compression behaviour of spacer fabric

Fibers and Polymers 2009, Vol.10, No.1, 116-123 DOI 10.1007/s12221-009-0116-7

116

A Study on the Compression Behavior of Spacer Fabrics Designed forConcrete Applications

Diren M. Armakan* and Andreas Roye1

Textile Engineering Department, Ege University, Izmir, Turkey1Robatex GmbH, Würselen/Aachen, Germany

(Received June 26, 2008; Revised October 10, 2008; Accepted November 16, 2008)

Abstract: Spacer fabrics have been used in many areas varying from medical applications to protection applications. Espe-cially the three dimensional characteristic of spacer fabrics presents different opportunities for special applications. The com-pression resistant characteristic of spacer fabrics is one of their main properties. In this research the compression behaviour ofspacer fabrics designed for concrete applications has been investigated. The effects of some parameters such as spacer yarnmaterial, pattern and threading on the compression behaviour of spacer fabrics have been studied. According to the testresults it was found that the material, pattern and the threading of spacer yarns are important parameters for the compressioncharacteristics of spacer fabrics. It was also observed that the location angle of spacer yarn and the amount of the spacer yarnsinfluence the compression behaviour of spacer fabrics. Keywords: Spacer fabric, Compression resistance, Spacer yarn parameter, Textile reinforced concrete

Introduction

Spacer fabrics are three dimensional textile structures withversatile properties. Though spacer fabrics are nottechnologically new, they take more attentions in recentyears thanks to their special properties [1]. Spacer fabricscan be defined as a special type of 3D-textiles, with three-dimensional yarn architecture and three-dimensional textilearchitecture. The yarn architecture used in the definitionmeans the arrangement of yarns in the level of textile whiletextile architecture means the geometry of the textile [2,3].The location of yarns in the x, y and z axes, the spacer layerbetween outer surfaces, the production of three dimensionalstructures in one step, production possibility of load tailoredstructures and application possibility of technical fibersmake spacer fabrics ideal for functional applications [4].

Nowadays, spacer fabrics take attentions especially forconcrete applications [2,4-10]. In many cases cement basedmaterials are combined with reinforcements such as steel,types of fibers, etc. for optimizing their properties [10].However during last few years, examinations of concretestructures reinforced with fabrics showed that fabrics withan adequate geometry could improve the mechanicalperformance of cement composites due to the increasedfabric-cement bond by mechanical anchoring which isprovided by the structure of the fabric and the geometry ofthe yarn in the fabric [11-14]. As a special kind of fabrics,spacer fabrics present different advantages for concreteapplications as they provide reinforcement in the thirddirection and a defined positioning of the two outer layers[5]. The three dimensional construction of spacer fabricsleads to a three dimensional type of mesh which has theadvantage of providing an armature system that can be

easily placed in a mould and infiltrated to its full thicknessby a matrix in one step [6]. Furthermore they can also beused to increase both textile production and concreteelement production [8-10]. Therefore special spacer fabricswith additional components has been developed andproduced in some researches [2,5,7-10].

Compression can be defined as a decrease in intrinsicthickness with an appropriate increase in pressure. Intrinsicthickness is the thickness of the space occupied by a fabricsubjected to barely perceptible pressure [15]. The compressionproperty of 3D spacer fabrics which is one of their maincharacteristics is different from the conventional 2D textilesas they have thickness in the third dimension. Spacer fabricsprovide a stable structure due to the spacer yarns in theirstructures. However the effect of spacer fabric componentson the compression resistance of spacer fabrics is notcompletely known at the moment. The compressionresistance of spacer fabrics to be used in concrete structuresis also important in order to obtain stable spacer fabrics thatcan be handled easily during the manufacturing processessuch as concrete injection, handling, etc.. In this study thecompression resistant characteristics of spacer fabrics wasinvestigated on the basis of spacer yarns in their structure.The effects of spacer yarn related properties such as spaceryarn material, spacer yarn pattern and spacer yarn threadingon the compression resistance of spacer fabrics wereexamined and evaluated.

Structure of Spacer Fabrics Designed for Concrete Applications

In this study warp knitted spacer fabrics designed forconcrete applications are investigated. This special textilestructure varies from conventional warp knitted spacerfabrics as it contains additional components. Furthermore*Corresponding author: [email protected]

Investigation of Compression Behavior of Spacer Fabrics Fibers and Polymers 2009, Vol.10, No.1 117

these structures are usually produced with technical fiberssuch as glass, carbon, so on. The additional components inthe spacer fabric construction are 0 o and 90 o yarns. The 0 o

yarns in the warp direction are inserted into the stitches andassembled together with the 90 o yarns in the weft direction.By this way a grid net like structure for the concreteapplications can be produced. Additionally two differentkinds of spacer yarns can be inserted to the structure as themachine concept allows the different movement of spaceryarn’s guide bars. The view of the spacer fabric and thecomponents inside the structure are shown in Figure 1.

The 0 o yarns (wale direction) and 90 o yarns (coursedirection) in the spacer fabric construction are straight yarnsthat are placed to the spacer fabric in x and y coordinates,respectively and do not participate to the loop formationduring the knitting process. Spacer yarns which combinetwo outer surfaces of spacer fabrics to each other are theyarn systems located in the z direction. The last yarn systemin the construction is warp knitting yarns which fulfill thecombining of yarn systems through the knitting process,forming altogether spacer fabric construction.

Production Method

Spacer fabrics designed for concrete applications wereproduced on a double needle bar Rachel machine, on thebasis of a Karl Mayer HDR 6-7 DPLM. The machine wasmodified with additional systems such as computercontrolled 90 o weft insertions, computer controlled guidebar and two weft insertion catchers attached on each side byCetex Textilmaschinenentwicklung GmbH, Germany. Thecross section of the machine concept with knitting elements

is shown in Figure 2.Two guide bars (guide bar 3 and guide bar 4) of machine

were used in order to insert spacer yarns into the structure. Themovement of the guide bar 3 is controlled by a gear box whilethe movement of the guide bar 4 is realized with a computercontrolled linear motor. Therefore the patterning possibilitieswith computer controlled guide bar can be varied widely. Theworking principle of this machine is based on the proceduredescribed as follow. The needles on each side of the machineare performing the up and the down movement in this process.By catching a warp knitting yarn on its top position, eachneedle produces one mesh per cycle. These meshes areconnection binding system of the entire textile structures. Both,the 0 o as well as the 90 o yarns are inserted into these mesheswhen the needles pass their low position. Patterning can berealized by changing the threading and the guide barmovements on this machine. Threading can be changed byvarying the placement of yarns in the guide bar needles.Additionally by changing the movement of guide bars differentpatterns can be obtained [4,10].

Experimental Work

MaterialsIn this study the influence of the spacer yarn parameters

on the compression characteristics of spacer fabricsproduced with abovementioned technique was investigated.Different spacer fabrics were produced and theircompression behaviors were measured for this purpose. Inall samples same parameters and materials were used forwarp knitting yarn, 0 o yarn, 90 o yarn and spacer yarn I. Thematerials and the parameters used for these components areshown in Table 1.

The production of different spacer fabric constructions wererealized by only changing the parameters and materials ofspacer yarn II. Two different materials were used as spacer yarnII and their properties are shown in Table 2. The shrinkage testsof spacer yarn II materials were realized under temperature of

Figure 1. The view and the components of the spacer fabricsdesigned for concrete applications [4,16].

Figure 2. Cross section of the machine concept [4,10].

118 Fibers and Polymers 2009, Vol.10, No.1 Diren M. Armakan and Andreas Roye

180 oC during 10 minutes and the cool down time was 1 hour.The tenacity and the elongation at break values of mono-filaments were measured on Textechno Statimat testing devicewith test speed of 250 mm/min, pretension of 0,5 cN/tex and adistance between grips of 250 mm.

A constant production speed of 0.025 m/min was used forproduction of all types of spacer fabrics. The needles withfinenesses of E6 were used and the distance between theneedle beds were kept constant, 25 mm, for all spacer fabrictypes.

Methods Three groups of examinations were done to investigate the

influence of spacer yarn parameters on the compressionbehavior of spacer fabrics. In the first group spacer fabricswith different spacer yarn II patterns were produced withPES 1. In the second group spacer fabrics with differentpatterns were produced with PES 2. In the third group spacerfabrics with different threading and pattern combinationswere produced with PES 2. The examination groups and theparameters used in these groups are shown in Table 3.

The pattern of spacer yarn refers the movement of guide

bar carrying the spacer yarn between the needle beds. Thepattern contains the underlapping and overlappingmovements of guide bar. The term of threading means theemplacement of the spacer yarns into the guide bars thatwould be used in the spacer fabric structure. In the study, thelocation angle was defined as the angle between spacer yarnand the lower surface of the spacer fabric.

For all types of spacer fabrics in the first and secondexamination groups, same threading was used, eight spaceryarns were threaded and only the pattern of spacer yarn IIwas changed. The difference between the spacer fabrics inthe first and second examination groups is only the spaceryarn material. The realized constructions of spacer fabricswith related patterns in first and second examination groupsare shown in Table 4.

In the third group of examinations both the threading andthe pattern of the spacer yarn II were changed for eachstructure type. PES 2 was used as spacer yarn II material.For all spacer fabrics in the third examination group eightspacer yarns were threaded. The produced spacer fabricconstructions by this way and the schemes of the patterns areshown in Table 5.

Table 1. The materials of spacer fabric components

Component Material Threading Pattern0 o yarn 2400 tex AR-glass roving 1 full 1 empty 00,00/11,11

90 o yarn 2400 tex AR-glass roving cabled with PA twisted yarn 1 full 1 empty Weft insertionWarp knitting yarn 16 tex multifilament PP 1 full 1 empty 01,01//

Spacer yarn I φ0.25 mm PES monofilament 1 full 1 empty 01,10//

Table 2. Spacer yarn II materials and their properties

Name Materials Diameter (mm) Fineness (dtex) Shrinkage (%) Tenacity (cN/tex) Elongation at break (%)PES1 PES monofilament 0.28 866 5.97 39.76 58.52PES2 PES monofilament 0.30 1140.8 7.63 41.10 50.46

Table 3. The examination groups and relevant parameters

Examinationgroup

Samplename

Material of spaceryarn II

Threading of spacer yarn II

Pattern of spaceryarn II

Location angle of spaceryarn II

1

1A PES 1 1 full 1 empty (A) 1 2, 5 6 / 6 5, 2 1 55.87 o

1B PES 1 1 full 1 empty (B) 1 2, 7 8 / 8 7, 2 1 44.53 o

1C PES 1 1 full 1 empty (C) 1 2, 9 10 / 10 9, 2 1 36.44 o

1D PES 1 1 full 1 empty (D) 1 2 ,11 12 / 12 11, 2 1 30.53 o

2





3






Testing MethodIn order to investigate the compression behavior of spacer

fabrics, a testing method defined by Mecit was used [4].Compression tests were realized on the Zwick MaterialTesting Machine. The pressure stamp (Ø50 mm) wasmounted to the testing device and five test samples with areaof 300 cm2 and circular form were prepared. Thecompression test option of the software program was usedand test speed was adjusted to 100 mm/min. The limit forcesand displacement introduced to the software in order to stopthe test at relevant values. The pressure stamp was loweredto the test sample until it reaches the nearest position withouttouching and this point was adjusted as the reference pointon the software. The testing device measures the forces thatare necessary for certain displacements. The test results were

given in force-compression graphic. For each spacer fabrictype five samples are tested. For the evaluation of testresults, the graphics were analyzed and the areas under theeach curve were calculated. It is also possible to determinethe forces at certain displacements or the displacements atcertain forces in order to compare the test results.

Results and Discussion

Test Results of Examination GroupsCompression test results of samples were obtained from

the material testing device as force-compression graphics.Each graph includes five measurements taken from fivesamples. The graphics obtained from the compression testsof all examination groups are shown in Figure 3, Figure 4and Figure 5, respectively.

To obtain numerical values in order to evaluate the force-compression curves of the samples, the area under the eachcurve was calculated. 15 mm of compression was selected asa limit value. Calculation of the area under the curve is basedon the determination of work achieved during thecompression measurement. In order to determine the area,compression and force values obtained from material testingequipment were used. The area under compression curve ofeach sample was calculated. The calculated average areavalues for each curve are given in Figure 6.

Evaluation of First Examination Group’s Test ResultsThe force–compression graphics and the average values

obtained from the area under compression curves of firstexamination group showed that the compression resistancedecrease as the pattern of spacer yarn II changes from A to D(Figure 3). The difference between patterns implies differentamount of underlapping and therefore the spacer yarnlocation angle. As can be seen in Table 3, the spacer yarnlocation angle decreases from pattern A to pattern D(α1A:55.87>α1B:44.53>α1C:36.44>α1D:30.53). As the sametendency was observed from the compression results, it canbe said that the compression of spacer fabrics decreases asthe spacer yarn II’s location angle decreases.

Evaluation of Second Examination Group’s Test Results

In the second examination group it was also observedfrom the force-compression graphics and results of areaunder compression curves that the compression resistancedecreases from pattern A to pattern D (Figure 4). Althoughpattern A and pattern B in the second examination grouphave nearly the same values (2A: 452.73, 2B:453,46), theresults of pattern C and D are lower than that of pattern Aand pattern B. Pattern A has the greatest location anglecompared to that of pattern B, C and D as can be seen inTable 3. The location angle decreases as the pattern changesfrom A to D. Therefore it can be concluded from the resultsof first and second examination groups that the spacer yarn

Table 4. The spacer fabric constructions of first and secondexamination groups

1A-2A

1B-2B

1C-2C

1D-2D

Table 5. The spacer fabric constructions of third examinationgroup and schemes of patterns

Spacer fabric figure Spacer fabric construction

3A

3B

3C

3D


location angle influences the compression characteristics ofspacer fabrics. The compression resistance decreases as thelocation angle decreases.

Comparison of Test Results of First and Second Exami-nation Group

In the study same parameters and same materials wereused for the samples in first and second examination groups

except the material of spacer yarn II. Thus comparison of theresults of two groups gives the effect of spacer yarn materialon the compression. The comparison of the first and secondexamination groups show that the material of spacer yarn IIinfluences the compression properties. The average value ofstructures with pattern A in first examination group wasnearly 288.42 Nmm while the average of structures withpattern A in second examination group was 452.73 Nmm.

Figure 3. The force-compression graphics of first examination group.

Figure 4. The force-compression graphics of second examination group.


This difference was observed also from the comparison ofall kinds of patterns (1B:244.84-2B:453.46, 1C:243.98-2C:432.83, 1D:213.09-2D:406.99).

The compression resistances of structures produced withPES 2 are higher than the compression resistance ofstructures produced with PES 1 for all pattern types.Therefore it can be concluded that the material of the spaceryarn II have a great influence on the compression propertiesof spacer fabrics. This is thought to be the result of spaceryarn’s material properties such as diameter, stiffness, densityetc. The diameter of PES 2 is higher than diameter of PES 1and the fineness of PES 1 is higher than that of PES 2. Anincrement in the diameter of spacer yarn may cause anincrease in compression of spacer fabric.

Furthermore it is also thought that the bending or stiffnessproperties of spacer yarn II materials which have not beentested in this study also influence the compression resistanceof samples. The difference between these material propertiescauses diversity of compression characteristics.

To evaluate the test results of the samples statistically,analysis of variance was done on MINITAB 15 statisticalanalysis program on the basis of 95% confidence interval(α=0.05). The area under curve values of samples was usedfor this purpose. As result it was found that both the spaceryarn II material (p=0.000) and the pattern of the spacer yarnII (p=0.000) influence the compression results of spacerfabrics significantly.

Evaluation of Third Examination Group’s Test ResultsThe samples in the third examination group have different

threading and patterns. Changing the pattern and thethreading of spacer yarn II at the same time provide spacerfabric structures as shown in Figure 7. As can be seen fromthe Figure 6 and Figure 7, the results of third examinationgroup decrease as the structure changes from 3A to 3D.Depending on the threading used for each type, the numberof the spacer yarns in per unit area is decreased. For instancethreading with 1 full 3 empty which is used for structure 3Ainclude more spacer yarn per unit area compared tothreading with 1 full 9 empty which is used for structure 3D.

Furthermore the patterns used in the third examinationgroup are the same in first and second examination groupsand the spacer yarn location angle decreases as the patternchanges from A to D (α3A>α3B>α3C>α3D).

The compression values of the samples, both force-compression curves and the area under the compressioncurves in third examination group show considerablevariation between each other. The values calculated from theforce-compression curves of 3A was nearly 324.76 Nmmwhile the values calculated from the force-compressioncurves of 3D was 198.70 Nmm. As both the amount and thelocation angle of spacer yarn II decreases as the patternchanges from A to D, both these two factors influence thecompression resistance of spacer fabrics.

Comparison of Test Results of Second and Third Exami-nation Group

In order to evaluate the effect of threading of spacer yarnII, second and third examination groups can be comparedsince the related parameters except the threading are same

Figure 5. The force-compression graphics of third examination group.


both for two examination groups. As can be seen in Figure 6,the results show differences in all structures. Although theresults decrease from pattern A to D for both groups, thedifferences between structure types (2A-3A, 2B-3B, so on)show considerable variations. For instance, the compressionvalue of 2A is nearly 452.73 while the compression value of3A is 324.76 Nmm. Although all the other parameters werethe same for two structures accept the threading, thedifference between the compression values of structures isquite high. This difference is really high between structure2D (406.99) and 3D (198.7) as the threading of structure 2Dcontains the location of yarns 1 full 1 empty, while thethreading of structure 3D contains the location of yarns 1 full9 empty.

The comparison of the samples with same patterns insecond and third examination (2A-3A, 2B-3B, so on)showed that the threading of the spacer yarns influences thecompression characteristics of spacer fabrics. As thethreading can be an indicator of the spacer yarn amount inthe structure, it can be said that the compression resistanceof the spacer fabrics decreases as the spacer yarn amountdecreases.

The statistical evaluation of test results of spacer fabrics inthe second and third examination group were also realized inorder to see the effect of threading on the compressionresults. Analyses of variance results showed that thethreading of the spacer yarns and therefore the amount of thespacer yarn influences the compression results of spacer

fabrics significantly (p=0.000).

Conclusion

In this study the compression characteristics of spacerfabrics designed for concrete applications were investigatedon the basis of spacer yarns in their structure. In order toevaluate the effect of material, pattern and threading ofspacer yarn, three different examination groups wereproduced and their compression tests were realized. Theresults of the compression tests were analyzed andcompared.

From the results of first and second examination groups itwas obtained that the spacer yarn material and patterninfluences the compression resistance of spacer fabrics.Since the spacer yarns used in the first and secondexamination groups have different properties, it is thoughtthat the properties of spacer yarn material affect thecompression resistance of spacer fabrics.

Furthermore patterns used in examination groups consistof spacer fabrics with different spacer yarn location anglesand different amount of underlappings. In the study it wasfound that the compression resistance decreases as thespacer yarn location angle decreases.The statistical analysesalso showed that pattern and material of spacer yarninfluence the compression behaviour of spacer fabricssignificantly.

The comparison of the second and third groups ofexaminations showed that the threading of the spacer yarnsinfluences the compression characteristics of spacer fabricssignificantly. Threading of spacer yarns is related with theamount of the spacer yarn in the unit spacer fabric area. Itwas obtained from the test results that the compressionresistance of the spacer fabrics decreases as the amount ofthe spacer yarn in the unit spacer fabric area decreases. Thestatistical analyses of the results also showed that thethreading of the spacer yarns influences the compressionbehavior of spacr fabrics significantly.

Acknowledgements

The authors wish to express special thanks to Institiut fürTextiltechnik der RWTH Aachen, Germany for theproduction of samples and Ege University TextileEngineering Department and Textile Research Centre, Izmir,Turkey for supporting Diren Mecit.

References

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Figure 6. The average values of area under force-compressioncurves of all examination groups [Nmm].

Figure 7. The patterned constructions of spacer fabrics used inthird examination group.


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compression behaviour of spacer fabric