Effect and limitation of free lime content in cement-fly ash mixtures

Construction and Building Materials 102 (2016) 515–530

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Effect and limitation of free lime content in cement-fly ash mixtures Adnan Nawaz a, Parnthep Julnipitawong b,⇑, Pitisan Krammart c, Somnuk Tangtermsirikul d a

School of Engineering and Technology, Asian Institute of Technology, Thailand Construction and Maintenance Technology Research Center, School of Civil Engineering and Technology, Sirindhorn International Institute of Technology, Thammasat University, Thailand c Department of Civil Engineering, Rajamangla University of Technology, Thailand d School of Civil Engineering and Technology, Sirindhorn International Institute of Technology, Thammasat University, Thailand b

h i g h l i g h t s
High free lime fly ash mixtures show satisfactory basic and mechanical properties.
Higher free lime in fly ash leads to higher expansion in the durability tests.
High free lime fly ash can partly replace cement if SO3 content is low and vice versa.
Tested fly ash with free lime content up to 4.23% can be utilized, if SO3 <5%.
If 5% > SO3 < 10%, tested fly ash with free lime content up to 3.73% can be used.

a r t i c l e

i n f o

Article history: Received 7 May 2015 Received in revised form 8 October 2015 Accepted 28 October 2015 Available online 13 November 2015 Keywords: Fly ash Free lime Autoclave expansion Alkali aggregate reaction Sulfate resistance Durability

a b s t r a c t This study emphasizes the limitation of free lime content in fly ash. A detailed experimental program was carried out in order to evaluate the extent to which free lime content in fly ash can be tolerated, particularly for fly ashes with different sulfur trioxide contents. Some basic and durability properties of fly ash mixtures with varied free lime contents were considered. Four distinct types of fly ashes were obtained from two different sources, and free lime was added to obtain overall free lime contents of 5%, 7% and 10% for each type of fly ash. Water requirement, initial and final setting times, compressive strength, autoclave expansion, alkali aggregate reaction (AAR), and sulfate resistance tests of fly ash mixtures, containing various free lime contents, with two fly ash replacement percentages (20% and 40%), were conducted. Experimental results revealed that an increase in the free lime content caused an increase in water requirement. Higher free lime content also lead to faster setting times, improved compressive strength, and higher autoclave expansion. Mixtures with 20% fly ash replacement and free lime content up to 10% as well as mixtures with 40% fly ash replacement and free lime content up to 7.72% experienced autoclave expansion within the specified limit of ASTM C618. Similar trends of expansion were observed in cases of alkali-aggregate reaction and sulfate resistance tests where fly ash mixtures with high free lime led to higher expansion. In alkali-aggregate reaction testing, the mixtures with 20% fly ash replacement and free lime content up to 7.95%, as well as mixtures with 40% fly ash replacement and free lime content up to 10%, expanded less than the cement-only mixtures. The effect of added free lime was more severe in the sulfate resistance test, as fly ash mixtures tend to expand more than cement-only mixtures, especially in the case of fly ashes with very high SO3 content (>5%). Test results also revealed that it is possible to utilize 20% of tested fly ash in a mixture as binder, with SO3 content <5% and free lime content up to 10% while not compromising the basic and durability properties. In the case of 40% fly ash replacement, tested fly ashes with SO3 < 5% and free lime content up to 4.23% can be utilized. In the case of high SO3 content in fly ash, i.e., 8.53% and 9.44% in this study, the limit of free lime content of fly ash is reduced to 5.31% and 3.73%, for 20% and 40% fly ash replacements, respectively to satisfy the durability requirements. Ó 2015 Elsevier Ltd. All rights reserved.

1. Introduction ⇑ Corresponding author. E-mail address: [email protected] (P. Julnipitawong). http://dx.doi.org/10.1016/j.conbuildmat.2015.10.174 0950-0618/Ó 2015 Elsevier Ltd. All rights reserved.

Fly ash, a by-product from the coal combustion process, is one of the most widely used supplementary materials in various

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high-performance cementitious systems. Various studies [1,2] have confirmed that depending upon the chemical composition and other factors, a partial replacement of ordinary Portland cement with fly ash results in an increase in long-term strength and durability of the resulting concrete. This strength increase is attributed to the pozzolanic reaction between fly ash and calcium hydroxide produced as a result of cement hydration. The pozzolanic reaction produces additional calcium silicate hydrate (C–S–H) product to fill up capillary pores, making the fly ash mixtures denser in microstructure as compared to normal concrete [3]. Chemical composition and mineralogy of fly ashes vary significantly depending on many factors including source, type and chemical composition of the coal, type of boilers, burning process, temperature, and emission control procedure, etc., of the power plants. Different countries’ standards [4–6] cannot be applied directly because of the variations in properties and characteristics of fly ashes. In Thailand, although the production of fly ash started in early 1980’s, the considerable use of fly ash as a cement replacement in concrete industry was initiated around mid-1990. In 2005, Thailand started using almost all of its fly ash in the concrete industry and is considered a successful country in terms of fly ash utilization [7]. In recent years, various studies have been conducted to modify and improve standards and guidelines for the use of fly ash in Thailand. Outcomes of these studies are reflected in Thai industrial standards, TIS 2135 [8]. The Mae Moh power plant of the Electricity Generating Authority of Thailand (EGAT) is one of the main production sources of fly ash, contributing around 90% of total national production. Recently, fly ash obtained from this source has shown increased content of free lime [9]. During the coal burning process, when heated, calcium carbonate (CaCO3) decomposes into calcium oxide (CaO) and carbon dioxide (CO2). It is a reversible process and a recarbonation reaction can take place due to the reaction of CaO and CO2 forming CaCO3. The degree of re-carbonation reaction depends mainly on the porosity and reactivity of the resulting CaO with CO2 and sintering at high temperatures [10]. The thermal disruption of CaCO3 results in unreacted CaO which explains the occurrence of free lime in fly ash. Free lime may result in undesired expansion and volume instability when used in concrete as a cement replacement. Therefore, due consideration must be paid toward durability issues and time-dependent properties of concrete containing fly ash with elevated percentages of free lime. In ASTM C618 [4] and many other standards, no limit is established for free lime content of fly ash. However, EN-450 [6] restricts the free lime content to 1%, or up to 2.5% if the autoclave expansion is still within the established limits. Kaewmanee et al. [9] conducted a comprehensive study on expansion properties of fly ash mixes, with various free lime contents and reported a set of experimental results to clarify the effect of free lime content on fly ash mixes. Results showed that basic properties (normal consistency and water demand) were not much affected by free lime added, and a free lime content up to 4.51% had only slight effect on chemical properties of fly ash–cement mixtures. The values of autoclave expansion of the tested mixtures, with 4.51% free lime content in fly ash, were observed to still remain within the limit imposed by ASTM C618. It was further concluded that mixtures with fly ash acquiring 4.51% free lime contents led to higher expansion due to alkali-aggregate reaction (AAR), but the expansion was still smaller as compared to the expansion of cement-only mixture. Free lime content in fly ash is not the only cause of volumetric expansion in concrete. In recent times, fly ash obtained from the Mae Moh power plant has not only shown increased contents of free lime, but also tendency of higher sulfur trioxide (SO3) content, which may contribute to long term expansion and volume instability. ASTM C618 limits the sulfur trioxide (SO3) content to 5%. Although Kaewmanee et al. [9] concluded that free lime content

up to 4.51% can be used, still there is research gap for of further investigation to simultaneously consider the effect of high free lime and high SO3 content in fly ashes as well as their limits of free lime and SO3 contents. This study is an attempt to further explore the limitation and knowledge of the effect of high free lime content in different fly ashes of Thailand, particularly in the case of fly ashes with different sulfur trioxide (SO3) contents.

2. Experimental program 2.1. Materials Four primary fly ashes F(A), F(B), F(C), and F(R) from two different sources and an ordinary Portland cement (OPC) type I, were used in this study. F(A), F(B), and F (C) were obtained from the Mae Moh power generating plant of the Electricity Generating Authority of Thailand (EGAT) in Lampang province (located in the north of Thailand), whereas F(R) was obtained from the coal burning thermal power plant in Rayong province (Eastern part of Thailand). Table 1 illustrates the physical properties of the mentioned materials. Chemical compositions of the materials, as listed in Table 2, are determined by XRF which is mainly used to measure total elemental composition only [11] whereas, free lime content is measured using titration method [9]. Based on chemical requirements of TIS 2135, F(R) was categorized as Class 2a (low CaO fly ash) whereas F(A), F(B) and F(C) were classified as Class 2b (high CaO fly ash). The amount of sulfur trioxide (SO3) in F(B) and F(C) exceeded the maximum allowable limit of 5%, as specified by TIS 2135. Free lime from an external source was added in F(A), which had a natural free lime content of 1.71%, to prepare three additional high free lime fly ashes. These fly ashes were designated as F(A5), F(A7) and F(A10) with the total free lime contents of 5%, 7% and 10%, respectively. Similarly, F(B5), F(B7), F(B10) were prepared by adding free lime in F(B) (with a natural free lime content of 3.93%), and F(C5), F (C7), F(C10) were prepared by adding free lime in F(C) (with a natural free lime content of 3.03%), in order to obtain the total free lime contents of 5%, 7% and 10%, respectively. As mentioned earlier, Mae Moh power generating plant contributes almost 90% of the total fly ash national production whereas other sources, including the source of F(R), produce a small amount of fly ash. Also, free lime content of F(R) (0.03%) is considerably lower than that of Mae Moh fly ashes (1.71–3.93%) used in this study, therefore free lime was added only to the Mae Moh fly ashes in order to determine the effect of high free lime content on the properties of cement-fly ash mixtures. Table 3 shows the physical characteristics of the fly ashes after the addition of free lime in the primary fly ashes. In this study, river sand compatible with ASTM C33-92a [12], with a specific gravity of 2.60 was used as the fine aggregate.

Table 1 Physical properties of ordinary Portland cement type I, Mae Moh fly ashes A, B, C, Rayong fly ash R and free lime. Physical properties

OPC type I

Fly ash A

Fly ash B

Fly ash C

Fly ash R

Free lime

Specific gravity Blaine fineness (cm2/g)

3.15 3100

2.21 2867

2.57 2820

2.57 2722

2.17 2723

2.96 3749

Table 2 Chemical compositions of ordinary Portland cement type I, Mae Moh fly ashes A, B, C and Rayong fly ash R.

*

Chemical compositions (mass %)

OPC type I

Fly ash A

Fly ash B

Fly ash C

Fly ash R

SiO2 Al2O3 Fe2O3 CaO* MgO Na2O K2O SO3 LOI Minor oxides Total Free lime* Equivalent sodium oxide (Na2O + 0.658 K2O)

18.93 5.51 3.31 65.53 1.24 0.15 0.31 2.88 – 2.14 100 0.75 0.35

35.71 20.44 15.54 16.52 2 1.15 2.41 4.26 0.49 1.48 100 1.71 2.74

26.61 13.6 18.34 24.97 2.33 1.75 1.77 8.53 0.53 1.57 100 3.93 2.91

25.22 13.88 17.39 26.25 2.38 1.4 1.92 9.44 0.56 1.56 100 3.06 2.66

61.46 20.27 5.56 1.73 0.96 0.73 1.36 0.38 5.38 2.17 100 0.03 1.62

CaO content includes the free lime content.

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A. Nawaz et al. / Construction and Building Materials 102 (2016) 515–530 Table 3 Physical properties of Mae Moh fly ashes with added free lime. Physical properties

F(A5)

F(A7)

F(A10)

F(B5)

F(B7)

F(B10)

F(C5)

F(C7)

F(C10)

Specific gravity Blaine fineness (cm2/g)

2.24 2884

2.25 2891

2.26 2904

2.52 2799

2.53 2807

2.53 2818

2.57 2753

2.59 2770

2.61 2790

Table 4 Details of mix proportions and specimen sizes. Test items

Paste/mortar

Dimensions of specimens

Fly ash replacement ratio

w/b

Sand to binder ratio

Free lime content

Autoclave expansion Setting time Water requirement Compressive strength Alkali-aggregate reaction expansion

Paste Paste Mortar Mortar Mortar

2.5  2.5  28.5 cm – – 5  5  5 cm 2.5  2.5  28.5 cm

0.4 0.4 0.4 0.4

NM NM WR WR 0.47

– – 2.75 2.75 2.25

Expansion due to Na2SO4 solution Expansion due to (Na2SO4 + Mg2SO4) solution

Mortar Mortar

2.5  2.5  28.5 cm 2.5  2.5  28.5 cm

0.2, 0.2, 0.2, 0.2, 0.2 0.4 0.2, 0.2,

0.4 0.4

0.55 0.55

2.75 2.75

NF, NF, NF, NF, NF, NF, NF, NF,

5, 7, 10 5, 7, 10 5, 7, 10 5, 7, 10 5, 7, 10 10 5, 10 5, 10

Remarks: NM = water to binder ratio that achieves normal consistency (10 ± 1 mm penetration depth determined by Vicat apparatus) and WR = water to binder ratio that achieves flow of 110 ± 5%. NF = free lime content naturally present in each original fly ash. Table 5 Mix designation. Mix designation

C100 C80F(A)20 C60F(A)40 C80F(A5)20 C60F(A5)40 C80F(A7)20 C60F(A7)40 C80F(A10)20 C60F(A10)40 C80F(B)20 C60F(B)40 C80F(B5)20 C60F(B5)40 C80F(B7)20 C60F(B7)40 C80F(B10)20 C60F(B10)40 C80F(C)20 C60F(C)40 C80F(C5)20 C60F(C5)40 C80F(C7)20 C60F(C7)40 C80F(C10)20 C60F(C10)40 C80F(R)20 C60F(R)40

OPC (%)

Fly ash (%)

Type I

A

B

C

R

100 80 60 80 60 80 60 80 60 80 60 80 60 80 60 80 60 80 60 80 60 80 60 80 60 80 60

– 20 40 20 40 20 40 20 40 – – – – – – – – – – – – – – – – – –

– – – – – – – – – 20 40 20 40 20 40 20 40 – – – – – – – – – –

– – – – – – – – – – – – – – – – – 20 40 20 40 20 40 20 40 – –

– – – – – – – – – – – – – – – – – – – – – – – – – 20 40

Free lime (%)

Fly ash replacement ratio

0.75 NF = 1.71% NF = 1.71% 5 5 7 7 10 10 NF = 3.93% NF = 3.93% 5 5 7 7 10 10 NF = 3.03% NF = 3.03% 5 5 7 7 10 10 NF = 0.03% NF = 0.03%

0 0.2 0.4 0.2 0.4 0.2 0.4 0.2 0.4 0.2 0.4 0.2 0.4 0.2 0.4 0.2 0.4 0.2 0.4 0.2 0.4 0.2 0.4 0.2 0.4 0.2 0.4

Remarks: NF = Free lime content naturally present in each primary fly ash. 2.2. Experiments and sample designation A titration method (Kaewmanee et al. [9]) was used in order to determine the free lime content of all cement-fly ash binders. One gram of binder was dissolved in 50cm3 of ethylene glycol at a temperature of 60–70 °C for 30 min. The resulting solution was then filtered using #1 filter paper. Meanwhile, another 30 cm3 of ethylene glycol was added at same temperature to make sure that all particles were washed out. Using Bromocresol green as an indicator, the filtrate was titrated with 0.1 N hydrochloric acid. The free lime content was determined as the percentage of the binder weight. Some of the basic characteristics including initial and final setting times, water requirement, compressive strength and autoclave expansion were determined in this study. Moreover the alkali aggregate reaction test and sulfate resistance test, were also conducted. A normal consistency test was carried out as per ASTM C187 [13] in order to execute autoclave and setting time tests. Setting times were determined according to ASTM C191 [14]. Compressive strength and water requirement were determined as per ASTM C109/C109M [15] and ASTM C311 [16], respectively. The autoclave expansion test was performed as per ASTM C151 [17]. Mixtures for the autoclave expansion test were prepared by substituting 20% and

40% weight of cement with each type of fly ash, i.e., F(A), F(A5), F(A7), F(A10), F (B), F(B5), F(B7), F(B10), F(C), F(C5), F(C7), F(C10), and F(R). The sand to binder ratio for casting mortar samples was set to 2.75 by weight. To determine the expansion due to alkali aggregate reaction, tests were carried out as per ASTM C1260 [18]. Mortar bar specimens (2.5  2.5  28.5 cm) were prepared with crushed reactive gravel, graded as per ASTM C1260. Mixtures were prepared by substituting 20% and 40% weight of cement with each type of fly ash, with a sand to binder ratio of 2.25 and a water to binder ratio of 0.47, for all mixtures. Mortar bars were submerged in a sodium hydroxide (NaOH) solution and kept at the control temperature of 80 ± 2 °C. The expansion due to alkali aggregate reaction was recorded for 14 days. For sulfate resistance, 2.5  2.5  28.5 cm mortar bar specimens were prepared. Mixtures were prepared by substituting 20% and 40% weight of cement, with each type of fly ash with a sand to binder ratio of 2.75 and water to binder ratio of 0.55, for all mixtures. As mentioned in previous studies [9,19,20], mortar bars were cured in water for 28 days after 24 h of mixing and then immersed in a sodium sulfate solution for the sulfate expansion test. A separate set of specimens was also submerged in a combined Na2SO4–MgSO4 solution to determine the combined effect of sodium sulfate and magnesium sulfate.

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A summary of mix proportions and dimensions of samples for different tests is illustrated in Table 4, whereas Table 5 shows the designations and binder proportions of the tested mixtures. For the mix designations in Table 5, letters C and F represent the cement and fly ash, respectively. Types of fly ashes are written in the parenthesis after letter ‘F’. Numbers after letters ‘C’ and ‘F’ represent the percentage by weight of OPC type I and fly ash, respectively, in the total binder.

3. Results and discussion

can be seen, dispersed around fly ash particles. Moreover F(R) particles are relatively less spherical than those of the Mae Moh fly ash. Fig. 1c and d illustrate the results of EDX (energy-dispersive X-ray) technique applied on particle #1 and #2, respectively. The main composition of particle #1 is silica, which is common for fly ash and particle #2 indicates a calcium rich particle, which is typical for free lime.

3.1. Scanning electron microscope (SEM) images

3.2. Free lime content in binder

SEM images of fly ashes from both sources are shown in Fig. 1a and b. It can be observed that the particles of fly ash obtained from the Mae Moh electricity generating power plant are round or spherical shape while irregular particles of free lime

Table 6 shows the total free lime content in different binders (cement-fly ash blended mixtures) determined through titration. Fig. 2 shows the comparison of calculated and measured values of free lime contents of various blends of cement and fly ash. Free

Free lime particles #1 #2

Fly ash particle (a) Mae Moh fly ash

(b) Rayong fly ash

(c) EDX of particle #1

(d) EDX of particle #2 Fig. 1. (a) SEM image of Mae Moh fly ash, (b) SEM image of Rayong fly ash, (c) EDX of particle #1, (d) EDX of particle #2.

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A. Nawaz et al. / Construction and Building Materials 102 (2016) 515–530 Table 6 Free lime content in OPC type I, fly ashes and binders. Mix designation

Type of fly ash

Free lime content in fly ash (%)

Total free lime content in binder (%)

C100 C80F(A)20 C60F(A)40 C80F(A5)20 C60F(A5)40 C80F(A7)20 C60F(A7)40 C80F(A10)20 C60F(A10)40 C80F(B)20 C60F(B)40 C80F(B5)20 C60F(B5)40 C80F(B7)20 C60F(B7)40 C80F(B10)20 C60F(B10)40 C80F(C)20 C60F(C)40 C80F(C5)20 C60F(C5)40 C80F(C7)20 C60F(C7)40 C80F(C10)20 C60F(C10)40 C80F(R)20 C60F(R)40

– A

– 1.71

A5

5.0

A7

7.0

A10

10

B

3.93

B5

5.0

B7

7.0

B10

10.0

C

3.03

C5

5.0

C7

7.0

C10

10

R

0.03

0.75 1.04 1.26 1.54 2.21 1.88 2.69 2.24 4.68 1.18 2.04 1.60 2.49 2.07 3.30 2.63 4.76 1.18 1.71 1.46 2.47 1.82 3.34 2.38 3.89 0.70 0.53

3.3. Water requirement

3

2

1

0 1

2

3

4

5

%Free lime content in binder (calculated from free lime content of cement and fly ash)

Water requirement %

Fig. 2. Comparison of calculated and measured free lime content of different binders.

125

100

100

94.97 94.53 94.88 100.20

91.05 88.28 89.00

100.51

75 50 25 0

Water requirement %

(a) Mixtures with primary fly ashes 125 100 75 50 25 0

100

94.53 94.64 95.00 95.74

(c) Mixtures with F(B) based fly ashes

125 100 75 50 25 0

100

94.97 95.45 96.16 97.03

91.05 92.22 92.91 94.06

(b) Mixtures with F(A) based fly ashes

88.28 88.69 89.62 91.02

Water requirement %

% Free lime content in binder (measured by titration)

1:1 Line 4

Water requirement results (Fig. 3a) reveal that to attain a similar degree of flow, mixtures of primary fly ashes from Mae Moh, F (A), F(B), and F(C) required a lower amount of water as compared to the cement-only mixtures, due to spherical particle shape. Mixtures with 20% fly ash replacement required water within the range of 94.53–94.97% of the cement-only mixtures and for 40% fly ash mixtures, water requirement further reduced to 89.00–91.05%. However, F(R) mixtures required more water than the cementonly mixtures in order to achieve the same flow, implying that fly ash may not always improve the workability of the mixture. Similar outcomes were found by Kiattikomol et al. [21] and Felekog˘lu [22]. Kiattikomol et al. used Rayong fly ash along with some other fly ashes and reported tendency of increased water requirement and normal consistency for Rayong fly ash mixtures than standard cement mix and concluded that fly ashes did not always improve the workability of mortar or concrete. The higher water demand of some of these ashes was attributed to their irregular shape and porous particles, which can also be observed in the case of F(R) used in this study, as shown in Fig. 1b. It is evident from the SEM images that F(R) particle shape is relatively more porous and irregular as compared to the Mae Moh fly ash particles. Feng et al. [23] developed the relationship between loss on ignition (LOI) and water requirement of fly ashes and observed that water requirement is likely to be higher than cement only mixtures if LOI is more than 3%. A higher value of LOI in the case of F(R) (5.38%) as compared to much lower values of the Mae Moh fly ashes (0.49–0.56%), can contribute to an increase in water requirement because the water/(cement + fly ash) ratio, needed to obtain a cement paste with the required rheological properties, is higher for fly ashes with a high carbon content [24–26]. LOI is a measure of unburnt carbon and high LOI value of fly ash indicates the existence of higher unburnt carbon content, which results in higher water demand. Moreover, as discussed earlier, relatively fewer spherical particles of F(R) can also result in increased water requirement. Increase in fly ash content from 20% to 40% in Water requirement %

5

0

lime contents of cement and fly ashes are used to obtain the calculated values, whereas measured values are taken from the titration. Relationships of calculated and measured values indicate linear tendency, which depicts the homogeneity of the mixtures and confirms the validity of the method of adding free lime to fly ashes.

125 100 75 50 25 0

100

94.88 94.91 95.08 95.55

(d) Mixtures with F(C) based fly ashes Fig. 3. Water requirement of mortar mixtures.

89.00 89.17 89.87 91.18

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A. Nawaz et al. / Construction and Building Materials 102 (2016) 515–530

109

C80F(R)20 C80F(C)20

85

C80F(B)20

80

72

C100 0

50

77

127

C80F(A5)20

82

72 0

150

Time (minutes)

131 164 94 88 104

C60F(A)40 72

C100 0

50

72

127

C80F(B5)20

76

C80F(B)20

80

136

C60F(A7)40

140

C60F(A5)40

146

Time (minutes)

(ii) 40% fly ash replacement (a) Primary fly ash mixtures

127

95 104

C60F(A)40 72

C100 150

114

88

0

137 146

101

0

Initial setting

107

C80F(C7)20

75

123

C80F(C5)20

77

127

C80F(C)20

117

101

125

85 72

C100 0

50 100 150 Time (minutes)

116

130

101

50 100 150 Time (minutes)

Final setting C60F(B10)40

74

C60F(B7)40

77

C60F(B5)40

80

114 124 132

88

C60F(B)40

72

C100

50 100 150 Time (minutes)

(b) F(A) based fly ash mixtures

68

C80F(C10)20

108

72

C100

101

74

C60F(A10)40

142

101

100

C80F(B7)20

Initial setting

C60F(R)40

C60F(B)40

123

50 100 150 Time (minutes)

(i) 20% fly ash replacement

C60F(C)40

68

91

C80F(A)20 C100

101

C80F(B10)20

108

C80F(A7)20

136

100

70

C80F(A10)20

130

91

C80F(A)20

145

0

140

101

50 100 150 Time (minutes)

76

C60F(C10)40

114

C60F(C7)40

84

C60F(C5)40

89

C60F(C)40

94 72

C100 0

129 136 142

101

50 100 150 Time (minutes)

Final setting

(c) F(B) based fly ash mixtures

(d) F(C) based fly ash mixtures

Fig. 4. Initial and final setting times of different mixtures.

mortars further reduced the water requirement of Mae Moh fly ash mixtures. In F(R) mixtures, water requirement increased as F(R) content is increased from 20% to 40%. Fig. 3b–d show the effect of addition of free lime in fly ashes on the water requirement of mixtures. Mixtures with a higher amount of free lime required more water to attain the same flow. The water requirement of F(A) based mixtures with 20% fly ash replacement and no additional free lime is 94.97% of the cement-only mixture and increased to as much as 97.03% for mixtures with 10% free lime in fly ash (Fig. 3b). Moreover, for 40% fly ash mixtures, water requirement ranges from 91.05% to 94.06% as free lime content is increased. Similar tendency of increased water requirement, with the addition of free lime in the fly ash, is observed in the case of F(B) (Fig. 3c) and F(C) (Fig. 3d) fly ash mixtures. Hydration reaction of CaO results in formation of calcium hydroxide Ca(OH)2) and liberation of heat energy. Ca(OH)2 is sparingly soluble in water and excess forms a precipitate [27,28]. Miller [29] stated that the reaction between CaO and water is very quick and when a particle of calcium oxide comes in contact with water, the lime immediately absorbs the water into the pores left by the escaping of CO2 during the calcination process and hydration begins immediately. This consumption of water can lead to reduced fluidity in the system hence increasing the water requirement of the cement-fly ash mixtures with added free lime.

3.4. Initial and final setting times As demonstrated in Fig. 4a, the mixtures containing primary fly ashes F(A), F(B), F(C), and F(R) exhibited longer setting times than the cement-only mix which undergo initial and final sets at 72 and 101 min, respectively. 20% Mae Moh fly ash mixtures experienced initial and final sets within 80–91 min and 127–136 min, respectively. For 40% fly ash mixtures, initial and final setting times fall within 88–104 and 140–146 min, respectively. For F(R) mixtures, initial setting time for 20% and 40% fly ash replacements is 109 and 131 min, respectively and final setting time is 145 and 164 min, respectively. As shown in Fig. 4b, the setting times of F (A) based mixtures with added free lime reduced as compared to F(A) mixtures with no extra free lime added. Similarly, F(B) and F

(C) fly ash mixtures with added free lime exhibited reduced setting times as shown in Fig. 4c and d, respectively. Higher calcium oxide and free lime content and lower water requirement of F(B) and F(C) mixtures as compared to F(A) mixtures, resulted in faster setting times. In contrast, F(R) mixtures set slower because of lower calcium oxide (CaO) and free lime contents in F(R). Also, higher water consumption in the case of F(R) mixtures to attain normal consistency and standard flow, contributed to the delayed setting. The increase of fly ash percentages from 20% to 40% lead to longer setting times. High-calcium fly ash results in the fast setting due to the presence of calcium and the formation of calcium silicate hydrate and/or calcium aluminate silicate hydrate [30]. It was reported [31,32] that the reactions of C3A from cement and high calcium fly ash resulted in formation of enttringite, monosulphoaluminate hydrate, calcium aluminate hydrates, and calcium silicate hydrate. The presence of pozzolan accelerated hydration of C3A due to adsorbing Ca2+ from the liquid phases and providing precipitation sites for the hydration products. Khunthongkeaw et al. [33] observed that Mae Moh fly ash with higher CaO content provides higher amount of calcium hydroxide (CH) content in cement-fly ash mixture than that of fly ash with lower CaO content. CH content reacts with pozzolanic material to form calcium silicate hydrate and/or calcium aluminate silicate hydrate. As discussed in Section 3.2, the reaction between quick lime (CaO) and water is very quick and when a particle of calcium oxide comes in contact with water, the limes immediately absorbs the water into the pores left by the escaping of CO2 during the calcination process and hydration begins immediately [29]. This consumption of water can also lead to reduced fluidity and faster setting in the system. The influence of free lime addition on setting time is noticeable. It is evident from Fig. 4b–d that mixtures showed faster setting times as the free lime percentage increases. Free lime provides additional calcium hydroxide to react with fly ash and results in accelerated reaction and faster setting time. Somna et al. [34] indicated that calcium in fly ash can be present as a glass component or as a free lime. External calcium in the form of free lime is mostly distributed outside the fly ash particles [9] whereas internal calcium is present in the glassy phase [34]. Free lime particles are more readily available and undergo rapid hydration compared

521

A. Nawaz et al. / Construction and Building Materials 102 (2016) 515–530 70 Compressive strength (MPa)

Compressive strength (MPa)

70 60 50 40 30 18.3

20

13.6

15.0 10.1

9.3

14.7 9.8

12.3 7.1

10 0

50 38.8

40

34.6

31.4

30

32.8 25.4

23.5

30.4

24.0 18.3

20 10 0

C100

F(A)

F(B)

F( C)

F( R)

C100

C80F20

C100

F(A)

F(B)

F( C)

51.7

53.7 51.6

55.4 53.4 54.5 51.7

F( R)

C60F40

(a) 1 day

(b) 7 days

70

70 Compressive strength (MPa)

Compressive strength (MPa)

60

60 47.3

50

45.3

44.3 37.3

40

44.4 40.8 40.6

41.5 30.9

30 20 10

60

56.2

50

42.3

40 30 20 10 0

0 C100

F(A)

F(B)

F( C)

C100

F( R)

C100

C80F20

F(A)

F(B)

F( C)

F( R)

C60F40

(c) 28 days

(d) 91 days

50 40 30 20

18.3

14.0

13.6 9.3

10

10.1

14.5 10.5

14.8 11.2

0 C100

F(A)

F(A5)

F(A7)

F(A10)

70 60 50 38.8

40 30

24.0

24.4

20 10 0 C100

(a) 1 day

23.7

23.5

32.6

32.2

31.9

31.4

F(A)

F(A5)

F(A7)

F(A10)

(b) 7 days C100

C80F20

70 60 50

47.3

37.3

40

45.2

44.8

44.3

37.4

37.9

45.9 38.6

30 20 10 0 C100

F(A)

F(A5)

F(A7)

F(A10)

(c) 28 days

Compressive strength (MPa)

60

Compressive strength (MPa)

70

Compressive strength (MPa)

Compressive strength (MPa)

Fig. 5. Compressive strength of mortar specimens with primary fly ash mixes.

70 60

51.7

53.7 51.6

C100

F(A)

53.8 51.8

54.0 51.8 54.3 51.9

50 40 30 20 10 0 F(A5)

F(A7)

F(A10)

(d) 91 days

C60F40

Fig. 6. Compressive strength of mortar specimens with F(A) based fly ash mixes.

to the internal calcium as the internal calcium, inside the glassy phases, might not dissolve all out at early age. Thus, the system with external calcium would have more calcium products than the system with internal calcium [34]. Rapid hydration of free lime results in faster setting time.

3.5. Compressive strength Fig. 5 portrays the comparison of compressive strength (at different ages) of cement-only mix and primary fly ashes mixtures with 20% and 40% fly ashes. The water to binder ratio was varied in order to control the flow of mortar within the range of 110 + 5% in order to develop the strength activity indices for various mixtures [16]. At ages of 1, 7 and 28 days, compressive strengths of primary fly ash mixtures are lower than that of the standard mortar. For instance at 28 days, the compressive strength of cement-only mix is 47.3 MPa while the compressive strengths of 20% fly ash mixtures are between 41.5 and 45.3 MPa (Fig. 5c). During this phase, lowest strength is observed in F(R) mixtures as compared to Mae Moh fly ash mixtures. Also, F(B) and F(C) exhibited relatively higher compressive strength as compared to F(A) mixtures. At the later age of 91 days (Fig. 5d), the compressive strengths of most of primary fly ash mixtures are higher than that of cement-only mixture, where the compressive strength of

cement-only mix is 51.7 MPa while the compressive strengths of 20% fly ash mixtures are between 53.7 and 56.2 MPa. At the age of 28 days, lower compressive strength of primary fly ash mixtures as compared to the cement-only mixture is due to the replacement of cement with fly ash resulting in less hydration products in the mixture. Furthermore, lower compressive strength of F(R) mixtures as compared to the Mae Moh fly ash mixtures, during the early age of 28 days, is due to the higher water requirement and considerably lower CaO and free lime contents in F(R). Similarly, in the case of Mae Moh fly ash mixtures, slightly lower water requirement and higher calcium oxide (CaO) and free lime contents of F(B) and F(C) in comparison with F(A) resulted in relatively higher compressive strength. The increase of compressive strength at later age is due to the delayed pozzolanic reaction of fly ash silica with the CH produced from the cement hydration, resulting in higher calcium silicate hydrate [35]. Highest rate of strength gain can be observed in the case of 20%F(R) mixture, which achieved 56.2 MPa at the age of 91 days, due to higher SiO2 content (61.4%) as compared to Mae Moh fly ashes (25.22– 35.71%), leading to enhanced pozzolanic reaction in the long term. Fineness of fly ash has a positive effect on the compressive strength of cement-fly ash mixtures and many studies have shown that compressive strength increases with the increase of fineness [21,36,37]. In this study, the fineness of tested fly ashes is not much different from each other as shown in Table 3, therefore effect of

50 40 30 20

18.3

16.7

15.0

16.7 13.5 13.2

10.1

16.6 12.7

10 0 C100

F(B)

F(B5)

F(B7)

70 60 50 38.8

40

34.6

34.2 25.7

25.4

30

34.2

34.3

25.7

25.6

20 10 0 C100

F(B10)

(a) 1 day

F(B)

F(B5)

F(B7)

70 60 50

C80F20

45.3 40.8

45.1 40.4

45.0 40.4

44.9 40.4

40 30 20 10 0 C100

F(B10)

(b) 7 days C100

47.3

F(B)

F(B5)

F(B7)

Compressive strength (MPa)

60

Compressive strength (MPa)

70

Compressive strength (MPa)

A. Nawaz et al. / Construction and Building Materials 102 (2016) 515–530

Compressive strength (MPa)

522

70 60

51.7

55.4 53.4

53.6 52.9 52.6 52.8 52.2 52.5

F(B)

F(B5)

50 40 30 20 10 0

F(B10)

C100

(c) 28 days

F(B7)

F(B10)

55.3

55.5

(d) 91 days

C60F40

50 40 30 20

18.3

16.9

14.7 9.8

10

13.1

16.8 12.8

16.5 12.3

0 C100

F(C)

F(C5)

F(C7)

F(C10)

(a) 1 day

70 60 50 38.8

40

33.5

32.8

30

24.0

33.4 25.4

25.4

33.3 25.5

20 10 0 C100

F(C)

F(C5)

F(C7)

F(C10)

(b) 7 days C100

C80F20

70 60 50

47.3

44.4 40.6

44.6 42.3

44.7

44.6 40.8

38.6

40 30 20 10 0 C100

F(C)

F(C5)

F(C7)

F(C10)

(c) 28 days

Compressive strength (MPa)

60

Compressive strength (MPa)

70

Compressive strength (MPa)

Compressive strength (MPa)

Fig. 7. Compressive strength of mortar specimens with F(B) based fly ash mixes.

70 60

51.7

54.5 52.0

C100

F(C)

55.1 52.3

51.7

50.7

50 40 30 20 10 0 F(C5)

F(C7)

F(C10)

(d) 91 days

C60F40

Fig. 8. Compressive strength of mortar specimens with F(C) based fly ash mixes.

difference of fineness on compressive strength may not be significant. Fig. 6 indicates that in the case of F(A), with natural free lime of 1.71%, an increase in free lime content to make F(A5), F(A7) and F (A10), improved compressive strength for both 20% and 40% fly ash mixtures. The improvement is more obvious at an early age of 1-day (Fig. 6a) where compressive strength of as much as 14.8 MPa is achieved for 20%F(A10) mixture compared to 13.6 MPa for 20%F(A) mixture without added free lime. As illustrated in Fig. 7a, in the case of F(B), with natural free lime content of 3.93%, an increase in free lime content to make F(B5), F(B7), F(B10), increased compressive strength at an early age of 1 day i.e. up to 16.7 MPa compared to 15 MPa for 20%F(B) mixtures without added free lime. At 7 and 28 days (Fig. 7b and c), the differences in the compressive strengths of F(B) mixtures, with and without added free lime, are not significant. At the later age of 91 days (Fig. 7d), the compressive strength of 20%F(B) mixture is 55.4 MPa while the compressive strengths of mixtures with 20%F (B5), 20%F(B7), and 20%F(B10) are 53.6, 52.6 and 52.2 MPa, respectively. For F(C), with natural free lime content of 3.06%, an increase in free lime content to make F(C5), F(C7), F(C10), improved compressive strength particularly for 20% fly ash mixtures (Fig. 8a–d). For instance at the later age of 91 days (Fig. 8d), the compressive strength of 20%F(C) mixture is 54.5 MPa while the compressive strengths of mixtures with 20%F (C5), 20%F(C7), and 20%F(C10) are 55.1, 55.3 and 55.5 MPa, respectively. However, F(C10) mixture with 40% fly ash exhibited relatively lower compressive strengths at 28 and 91 days, 38.6 and 50.7 MPa respectively, as compared to 40.6 and 52 MPa for 40%F(C) mixture without added free lime (Fig. 8c and d). An increase in the compressive strength due to the addition of free lime, particularly at an early stage, is because of the reaction of fly ash with the additional calcium hydroxide provided by free lime in the system. As mentioned in Section 3.4, calcium in fly ash can be present as a glass component or as a free lime where free lime is mostly distributed outside the fly ash particles [34] as compared to the internal calcium which is present in the glassy phase [9]. Both calcium oxide and free lime can produce CSH gel [38–40]. Free lime particles are more readily available and undergo rapid hydration [41] and seems to contribute early strengths. Tsimas et al. [42] reported that a suitable amount of free lime is

essential for the initial activation of fly ash, which results in higher strength. In comparison, the internal calcium, inside the glassy phases, might not dissolve all out at early age [34] and start contributing to the compressive strength at later age. The reduced strength of F(C10) and mixtures of F(B) with added free lime is because of too much of free lime in the mixtures of F(B) and F(C), which is not compatible with the low SiO2 contents, 26.21% and 25.22%, respectively. Whereas in the case of F(A), SiO2 content is higher (35.71%) than F(B) and F(C), which can cause continuing strength development of the F(A) mixtures with high free lime content (10%). Tsimas et al. [42] observed similar findings and described that the samples with higher free lime contents showed lower compressive strengths compared to samples with moderate free lime, due to the formation of Ca(OH)2 in large quantities. 3.6. Strength activity index Fig. 9 demonstrates that the strength activity indices of mixtures, containing Class 2a fly ash [F(R)] and Class 2b fly ashes [F(A), F(B), F(C)], are higher than 70%, 75%, and 85% of the strength of the reference cement-only mixture at 7, 28, and 91 days, respectively. Thus, all tested fly ashes fulfilled the strength requirement of TIS 2135. 3.7. Autoclave expansion The autoclave expansion test provides an index of potential delayed expansion caused by the hydration of CaO, or MgO, or both, when present in hydraulic cement [17], where the effect of free lime is typically more aggressive than periclase [43]. Autoclave test results showed higher expansion in the case of Mae Moh fly ash mixtures in comparison with F(R) mixtures (Fig. 10a). Higher amount of free lime in Mae Moh fly ashes resulted in higher expansion of mixtures containing F(A), F(B), and F(C) as compared to F(R) mixtures [43]. Fig. 10a shows that F(B) mixtures exhibited highest autoclave expansion as compared to other primary fly ash mixtures. Similarly, F(C) mixtures showed higher expansion as compared to F(A) mixtures. This is because of the highest original free lime content of 3.93% in F(B), as compared to 3.03% in F(C)

523

Strength Index %

A. Nawaz et al. / Construction and Building Materials 102 (2016) 515–530

120 100 80 60 40 20 0

min. strength index for fly ash class 2a and 2b (70%, TIS 2135) 100 89 88 88 88 84 86 86 86 81 82 83 84

-0.017

F(R) 78

-0.036

F(C)

0.063 0.040

F(B)

C100

Strength Index %

88

0.000

min. strength index for fly ash class 2a and 2b (85%, TIS 2135) 107 104 102 101 105 107 107 107 104 104 104 105

100

F(A10)

0.031

F(A7)

0.028

C100 109

0.050 Expansion (%)

0.100

0.150

(a) Primary fly ash mixtures

F(A)

(b) 28 days Strength Index %

C80F20 C60F40

-0.050 min. strength index for fly ash class 2a and 2b (75%, TIS 2135) 96 95 95 95 100 94 94 94 95 94 95 96 97

2.104 0.299 0.012 0.047

F(A5)

120 100 80 60 40 20 0

0.138

-0.009 -0.007 -0.016

F(A)

(a) 7 days 120 100 80 60 40 20 0

0.024

-0.500

-0.009 -0.007 -0.016

C80F20 C60F40 ASTM C618 Limit (0.8%)

0.000

0.500

1.000 Expansion (%)

1.500

2.000

2.500

(b) F(A) based fly ash mixtures 0.093

F(B10)

(c) 91 days Fig. 9. Strength index of mortar specimens.

F(B7)

0.057

F(B5)

0.049 0.158 0.040 0.138

F(B) C100

and 1.71% in F(A). Moreover, for Mae Moh fly ashes, F(A), F(B), and F(C), an increase of fly ash replacement from 20% to 40% lead to higher expansion due to increased amount of free lime in the whole mixture. The cement-only mixtures showed shrinkage as compared to the expansion of Mae Moh fly ash mixtures. Also for F(R), the trend is reversed, and F(R) mixtures showed shrinkage which increases, as the replacement percentage of fly ash is increased from 20% to 40%. F(R) showed more shrinkage than the cement-only mixtures because F(R) has lower free lime content (0.03%) than cement (0.75%), so the total free lime content of F (R) mixtures is reduced. Though the autoclave expansion of Mae Moh fly ash mixtures is higher than that of the cement-only mixture, the expansion values are not over the specified limit of 0.8%, as indicated by ASTM C618, even in the cases of fly ashes with high calcium oxide and high free lime contents. Fig. 10b–d show that the mixtures of fly ashes F(A), F(B), and F (C) with added free lime experienced a greater degree of expansion with an increase of free lime percentage. Although the expansion values of mixtures with added free lime is higher than the cement-only mix, they are within the ASTM C618 limit, i.e., smaller than 0.8%, except in the cases of mixtures containing F(A10), F (B10), and F(C10), where higher expansions than the specified limit are observed in the mixtures containing 40% fly ash replacement percentage. Autoclave test results indicated that in the case of 20% fly ash replacement, mixtures with fly ashes, containing free lime content up to 10%, undergo expansion within the ASTM C618 limit of 0.8%. An increase in fly ash replacement percentage from 20% to 40% also resulted in higher expansions, and mixtures with fly ashes, containing free lime up to 7%, showed expansion within the specified limit. 3.8. Alkali-aggregate reaction Tests for alkali aggregate reaction revealed that the expansion of cement only mixtures is higher (0.207%) than that of primary fly ash mixtures which is between 0.040 and 0.157% for 20% fly ash mixtures (Fig. 11a). Moreover, the expansion further decreases as the fly ash content increases in the mixture from 20% to 40%. The expansion of 20% Mae Moh fly ash (F(A), F(B), F(C)) mixtures is con-

-0.500

2.490 0.372 C80F20 C60F40 ASTM C618 Limit (0.8%)

-0.016 0.000

0.500

1.000 Expansion (%)

1.500

2.000

2.500

(c) F(B) bases fly ash mixtures F(C10)

0.061

F(C7)

0.054

1.309 0.398 0.041 0.162 0.024 0.063

F(C5) F(C) C100 -0.500

C80F20 C60F40 ASTM C618 Limit (0.8%)

-0.016 0.000

0.500

1.000 Expansion (%)

1.500

2.000

2.500

(d) F(C) based fly ash mixtures Fig. 10. Autoclave expansion of mixtures.

siderably higher (0.110, 0.156 and 0.157% respectively) compared to the expansion of 20%F(R) mixtures (0.040%), as shown in Fig. 11a. This is because of originally higher free lime and CaO contents in Mae Moh fly ashes compared to lower values in F(R). Due to the same reason, mixtures containing F(B) and F(C) exhibited higher expansion as compared to F(A) mixtures, as illustrated in Fig. 11a. The addition of free lime increased expansion as shown in Fig. 11b. For instance, 20%F(A10) mixture with added free lime expanded 0.138% compared to 0.110% for mixtures when free lime is not added in the fly ash. Similarly 20%F(B10) and 20%F(C10) mixtures showed higher expansion, as much as 0.191% and 0.214%, respectively, because of the additional alkalinity in the form of calcium hydroxide provided by the free lime. 20%F(C10) mixture showed higher expansion than the cement-only mixture, whereas all other mixtures exhibited smaller expansion than the standard mortar. In the case of 40% fly ash replacement (Fig. 11b), although addition of free lime caused more expansion, the magnitude of expansion for all mixtures is still lower than that of the cement-only mixture. As calcium hydroxide is consumed in the pozzolanic reaction, the alkalinity level of the fly ash mixtures is reduced, resulting in lower expansion as compared to the cement-only mixture.

A. Nawaz et al. / Construction and Building Materials 102 (2016) 515–530

Kawabata et al. [44] stated that in mortar, the appropriate replacement of cement with a supplementary cementitious material such as fly ash, can help in reducing the alkali-aggregate reaction as it causes the formation of C-S-H gel with a low Ca/Si ratio, resulting in lower concentrations of alkali and hydroxide ion in the pore solution, which is the most effective factor for alkali aggregate reaction suppression. Shehata et al. [45] reported that higher calcium and lower silica contents of fly ash increase the Ca/Si ratio of the hydrates, reducing the amount of alkalis removed from the solution, which results in a high-alkali pore solution. For fly ashes of low- to moderate-alkali content (e.g. <3.1%), the calcium content of the individual fly ash affects the ability of fly ash to lower the availability of alkali and hydroxyl ions in solution. Although the alkali silica reaction expansion reduced in the case of tested fly ash mixtures compared to the control mixture, the expansion generally increased as the calcium or alkali content of the fly ash increased or as its silica content decreased [46]. Furthermore, Khunthongkeaw et al. [33] observed that Mae Moh fly ash with higher CaO content provides higher amount of calcium hydroxide (CH) in cement-fly ash mixture than that of fly ash with lower CaO content. Malvar et al. [47] indicated that calcium oxide is considered as having one of the most deleterious effects on expansion, and alkali-silica expansion has often been correlated to CaO, or CaO/SiO2. Mingyu [48] mentioned that there is an increasing tendency to expansion due to AAR as the CaO content or the value of CaO/(SiO2 + A12O3 + Fe2O3) in fly ash increases. Fig. 12 shows the relationship between calculated CaO/SiO2 ratio in the cement-fly ash mixtures and AAR expansion. It is observed that expansion increases as CaO/SiO2 ratio increases in the mixtures. As discussed earlier, the expansion decreases as the fly ash content increases in the mixture from 20% to 40% (Fig. 12a). Moreover, addition of free lime increased CaO/SiO2 ratio and hence more expansion is experienced (Fig. 12b).

0.250 0.157

0.156

0.150

0.110

0.100

0.056

0.053

0.045

0.050

0.040

0.000

(a) Primary fly ashes 0.250

Expansion (%)

0.207 0.200 0.150

0.110 0.115

0.126 0.138

0.156

0.174 0.180

0.191 0.157

0.179 0.190

0.214

0.100 0.050 0.000

(i) 20% fly ash replacement

Expansion (%)

0.250

0.207

0.200 0.150

0.050

0.112

0.091

0.086

0.100

0.056

0.053

0.045

0.000

(ii) 40% fly ash replacement (b) Fly ashes with added free lime

AAR Expansion %

Fig. 11. Expansion due to alkali-aggregate reaction.

0.25 0.20 0.15 0.10 0.05 0.00

F(C)

F(B)

C100

F(A) F(R)

1.0

2.0

3.0

4.0

0.25 0.20 0.15 0.10 0.05 0.00

C100

F(A)

1.0

2.0

AAR Expansion %

F(A)

F(A7)

2.50

2.55

2.60

CaO/SiO2

AAR Expansion %

(i) 20%F(A) mixtures 0.25 0.2 0.15 0.1 0.05 0 2.85

4.0

(ii) 40% fly ash replacement

F(A10)

F(A5)

3.0 CaO/SiO2

(i) 20% fly ash replacement (a) Primary fly ashes 0.25 0.2 0.15 0.1 0.05 0 2.45

F(C)

F(B)

CaO/SiO2

AAR Expansion %

Expansion (%)

0.207 0.200

AAR Expansion %

524

0.25 0.2 0.15 F(B5) 0.1 F(B) 0.05 0 2.80

F(B7)

2.85 CaO/SiO2

F(B10)

2.90

(ii) 20%F(B) mixtures

F(C10) F(C)

F(C5)

F(C7)

2.90 CaO/SiO2

2.95

(iii) 20%F(C) mixtures (b) Fly ash mixtures with added free lime Fig. 12. Relationship between AAR expansion and CaO/SiO2 ratio in cement-fly ash mixtures.

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A. Nawaz et al. / Construction and Building Materials 102 (2016) 515–530

0.8

C80F(A5)20

1.2

C80F(A10)20

0.8 0.4

0.4

0

0

56

112 168 Immersion period (days)

0

224

56

112 168 Immersion period (days)

C80F(B5)20 C80F(B10)20

0.8

0

C100

1.6

C80F(B)20

1.2

0.4

0

2

C100

1.6

C80F(A)20

Expansion (%)

1.2

2

C100

1.6 Expansion (%)

Expansion (%)

2

C100 C80F(R)20 C80F(A)20 C80F(B)20 C80F(C)20

Expansion (%)

2 1.6

C80F(C)20 C80F(C5)20

1.2

C80F(C10)20

0.8 0.4 0

0

224

56

112 168 Immersion period (days)

224

0

56

112 168 Immersion period (days)

224

(i) 20% fly ash mixtures

0.8

C60F(A5)40

1.2

C60F(A10)40

0.8 0.4

0.4

0

0

56

112 168 Immersion period (days)

224

0

56

112 168 Immersion period (days)

C60F(B5)40 C60F(B10)40

0.8

0

C100

1.6

C60F(B)40

1.2

0.4

0

2

C100

1.6

C60F(A)40

Expansion (%)

1.2

2

C100

1.6 Expansion (%)

Expansion (%)

2

C100 C60F(R)40 C60F(A)40 C60F(B)40 C60F(C )40

Expansion (%)

2 1.6

C60F(C )40 C60F(C5)40

1.2

C60F(C10)40

0.8 0.4 0

224

0

56

112 168 Immersion period (days)

224

0

56

112 168 Immersion period (days)

224

(ii) 40% fly ash mixtures (a) Primary fly ashes

(b) F(A) based fly ashes

(c) F(B) based fly ashes

(d) F(C) based fly ashes

Fig. 13. Expansion of mortar bars submerged in Na2SO4 solution after 224 days.

0.8 0.4

C80F(A5)20

1.2

C80F(A10)20

0.8 0.4

0 56

112 168 Immersion period (days)

224

C80F(B5)20

1.2

C80F(B10)20

0.8

56

112 168 Immersion period (days)

224

C80F(C)20 C80F(C5)20

1.2

C80F(C10)20

0.8 0.4

0 0

C100

1.6

C80F(B)20

0.4

0 0

2

C100

1.6

C80F(A)20

Expansion (%)

1.2

2

C100

1.6 Expansion (%)

Expansion (%)

2

C100 C80F(R)20 C80F(A)20 C80F(B)20 C80F(C)20

Expansion (%)

2 1.6

0 0

56

112 168 Immersion period (days)

224

0

56

112 168 Immersion period (days)

224

(i) 20% fly ash mixtures

0.4

C60F(A5)40

1.2

C60F(A10)40

0.8

56

112 168 Immersion period (days)

224

0.8

0

56

112 168 Immersion period (days)

224

C60F(C )40 C60F(C5)40

1.2

C60F(C10)40

0.8 0.4

0

0 0

C60F(B10)40

0.4

0.4

0

C60F(B5)40

1.2

C100

1.6

C60F(B)40 Expansion (%)

0.8

1.6

C60F(A)40

2

C100

C100

1.6 Expansion (%)

Expansion (%)

1.2

2

2

C100 C60F(R)40 C60F(A)40 C60F(B)40 C60F(C )40

Expansion (%)

2 1.6

0 0

56

112 168 Immersion period (days)

224

0

56

112 168 Immersion period (days)

224

(ii) 40% fly ash mixtures (a) Primary fly ashes

(b) F(A) based fly ashes

(c) F(B) based fly ashes

(d) F(C) based fly ashes

Fig. 14. Expansion of mortar bars submerged in combined Na2SO4 and MgSO4 solution after 224 days.

3.9. Sulfate resistance Fig. 13a–d show the expansion results of specimens immersed in Na2SO4 solution up to 224 days. Fig. 13a specifies that the expansion of cement-only mixture (0.361%) is higher as compared to the expansion of 20% primary fly ash mixtures (0.025–0.212%), and 40% fly ash mixtures (0.030–0.100%). Moreover, Mae Moh fly ash mixtures expanded more than F(R) mixtures. Fig. 13b–d show that the mixtures of fly ashes F(A), F(B), and F(C) with added free lime tend to expand more with the increase of free lime content. Fig. 13b shows that the expansion of 20%F(A) mixtures with added free lime is lower (<0.303%) than that of the control mix (0.361%) where as 40%F(A) mixtures with 10% free lime in F(A) showed higher expansion (0.705%). Similarly, the expansion of 20%F(B) mixtures with added free lime (Fig. 13c) is lower (<0.319%) than the expansion of the cement-only mixture (0.361%) but 40%F(B) mixtures with added free lime exhibited higher expansion (0.480–0.919%). Fig. 13d shows that F(C) mixtures with added free lime showed higher expansion (0.631–0.758%) than the cementonly mixtures (0.361%) except for 20%F(C5) mixture (0.259%). Fig. 14a–d depict the expansion results of mixtures submerged in combined Na2SO4–MgSO4 solution up to 224 days, and similar expansion trends can be observed as noticed in the case of the Na2SO4 solution however, the expansion in Na2SO4 solution is higher than that in the combined Na2SO4–MgSO4 solution. This is due to the volume expansion of more gypsum and ettringite formation in Na2SO4 attacking mechanism [19,49]. Fig. 14a demonstrates that

cement-only mixtures exhibited higher expansion (0.233%) than primary fly ash mixtures (0.015–0.098%). Mae Moh fly ash mixtures expanded more than F(R) mixtures and addition of free lime in the Mae Moh fly ashes resulted in higher expansion of the mixtures as shown in Fig. 14b–d. Moreover, as shown in Fig. 14b and c, expansion of F(A) and F(B) mixtures, with added free lime and 20% fly ash replacement, is lower than the cement-only mixtures. In the case of F(C) mixtures with added free lime, only mixtures with 20% fly ash replacement containing 5% free lime exhibited lower expansion than the cement-only mixtures (Fig. 14d). Calcium is widely recognized as an aggressive factor in the sulfate resistance of fly ash concrete [50]. The mechanism of sulfate attack on concrete apparently involves two chemical reactions [51]. First is called acidic attack and involves combination of sulfate ions with Ca(OH)2 to form gypsum and starts the expansive series of reactions. It can be symbolically represented as

CaðOHÞ2 þ Na2 SO4 !CaSO4 þ 2NaOH

ð1Þ

and/or

CaðOHÞ2 þ MgSO4 !CaSO4 þ 2MgðOHÞ2

ð2Þ

The CaSO4 precipitates as CaSO42H2O (secondary gypsum). The second type of attack mainly includes the chemical reaction between the tricalciumaluminate (C3A) present in Portland cement and sulfate ions supplied by the aggressive environment resulting in formation of secondary ettringite. The chemical reaction can be represented as:

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A. Nawaz et al. / Construction and Building Materials 102 (2016) 515–530

3CaSO4 þ 3C3 A þ 32H2 O!3C3 A  3CaSO4  32H2 O

ð3Þ

The reaction products, i.e. gypsum and ettringite have greater volume than the compounds they replace. This expansion causes cracking of the matrix, which leads to the loss in strength and disruption. Although fly ash helps in improving sulfate resistance of concrete however, concretes made with low calcium fly ashes (with CaO content < 15%) perform better against sulfate attack than concretes made with high calcium fly ashes [51]. Khunthongkeaw et al. [33] observed that Mae Moh fly ash with higher CaO content provides higher amount of calcium hydroxide (CH) content in cement-fly ash mixture than that of fly ash with lower CaO content. CH content combines with sulfate ions to form gypsum. Calcium in the form of free lime is also thought to be of some important in the sulfate resistance. Hartmann et al. [52] found a relationship between the free lime content of the cementitious material and the sulfate resistance of concrete containing fly ash. Tikalsky et al. [50] tested series of fly ashes and observed more severe sulfate attack in the case of fly ash mixtures with high calcium oxide and high free lime contents, as can be seen in cases of F(B) and F(C) mixtures. Also the expansion of Mae Moh fly ash mixtures is higher than that of F(R) mixtures because originally higher free lime and lower SiO2 contents in Mae Moh fly ashes result in higher alkalinity of the system. 4. Free lime limit in fly ash As discussed in Section 3, though most of the tested performances of high free lime mixtures is worse than the low free lime fly ash mixtures, they are still better than the performances of cement-only mixtures for most of the tested properties. All basic and mechanical properties show no sign of worse performance in comparison to the cement-only mixtures and pass the standards, TIS 2135. Since the original problem of free lime involves expansion of the mixtures, the remaining three expansion properties including autoclave expansion, expansion due to alkali aggregate reaction, and expansion in sulfate solutions, are selected to outline the limit of total free lime content in binder (cement and fly ash) and ultimately free lime content of fly ash.

In the case of autoclave expansion, most of the high free lime fly ash mixtures performed better than the cement-only mixtures except when 10% free lime content with 40% fly ash replacement is used in the mixtures (Fig. 10b–d). Fig. 15 shows the effect of total free lime content of binders (cement and fly ash) on the autoclave expansion of different fly ash mixtures. It can be seen that an increase in autoclave expansion is directly proportional to the total free lime content of binder. Autoclave expansion of mixtures with 20% fly ash replacement and high free lime content is smaller than 0.8% (ASTM C618 limit), as described in Fig. 15a. However, in the case of 40% fly ash replacement, mixtures with very high total free lime content in binder expanded more than 0.8% (Fig. 15b). Threshold values of total free lime content in binder, which may cause autoclave expansion less than 0.8%, can be obtained from Fig. 15b. The allowable free lime content in fly ash is calculated, as shown in Table 7 (see remarks under Table 7). Moreover Fig. 15c shows the relationship of total free lime content of binder with autoclave expansion of mixtures with 20% and 40% fly ash replacements, and it is evident that autoclave expansion increases with the increase in total free lime content of the mixtures. Fig. 16 shows the effect of total free lime content of binders (cement and fly ash) on the expansion due to alkali aggregate reactions for different fly ash mixtures. It is observable that an increase in total free lime content of binder causes higher expansion. In the case of 20% fly ash replacement, only F(C) mixtures with very high total free lime content in binder expanded more than the cementonly mixtures (Fig. 16a), whereas expansion of mixtures with 40% fly ash replacement and high free lime content is smaller than the expansion of cement-only mixtures (0.207%), as shown in Fig. 16b. Threshold values of total free lime content in binder, which may cause expansion less than that of the cement-only mixture, can be obtained from Fig. 16a, and allowable free lime content in fly ash, (as far as alkali aggregate reaction is concerned) is calculated, as shown in Table 7 (see remarks under Table 7). Furthermore, it can be observed from Fig. 16 that the same amount of free lime content with different fly ash replacements, caused different expansions. Higher fly ash replacement exhibited lower expansion, which is because more Ca(OH)2 is consumed during the resulting pozzolanic reaction. Also, fly ash with higher SO3 content leads to a higher expansion due to the add-up expansion resulted from ettringite formation by internal sulfate effect. 3 Autoclave expansion (%)

Autoclave expansion (%)

1 0.8 0.6

C80F(A)20 C80F(B)20 C80F(C)20 ASTM C618 Limit (0.8%)

0.4 0.2

C60F(A)40 C60F(B)40 C60F(C)40 ASTM C618 Limit (0.8%)

2.5 2 1.5 1 0.5 0

0 0

0.5

1

1.5

2

2.5

3

% Free lime content in binder (C80F20)

(a) 20% fly ash mixtures

0

0.5 1 1.5 2 2.5 3 3.5 4 4.5 % Free lime content in binder (C60F40)

(b) 40% fly ash mixtures

Autoclave expansion (%)

3 F(A) F(B) F(C) ASTM C618 Limit (0.8%)

2.5 2 1.5 1 0.5 0 0

0.5

1 1.5 2 2.5 3 3.5 4 % Free lime content in binder

4.5

5

(c) 20% and 40% fly ash mixtures Fig. 15. Effect of total free lime content of binder on autoclave expansion.

5

527

A. Nawaz et al. / Construction and Building Materials 102 (2016) 515–530 Table 7 Allowable free lime content in fly ash. Mix designation Autoclave expansion C80F(A)20 C60F(A)40 C80F(B)20 C60F(B)40 C80F(C)20 C60F(C)40

Type of fly ash

SO3 content (%)

Threshold value of total free lime content in binder (%)

Allowable value of free lime content in fly ash (%)

A

4.26 < 5%

B

8.53 > 5%

C

9.44 > 5%

– 3.6(3) – 3.6(3) – 3.54(3)

>10(3) 7.88(2) >10(3) 7.88(2) >10(3) 7.72(2)

– – – – 2.19 –

>10(4) >104) >10(4) >10(4) 7.95 (1) >10(4)

Alkali aggregate reaction C80F(A)20 A C60F(A)40 C80F(B)20 B C60F(B)40 C80F(C)20 C C60F(C)40

2 3 4 5

9.44 > 5%

(4)

Sulfate resistance: combined sodium and magnesium sulfate solution (based on 224 days expansion results) C80F(A)20 A 4.26 < 5% – C60F(A)40 2.60(5) C80F(B)20 B 8.53 > 5% – C60F(B)40 2.79(5 C80F(C)20 C 9.44 > 5% 2.13(5) C60F(C)40 2.06(5)

>10(5) 4.23(2) >10(5 4.68(2) 6.8(1) 3.73(2)

Sulfate resistance: sodium sulfate solution (based on 224 days expansion results) C80F(A)20 A 4.26 < 5% – C60F(A)40 2.78(6) C80F(B)20 B 8.53 > 5% – C60F(B)40 2.46(6) C80F(C)20 C 9.44 > 5% 1.92 (6) C60F(C)40 2.19 (6)

>10(6) 4.63(2) >10(6) 4.5(2) 5.31 (1) 3.94 (2)

% free lime in fly ash = (total free lime in binder – 0.8  free lime in cement)/0.2. % free lime in fly ash = (total free lime in binder – 0.6  free lime in cement)/0.4. See Fig. 15. See Fig. 16. See Fig. 17. See Fig. 18.

AAR expansion (%)

6

8.53 > 5%

0.25

0.25

0.2

0.2

AAR expansion (%)

1

4.26 < 5%

0.15 0.1 Expansion of C100 (0.207%) C80F(A)20 C80F(B)20 C80F(C)20

0.05 0 0

0.5 1 1.5 2 2.5 % Free lime content in binder (C80F20)

Expansion of C100 (0.207%) C60F(A)40 C60F(B)40 C60F(C)40

0.15 0.1 0.05 0

3

(a) 20% fly ash mixtures

0

0.5

1 1.5 2 2.5 3 3.5 4 4.5 % Free lime content in binder (C60F40)

5

(b) 40% fly ash mixtures

Fig. 16. Effect of total free lime content of binder on alkali aggregate reaction.

The effect of total free lime content of binders (cement and fly ash) on the sulfate resistance of different fly ash mixtures submerged in combined Na2SO4-MgSO4 solution and in Na2SO4 solution, is demonstrated in Figs. 17 and 18, respectively. It can be seen from these figures that the effect of high free lime content is more vigorous in the case of sulfate expansion. High free lime fly ash mixtures expanded more than the cement-only mixtures, and an increase in fly ash replacement from 20% to 40% resulted in higher expansion. As discussed earlier, threshold values of total free lime content in binder, which may cause smaller expansion than the cement-only mixture, can be obtained from Figs. 17 and 18, and allowable free lime content in fly ash is calculated, as presented in Table 7 (see remarks under Table 7). Moreover, Table 7 indicates that sulfate resistance is the most critical property which influences the limit of free lime content in fly ash when compared to autoclave expansion and alkali aggregate reaction. Also, the free

lime limit decreases if SO3 content in fly ash becomes higher, as can be seen that F(A) mixtures with SO3 content of 4.26% (<5%) allow higher free lime content, as compared to F(B) and F(C) mixtures containing 8.53% and 9.44% SO3 content, respectively. Based on results of autoclave expansion, alkali aggregate reaction, and sulfate resistance tests, Fig. 19 summarizes the allowable free lime content in fly ashes with different SO3 contents. From Fig. 19a, it can be stated that it is possible to replace 20% of cement in a mixture with a fly ash containing SO3 content of less than 5% and free lime content up to 10% while not compromising the basic and durability properties. In the case of 40% fly ash replacement, fly ashes with SO3 < 5% and free lime content up to 4.23% can be utilized. Moreover, when SO3 content in fly ash is very high, i.e., >5% but <10%, free lime content can be reduced to 5.31% and 3.73%, for 20% and 40% fly ash replacements, respectively, to satisfy the durability requirements.

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A. Nawaz et al. / Construction and Building Materials 102 (2016) 515–530

1 Expansion of C100 (0.23%) C80F(A)20 C80F(B)20 C80F(C)20

0.8 0.6

Expansion at 224 days (%)

Expansion at 224 days (%)

1

0.4 0.2

Expansion of C100 (0.23%) C60F(A)40 C60F(B)40 C60F(C)40

0.8 0.6 0.4 0.2 0

0 0

0.5

1 1.5 2 2.5 3 3.5 4 4.5 % Free lime content in binder (C80F20)

0

5

(a) 20% fly ash mixtures

0.5

1 1.5 2 2.5 3 3.5 4 4.5 % Free lime content in binder (C60F40)

5

(b) 40% fly ash mixtures

Fig. 17. Effect of total free lime content of binder on sulfate resistance of mortar bars submerged in combined Na2SO4–MgSO4 solution.

1.4 Expansion of C100 (0.36%) C80F(A)20 C80F(B)20 C80F(C)20

1.2 1 0.8

Expansion at 224 days (%)

Expansion at 224 days (%)

1.4

0.6 0.4 0.2

Expansion of C100 (0.36%) C60F(A)40 C60F(B)40 C60F(C)40

1.2 1 0.8 0.6 0.4 0.2 0

0 0

0.5

1 1.5 2 2.5 3 3.5 4 4.5 % Free lime content in binder (C80F20)

5

(a) 20% fly ash mixtures

0

0.5

1 1.5 2 2.5 3 3.5 4 4.5 % Free lime content in binder (C60F40)

5

(b) 40% fly ash mixtures

Allowable free lime content (%)

Fig. 18. Effect of total free lime content of binder on sulfate resistance of mortar bars submerged in sodium sulfate (Na2SO4) solution.

12 10

10

10

10

needed in the future to establish a limit of free lime content of different fly ashes.

10

10 7.88 8 6

4.63

4.23

Conclusions drawn from this study are as follows:

2 0 Autoclave

AAR 20%

Sodium-Magnesium Sodium sulphate sulphate solution solution 40%

(a) For fly ashes with SO3 content < 5% (F(A)) Allowable free lime content (%)

5. Conclusions

4

12 10

10

10 8

7.72

7.95 6.8 5.31

6 3.73

4

3.94

2 0 Autoclave

AAR 20%

Sodium-Magnesium Sodium sulphate sulphate solution solution 40%

(b) For fly ashes with SO3 content > 5% but <10% (F(B) and F(C)) Fig. 19. Free lime content limit in different fly ashes.

It should be noted that fly ash, a by-product from the coal combustion process, has large variations in properties and characteristics as compared to cement, and it is not possible to include all types of fly ash in this study. This is a preliminary study to investigate and verify the maximum limit of free lime content in fly ashes with different SO3 contents and fly ash replacement ratios. Also, this study includes fly ash replacement percentage only up to 40% while in real practice a higher replacement percentage is occasionally used. Further verification and more test data are

i. Water requirement of Mae Moh fly ashes is lower than the Rayong fly ash because of the high LOI and relatively irregular particle shape of the Rayong fly ash. ii. Water requirement of fly ash mixtures increases as the free lime content is increased, and the fly ash mixtures containing higher free lime content tend to set earlier. iii. Higher free lime content in fly ash results in improved compressive strength, particularly at early ages. In the case of fly ashes with a naturally high free lime content, an increase in compressive strength due to the addition of free lime is less significant at a long age of 91 days. All the tested mixtures of fly ashes with free lime content up to 10% fulfill the compressive strength requirements of TIS 2135. iv. Autoclave expansion increases with the addition of free lime in fly ash mixtures. Mixtures with 20% fly ash replacement and free lime content up to 10% exhibited autoclave expansion within the specified limit of ASTM C618. In the case of 40% fly ash replacement, mixtures of fly ashes with 7.72% free lime, exhibited autoclave expansion within the specified limit of ASTM C618. v. Addition of free lime content increases the expansion due to alkali-aggregate reaction. Mixtures with 40% fly ash replacement and free lime content up to 10% showed lower expansion than the cement-only mixtures. In the case of 20% fly ash replacement, mixtures of fly ashes with 7.95% free lime, exhibited lower expansion than the cement-only mixtures. vi. In the sulfate expansion test, Mae Moh fly ash mixtures expanded more as compared to Rayong fly ash mixtures, because of higher CaO, SO3, and free lime contents. The tests

A. Nawaz et al. / Construction and Building Materials 102 (2016) 515–530

also indicated higher expansion due to addition of free lime in fly ash mixtures. Moreover, the effect of high free lime content in fly ash is more severe in the case of sulfate expansion test as compared to autoclave expansion and AAR testing. vii. It is possible to utilize 20% of tested fly ash in a mixture as binder, with SO3 content <5% and free lime content up to 10% while not compromising the basic and durability properties. In the case of 40% fly ash replacement, tested fly ashes with SO3 < 5% and free lime content up to 4.23%, can be utilized. When SO3 content in fly ash is very high, i.e., >5% but <10%, free lime content can be reduced to as much as 5.31% and 3.73%, for 20% and 40% fly ash replacements, respectively, to satisfy the tested expansion performances. viii. Limits of free lime and SO3 contents of fly ash mixtures are interrelated to each other. A higher free lime limit can be used if SO3 content is low (<5%), whereas in the case of higher SO3 content (>5% and <10%), the free lime limit should be reduced.

Acknowledgements The authors would like to thank the Electricity Generating Authority of Thailand for providing research support and fly ash samples for this study. This research is also supported by Center of Excellence in Material Science, Construction and Maintenance Technology, Thammasat University, the Higher Education Research Promotion and National Research University Project, the Office of the Higher Education Commission of Thailand. The authors also gratefully acknowledge the support of the Higher Education Commission of Pakistan. References [1] C.S. Poon, L. Lam, Y.L. Wong, A study on high strength concrete prepared with large volumes of low calcium fly ash, J. Cem. Concr. Res. 30 (2000) 447–455. [2] C.W. Tang, Hydration properties of cement pastes containing high-volume mineral admixtures, J. Comput. Concr. Res. 7 (2013) 17–38. [3] L. Lam, Y.L. Wong, C.S. Poon, Degree of hydration and gel/space ratio of highvolume fly ash/cement systems, J. Cem. Concr. Res. 30 (2000) 747–756. [4] Annual Book of ASTM Standards, ASTM C618 Standard Specification for Fly Ash and Raw or Calcined Natural Pozzolan for Use as a Mineral Admixture in Portland Cement Concrete, 2003. [5] British Standard, BS 3892 Part 1 Specification for Pulverized-Fuel Ash for use with Portland Cement Part 1, London, 1993. [6] European Standard, EN 450 Fly Ash for Concrete – Definitions, Requirement and Quality Control, Brussels, 1994. [7] S. Tangtermsirikul, Development of fly ash usage in Thailand, in: The International Workshop on Project Management, IWPM, March 9–11, 2005, Kochi (Japan). [8] Thai Industrial Standards, TIS 2135 Standard Specification for Coal Fly Ash, 2002. [9] K. Kaewmanee, P. Krammart, T. Sumranwanich, P. Choktaweekarn, S. Tangtermsirikul, Effect of free lime content on properties of cement–fly ash mixtures, J. Constr. Build. Mater. Res. 38 (2013) 829–836. [10] G.S. Itskos, S. Itskos, N. Koukouzas, The effect of the particle size differentiation of lignite fly ash on cement industry applications, Third World of Coal Ash Conference WOCA May 4–7, 2009, KY (USA). [11] D. Bonvin, R. Yellepeddi, A. Buman, Applications and perspectives of a new innovative XRF–XRD spectrometer in industrial process control, The international center for diffraction data (ICDD), Res 42 (2000) 126–136. [12] Annual Book of ASTM Standards, ASTM C33 Standard Specification for Concrete Aggregates, 2003. [13] Annual Book of ASTM Standards, ASTM C187 Standard Test Method for Normal Consistency of Hydraulic Cement, 1998. [14] Annual Book of ASTM Standards, ASTM C191 Standard Test Method for Time of Setting of Hydraulic Cement by Vicat Needle, 1999. [15] Annual Book of ASTM Standards, ASTM C109/C109M Standard Test Method for Compressive Strength of Hydraulic Cement Mortars (Using 2-in. or [50-mm] Cube Specimens). [16] Annual Book of ASTM Standards, ASTM C311 Standard Test Methods for Sampling and Testing Fly Ash or Natural Pozzolans for use in Portland-Cement Concrete, 2004. [17] Annual Book of ASTM Standards, ASTM C151 Standard Test Method for Autoclave Expansion of Portland Cement, 2000.

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