etude du comportement en traction et en compression du beton de ...

ICSAAM 2011 September 7-11, 2011 Bucharest, Romania.

STUDY OF MECHANICAL BEHAVIOR OF CONCRETE IN DIRECT TENSILE FIBER CHIPS BOUAFIA Youcef, KACHI M. Said, ATLAOUI Djamel, DJEBALI Said Laboratoire de modélisation expérimentale et numérique des matériaux et structures en génie civil (LAMOMS), Université M.MAMMERI TIZI-OUZOU, ALGERIE, E- mail : [email protected]

Abstract In this experimental study, we are interested in local fiber wavy chips derived from waste machining steel parts. This work has focused on studying the mechanical behavior of reinforced concrete in tension of this type of fiber. Direct tensile tests were carried out on samples in free weights section and square (100x100) mm2. This test involves the design and implementation of a special. mounting specimens on the tensile machine type IBERTEST. Five (05) fiber percentages were retained in (W = 0.5%. W = 0.8%, W = 1%, W = 1.2%, W = 1.5%) with W: volume fraction of added fiber) and two (02) concrete witness whose report on gravel sand is equal to: S / G = 0.8 and S / G = 1. The fibers have been characterized to the strength and tear by the tensile test. The interest lies in optimizing the fiber length and the number of undulations to use in a cement matrix, which will improve the mechanical properties especially tensile strength and post-cracking behavior. The comparison of different results obtained in direct tension on different percentages of fiber, as well as two reports showed that the fibers have conferred a significant ductility to the material after cracking of concrete for different percentages of fiber and a larésistance for improving the S / G = 0.8.

Key words: fibes in chips / characterization / cracking / tensile / undulations

ICASAAM 2011

1 7-10 September 2011 – Bucharest – Romania

1 Introduction The direct tension test is most recommended to characterize the behavior of a material under a longitudinal force. However, the complexity of the implementation of a direct tensile test on concrete specimens that this test is often replaced by a test or splitting tensile bending. The purpose of this work is the realization of direct tensile tests on specimens of steel fiber concrete in order to characterize the behavior of the latter. This fiber concrete with optimum composition was determined by the test of workability is obtained by adding the fibers are revered spiral waste from machining steel parts (chips) on bare concrete. Tensile tests were performed, The end to optimize the fiber length and the number of waves that will ensure a good anchoring of chips in the cement paste, and the determination of the maximum strength of these fibers break. This study conducted on dumbbell specimens of square section of 100 x 100mm2 required the design and implementation of a special mounting specimens on the tensile machine. Three (5) fiber contents were used (W = 0.5%, 0.8% W = W = 1%, 1.2% and 1.5%) with W: volume fraction of added fiber) and two (2) for control concrete Reports sand / gravel (S / G = 0.8 and S / G = 1).

2 Characterization fiber corrugated spirals. This study consists of experimental characterization of mechanical behavior of corrugated fiber (wood chips) under static (uniaxial traction) to determine the maximum resistance to breakage and fiber pullout. The interest lies in optimizing the fiber length and the number of waves to use in a cement matrix, which will improve the mechanical performance in particular resistance.

2.1 Experimental Study The chips are cut into three lengths (30, 40 and 50 mm) and for each length, the number of waves or spirals instead of 3, 6 and 8. The number of trials is 3 for each combination type (length and number of spirals). The tests include establishing direct tensile tests with controlled deformation. We give in what follows: The characteristic value of the stress at rupture, and the curve obtained and confrontations made.

2.2 Fibre geometry and anchoring system. The fibers used waste from machining steel parts. They are recovered to the national industrial vehicles in Algeria (SNVI). Their geometry and corrugated spiral gives them a perfect anchor in the cement matrix. A view of these chips is given in Figure 1. The width, diameter and thickness of the fibers are given respectively as follows: l = 2 mm, and e = 0.5 mm.Les both ends of the chips were lubricated with using a resin and fiberglass end in a special mold to improve their foothold in the clamping jaws of the hydraulic press during the tensile test on the fiber itself (see Figure 2).

Fibres. L=30mm, n=3,6 et 8



Figure 1 for chips

ICASAAM 2011


Figure 2 Preparation of the anchoring system in the mold resin ugly

2.3 Apparatus and tests The tests were performed on a hydraulic press controlled deformation type IBERTEST (laboratory modeling of materials and structures of civil engineering at the University MM Tizi-Ouzou, Algeria). The press is equipped with an acquisition chain of command and control digital (see view given in Figure 3). The geometrical characteristics are entered automatically and the length of the fiber is 100 mm. The loading speed is 20 mm / min.

Figure 3 to test device

3 Presentation of results For each series of tests for different lengths (30, 40 and 50mm) and for a number of undulations 3.La 8.6 and average curve of stress as a function of strain σ = f (ε%) for the fiber that gave the best tensile strength is shown in Figure 4. σ[MPA] :

L=50mm, n=8

3,00E+02 2,50E+02 2,00E+02 1,50E+02 1,00E+02 5,00E+01

ε

0,00E+00 0

0,002 0,004 0,006 0,008

0,01

0,012 0,014

Figure 4 Mean curve σ = f (ε) for L = 50mm, n = 8.

ICASAAM 2011


During the test, we see that the undulations of the fiber gradually open up flattening of the fiber. Beyond that, there is a ductile steel. The tensile strength increases with the number of waves: it reaches Rm = 268 MPa for a length L = 50mm and n = 8 (ripples).

4 Characterization of fiber concrete To fix the specimens (Figure 5) on the jaws of the tensile machine we designed, helping us on the method of value analysis, and produced a special device (Figure 5).

Figure 5 Device for tensile testing This device was adapted to the traction machine "IBERTEST" 200kN. It consists of two identical parts which are mounted on the upper and lower jaws of the tensile machine using the fixed jaws. The specimens are packed in the interior of the device on the supports in corners. The adjustment screw adjusts the position of the sliding jaws in order to receive samples of different sizes. The coincidence of the axis of the specimen with the axis of the machine is ensured by stops. Because the device is secured to the jaws of the tensile machine does not need to bring a ball. The vertical force is applied progressively loading speed controlled (or 0.005 MPa / second). The software programmed for 32 WINTEST this press records for each load step, the value of the vertical force and corresponding deformation and stress as a function of the deformation. .

4.1 Geometry and composition of the specimens 4.1.1 Geometry of test specimens . The test specimens used are dumbbells 100x100mm2 cross section and length 100mm (Figure

6). They are equipped with a U-shaped notch 5 mm deep by 5mm opening to locate the break. 150

70 30 100

100 100 30 70 150

Figure 6 Fiber concrete specimen. ICASAAM 2011


4.1.2 Composition of specimens The specimens are composed of metal fibers embedded in a concrete matrix. The optimum composition of concrete to 1m3. Determined by testing for handling different volume fractions of fiber (W = 0.5%, W = 0.8%, W = 1%, W = W = 1.2% and 1.5%) and various reports sand / gravel (S / G = 0.64, S / G = 0.8, S / G = 1 and S / G = 1.4). The two compositions chosen for the following tests for 1m3 of concrete, consistent with the relationship Sand / gravel (S / G = 0.8 and S / G = 1) are given in Table 1 below.

Table 1 Optimized compositions for 1 m3 of concrete. Concrete components for 1m3 - Sand 0 / 3 (kg)

- Gravel 3 / 8 (kg) - Gravel 8/15(kg) - Cement CPJ CEMII / A 42.5 (C) (kg) - Water (W) (kg) - Plasticizer (0.05% of cement weight) (ml)

S/G=0.8 797 106.33 890 380 206.52 190

S/G=1 869.67 95.67 801 380 206.52 190

Mass for different fiber contents for 1m3 of concrete are given in the table below.

Table 2 Mass for different fiber contents for 1m3 of concrete,. Volume fractions of fiber (W =%) Weight (kg)

0.5% 39.3

0.8% 62.88

1%

78.6

1.2% 94.32

1.5% 117.9

5. Presentation of results A crash near specimens of fiber reinforced concrete on the tensile machine "IBERTEST, for different fiber contents (0.5%, 0.8%, 1%, 1.2% and 1.5%) and two for concrete (02 ) concrete witness to the percentage sand / gravel (S / G = 0.8 and S / G = 1). The curves representing the stress as a function of strain for each fiber content, are given respectively in graph form as follows:

ICASAAM 2011


σ[MPA]

σ[MPA] 2

1,2

1,8

1

1,6

S/G=1, W=0,8%

1,4

0,8 1,2 BT- S/G=1 1

0,6

0,8

0,4

0,6 0,4

0,2 0,2

ε

0 0

0,0005

0,001

0,0015

0,002

ε

0

0,0025

0

Figure 7 curve σ=f(ε) pour BT- S/G=1

0,005

0,01

0,015

0,02

0,025

0,03

Figure 10 curve σ=f(ε) pour S/G=1, W=1%

σ[MPA]

σ[MPA]

1,6

1,2

1,4

S/G=1, W=0,5%

1

1,2 1

0,8

0,8

0,6

S/G=1, W=1,2%

0,6 0,4

0,4 0,2

0,2

ε

0

ε 0

0

1

2

3

Figure 8 curve σ=f(ε) pour S/G=1, W=0.5%

σ[MPA]

0

0,002

0,004

0,006

0,008

0,01


σ[MPA]

1,6

0,8

1,4

0,7

1,2

0,6

S/G=1, W=1% 1

0,5

0,8

0,4

0,6

0,3

0,4

0,2

0,2

S/G=0,8, W=1,5%

0,1

ε

0 0

0,002

0,004

0,006

0,008

0,01

0,012


ICASAAM 2011

ε

0 0

0,01

0,02

0,03

0,04



σ[MPA]

σ[MPA]

1,2

1,4 1

1,2 1

BT, S/G=0,8

0,8

S/G=0,8, W=1%

0,8 0,6

0,6 0,4

0,4 0,2

0,2

0

0,0002

0,0004

0,0006

0,0008

0,001

ε

0

ε

0

0

0,0012

0,01

0,02

0,03

0,04

Figure 16 curve σ=f(ε) pour S/G=0.8,W=1%

Figure 13 curve σ=f(ε) pour BT- S/G=0.8

σ[MPA]

σ[MPA] 1,4

1,6

1,2

1,4

1

1,2 S/G=0,8, W=0,5%

1

0,8

S/G=0,8, W=1,2%

0,8

0,6

0,6 0,4

0,4 0,2

0,2

ε

0 0

0,002

0,004

0,006

0,008

0,01

0,012

ε

0

0,014

Figure 14 curve σ=f(ε)pour S/G=0.8- W=0.5%

0

0,005

0,01

0,015

0,02

0,025

Figure 17 curve σ=f(ε) pour S/G=0.8, W=1.2%

σ[MPA]

σ[MPA]

0,7

1,4

0,6 1,2

0,5 1

S/G=0,8, W=1,5% 0,4

S/G=0,8, W=0,8%

0,8 0,6

0,3

0,4

0,2

0,2

0,1

ε

0 0

0,005

0,01

0,015

0,02

Figure 15 curveσ=f(ε)pourS/G=0.8, W=0.8%

ICASAAM 2011

ε

0 0

0,005

0,01

0,015

Figure 18 curve σ=f(ε) pour S/G=0.8, W=1.5%


6 Results and Discussions The results obtained showed that the addition of fibers makes the material ductility significantly compared to control concrete (without fibers), reports to sand / gravel (S / G = 0.8, S / G = 1). On the other hand the behavior of fiber concrete in tension to levels (0.5%, 0.8%, 1%, 1.2% .1.5%), and for reporting S / G = 0.8, S / G = 1), characterized by the presence of two (2) phases. A linear phase corresponding to behave quasi - elastic material is the pre concrete cracking. This phase ends with the appearance of the macro crack. A second phase in which there is a sudden fall without sudden rupture of the specimen, the bearing capacity of the material, the post cracking. In this phase the concrete matrix breaks and the edges of the crack are connected by fiber (see Figure 19) which avoids a sharp break.

Figure 19 edges of the crack connected by fiber. We compare the results obtained for the two reports sand / gravel (S / G = 0.8, S / G = 1), it appears that, for S / G = 1, the resistance drops more than the percentage increases in fiber). In this case the quantity of sand equal to gravel, the bundles are wavy dress by sand and gravel which explains the drop in strength. By cons for S / G = 0.8 we found that the fibers improves the stiffness and strength of the composite, for contents (0.5%, 0.8%, 1% and 1.2%), by cons for (W = 1.5%) resistance decreases relative to the control concrete and it is explained by the fact that the percentage is very high, which creates a lot of vacuum in the cement matrix, to form the corrugated fiber spirals. the amount of sand under the gravel, the fibers are dress by the cement and gravel.

7 Conclusions This study allowed us to highlight the influence of fiber length and number of undulations on their tensile strength. It appears that the resistance is achieved for a length l = 50 mm, n = 8 undulations. During the tensile test, the corrugations tend to flatten out before the steel fiber lengthens. This study allowed us to establish the composition of concrete with the ratio (S / G = 0.8) and the fiber content (0.5%, 0.8%, 1% and 1.2%), which ensures good adhesion between the concrete armed with these fibers to improve the rigidity and tensile strength. The objectives of this study is the implementation of a direct tensile test, despite its complexity, on concrete specimens for the characterization of the tensile behavior of fiber concrete and study the influence of adding waste machining steel parts (chips) on the workability and mechanical behavior of concrete

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In conclusion, we can say that the equipment designed and built for the conduct of direct tensile tests was tested successfully and waste processing (chips) can be upgraded by using them in the preparation of fiber concrete in the field of industrial floors and in the shotcrete in the case of tunnels and repair of large diameter pipes [1-5], and for the repair of road surfaces, the concrete can also be used to increase the fire resistance of reinforced concrete because the fibers would restrict crack openings and protect traditional frames of thermal radiation.

8 Bibliography [1] Y. Bouafia, MS. Kachi, B. Fouré, Relation contrainte déformation en traction du béton armé de fibres d’acier, Annales de l’ITB, n° 3, juin 2002. [2] Y.Bouafia, A. Adjrad, Utilisation des fibres locales pour renforcement du béton, Séminaire national de génie civil, M’sila (Algérie), 16 et 17 novembre 1997. [3] P. Casanova., P. Rossi., I. Schaller, Les fibres d’acier peuvent-elles remplacer les armatures transversales dans les poutres en béton armé, Bulletin de liaison, LCPC, n° 195, janvier 1995. [4] P. Rossi, N. Harrouche, et A. Belloc, «Méthode de composition des béton de fibres métalliques» Annales de L’ITBTP° 475, Juin-[5]Juillet 1989. [5] T.Y LIM, P. PARAMASSIVAM, S.L. LEE, Analytical model for tensile behaviour of steel – fiber concrete, ACI Materials Journal, n° 84, pp 286 – 289, July – August 1987.

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