This paper presents experimental behaviour of eccentrically loaded plain and steel fiber high strength rein-forced concrete and concrete-encased composite columns. In the experimental study, a total of 32 square sec-tion both reinforced concrete and composite column specimens were fabricated at 0, 0.5, 0.75 and 1.0%volume fractions of steel fiber contents to examine the effects of steel fibers on column behaviour. Besidesthis, the composite columns were constructed and tested using almost the same conditions with reinforcedconcrete columns to investigate the column experimental behaviour. The complete load−deflection behav-iour and strength of column specimens were obtained and the results were discussed in the study. In addi-tion, the column specimens were analysed based on a theoretical method considering the nonlinearbehaviour of the materials. The presented experimental study indicates that the inclusion of steel fibers inthe range 0.75 to 1.0% volume fraction improves confinement and ductility features of high strength rein-forced concrete and composite columns significantly.
High strength concrete has been increasingly used in the construc-tion of structures, such as high-rise buildings, bridges, piles etc. Highstrength concrete offers many significant benefits in terms of strength,durability, and modulus of elasticity. However, it is widely believedthat high strength concrete exhibits brittle behaviour under compres-sion. The inclusion of steel fibers into high strength concrete definitelyimproves confinement, ductility and deformability of concrete. Severalexperimental and analytical studies were carried out to describe themechanical behaviour of steel fiber high strength concrete. Fanellaand Naaman [1] studied on the stress–strain properties of fiber rein-forced concrete and an analytical relationship was proposed to predictthe complete stress–strain curve of fiber reinforced mortar in compres-sion. Ezeldin and Balaguru [2] presented experimental stress–strainbehaviour of fiber reinforced concrete with compressive strength rang-ing from 35 MPa to 85 MPa. An analytical expression was proposedto represent the complete stress–strain curve of steel fiber reinforcedconcrete. Hsu and Hsu [3] conducted an experimental research to deter-mine the complete stress–strain relationship of steel fiber high strengthreinforced concrete under compression and empirical stress–strain equa-tions were proposed in the study. Taerwe and Van Gysel [4] presented
experimental and analytical researches to describe the realistic stress–strain curve for high strengthfiber concrete.Maalej and Lok [5] examinedtheflexural behaviour of steelfiber concrete. Nataraja et al. [6] proposed asimple analytical model to generate both ascending and descending por-tions of the stress–strain curve of steel fiber reinforced concrete. Rameshet al. [7] tested prism specimens to study the behaviour of confined steelfiber reinforced concrete and an analytical model was suggested to pre-dict the stress–strain behaviour of confined fiber reinforced concrete.Lim and Nawy [8] investigated the mechanical characteristics of plainand steel fiber reinforced high strength concrete under uniaxial and biax-ial loading conditions. Thomas and Ramaswamy [9] reported an experi-mental program and analytical assessments of the influence of additionoffibers on themechanical properties of concrete. Empirical relationshipswere developed to assess the strength properties of steel fiber reinforcedconcrete. Bencardino et al. [10] researched the stress–strain behaviour ofsteel fiber reinforced concrete in compression and the validity of themodels proposed in literature in defining the post peak behaviour ofsteel fiber concrete was examined.
Ductility and confinement are very important features for highstrength concrete column members especially in the seismically ac-tive regions. Therefore, using steel fibers into high strength concretecolumns has become popular. It is significant to describe the behav-iour of such members for analysis and design. Ganesan and RamanaMurthy [11] conducted experimental research to describe the behav-iour of steel fiber reinforced concrete columns under axial load. Hsuet al. [12] and Foster and Attard [13] tested square section steelfiber high strength reinforced concrete columns to investigate the ef-fects of steel fibers on the strength and ductility of columns. Foster
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[14] proposed a model to determine the quantity of effective fibersto ensure a good level of ductility for high strength reinforced con-crete columns. Tokgoz [15] conducted experimental study to describethe biaxially loaded steel fiber high strength reinforced concretecolumns.
In addition to reinforced concrete columns, it is known that com-posite columns with symmetrical and unsymmetrical cross sectionshave been employed in high rise buildings, bridges and earthquakeresistant structures. Composite columns provide effective stiffnessand load carrying capacity and also prevent local buckling effect dueto the contribution of structural steel material. Many experimentaland theoretical studies were carried out to determine the behaviourof composite columns in the past years. Research outcomes of themost of these works were notified in the previous studies [16,17]. Ad-ditional theoretical researches to determine the behaviour of plainconcrete composite columns using finite element method were alsoperformed by Liang [18], Ellobody et al. [19], Ellobody and Young[20] and Young and Ellobody [21]. In these studies, the suggested the-oretical methods were verified with design rules [22–24]. Apart fromthe highlighted studies, Tokgoz and Dundar [25] examined the influ-ence of steel fibers on the experimental behaviour of L-shaped sectionhigh strength reinforced concrete and composite columns. Very limit-ed experimental data mainly on steel fiber high strength compositecolumns under eccentric compression is available. Thus, further ex-perimental studies are necessary to better describe the behaviour ofsteel fiber high strength composite columns for rational design ofconcrete structures.
This research study focuses primarily on the determination of thestructural behaviour of steel fiber high strength concrete-encasedcomposite columns. Therefore, a total of 32 square section plain and
Fig. 2. The typical stress−strain diagrams of plain and steel fiber concrete.
100 S. Tokgoz et al. / Journal of Constructional Steel Research 74 (2012) 98–107
steel fiber high strength reinforced concrete and similar compositecolumn specimens were constructed with using different steel fibercontents. The specimens were tested under biaxial bending and short-term axial compression in order to investigate the column strengthcapacities and to examine the effects of steel fibers on the experimentalbehaviour of columns. In addition, the column specimens were ana-lysed based on a theoretical method [15,17] to predict the ultimatestrength capacities and to attain complete load–deflection curves. Agood degree of correlation has been achieved between the test andthe theoretical results in the study.
2. Experimental program
2.1. Test specimens
The experimental work includes a total of 32 square section highstrength reinforced concrete and composite columns. The specimenswere fabricated using different portions of concrete mixtures at 0,0.5, 0.75 and 1.0% volume fractions of steel fibers to examine theinfluence of steel fibers on both types of columns. Eight specimens
Table 2Experimental properties of the column specimens.
Specimen no. fc (MPa) L/r (r=0.3B) ex (mm) ey (mm)
were short reinforced concrete columns (SC-0,I,II,III) and short com-posite columns (SCC-0,I,II,III). The other specimens were designedas slender reinforced concrete columns (C1-0,I,II,III, C2-0,I,II,III, C3-0,I,II,III) and concrete-encased composite columns (CC1-0,I,II,III, CC2-0,I,II,III, CC3-0,I,II,III). The short and slender column specimens were850 mm and 1300 mm in length, respectively. The cross section de-tails of the column specimens are presented in Fig. 1. According tothe ACI Standard 318-08 [24], it shall be permitted to neglect the ef-fects of slenderness when the ratio of column effective length to theradius of gyration of cross section of compression member (L/r) isless than 22. Here, the radius of gyration of cross section is approxi-mately taken as 0.3B based on gross section. Therefore, the value ofthe L/r ratio of 22.67 for the series of SC and SCC columns almost rep-resents the lower limit for slenderness effect and these specimenshave been considered as short columns in this study.
The reinforced concrete and composite column specimens hadconsisted of four 8 mm in diameter longitudinal deformed bars locat-ed at each corner of the section. The composite columns were fabri-cated with considering T-shaped structural steel material (Fig. 1).The ratio of structural steel section area to the gross concrete areaof the cross section was 0.0304. The yield strength of the longitudinalbar and the structural steel were 550 MPa and 235 MPa, respectively.The lateral reinforcements were designed at 80 mm and 100 mm
Fig. 4. (a,b) The typical failure mode of the column specimens.
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spacing for short and slender column specimens, respectively. Thelateral reinforcements were bent into 135° hooks at the ends. Theheavily reinforced brackets were designed at both ends of the columnspecimens to prevent any local failures of the end zones.
The materials of the column specimens consisted of Portland CEMI 42.5 R type cement content, maximum size of 16 mm well dry andclean aggregate, tap water and super plasticizer to maintain goodworkability. The end hooked RC 65/35 BN-type steel fibers wereused and randomly distributed in high strength concrete mixture.The fibers had a length of 35 mm, diameter of 0.55 mm, aspect ratioof 64, and density of 7850 kg/m3. Concrete composition of the rein-forced concrete and concrete-encased composite column specimensare given in Table 1.
All the column specimens were cast horizontally inside a steelformwork in the Structural Laboratory at Cukurova University in
Adana, Turkey. The specimens were compacted using hand-heldmechanical vibrator to vibrate and compact the concrete material.Three control concrete cylinder specimens (150 mm in diameter and300 mm in length) were cast from each concrete mixture. The cylinderspecimens were cured under the same condition of the columnspecimens.
The control cylinder specimens were tested in axial compressionon the day of column test to determine the main concrete compres-sive strength and to attain complete stress−strain relationship. In ad-dition, the mechanical behaviour of plain and steel fiber high strengthconcrete has been examined. The typical experimental concrete stress−strain diagrams containing various steel fiber contents are shown inFig. 2. The column specimen features of the concrete compressivestrength (fc), approximate slenderness ratio (L/r) and the load eccen-tricity (ex,ey) are given in Table 2. The average concrete compressive
Table 3Ultimate strength results of the column specimens.
Specimen no. Ntest (kN) Nu (kN) Mux (kN.cm) Muy (kN.cm) Nu/Ntest
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strength of reinforced concrete and composite column specimensvaried from 50.48 to 76.87 MPa. The eccentricities for composite col-umns have been given with respect to the plastic center of the crosssection [16]. The reinforced concrete and composite column speci-mens (e.g., C1-0,I,II,III and CC1-0,I,II,III) were constructed and testedusing almost the same experimental conditions in order to comparetheir experimental results (Tables 1 and 2).
The stress−strain relations indicate that the inclusion of steel fi-bers has significantly effect on mechanical behaviour of high strengthconcrete material. Considerable increase in strain at peak stress hasbeen observed. Beneficial effect is noticed especially in the descendingbranch of the stress–strain curve (Fig. 2). Higher values of ultimatefiber strain have been achieved by increasing steel fiber content.But, the stress−strain curves are exposed that steel fibers have no con-siderable effect on the concrete compressive strength and modulus ofelasticity of concrete [25].
2.2. Test setup and instrumentation
The column specimens were tested with pinned conditions at bothends under short-term axial load and biaxial bending. The columnswere loaded vertically using universal testing machine in the Struc-tural Laboratory at Cukurova University. A data acquisition systemwas used to collect the digital measurements during the tests. Linearvariable differential transducers were instrumented to the columnspecimens to measure the lateral deflections in both principal direc-tions and axial deformations at the most heavily compressed region.Besides this, a 500 kN capacity load cell was used in order to measurethe applied axial load. The transducers and the load cell were calibrat-ed before they were used in this test study. The typical test setup andinstrumentation are illustrated in Fig. 3.
The column specimens were tested in a vertical position subjectedto monotonically increasing axial load at a rate of 1 kN/s. The axialload was applied to the column specimens with different eccentricityvalues. During the tests, the lateral deflections in both principal direc-tions were recorded at each load increment by using the data acquisi-tion system. The column specimens were loaded from zero load up tofailure.
2.3. Test results and discussion
The plain and steel fiber column specimens initially behaved in anearly similar manner. First cracks generally appeared at almostclose to midheight on the tension region of columns. As the load in-creased, it was seen that the existing cracks propagated and new flex-ural cracks appeared before reaching the ultimate load. These tensilecracks occurred along the column length. Cover spalling started at thecompressed region of the section especially for plain high strengthconcrete columns. After that, for plain concrete columns, a suddenloss of strength was measured, concrete cover spalled off and thesecolumns failed suddenly and explosively manner owing to the brittle-ness behaviour of high strength concrete material. Besides this, buck-ling of longitudinal reinforcement was observed. On the other hand, itwas seen from the tested steel fiber columns that cover spalling wasprevented by addition of steel fibers and significant deformabilitywas observed. The crack length for both steel fiber high strength rein-forced concrete and composite columns occurred shorter than plainconcrete columns.
The column specimens including 0.5% volume fraction of steel fi-bers exhibited moderate ductile behaviour. On the other hand, theremaining columns had 0.75 and 1.0% volume fractions of steel fibersbehaved significantly more ductile. These columns exhibited suffi-cient degree of deformation beyond the peak load. Therefore, the ex-plosive type of failure was prohibited by adding steel fibers and theload carrying capacity dropped more slowly for both reinforced con-crete and composite column specimens. The typical failure mode of
the column specimens is illustrated in Fig. 4(a,b). The ultimate loadcapacity of composite column specimens is significantly influencedby load eccentricity, concrete compressive strength, structural steeland slenderness effect as well as high strength reinforced concretecolumns. The ultimate strength results of columns were recordedhigher at low eccentricity. In addition, the strength capacity of com-posite columns were significantly higher than that of reinforcedconcrete columns resulted from the contribution of structural steel(Tables 2 and 3). Moreover, the composite columns behaved more re-sist and less buckled than that of reinforced concrete columns.
It was seen that no significant lateral deformation was recordedfor short columns, but the lateral displacements were considerablefor slender columns. The slender columns started to buckle at a loadlevel less than failure load due to the slenderness effect. The typicalcolumn experimental load−deflection diagrams for x axis (Exp-XAxis) and y axis (Exp-Y Axis) are presented in Fig. 5(a,b). The dia-grams indicate that the inclusion of steel fibers into high strengthconcrete improves the ductility and deformability of reinforced con-crete and composite columns. No significant distinction from zeroload to peak load has been obtained for plain and steel fiber columns.It is concluded that steel fiber does not significantly affect the columnultimate load capacity (Fig. 5(a,b)).
The experimental study indicates that the addition of 0.75 and 1.0%volume fractions of steel fibers has provided significant confinement,ductility and deformability for high strength reinforced concrete andcomposite columns. However, loss of workability of concrete has startedto appear at 1.0% volume fraction of steel fibers especially for steel fiberhigh strength composite columns. Thus, it is concluded that the inclu-sion of steel fibers in the range 0.75 to 1.0% volume fraction has givenreasonable effect on the behaviour of high strength both reinforced con-crete and composite columns.
Photographs of all the short and slender column specimens tested inthis study are shown in Fig. 6(a,b). The modes of failure exhibited that
Fig. 5. (a,b) The typical experimental load−deflection curves of the column specimens.
103S. Tokgoz et al. / Journal of Constructional Steel Research 74 (2012) 98–107
most of the tested columns crushed near themidheight of the specimenindicating a typical compression failure of the column in compression.More critical local buckling and crushing were observed especially for
(a)
(b)
Fig. 6. (a,b) Column spe
slender plain high strength reinforced concrete and also compositecolumns than those of short columns. The failure modes designate thatthis type of failure has been reduced by inclusion of steel fibers.
cimens after failure.
104 S. Tokgoz et al. / Journal of Constructional Steel Research 74 (2012) 98–107
Additionally, the results of the effects of steel fibers on the exper-imental behaviour of plain and steel fiber high strength reinforcedconcrete columns and also L-shaped section reinforced concrete andcomposite columns have been reported in the previous works [15,25].
3. Analysis method
The analysis of eccentrically loaded plain and steel fiber reinforcedconcrete and composite columns has been previously studied by Tok-goz [15] and Tokgoz and Dundar [17]. In the proposed method, thenonlinear stress−strain relation can be used for the materials andslenderness effect is taken into account. The proposed analysis meth-od is based on the following assumptions:
(i) Plane sections remain plane before and after bending.(ii) Empirical expressions to represent the stress−strain relations
of plain and steel fiber high strength concrete suggested byHsu and Hsu [3] were used for the compression zone of thecolumn member.
(iii) Elastic−perfectly plastic relation was assumed for the steelmaterials.
(iv) Perfect bond exists between concrete and steel.(v) The effects of creep and any tensile stresses due to shrinkage
are ignored.(vi) Axial and shear deformation effects are neglected.
A biaxially loaded composite column cross section and the typicalstress and strain distribution are shown in Fig. 7. The proposed anal-ysis procedure has taken into account the stress–strain relationshipsof the materials. Thus, the compression zone of the concrete sectionand entire section of structural steel are divided into segmental sub-divisions parallel to the neutral axis. The stress resultants of the con-crete and structural steel material have been calculated in the centreof each segment [16]. The centroidal strain value at each segment ofthe cross section can be expressed as a linear strain relationshipbased on the assumption that plane section remains plane duringbending. Then, the stress resultants of the members can be obtainedby using the assumed stress–strain relationships of the materials[15,17].
y
As
Structural steel
PC
xpc
N
ex
ey
ypc
a
c
Fig. 7. Composite column section und
The basic equations of equilibrium for the axial load N, and thebending moments Mx and My are determined in terms of the stressresultants as follows:
N ¼X
AcσcþX
Atσ tþX
Asσs ð1Þ
Mx¼X
Acσc ycþX
Atσ t ytþX
Asσsys ð2Þ
My¼X
Acσc xcþX
Atσt xtþX
Asσsxs ð3Þ
where Ac, At and As are the elemental area of concrete segment, ele-mental area of structural steel segment and area of reinforcing steelbar, respectively; σc, σt and σs are the concrete stress, structuralsteel stress and reinforcing steel stress, respectively; (xc, yc), (xt, yt)and (xs, ys) indicate the distance between, respectively, the centreof elemental area of concrete, the centre of elemental area of structur-al steel and reinforcing steel bar, and the plastic centre in x–y plane.
The slenderness effect is taken into account by using the MomentMagnification Method recommended by ACI 318-08 Building Code[24]. In the essence of analysis, the primary moments are magnifiedwith the moment magnification factor (δ). The precise analysis algo-rithm to determine the ultimate strength and load−deformation be-haviour of reinforced concrete and composite columns can be attainedfrom References [15,17]. In the study, a computer programhas been de-veloped to perform the analysis procedure of biaxially loaded both shortand slender plain and steel fiber high strength reinforced concrete andcomposite columns.
4. Comparison of experimental and theoretical results
The short and slender reinforced concrete and composite columnspecimens with and without steel fibers were analysed based on theproposed theoretical method [15,17] for the prediction of ultimatestrength capacities and load−deflection curves. The nonlinearstress–strain relations were considered for plain and steel fiber highstrength concrete materials [3,12]. Besides this, elastic–perfectly
x
NA
Strain
Stress
εc
h
σc
εs
er axial load and biaxial bending.
105S. Tokgoz et al. / Journal of Constructional Steel Research 74 (2012) 98–107
plastic behaviour was assumed for reinforcing steel bars and structur-al steel in the analysis.
The experimental results, computed theoretical strength capaci-ties and comparative results of the predicted load to test load areshown in Table 3.
A good degree of correlation has been achieved between the testand the analysis results for most of the column specimens (Table 3).The values of predicted load to test load ratio (Nu/Ntest) have beencomputed below 0.90 for a few specimens. This is due to gain a littlehigher experimental ultimate strength than expected. In the study,the average value of predicted load to test load has been obtained0.938. By comparing the experimental results of columns constructedand tested using the same experimental conditions, the addition ofvarious amounts of steel fibers has no significant effect on ultimatestrength capacity of both reinforced concrete and composite columnspecimens (Table 3).
The theoretical load−deflection curves for x axis (Theo-X Axis)and y axis (Theo-Y Axis) have been obtained using the developedcomputer program. The typical experimental and theoretical load−deflection curves of plain and steel fiber high strength reinforcedconcrete and composite columns are presented in Fig. 8(a−f). Thediagrams have been found to be in good agreement. It is shown inthe diagrams that the addition of steel fibers has considerable effect
Load-Deflecti
0
50
100
150
200
250
Deflec
Loa
d (k
N)
(a)
Load-Deflecti
0
50
100
150
200
250
Deflec
Loa
d (k
N)
(b)
Load-Deflect
0
50
100
150
200
Defle
Loa
d (k
N)
(c)
0 2 4 6 8
0 2 4 6 8
0 2 4 6 8
Fig. 8. (a–f) Experimental and theoretical load−
on the deformability and ductility features of column specimens. Inaddition, the typical experimental and theoretical load−axial straincurves are shown in Fig. 9. The comparative results indicate that theuse of the stress−strain relation has given reasonable accuracy to de-termine the load−deflection behaviour of plain and steel fiber highstrength reinforced concrete and composite columns.
5. Conclusions
A total of 32 both short and slender reinforced concrete and simi-lar composite column specimens including different volume fractionof steel fibers have been tested in this study. The following conclu-sions can be drawn based on the experimental results of the study:
(1) Adding steel fibers into high strength concrete definitely im-proves mechanical behaviour of composite columns. Crushingof concrete core, cover spalling, and buckling of the compressedreinforcing bars have been prevented by inclusion of steel fibers.
(2) Local buckling is more extensive especially for slender plain highstrength reinforced concrete columns than that of short columns.More structural stiffness has been provided due to the presenceof shaped steel in composite columns. It is observed that buckling
on Curve (C1-I)
tion (mm)
Exp-X AxisExp-Y AxisTheo- X&Y Axes
on Curve (C2-II)
tion (mm)
Exp-X AxisExp-Y AxisTheo- X&Y Axes
ion Curve (C3-III)
ction (mm)
Exp-X AxisExp-Y AxisTheo- X&Y Axes
10 12 14 16 18
10 12 14 16 18
10 12 14 16 18 20
deflection curves of the column specimens.
Load-Deflection Curve (CC1-I)
0
50
100
150
200
250
Deflection (mm)
Loa
d (k
N)
Exp-X AxisExp-Y AxisTheo-X AxisTheo-Y Axis
(d)
Load-Deflection Curve (CC2-II)
0
50
100
150
200
250
Deflection (mm)
Loa
d (k
N)
Exp-X AxisExp-Y AxisTheo- X AxisTheo- Y Axis
(e)
Load-Deflection Curve (CC3-III)
0
50
100
150
200
250
Deflection (mm)
Loa
d (k
N)
Exp-X AxisExp-Y AxisTheo-X AxisTheo-Y Axis
(f)
0 2 4 6 8 10 12 14 16 18
0 2 4 6 8 10 12 14 16
0 2 4 6 8 10 12 14 16 18 20
Fig. 8 (continued)
Load-Axial Strain Relation (CC3-III)
00 0.001 0.002 0.003 0.004 0.005 0.006
50
100
150
200
250
Axial Strain
Loa
d (k
N)
Experimental
Theoretical
Fig. 9. The typical experimental and theoretical load−axial strain diagrams.
106 S. Tokgoz et al. / Journal of Constructional Steel Research 74 (2012) 98–107
failure has been reduced by inclusion of steel fibers for both rein-forced concrete and composite columns.
(3) The slenderness and load eccentricity have significant effects onthe load carrying capacity of reinforced concrete and compositecolumns. On the other hand, steel fibers have no considerableeffect on modulus of elasticity of concrete and column ultimatestrength capacity.
(4) The experimental study reveals that the addition of steelfibers at a volume fraction in the range 0.75 to 1.0% signifi-cantly improves the confinement, ductility and deformabilityof high strength both reinforced concrete and compositecolumns.
(5) The tested columns have been analyzed for the prediction ofultimate strength capacities and complete load−deflectioncurves. Good degree of accuracy has been obtained betweenthe test and the theoretical results of plain and steel fiberhigh strength reinforced concrete and composite columns.
6. Notations
a horizontal distance between the origin of the x–y axis sys-tem and the neutral axis;
Ac elemental area of concrete segment;As area of reinforcing steel bar;At elemental area of structural steel segment;B dimension of section in the stability direction;c vertical distance between the origin of the x–y axis system
and the neutral axis;ex eccentricity of column in x direction;ey eccentricity of column in y direction;fc peak stress of concrete;h distance from the maximum compressive fiber to the neu-
tral axis;
107S. Tokgoz et al. / Journal of Constructional Steel Research 74 (2012) 98–107
L column length;Mux theoretical bending moment about x–axis;Muy theoretical bending moment about y-axis;Mx bending moment about x-axis;My bending moment about y-axis;N axial load;NA neutral axis;Ntest experimental axial load;Nu theoretical ultimate axial load;PC plastic center;r radius of gyration of cross section;s lateral reinforcement spacing;x, y coordinates of cross section point in x–y plane;xpc, ypc plastic centre coordinates of cross section;xc, yc distance between the centre of elemental area of concrete
and the plastic centre in x–y plane;xs, ys distance between reinforcing steel bar and the plastic centre
in x–y plane;xt, yt distance between the centre of elemental area of structural
steel and the plastic centre in x–y planeεc concrete compressive strain;εs steel strain;σc concrete stress;σt structural steel stress;σs reinforcing steel stress;δ moment magnification factor.
Acknowledgements
The research described in this paper was funded by the Scientificand Technological Research Council of Turkey (TUBITAK, Project No.108M511). The authors would like to thank to BEKAERT Izmit SteelCord Industry and Trade Co., and CIMSA Cement Industry and TradeCo. The assistance of Cukurova University laboratory staffs is alsoacknowledged.
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