Short Communication

Utilisation of Turkish fly ashes in cost effective HVFA concrete production

Burak Felekoglu

Civil Engineering Department, Dokuz Eylul University, 35160 Izmir, Turkey

Received 24 November 2005; received in revised form 16 January 2006; accepted 24 January 2006

Available online 24 February 2006

Abstract

High-volume fly ash (HVFA) concrete is an economical and durable option for structural as well as general concreting purposes, if properly

controlled ashes are employed. The aim of this study was to investigate the possibility of the use of three types of Turkish fly ashes from different

sources in cost effective high-volume fly ash concrete production. For this purpose HVFA concrete mixtures were prepared by substituting 40, 50,

60 and 70% of cement by fly ash. The mechanical properties and material costs of mixtures were compared with conventional concrete at the same

strength grade at 28 days. It should be noted that as an additional benefit, the long-term strength development and durability advantageous of

HVFA concrete is not taken into consideration in cost analysis. Results showed that for structural applications a technically suitable and cost

effective HVFA concrete can only be produced by using the fly ashes within the limits of specific chemical and physical properties. It may be

possible to use other fly ashes with rehabilitation and pre-process, which may reduce the economical feasibility of fly ash usage.

q 2006 Elsevier Ltd. All rights reserved.

Keywords: Fly ash; Admixtures; Compressive strength

1. Introduction

Fly ash, a principal by-product of the coal-fired power

plants, is well accepted as a pozzolanic material that may be

used either as a component of blended Portland cements or as a

mineral admixture in concrete. According to ASTM C 618 [1]

fly ashes can be classified into two groups: Class C fly ash,

which is typically light or tan colored and is produced from

burning lignite or sub-bituminous coal, and Class F fly ash,

which is dark grey and is produced from burning anthracite or

bituminous coal. In commercial practice, the dosage of fly ash

is limited to 15–20% by mass of the total cementitious

material. Usually, this amount has a beneficial effect on the

workability and cost economy of concrete but it may not be

enough to sufficiently improve the durability to sulfate attack,

alkali–silica expansion, and thermal cracking. For this purpose,

larger amounts of fly ash, on the order of 25–35% are being

used [2]. Concrete mixtures containing more than 40–50% fly

ash by mass of the cementitious material can be defined as

high-volume fly ash (HVFA) concrete. Because there is a direct

link between durability and resource productivity, the

0016-2361/$ - see front matter q 2006 Elsevier Ltd. All rights reserved.

doi:10.1016/j.fuel.2006.01.019

E-mail address: burak.felekoglu@deu.edu.tr

increasing use of high-volume fly ash concrete will help to

enhance the sustainability of the concrete industry.

The characteristics defining a HVFA concrete mixture are

not strictly accepted rules, mostly depends on the fly ash used.

These are principally as follows:

1. Minimum of 50% of fly ash by mass of the cementitious

materials must be maintained. Low water content,

(generally less than 130 kg/m3) and low cement content,

(generally no more than 200 kg/m3) is desirable.

2. For concrete mixtures with specified 28-day compressive

strength of 30 MPa or higher, slumps O150 mm, and

water-to-cementitious materials ratio of the order of 0.30,

the use of high-range water-reducing admixtures (super-

plasticizers) is mandatory.

3. For concrete exposed to freezing and thawing environ-

ments, the use of an air-entraining admixture resulting in

adequate air-void spacing factor is mandatory.

4. For concrete mixtures with slumps less than 150 mm and

28-day compressive strength of less than 30 MPa, HVFA

concrete mixtures with a water-to-cementitious materials

ratio of the order of 0.40 may be used without

superplasticizers.

The properties of HVFA concretes, when compared to

conventional Portland cement concrete, are summarized by

Mehta [3] as follows:

Fuel 85 (2006) 1944–1949

www.fuelfirst.com

Table 1

The chemical, physical and mechanical properties of cement

Chemical

composition

Percentage Physical and mechanical properties

SiO2 20.05 Specific gravity 3.12

Al2O3 5.92 Blaine SSA (m2/kg) 369

Fe2O3 2.54 90 mm sieve passing (%) 99.5

CaO 63.91 32 mm sieve passing (%) 86.5

MgO 0.94 Initial setting time

(hh:mm)

02:10

Na2O 0.26 Final setting time

(hh:mm)

02:55

K2O 0.85 2 days comp. str. (MPa) 23.6

SO3 2.65 7 days comp. str. (MPa) 39.7

Loss of

ignition

2.90 28 days comp. str. (MPa) 48.5

Immeasurable 0.97

Free CaO 1.35

C3S 56.80

C2S 14.64

C3A 11.40

C4AF 7.73

B. Felekoglu / Fuel 85 (2006) 1944–1949 1945

1. A high-grade fly ash can act as a water reducer in concrete

production depending on the particle size distribution,

surface characteristics and morphology. According to

Mehta [4], the fly ashes with small size and glassy texture

make it possible to reduce the amount of water required to a

given consistency. However, the fineness of cement

substituted with fly ash should also be taken into

consideration. Another factor affecting the workability

improvement capacity of fly ash is the unburned carbon

content. Large amounts of carbon in fly ash are harmful for

concrete production because the cellular particles of carbon

tend to increase the water requirement and the admixture

requirement for a specified consistency and/or air content

[5]. High-grade fly ashes at high-volumes in concrete

usually improve flowability, pumpability, compactability

and finishability. High-volume fly ash concrete does not

required any special efforts in terms of mixing and placing

and can be mixed, transported and placed using conven-

tional means. The improvements in cohesiveness and

finishability are particularly valuable in lean concretes or

those made with aggregates deficient in fines [5] especially

at long distance pumping.

2. Slower setting time, which will have a corresponding effect

on the jointcutting and lower power-finishing times for

slabs.

3. Early-strength up to 7 days, which can be accelerated with

suitable changes in the mix design when earlier removal of

formwork or early structural loading is desired. As

previously mentioned, HVFA concrete requires minimum

of 50% of fly ash by mass of the cementitious materials.

Such high proportions of fly ash are not readily accepted by

the construction industry due to a slower rate of strength

development at early age. The high-volume fly ash concrete

system overcomes the problems of low early strength to a

great extent through a drastic reduction in the water–

cementitious materials ratio by using a combination of

methods, such as taking advantage of the superplasticizing

effect of fly ash when used in a large volume, the use of a

chemical superplasticizer, and a judicious aggregate

grading.

4. Much later strength gain between 28 and 90 days or more.

(With HVFA concrete mixtures, the strength enhancement

between 7 and 90 days often exceeds 100%, therefore, it is

unnecessary to overdesign them with respect to a given

specified strength).

5. Superior dimensional stability and resistance to cracking

from thermal shrinkage, autogenous shrinkage, and drying

shrinkage. In unprotected concrete, a higher tendency for

plastic shrinkage cracking should be expected.

6. After 3–6 months of curing, much higher electrical

resistivity, and resistance to chloride ion penetration.

7. Better cost economy due to lower material cost and highly

favorable lifecycle cost.

8. Superior environmental friendliness due to ecological

disposal of large quantities of fly ash, reduced carbon-

dioxide emissions, and enhancement of resource

productivity of the concrete construction.

9. If properly cured high-volume concrete products are very

homogenous in microstructure, virtually crack-free, and

highly durable. Very high durability to the reinforcement

corrosion, alkali–silica expansion, and sulfate attack can be

obtained.

The technology of HVFA concrete is particularly significant

for Turkey, where, given the limited amount of financial and

natural resources, the huge demand for concrete needed for

infrastructure and housing can be easily met in a cost effective

and ecological manner. As for today, the annual production of

fly ash in 11 power plants in Turkey is more than 20 million

tonnes. In particular, due to the energy demand, the production

rate of fly ash is expected to increase in the future.

Bayat and Turker et al. [6] made an extensive research on

the characterization of Turkish fly ashes from the view point of

mineralogical, morphological, physical and chemical proper-

ties. It is not possible to make a generalization for all fly ashes

due to differences between their characteristics [7]. The

chemical composition (reactive silica, free lime, unburned

carbon and sulfur content), physical properties (shape

morphology, surface texture, particle size distribution, fine-

ness), and pozzolanic activity of fly ashes are responsible for

the good or bad performance in HVFA concrete production.

These factors are mainly related with the coal burned and

burning process in plant. It is not possible or hard to change

these factors. It is only possible to use these inappropriate ashes

by pre-processing (by using physical separation and chemical

filtration techniques). However, these kinds of rehabilitations

usually reduce or omit the economical value of these by-

products.

The aim of this study was to investigate the possibility of the

use of three Turkish fly ashes from different sources in cost

effective HVFA concrete production. For this purpose HVFA

mixtures were prepared and the mechanical properties and

Table 2

The physical and chemical properties of fly ashes

Chemical composition Soma Kangal Yatagan

SiO2 (S) 42.14 33.14 52.05

Al2O3 (A) 19.38 14.70 23.69

Fe2O3 (F) 4.64 4.32 5.94

SCACF 66.16 52.16 81.68

CaO 26.96 35.18 10.60

MgO 1.78 1.18 2.38

SO3 2.43 7.85 1.45

K2O 1.13 0.92 2.51

Na2O 0.34 0.58 0.90

Na2O equiv. 1.09 1.19 2.56

Loss of ignition 1.34 2.15 1.34

Free CaO 4.34 6.35 1.20

Reactive silicous 32.03 28.85 26.5

Reactive CaO 15.90 25.60 9.98

Physical properties

Density (g/cm3) 2.20 2.24 2.12

Dry loose unit weight (g/cm3) 0.67 0.81 0.88

Amount retained on 90 mm

sieve (%)

14 28 21

Amount retained on 45 mm

sieve (%) Pozzolanic activity

(TS EN 450 [9])

23 52 38

(%) 7D 73 72 68

(%) 28D 95 78 75

B. Felekoglu / Fuel 85 (2006) 1944–19491946

material costs of mixtures were compared with conventional

concrete at the same strength grade.

2. Experimental

2.1. Materials

Ordinary Portland Cement (CEM I 42.5) conforming to TS

EN 197-1 [8] was used. The chemical, physical and mechanical

properties of cement are listed in Table 1. Three different fly

ashes of power plants (Soma, Yatagan and Kangal) from

eastern and western lignite and bituminous coal fields in

Turkey were used in this study. According to ASTM C 618 [1]

fly ashes from Soma and Kangal can be classified as type C and

Table 3

The mixture proportions of HVFA concretes

Mix code Cement

(kg/m3)

Fly ash

(kg/m3)

Coarse aggregate

(15–25 mm)

(kg/m3)

Coarse ag

(5–15 mm

(kg/m3)

S40 210 140 434 647

S50 175 175 428 638

S60 140 210 424 631

S70 105 245 418 623

K40 210 140 430 641

K50 175 175 423 630

K60 140 210 417 622

K70 105 245 409 609

Y40 210 140 430 640

Y50 175 175 425 633

Y60 140 210 419 624

Y70 105 245 414 616

fly ash from Yatagan as type F. The physical and chemical

properties are given in Table 2. The pozzolanic activity of fly

ashes was determined by TS EN 450 [9] standard. According to

IS 3812—1981 [10] standard grade I, the minimum SiO2

content of fly ash should be higher than 35%. Kangal ash could

not fulfill this requirement. On the other hand, the minimum

SCFCA content should be higher than 70%. Only Yatagan

ash passed this limit. The maximum sulfur content should be

2.75% or lower. Kangal ash again failed for this provision. All

ashes passed the loss on ignition limit (12%). Total equivalent

alkali content of Yatagan ash was higher than the limit of 1.5%.

In summary, none of the ashes used fulfilled the limits of grade

I ash according to IS 3812—1981 [10] standard. However, it

should be noted that both of three ashes are still being used

in concrete mixtures at low replacement levels in the order of

10–20%. Crushed limestone aggregates with a maximum size

of 25 mm were used as coarse aggregates. The specific gravity

and water absorption of the aggregates were 2.72 and 2.70

and 0.28–0.39%, respectively. A natural river sand with

specific gravity of 2.63 and water absorption of 1.63% was

also employed. A uniform grading of aggregate mixture was

prepared. In order to improve the workability, a sulfonated

naphthalene formaldehyde based high-range water reducing

admixture confirming to ASTM C494 [11] Type G was used.

2.2. Mix proportions

In general, the mix proportions of HVFACs can be divided

into three strength classes as low, medium and high [3]. In this

classification the total cementitious material is achieved to

obtain higher strength grades. In this study medium strength

class is targeted and the total cementitious material was fixed

to 350 kg/m3. However, due to the different performance of

fly ashes in water demand very different strength grades were

obtained at similar replacement ratios. The fly ash was replaced

with 40, 50, 60 and 70% of each cement by weight,

respectively. The concrete mixtures were prepared in a

horizontal-axis mixer. Mixing time was about 3 min.

gregate

)

Fine

aggregate (kg/m3)

Water (kg/m3) Sp (kg/m3) W/(CCF)

ratio

817 135 6.8 0.39

806 141 6.8 0.40

798 143 6.8 0.41

787 148 6.8 0.42

809 148 6.8 0.42

796 156 6.8 0.44

785 163 6.8 0.47

770 168 6.8 0.48

809 140 6.8 0.40

800 143 6.8 0.41

788 148 6.8 0.42

778 151 6.8 0.43

0

10

20

30

40

50

60

70

0 20 40 60 80 100

time (days)

com

pres

sive

str

engt

h (M

Pa)

K40 K50K60 K70

Fig. 2. Compressive strength development of HVFA concretes with Kangal ash.

B. Felekoglu / Fuel 85 (2006) 1944–1949 1947

The mixtures were prepared with a slump value of 120G10 mm. Cubic specimens of 100 mm were used to determine

the compressive strength of concrete. Specimens were

compacted with a vibration table. The performance of

superplasticizers is also an important parameter in HVFA

concrete production [12]. For this reason the admixture content

was kept constant. In order to achieve the slump values, mixing

water was changed (Table 3).

3. Results and discussion

Generally, FA particles are spherical in shape, and

theoretically, this has a very positive effect on the water

requirement and workability of concrete mixtures [13].

However, all fly ashes used in this study increased the water

demand for the desired slump value. Depending of the fly ash

type, the magnitude of water demand varied. The highest water

demand was derived from Kangal ash. This behavior may be

attributed to the increasing carbon content (LOI%) and

differences between the specific gravity, particle shape and

surface texture of this ash from other ashes [14,15]. The water

content of Soma and Yatagan ashes were nearly the same at

replacement ratios of 70%. Compressive strength test results

indicate that, high-volume fly ash concrete with Soma ash is

more effective in strength gain with time (Figs. 1–3). Note that

the Kangal ash incorporated concrete mixture containing 70%

fly ash gave only 8 MPa strength at 91 days compared to

33 MPa for the 70% Soma ash incorporated mixture at the

same age. This result clearly showed that the use of appropriate

fly ash rather than any fly ash is vitally important. The bad

performance of Kangal ash at high-volumes of incorporation

can be attributed to low (SCFCA) pozzolanic activity, high

SO3 and high free CaO content. The latter is also potentially

detrimental to the long-term performance of HVFA concretes.

It is important to note that the 28 days pozzolanic activity of

Kangal ash was better than Yatagan ash. This unexpected result

can be attributed to the method of testing. As previously

mentioned Pozzolanic activity tests have been performed

according to TS EN 450 [9] standard. According to TS EN 450,

0

10

20

30

40

50

60

70

0 20 40 60 80 100

time (days)

com

pres

sive

str

engt

h (M

Pa)

S40 S50

S60 S70

Fig. 1. Compressive strength development of HVFA concretes with Soma ash.

the ratios of cement and fly ash to be tested are 75 and 25% by

weight, respectively. Tests have been performed on mortars

and the water content has been achieved to obtain the same

consistency. However, in case of HVFA concrete (in this

study), the minimum replacement ratio of cement with fly ash

was 40%. At higher replacement ratios the high unburned

carbon content (higher LOI%) (in particular Kangal ash) may

dramatically increase the water requirement of HVFA

concretes. For this reason the replacement ratio in pozzolanic

activity test should also be taken into consideration. This

phenomenon is also stated in TS EN 450. There is not a linear

relationship between the pozzolanic activities and water

requirements of fly ash incorporated concretes at different

replacement ratios. The change in water contents results with

different mechanical strengths.

With increasing amount of fly ash content, compressive

strength at all ages decreased. Soma ash showed the lowest

strength reduction. At 70% replacement ratio, the 91 days

compressive strength of this mixture was still higher than

30 MPa.

0

10

20

30

40

50

60

70

com

pres

sive

str

engt

h (M

Pa)

Y40 Y50

Y60 Y70

0 20 40 60 80 100

time (days)

Fig. 3. Compressive strength development of HVFA concretes with Yatagan ash.

Table 4

The mixture proportions of plain cement concretes

Mix code Cement

(kg/m3)

Fly ash

(kg/m3)

Coarse aggregate

(15–25 mm)

(kg/m3)

Coarse aggregate

(5–15 mm)

(kg/m3)

Fine aggregate

(kg/m3)

Water (kg/m3) Sp (kg/m3) W/(CCF)

ratio

C40 430 0 551 438 899 150 6.8 0.35

C50 380 0 560 450 912 158 6.8 0.42

C60 335 0 565 454 918 163 6.8 0.49

C70 300 0 570 462 930 174 6.8 0.58

0

10

20

30

40

50

60

70co

mpr

essi

ve s

tren

gth

(MP

a)

C40 C50

C60 C70

0 20 40 60 80 100

time (days)

Fig. 4. Compressive strength development of plain concretes without any ash.

B. Felekoglu / Fuel 85 (2006) 1944–19491948

In summary, the best fly ash was found as Soma ash, which

showed the minimum water demand for the desired slump.

Additionally, Soma ash incorporated mixtures gave the highest

compressive strength values at all replacement ratios. For

comparison purpose, normal concrete mixtures containing no

fly ash were produced at the same strength grade (at 91 days)

obtained from HVFA mixtures incorporating 40–70% Soma

ash, respectively. The slump values of these mixtures were also

kept constant (120G10 mm) by increasing mixing water

content. Mixtures containing only cement were labeled as

C40-70. The mix proportions are given in Table 4. Note that

the cement contents of concretes without fly ash could not be

kept constant. From Table 3 it can be seen that the cement

content of fly ash incorporated mixtures were between 210

Table 5

Unit cost of materials employed in HVFA concrete and normal concrete design

Material Cement Fly ash Coarse aggregate

(15–25 mm)

C

(

Unit cost (euro/kg) 0.061 0.012 0.001 0

Table 6

Total material cost of HVFA and normal concrete mixtures

Total material cost (euro/m3) S K

40 19.99 20.02

50 18.28 18.21

60 16.54 16.45

70 14.76 14.70

and 105 kg/m3. At these cement dosages without any additional

mineral additives it was not possible to obtain compressive

strength similar to Soma ash incorporated mixtures at 91 days.

In order to obtain high strength values similar to fly ash

incorporated mixtures, additional cement was mandatory. For

this reason the cement dosage of control mixtures were

increased up to 300–430 kg/m3 (Table 4). The cement dosages

and water contents were selected to obtain the targeted slump

values and the targeted strengths (that were similar to 91 days

strength of Soma ash incorporated mixtures). They were

obtained by some pre-tests with trial and error method. The

compressive strength development of control mixtures was

plotted in Fig. 4. It can be seen that the strength increase

beyond 28 days was negligible for control mixtures without

oarse aggregate

5–15 mm)

Fine aggregate Water Super plasticizer

.001 0.003 0.001 0.273

Y C

19.97 31.92

18.25 28.94

16.48 26.23

14.73 24.15

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

mat

eria

l cos

t (eu

ro/1

MP

a)

S40 S50 S60 S70 K40 K50 K60 K70 Y40 Y50 Y60 Y70 C40 C50 C60 C70

Fig. 5. The material cost comparison of HVFA and plain concretes for unit strength.

B. Felekoglu / Fuel 85 (2006) 1944–1949 1949

any fly ash incorporation. However, it is clear from Figs. 1–3

that, the pozzolanic reactivity (depending on the fly ash type

and incorporation amount) of fly ashes contributed to strength

beyond 28 days at different magnitudes.

An important advantage for increasing the market share of

HVFA concrete is the lower material cost caused by the

replacement of high-volumes of fly ash with cement. Tables 5

and 6 shows the local unit costs of materials used. Note that,

factors that change the overall cost of concrete production, i.e.

the transportation, handling and placement and quality control

were not taken into consideration. Only the material costs were

compared. However, there will be no change in method of

handling and placement when HVFA concrete is employed. So

no difference in other cost factors thought to be expected.

As can be seen in Table 6, the total material costs of all

HVFA mixes were lower than normal concrete mixes. The

difference seems to be enlarged if replacement ratios increased.

However, due to the differences in strength grade of mixes at

different ages, Table 6 is not enough to compare the cost

affectivity of HVFA concrete with traditional concrete. For this

reason the cost of unit compressive strength of all mixtures

were calculated. Due to the slower strength gain of fly ash

incorporated mixes, the strength of 91 days was used for this

calculation. Results were plotted in Fig. 5. It is clear that the

material cost of unit strength is a better parameter to compare

the cost effectivity. Although the total material cost of HVFA

concretes with Kangal ash was very low, the insufficient

mechanical performance of this ash increased the material

costs for unit strength. The material costs of unit strength of

normal concrete mixtures (series C) were 40–50% higher than

HVFA concretes with Soma and Yatagan ashes. It can be

concluded that depending on the strength grade targeted, cost

effective HVFA mixtures can be easily produced with

excessive amounts of Soma and Yatagan ashes.

4. Conclusions

The high-volume fly ash concrete (with fly ashes of

appropriate chemical and physical properties) offers a holistic

solution to the problem of meeting the increasing demands for

concrete in the future in a sustainable manner and at a reduced

or no additional cost, and at the same time, reducing the

environmental impact of two industries that are vital to

economic development namely the cement industry and the

coal-fired power industry. In this study, Soma ash showed the

best performance both in fresh and hardened state properties

and cost affectivity when compared with other ashes studied.

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