Tensile behaviour of Textile: influence of

multilayer reinforcement

I. Colombo, M. Colombo, A. Magri, G. Zani, M. di Prisco

Politecnico di Milano, Piazza Leonardo da Vinci, 32 Milano

colombo@stru.polimi.it

Abstract

The interest in the use of textile fabrics as reinforcement for cement based

composite materials has been increasing in the last few years. Textile cementitious

composites show improved tensile performances; as a matter of fact in addiction

to a considerable peak strength, these composites show a strain hardening behav-

iour even when the reinforcing yarns have a low modulus of elasticity. This was

explained by the enhancement in bonding due to the mechanical anchoring pro-

vided by the non-linear geometry of the individual yarn within the fabric.

The paper investigates the tensile behaviour of textile reinforced mortar as in-

fluenced by different geometrical reinforcement ratio in prismatic specimens. In

all the experimental tests the load direction will be parallel to the fabric warp.

Three different geometrical reinforcement ratio were investigated in order to eval-

uate their effectiveness and their influence both on tensile strength and on crack

pattern.

1 Introduction

Modern architecture shows a definite trend towards thinner structures made by

high-performance materials which demand a continuous development of their me-

chanical properties. Nowadays thin, light-weight and cost saving elements with

improved durability by using non-metallic reinforcement for concrete are an open

issue [1].

Textile Reinforced Mortar (TRM) is recently seen as a performing solution in

this framework [2, 3, 4]. The use of fabrics, mainly made by alkali resistant (AR)

glass, aligned to principal stress direction, allows the designer to optimize struc-

tural performance.

The application here considered refers to a layered prefabricated structure

where the TRM is located on the tensile side. The production procedure of the

2 I. Colombo et al.

TRM has to guarantee the shear stress transfer through the layer interface and a

relative simplicity in the assembling of the whole structure.

The property, the content and the layout of the fabric have a great influence on

the characteristics of the composite material. The fabric texture structure and the

special geometry of its yarns have a significant effect on bonding [5]. The geomet-

rical characteristics to be considered are the nature of the yarns and the various

geometries by which these yarns are combined together in the fabric. The structure

of fabrics can be modified by changing the warp and weft spacing. This paper ana-

lyzes the influence of different reinforcement ratio on the tensile strength and duc-

tility of the composite.

2 Materials

2.1 Matrix

The matrix of the TRM investigated is a high strength mortar characterized by

a water to binder ratio equal to 0.19. The maximum aggregate size was taken

equal to 600 m in order to allow the matrix to flow through the mesh of the fab-

ric. The mix design is summarized in Table 1.

Table 1 - Mix design. Table 2 - Bending and compressive strength.

Component Content Specimen fctf [MPa] fcc [MPa]

Cement I 52.5 600 kg/m³ N1 13.82 98.69 114.29

Sand 0 - 600 m 957 kg/m³ N2 17.45 103.23 107.47

Water 209 l/m³ N3 14.46 89.74 102.61

Superplasticizer 55.8 kg/m³ Average 15.24 102.67

Slag 500 kg/m³ STD 1.94 8.26

STD % 12.73 8.05

The mechanical properties of the matrix were characterized according to EN

196 Standard for mortar. Table 2 shows the bending tensile strength (fctf) together

with the cubic compressive strength (fcc).

2.2 Fabric

The fabric used was chosen after performing several investigations in order to

optimize performances in terms of ductility of the composite material, bond be-

tween matrix and fabric and internal filaments slip. The variables considered were

the fabric geometry (warp and weft spacing and their cross section), fabric weav-

Tensile behaviour of Textile 3

ing and fabric coating. The final purpose was to achieve in the TRM the largest

strength and ductility. The geometrical characteristics are summarized in Table 3.

Table 3 - Geometrical characteristic of fabric.

Warp wire spacing [mm] 5.0

Weft wire spacing [mm] 7.1

Warp [Tex] 640

Weft [Tex] 1200

Fabrication tecnique Leno weave

Ten uniaxial tensile tests were performed to characterize the fabric. The tensile

tests were carried out using an electromechanical press INSTRON 5867 with a

maximum load capacity of 30 kN. The specimens were 400 mm x 70 mm and

were clamped to the machine. At the upper and lower ends of the sample ten lay-

ers of adhesive paper tape were applied to prevent the slip between the clamps and

the fabric. The pressure applied to the pneumatic clamps was 3.4 bar. The tests

were displacement-controlled by imposing a constant stroke rate of 1.67 mm/sec.

The set-up is shown in Fig.1a, while the results in terms of load-displacement

curves are shown in Fig.2.

Fig. 1 - Set-up tensile test of fabric (a) and TRM (b).

(a) (b)

4 I. Colombo et al.

Fig. 2 - Load vs displacement of fabric under uniaxial tension.

2.3 Specimens preparation

The specimens used in the experimental investigation were 400 mm long, 70

mm wide and with different thickness varying between 6 and 12 mm. The differ-

ent reinforcement ratios investigated, summarized in Table 4, were achieved by

introducing different layers of the same fabric. Due to the production technology,

different thicknesses were obtained (Table 4).

Fig. 3 – Specimen preparation.

Table 4 – Geometrical characteristics

(average of 3 samples).

f

[%]

Layer

[-]

Thickness

[mm]

1.63 1 6.3

2.54 3 12.1

3.30 2 6.2

Specimen Loadpeak [kN]

N1 6.91

N2 6.45

N3 6.12

N4 6.77

N5 6.31

N6 6.58

N7 6.58

N8 6.71

N9 6.39

N10 6.97

Average 6.58

STD 0.27

STD % 4.10

Tensile behaviour of Textile 5

The specimen preparation was made by using a proper formwork with the

transparent bottom plate in order to check the penetration of the matrix into the

fabric mesh. Some overlapping steel rails (3 mm thick) were designed in order to

interpose different textile layers. The mortar was spread and smoothed with a roll-

er. After that, the reinforcement was tight and fixed at the edge. Repeating the

procedure it was possible to create a multilayer specimen. The layers of textile

were divided by about 2 mm thickness of mortar. In all the cases the warp was

parallel to the long side of the specimen.

3 TRM tensile behaviour

3.1 Test set up

The same set-up used to test fabric specimens was adopted (Fig.1b). 70 mm x

55 mm steel plates were glued on the surface of the specimen at the grips to mini-

mize damage. To prevent torsional and bending moments owing to a misalignment

of the constraints, spherical joints were placed at the ends. The pressure applied to

clamp the edge zone was 4 bar and the tests stroke rate imposed was equal to 0.02

mm/sec. For each reinforcement ratio, 3 nominally identical tests were carried out.

3.2 Experimental results

The experimental results are reported in the paragraph for all the specimens in-

vestigated by means of the nominal stress ( ) vs strain ( ) curves (Figs.4a, 5a, 6a).

The stress was obtained by dividing the load by the nominal area of the specimen

cross section and the strain was evaluated by the ratio between the elongation ( )

of the specimen and its initial length. A common trend can be observed: three sec-

tions characterize the non linear response. The first cracking was reached when

the tensile strength of the matrix was exceeded and then multicracking strain hard-

ening behaviour occurred. A final branch in which no further cracks develop takes

place: its extension depends on the reinforcement ratio. It is worth noting that the

scattering of the experimental results is really small (less than 7%).

The crack distance decreases with higher reinforcement ratios (Figs.4b, 5b, 6b).

In order to compare the results, the average stress-strain curves are plotted in Fig.7

showing for all the cases a good repeatability of the initial un-cracked stiffness

and a cracked regime that becomes stiffer with increasing reinforcement ratios.

Table 5 shows the average working ratios of the different cases investigated.

This parameter is computed as the ratio between the strength of the TRM compo-

site and the reinforcement only. The solution with f =3.30% has a working ratio

6 I. Colombo et al.

equal to 81% that shows that the fabric mechanical properties are quite well used

by the TRM composite.

Fig. 4 - Load vs displacement curve in uniaxial tension (a) and specimen

crack pattern (b).

Fig. 5 - Load vs displacement curve in uniaxial tension ( f = 2,54%) (a) and specimen crack

pattern (b).

(a) (b)

(b) (a)

Tensile behaviour of Textile 7

Fig. 6 - Load vs displacement curve in uniaxial tension ( f = 3,30%) (a) and specimen crack

pattern (b).

Fig. 7 - Comparison between average curves.

(a) (b)

8 I. Colombo et al.

4 Conclusions

The experimental investigation indicates that the strength grows with geomet-

rical reinforcement ratio increasing. In particular, in the case of f equal to 3.30%

the strength is around 25 MPa. A large ductility was guaranteed by the small crack

spacing which decreases for growing reinforcement ratios. The cracking occurs at

each weft wire (approximately 7 mm). The ductility behaviour was influenced by

a slip of the inner filaments getting a telescopic break.

Table 5 – Test result.

f [%} peak [MPa] Ductility u/ 1 [-] Working ratio [%]

1.63 11.36 24.71 76

2.54 14.82 13.43 64

3.30 24.42 24.68 81

The solution with f equal to 3.30% shows the best performance also in terms

of working ratio.

Acknowledgments

The authors would like to thank Gavazzi company for its cooperation and supply-

ing the AR glass fabrics. The research was financially supported by European

INTERREG IT/CH 2006_2013 project ACCIDENT ID7629770, Measure 2.2.

5 References

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(eds) Varenna, Italy p. 1505–14

[2] Brameshuber W (2006) (ed) Textile Reinforced Concrete state of art report of RILEM tech-

nical committee 201-TRC, Aachen

[3] Hegger J, Brameshuber W, Will N (2010) (ed) 2nd

ICTRC Textile Reinforced Concrete Pro-

ceedings International RILEM Conference on Material Science (MatSci)

[4] Jesse F, Curbach M (2003) Strength of continuous AR-glass fiber reinforcement of cementi-

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composites (HPFRCC 4) RILEM Publications p. 337–48

[5] U. Haubler-Combe, J. Hartig (2007) Bond and failure mechanisms of textile reinforced con-

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