112 110 108 106 104 102 100 98 96 0
5
10
15 20 Additive ratio (%)
276
25
30
Fig. 3.4. Change in water absorption percentage of fly-ash-blended cement mortars at 28 days.
M AN U
277
RI PT
Non-optimized
SC
Change in water absorption (%)
Optimized
278
The water absorption percentage was also increased by increasing the replacement
280
percentage of fly ash. In addition, the water absorption percentage was increased by 12.9%
281
and 11.3% at a replacement level of 30% using non-optimised and optimised fly ash,
282
respectively. The water absorption percentage of the optimised 5% fly-ash-blended cement
283
mortar was lower than that of the control cement mortar. The void ratio and permeability of
284
the concrete were increased by increasing the replacement level. By comparison, the water
285
absorption percentage of the optimised fly-ash-blended cement mortar at different
286
replacement levels was lower than that of the non-optimised fly-ash-blended cement mortar.
287
Thus, the void ratio of the optimised fly-ash-blended cement mortar was lower than that of the
288
non-optimised fly-ash-blended cement mortar at 28 days.
EP
AC C
289
TE D
279
12
ACCEPTED MANUSCRIPT Non-optimized
RI PT
116 114 112 110 108 106 104 102 100 98 96 0
5
10
SC
Change in water absorption (%)
Optimized
15 Additive ratio (%)
291
25
30
M AN U
290
20
Fig. 3.5. Change in water absorption percentage of fly-ash-blended cement mortars at 90 days.
292
Similarly, as shown in Table 3.2 and Fig. 3.5, the water absorption percentage at 90
294
days was increased by increasing the replacement level of fly ash. A replacement level of 30%
295
using non-optimised and optimised fly ash increased the water absorption percentage by
296
14.3% and 12.3%, respectively. The water absorption percentage of optimised 5% fly-ash-
297
blended cement mortar was lower than that of the control cement mortar as well. Thus, the
298
void ratio of concrete was increased by increasing the replacement level. Similarly, the water
299
absorption percentage of optimised fly-ash-blended cement mortar was lower than that of non-
300
optimised fly-ash-blended cement mortar, indicating higher compactness.
EP
TE D
293
The increase in fly ash replacement level also increased the water absorption
302
percentages. The water absorption percentage of the optimised cement mortar was lower than
303
that of the non-optimised cement mortar. The highest water absorption percentage was
304
achieved from the non-optimised sample replaced by 30% fly ash at 7 days. The lowest water
305
absorption percentage was obtained from the optimised sample replaced by 5% fly ash at 90
306
days. The water absorption percentage results obtained at 90 days were consistently lower
307
than those of other days in cement mortars having both optimised and non-optimised fly ash
308
with different replacement levels.
AC C
301
309
The fact that hydration products fill the voids in the concrete gradually as the concrete
310
matures accounts for these findings. The increase in void ratio and permeability increases the
311
water absorption percentage and decreases the mechanical properties. The highest 13
ACCEPTED MANUSCRIPT 312
compactness level that is achieved through fly ash PSD optimisation can reduce the water
313
absorption percentage and increase the strength of concrete.
314
319
RI PT
318
dry density values at 7, 28 and 90 days. Table 3.3. Dry density values calculated at 7, 28 and 90 days. Sample code 7 days (g/cm3) 28 days (g/cm3) 90 days (g/cm3) FA0
1.99
2.01
FA5
1.99
2.01
0.4FA5
1.99
2.01
FA10
1.99
2.01
2.01
0.4FA10
1.99
2.01
2.01
FA15
1.99
0.4FA15
1.99
FA20
1.98
0.4FA20
1.99
FA30
1.97
0.4FA30
1.98
SC
317
Dry density properties were calculated using Equation 3. Table 3.3 shows the calculated
M AN U
316
3.4. Dry Density Properties
TE D
315
2.01 2.01
2.02
2.00
2.01
2.01
2.01
1.99
2.00
2.00
2.01
1.98
1.99
1.99
2.00
Fig. 3.6 shows the percentage change in dry density of optimised and non-optimised
321
fly-ash-blended cement mortars after water curing for 7 days. The change in percentage was
322
calculated by setting the dry density value of the control cement mortar as 100%.
AC C
323
EP
320
14
ACCEPTED MANUSCRIPT
101.0 100.5 100.0 99.5 99.0 98.5 98.0 5
10
15 20 Additive ratio (%)
25
30
SC
0 324
Fig. 3.6. Percentage change in dry density of fly-ash-blended cement mortars at 7 days.
M AN U
325
Non-optimized
RI PT
Change in dry density (%)
Optimized
326
As shown in Table 3.3 and Fig. 3.6, dry density was decreased by increasing the
328
replacement level of fly ash, indicating an increase in void ratio. Dry densities of the samples
329
did not change at 15% replacement level. The dry density of the optimised fly-ash-blended
330
cement mortar was decreased at replacement levels of 20% and 30%. These results showed that
331
the void ratio at 7 days of the optimised fly-ash-blended cement mortar was lower than that of
332
the non-optimised fly-ash-blended cement mortar. In addition, PSD allowed for high
333
compactness in optimised cement samples. The cement mortar blended with 30% non-
334
optimised fly ash resulted in the lowest dry density values.
TE D
327
Similarly, Fig. 3.7 shows the percentage changes in dry density of optimised and non-
336
optimised fly-ash-blended cement mortars after 28 days of water curing. As shown in Table 3.3
337
and Fig. 3.7, dry density also increased as the replacement level of fly ash was increased,
338
indicating that the void ratio increased as the replacement level was increased. The change in
339
dry densities of the samples was neglected up to 10% replacement level. The dry density of the
340
optimised fly-ash-blended cement mortar was higher at high replacement levels than that of the
341
non-optimised fly-ash-blended cement mortar. This finding indicates that the optimised fly ash
342
offered low void ratios and allowed for higher compactness.
AC C
EP
335
343 344 345 346 347 15
ACCEPTED MANUSCRIPT Optimized
Non-optimized
100.5 100.0 99.5 99.0 98.5 98.0 5
10 15 20 Additive ratio (%)
348
30
Fig. 3.7. Percentage change in dry density of fly-ash-blended cement mortars at 28 days.
M AN U
349
25
SC
0
RI PT
Change in dry density (%)
101.0
350
As shown in Table 3.3 and Fig. 3.8, the dry density at 28 days was also decreased as the
352
replacement level of fly ash was increased. Similarly, the dry density of the optimised samples
353
was either identical or higher than that of the non-optimised cement mortars. At 90 days, the
354
void ratio of the optimised fly-ash-blended cement mortar was also lower than that of the non-
355
optimised fly-ash-blended cement mortar, indicating high compactness.
358 359 360 361 362 363 364
EP
357
AC C
356
TE D
351
16
ACCEPTED MANUSCRIPT Non-optimized
101.0 100.5 100.0 99.5 99.0 98.5 98.0 5
10
15 20 Additive ratio (%)
365
30
Fig. 3.8. Percentage change in dry density of fly-ash-blended cement mortars at 90 days.
M AN U
366
25
SC
0
RI PT
Change in dry density (%)
Optimized
367
In short, the dry densities of the optimised samples were either identical or higher than
369
those of the non-optimised cement mortars. The optimised 5% fly-ash-blended cement mortar
370
gave the highest value at 90 days, while the lowest value was obtained from non-optimised
371
30% fly-ash-blended cement mortar. The dry density values obtained at 90 days were higher
372
than the other experimental periods.
TE D
368
373
Table 3.4. Rapid chloride permeability values calculated at 7, 28 and 90 days. Sample code 7 days (C) 28 days (C) 90 days (C) FA0
EP
375
3.5. Rapid Chloride Permeability
4428
3125
2452
4560
3236
2720
AC C
374
0.4FA5
4214
2987
2056
FA10
5741
3579
2515
0.4FA10
5135
3109
1808
FA15
6157
3784
2216
0.4FA15
5863
3314
1726
FA20
7582
4158
1804
0.4FA20
6933
3446
1651
FA30
8423
4824
1376
0.4FA30
7418
3628
1232
FA5
376 377 17
ACCEPTED MANUSCRIPT Table 3.4 shows the rapid chloride permeability values calculated at 7, 28 and 90 days.
379
As shown in Table 3.4 and Fig. 3.9, rapid chloride permeability was increased by increasing
380
the replacement percentage of fly ash. All rapid chloride permeability values for 7 days were
381
above 4000 Coulombs. Thus, high rapid chloride permeability was achieved. A replacement
382
level of 30% using non-optimised and optimised fly ash increased the rapid chloride
383
permeability by 90.2% and 68.0%, respectively. The rapid chloride permeabilities of the
384
optimised samples were lower than those of the non-optimised samples at all replacement
385
levels. These results also indicate that the optimised fly-ash-blended cement mortar at 7 days
386
offered low void ratios and high compactness.
RI PT
378
SC
387
388
Non-optimized
M AN U
210 190 170 150
110 90 0
TE D
130
5
EP
Change in rapid chloride permeability (%)
Optimized
10 15 20 Additive ratio (%)
25
30
Fig. 3.9. Percentage change in rapid chloride permeability of fly-ash-blended cement mortars at
390
7 days.
391
AC C
389
Similarly, Figs. 3.10 and 3.11 show the percentage changes in rapid chloride
392
permeability of optimised and non-optimised fly-ash-blended cement mortars after water
393
curing for 28 and 90 days, respectively. Optimised fly-ash-blended cement mortars at 28 and
394
90 days also offered high compactness. The pozzolanic effect was intensified as the
395
replacement level increased, improving the durability.
396
18
ACCEPTED MANUSCRIPT Non-optimized
160 150 140
RI PT
130 120 110 100
SC
Change in rapid chloride permeability (%)
Optimized
90 0
5
10
25
30
M AN U
397
15 20 Additive ratio (%)
398
Fig. 3.10. Percentage change in rapid chloride permeability of fly-ash-blended cement mortars
399
at 28 days.
400
Non-optimized
TE D
120 110 100
EP
90 80 70
AC C
Change in rapid chloride permeability (%)
Optimized
60 50 40
0
5
10
15 20 Additive ratio (%)
25
30
401 402 403 404
Fig. 3.11. Percentage change in rapid chloride permeability of fly-ash-blended cement mortars at 90 days.
405
A comparison of the rapid chloride permeability at 7 and 28 days showed that rapid
406
chloride permeability was improved at 28 days. This finding further showed that the durability
407
was improved at 28 days with the intensified pozzolanic effect. All of the rapid chloride 19
ACCEPTED MANUSCRIPT permeability results obtained from 7 days were above the 4,000 Coulombs level. In
409
comparison, only the results obtained from non-optimised 20% and 30% fly-ash-blended
410
cement mortars were above 4,000 Coulombs at 28 days. All other results were around the
411
medium level of rapid chloride permeability. A comparison of the rapid chloride permeability
412
calculated at 28 days and 90 days showed that the rapid chloride permeability was
413
consistently reduced at 90 days for every replacement level. Different from 7 days and 28
414
days, the rapid chloride permeability was reduced at 90 days as the replacement level was
415
increased. The best rapid chloride permeability results were obtained from 90 days.
416
4. CONCLUSION
SC
417
RI PT
408
The compressive strength properties of fly ash having particle sizes ranging between 0
419
and 25, 25 and 50, 50 and 63, 63 and 75 and 75 and 90 µm were explored with respect to their
420
optimal PSDs using distribution modulus between q = 0 and q = 1 with gradual increments of
421
0.1. Properties such as water absorption capacity, dry density and rapid chloride permeability
422
of optimised fly ash were explored for varied replacement levels. The findings are
423
summarised as follows:
424
•
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High compactness was ensured with the filler effect in the PSD optimisation of fly ash. The distribution modulus of q = 0.3, q = 0.4 and q = 0.5 offered high
426
compressive and flexural strength values at 7, 28 and 90 days. The distribution
427
modulus of q = 0.4 offered the highest compressive strength and provided the
428
highest increase in compactness. •
The changes in the compressive strength clearly reveal the importance of PSD
EP
429
TE D
425
in the filler effect, which minimised the voids available in the distribution of
431
fly ash and resulted in high compactness.
432 433 434 435 436
AC C
430
•
The water absorption percentage of optimised cement mortar was lower than
that of the non-optimised cement mortar.
•
The dry density of the optimised samples was either identical or higher than
that of the non-optimised cement mortars.
•
Optimised fly-ash-blended cement samples consistently gave better rapid
437
chloride permeability than those obtained from non-optimised ones. These
438
findings showed that the void ratio was reduced and high compactness was
439
possible.
440
In conclusion, it was possible to improve the mechanical properties and rapid chloride
441
permeability of the cement using the optimised fly ash, ensuring the effect of high 20
ACCEPTED MANUSCRIPT compactness. With the PSD optimisation of fly ash, the necessary amount of cement can be
443
reduced for the target distribution and the use of fly ash can be widespread. Thus, the costs
444
involved in concrete production can be reduced. In addition, the use of waste materials could
445
be increased and carbon emissions could be reduced owing to the reduced amount of cement
446
used. The achievement of the best PSD for high compactness can allow for improved savings
447
in cement.
RI PT
442
448
It may also be of interest to explore the mechanical properties and durability of
449
mixtures having the optimised PSDs of different pozzolans such as blast-furnace slag and
450
silica fume. The future studies should explore the effects of cement of different types and
451
dosages on the optimal PSD.
454 455
Acknowledgement
The authors gratefully acknowledge the financial assistance of the Scientific and
M AN U
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SC
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Technical Research Council of Turkey (TUBITAK) provided under Project: 215M081.
456
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