Bond Properties and Experimental Methods

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Journal of Wuhan University of Technology-Mat er. Sci. Ed. Sept 2007 529

Bond Properties and Experimental Methods

of Textile Reinforced Concrete XU Shilang 1, LI He2*

(1. State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian 116024, China;

2. Research Department, Beijing Institute of Architectural Design, Beijing 100045, China)

Abstract: Textile reinforced concrete(TRC, for short) allows the low size production and offers a

high effectiveness of the reinforcement by using continuous roving instead of short-chopped bers. However,

whether textiles can cooperate with concrete very well depends on the bond between them. In this paper, the

bonding mechanism that the stress was transferred from ne concrete to textile was analyzed, and the inuences

of the initial bond length of textile, the surface treatment of textile , the strength and workability of concrete

as well as the level of prestressing force on bond behavior were investigated on the basis of pull-out tests. The

results reveal that with initial bond length increasing, the maximum pull force increases, and increasing concrete

strength and improving workability of concrete matrix, epoxy resin impregnating and sand covering of textile aswell as prestressing textile can obviously increase the bond strength between the textile and concrete.

Key words: textile; bond; pull-out test

(Received: Nov. 13,2006; Accepted: Apr.14,2007)

XU Shilang(徐世烺): Prof.; Ph D; E-mail: [email protected]

* Corresponding author: LI He(李赫): Ph D; E-mail: [email protected]

Funded by the Key Program of the National Natural Science

Foundation of China(No.50438010)

DOI 10.1007/s11595-006-3529-9

1 Introduction

In the past, the research on fiber reinforced

concrete(FRC, for short) mainly focused on short-

chopped bers. Due to the random distribution of short-

chopped bers in concrete, the strength of the bers is

usually not fully used and, therefore, a comparatively

high degree of reinforcement is needed. Hence it seems

appropriate to reinforce concrete with roving or textile

materials oriented in line with the occuring stresses

of concrete. To insure the bond between textile and

concrete, a kind of high performance fine concrete is

developed as the matrix of TRC. TRC shows some

obvious advantages, such as high carrying capacity and

ductibility, preventing magnetizing, no corrosion, thin

size and light self-weight as well as convenience for

construction, and so on.Even though the idea of TRC is not completely

new, basic mechanisms regarding bond, durability

and load-carrying capacity are not understood in

detail so far. The collaborative organization of TRC in

European and American came into existence in 2002,

the beginning of human exploring for TRC. In this

organization, the properties of TRC are investigated

from micro-level to macro-level, from material

characteristic to structural characteristic, and from basic

components to the assembly of structural system. Many

new experimental technologies have been adopted,

such as acoustic-emission technology that reects the

stress state of roving at the interface between concrete

and textile and measures the valid bond length[1]

, ber-

optic sensors that measures the strain of roving[2]

,

as well as digital photogrammetry, and computer

tomography that measures the deformation and crack

development of structure[3]

.

Recently, Shilang Xu and Hans W Reinhardt

studied the bond properties between high performance

fine concrete and carbon textile, and established

the base of TRC for structural application[4]

. In this

paper, to study bond properties between textiles and

concrete, pullout tests were performed using carbon

textiles, and the influences of the initial bond lengthof textile, the surface treatment of textile, the strength

and workability of concrete as well as the level of

prestressing force on bond behavior were investigated.

The results of study show that increasing concrete

strength and improving workability of concrete matrix,

epoxy resin impregnating and sand covering of textile

as well as prestressing textile can obviously increase

the bond strength between textile and concrete.

2 Experimental

2.1 Concrete matrix

To investigate the influence of the strength and



530 Vol.22 No.3 XU Shilang et al: Bond Properties and Experimental Methods...

workability on the bond, four different matrices were

developed, viz . C1,C2,C3,C4. To insure the matrices

penetrating into textile successfully, the biggest grave

size was limited, and it was 1.2 mm. The content of

the drier of these matrices is same. Every cubic-meter

matrix included 472 kg Portland cement, 168 kg fly

ash, 35 kg silica fume, 460 kg fine sands(grave size

0-0.6 mm), and 920 kg fine sands(grave size 0.6-1.2

mm). To achieve different strength and workability, the

dosages of super plasticizer and water-binder ratios of

those matrices were different. The detail and properties

of concrete are shown in Table 1.

2.2 Textile

The common textiles include carbon, glass and

Aramid ber fabric. There are many ways that textiles

are made from roving, of which three ones are primary:weft insertion warp knitted textile, short weft warp

knitted textiles, and woven textiles(plain weave);

The textile structures differ by the way the yarns are

combined together.

The geometries of textiles influence the bond

between concrete and them[8]

. As carbon ber was very

expensive, to save experimental materials, a kind of

woven textile whose warp yarns are made of carbon

fiber and weft yarns made of glass fiber was adopted

in this test. The research[1]

showed that the pronounced

weft effects do not occur so that the reinforcing effect

of weft for concrete can be omitted. Due to the damage

of a part of filaments in fabrication and construction,

after the yarn is loaded, the damaged laments rupture

firstly, and then the intact ones rupture, which makes

the reinforcing effect distract and is called as ‘tensile

weakening’. So the tensile strength of a yarn is much

smaller than that of a filament. Furthermore, as the

concrete cannot penetrate into the yarn and amongthe filaments, only the outer filaments can develop

better bond with concrete and the force is transferred

to inner one by friction. When the yarn is loaded,

outer filaments deform earlier and greater than inner

ones[9]

, which is called as ‘shear lag’. To decrease or

avoid the phenomena of tensile weakening and shear

lag, epoxy resin impregnating of textile is necessary

before it is embedded in concrete. Epoxy resin can

penetrate into the yarn and among the filaments, and

make the laments conglutinate as a whole, viz , a yarn.

To develop the bond, the sands were scattered on thesurface of a part of textile before epoxy resin hardens,

and epoxy resin hardens, the sands were stuck on it in

this test.

The tensile strength of a yarn is not the sum of

those of all laments, and need to be measured. As the

shape of the cross section of the yarn varies and the

width of it is very small, common clamping devices

cannot fix it up. Moreover, the surface of the yarn is

scraggy after impregnated by epoxy resin, the strain

gauge can not be stuck on it. So a special clamping

device and a special strain jig were designed for the

yarn

[10]

.Two elastic steel slices are xed on a rigid base,

and four strain gauges are pasted respectively on the

upper and the nether of steel slices. Four wires, viz , A, B,

C, D are connected with four strain gauges according

to the whole bridge circuit. Before the strain jib is

used, the relationship that the voltage changes along

with the corresponding change of distance between

elastic steel slices is calibrated. Hence two small steel

blocks with notches are fixed on the yarn, and then

the distance between them is recorded. After that, the

strain jigs get stuck on the notches of steel blocks. Sothe change of the distance between the two elastic steel

slices divided by the original distance between them



Journal of Wuhan University of Technology-Mat er. Sci. Ed. Sept 2007 531

is the mean strain. The tensile force can be gotten by a

tensile sensor. The tensile force divided by academic

area is the stress and the stress divided by the mean

strain is Young’s modulus. The test approved that the

tensile strength and ultimate strain were very discrete

but Young’s modulus was close to the theory value. The

ultimate tension of a yarn is between 1 kN to 2 kN. The

mean value is 1.5 kN, and the coefcient of variability

is 41%. On the other hand, the ultimate strain of a yarn

is between 0.01 and 0.02. The mean value is 0.015, and

the coefcient of variability is 62.5%.

2.3 Specimens

To get a representative specimen, thin test

specimens without prestressing force were sawn from

a plate with dimensions of 900 mm×900 mm×20 mm.

The textile fabric was placed in the mid cross-section.The nonprestressed plates were manufactured by

placing a 10 mm thick layer of concrete in a mould and

putting the textile layer on top of it. Another layer of

10 mm was then cast and slightly vibrated by a special

vibrator which has been developed for this purpose.

Thin prestressed specimens were cast according to

these dimensions of 600 mm×100 mm×20 mm. Firstly,

the textile fabric was placed in the mid cross-section

of the mould, and then was prestressed, after that the

concrete was cast into the mould. A kind of clamping

device was specially developed for this purpose.The prestressing force was implemented with

the rolling motion of a screw bolt, and the measure of

the prestressing force can be gotten by a tensile sensor

behind the clamping device.

2.4 Experimental process

The test set-up is shown in Fig.1. Before testing,

the specimen was glued with an epoxy resin into saw-

tooth shaped steel plates and fixed with a bolt to the

testing machine. An electro-mechanical machine(made

by Jinan Shijin Group Co. Ltd, WAW300) was used to

perform the tests. The loading rate was 1.0 mm/min.

3 Results and Discussion

The influences of strength and workability of

concrete on bond in different initial lengths are shown

in Fig.2. From Fig.2, one can see both the peak value

of pullout force of matrix C1 and the work that pullout

force of matrix C1 does to pull out the yarn completely

are greater than those of C2, which indicates the higher

the strength of concrete, the better the bond. On the

other hand, though the strength of C2 is higher than



532 Vol.22 No.3 XU Shilang et al: Bond Properties and Experimental Methods...

that of C3, the bond between C3 and the yarn is better

than that between C2 and the yarn because of the self-

compacting capacity of C3.

Fig.3 indicates that epoxy resin impregnating and

sand covering of textile can heighten the peak value of pullout force obviously when the initial bond length is

same. However, after the peak value, the pullout force

of the yarn impregnated by epoxy resin and covered

with sands nearly descends to 0, which indicates the

majority of filaments have ruptured so as not to bear

the load.

The peak value of pullout force increases with

initial bond length increasing, which is shown in Fig.4.

If the quantity of short-chopped bers that were mixed

into concrete is proper, the crack of matrix can be

limited, as a result of which the bond can be developed

and the peak value of pullout force can be heightened.

However, the heightened extent of the peak value

of pullout force due to short-chopped fibers is lower

than that due to epoxy resin impregnating and sand

covering, which is shown in Fig.5.

From Fig.6, one can see that the peak value of

pullout force is about 1 700 N for the prestressing force

600 N/yarn, above 1 400 N for the prestressing force

400 N/yarn and below 1 400 N for the prestressing

force 0, which can be explained by the Poisson’s ratio

effect and the bonding effect of prestressing force that

leads to an increase of the frictional bond strength between yarn and concrete as well as among the inner

filaments, and an increase of the contact zones of the

inner laments[1,4]

, which can be seen from Fig.7.

4 Conclusions

TRC is a new kind of reinforcing elements, and

understanding the bond nature is the first stage for

structural application. However, as textile is made of

many filaments and these filaments cannot bear the

load in the same phase, the reinforcing efficiency of TRC will be decreased. So epoxy resin impregnating of

textile is necessary. After impregnated by epoxy resin,

the textile can be seen as rigid thin fabric and the inner

action among filaments can be omitted. If a textile is

covered with sands after being impregnated by epoxy

resin, the peak value of pullout force can be increased,

which is due to the increasing of friction. With the

initial bond length increasing, the peak value of pulloutforce increases. Furthermore, it is advantageous for

bond to increase the strength of concrete and develop

the workability of concrete. Finally, as it leads to the

increase of both friction and contact zones of the inner

filaments, the prestressing force increases the bond

strength, too.

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Bond Properties and Experimental Methods

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