67
Static and cyclic behavior of concrete reinforced with materials composite
A. Irekti1*, B.Hami1, C. Aribi1, M.T.Abadlia1
1 Unité de Recherche Matériaux, Procédés et Environnement, University M’Hamed Bougara - Boumerdes , Avenue de l’indépendance, 3500 Boumerdes, Algeria
Abstract
This work includes the test results of static and cyclic compression specimens of plain concrete and reinforced by several folds of woven fiberglass.
The static compression tests were performed at a constant speed with gradual increase of the load. The results are expressed by curves representing the change of stress as a function of the strain to failure. The results give us three phases of behavior: a phase behavior similar to that of a homogeneous and elastic material resulting in an almost linear relationship between stress and strain. The second phase of development of shattered concrete that leads to progressive curvature of the curve until the maximum stress (σmax) for a certain amount of strain (ε), and third in imposing increases distortion, we can get a decreasing curve corresponding to the accentuation of the rupture, that is to say in the development of fracture surfaces and cracking more or less widespread.
The cyclic compression tests were conducted under load imposed on a percentage of the maximum load in static fracture, with a change in the number of cycles for each set of specimens. The results of cyclic compression tests show that the loss of stiffness to failure of the specimen is divided into three phases: in the first phase shows a gradual reduction of stiffness in the early rounds in the second phase decreased rigidity becomes slow, and finally in the third phase, the loss of stiffness abruptly accelerates to failure of the specimen.
Keywords: Concrete, materials composite, reinforcement, static behavior, dynamic behavior;
1.
INTRODUCTION
The strengthening of reinforced concrete structures is a great way to extend their lifespan. Indeed, it is often much cheaper to build some structural components to perform a complete reconstruction of the structure.
Several reinforcement techniques are available on the market, including that which is in the external reinforcement with composite materials[1-6].
Composite materials have many advantages for their use, since they show a high strength / weight ratio and do not corrode . Thus, composite materials can both be used for flexural strengthening and shear of reinforced concrete beams, as well as containment of columns damaged structures[7-11].
The study of reinforced concrete cylindrical specimens with composite materials requires knowledge of different materials that constitute them, that is to say, concrete and composite. From the stress strain curves of these materials, we can represent the behavior of the whole. There are experimental studies, to define a theoretical relationship between stress and strain. [12-16]
Corresponding author: Irekti Amar E-mail: [email protected]
Adress :URMPE, University M’Hamed Bougara - Boumerdes avenue de l’indépendance, 3500 Boumerdes, Algeria
2. EXPERIMENTAL PROGRAM:
The cylindrical specimens (NF P 18-400) were made from ordinary concrete made of local raw materials and the composite material is made from fiberglass and matte epoxy Table 1.
The cylindrical specimens were divided into four main groups Table 2, [A] [B] [C] [D], each with three specimens. Specimens of group [A] and [D] were healthy and used to control the ultimate strength of concrete. The specimens of groups [B] and [C] were reinforced with one, two and three-ply composite plate made of fiber glass and matte epoxy resin and then subjected to static compression tests and Cyclic compression tests.
Test results:
We present in this chapter the results of various tests on composite flat and curved, sound concrete and concrete reinforced with GFRP. A comparison between these results in terms of stress - strain is made at the end.
2.1.1. Static compression tests
In this step, we realize static crush tests on specimens prepared 8x16 and reinforced by different layers of composites, 1fold and 2 folds.
The machine used for these tests is (250-ZWICK SN5A) to be, you can set the parameters by the software testing experts to meet the test:
The pre-load 10 N
The rate of pre-load 10 mm / min
The speed test 0,5 N/mm2.s
68 Table 1 Origin of the materials
Materials
Origin
Manufacturer Town Country
Cement 42.5 MPa ACC Cement M’sila Algeria
Coarse sand Oued Baghlia Boumerdes Algeria
Sand Sand of dune Boussaâda M’sila Algeria
Gravel 3 / 8 Career SCAC Cap Djinet Algeria
Gravel 8 / 15 Career SCAC Cap Djinet Algeria
Fiberglass Johns Manville Trnava Slovakia
Resin and hardener Granitex Oued Smar Algeria
Water ADE Boumerdes Algeria
2.2. Test results:
We present in this chapter the results of various tests on composite flat and curved, sound concrete and concrete reinforced with GFRP. A comparison between these results in terms of stress - strain is made at the end.
2.2.1. Static compression tests
In this step, we realize static crush tests on specimens prepared 8x16 and reinforced by different layers of composites, 1fold and 2 folds.
The machine used for these tests is (250-ZWICK SN5A) to be, you can set the parameters by the software testing experts to meet the test:
The pre-load 10 N
The rate of pre-load 10 mm / min
The speed test 0,5 N/mm2.s
2.1.1.1 Graphical representation of specimens strengthened:
Figure.1. Graph representing the average curves of unconfined concrete compressive
Figure.2. Graph representing the average curves of concrete confined compression with 1 fold composite Failure mode of specimens
Failure mode of specimens
Constraint (MPa)
Lengthening . %
Constraint (MPa)
Lengthening. (%)
69
Figure.3. Graph representing the average curves of concrete confined compression with 2 folds composite The graphs (Fig.1.2.3.) represent the curves of
static compression of concrete non-reinforced and strengthened by 1 and 2 folds GFRP. These tests are supposed to reflect the behavior of concrete at
constant speed V = 0.5 MPa / s. From the curve of stress-strain can distinguish three phases of behavior.fig.4.
Figure.4. Exemple typique de courbe contrainte déformation pour un béton renforce avec 2 plis (1) a phase behavior similar to that of a homogeneous
and elastic, resulting in an almost linear relationship between stress and strain. (2) The development phase of shattered concrete that leads to progressive curvature of the curve until reaching the maximum
stress (σmax) for a certain strain value (ε).
(3) Imposing strain increments, you can get a decreasing curve corresponding to the accentuation of the rupture, ie the development of fracture surfaces and cracks more or less widespread.
Table 2
Gains constraints and elongation of specimens reinforced concrete
Table.2. provides a comparison of results obtained by the different folds. It highlights a trend very apparent stress and strain. The stress increases to 24.62 MPa and 27.36 MPa 1 ply 2 ply for the composite. The evolution of deformation (ε) is very significant. To
sound concrete (ε) is 2.46%, the deformation
increases with the use of reinforcement.
ε = 2.77% for 1 fold and ε = 3.16% for 2 folds The gains stresses and deformation are illustrated by the histogram fig.5. we observed a significant Age
(days )
σ max (MPa)
ε σ max
(mm)
σ break (MPa)
ε σ break
(mm)
Gain σ (%)
Gain ε (%)
Concrete + 0 fold [A] 35 18,22 2,46 14,05 2,66 - -
Concrete + 1fold [B] 35 24,62 2,77 19,33 3,09 35,09 12,7
Concrete + 2folds [C] 35 27,36 3,16 21,78 3,61 50,13 54,98
Failure mode of specimens
Constraint (MPa)
Lengthening . %
Constraint (MPa)
Lengthening . %
70
Constraint (MPa)
Lengthening ( %)
Figure.9. Average cyclic compression concrete confined with 1 fold test curve.
Constraint (MPa)
Lengthening ( %)
Figure.10. Average cyclic compression concrete confined with 2 folds test curve Figure.6. Increase by cycle 0.05 mm
increase of 35.09% is for specimens reinforced with 1 fold, 50.13% for the two folds. These earnings confirm the effectiveness of the GFRP reinforcement applied to concrete.
Figure.5. histogram represents gains modules of elasticity and stress.
2.2.2.Cyclic compression
The compression tests were regulated by cyclic strain imposed. The nature of cyclic loading is cyclical increments. The increase of deformation from one cycle to another is always constant, and it is 0.05 mm.
The main test parameters are: the loading rate, the rate of discharge, level of increase, and their values are listed below:
Test method load bearing
Speed unlo ad ing 0, 5 mm / min, Fig.6.
Cha nge in st rengt h 5%
Pre-load 0.2 MPa
point of no return than 0.1 mm
The machine used for these tests is the universal machine ZWICK 250-SN5A
Gain E (GPa) % Gain σ %
Constraint (MPa)
Lengthening . % Figure.8. Average of cyclic compression concrete test
curve not confine
Figure.7. Speed of loading 0.5 MPa .s
71 2.2.2.1. Graphical representation of specimens
reinforced
3. The graphs Fig.8.9.10. represent the results of cyclic compression tests on specimens of concrete reinforced and unreinforced. We note above that the evolution of deformation during cyclic loading is départagée into three phases: a phase of rapid growth, estimated at 20% of the test period, followed by a phase of slow growth until they drop structure, and finally, a brutal An identification between the graphs of cyclic and static test only shows similar resistance maximum failure.
The break in cyclic compression strengthened specimens is primarily caused by the rupture of concrete seconded the rupture of the composite.
This is due to buoyant cyclical composite materials.
What we found an opening of two cracks (concrete and composite) different, but the trends are similar, with phases similar to those identified by the deformation. The break in cyclic composite is strained at the crack of the most gaping. The deformational history of concrete is faster than that of the composite then there are a total rupture of the composite due to a number of cycles applied. In other words, there are only two phases: a level of stress
with composite concrete and another phase in the composite.
According to the results shown in the table.3. It notes the evolution of characteristics of sound concrete and reinforced with layers of composite. Can conclude that: the compressive strength of reinforced concrete ring increases proportionately with the use of pleats, which is confirmed on the histogram, giving σmax = 16.35 MPa for non-reinforced concrete, for 1fold composite σmax = 21.52 MPa, a gain of 31.62%, σmax = 28.5 MPa for 2folds or a gain of 74.31%.
According to the results shown in the table.3. It notes the evolution of characteristics of sound concrete and reinforced with layers of composite. Can conclude that: the compressive strength of reinforced concrete ring increases proportionately with the use of pleats, which is confirmed on the histogram , giving σmax = 16.35 MPa for non-reinforced concrete, for 1fold composite σmax = 21.52 MPa, a gain of 31.62%, σmax = 28.5 MPa for 2folds or a gain of 74.31%.
The number of cyclic concrete also increases with confinement by the GFRP composite material, and evolves with the number of folds. We recorded a cycle number CN = 28 cycle for the non- reinforced concrete, which believes in CN = 70 for cycle 1 ply composite with a gain of 210%. The 2- ply composite gives CN = 91 cycle with a gain of 225%.
Table.3.
Comparison of cyclic compression means of sound concrete and reinforced.
4. CONCLUSION
The present study aims to see the mechanical "static and dynamic" composite and reinforced concrete and not reinforced by fiberglass "matte." And from the tests and in light of the results obtained, it appears the following:
The application of composite material on the surface of concrete increases the resistance dramatically cyclic loading [17].
It was found that the gain in compressive strength increases with increasing the number of folds. Is this even for the number of cycles
Number of cycle
σ breaking (MPa )
ε max (%) Gain σ (%) Gain N
Concrete + 0 fold [D] 28 16,35 1,65 - -
Concrete + 1 fold [B] 70 21,52 2,805 31,62 210
Concrete + 2 folds [C] 91 28,5 3,975 74,31 225
Gain σ % Gain Nc %
Figure.11. histogram represents gains by constraints in terms of number of cycle
72 During cyclic compression tests, we recorded the evolution of the number of cycles depending on the number of folds. Analysis of these results shows that the loss of stiffness until failure of the test is conducted in 3 phases, the first phase occurs a progressive decrease in the early cycles, the decrease becomes very slow in second phase, corresponding to the quasi-totality of the life of the specimen, and finally in stage three short, which accelerates the loss of stiffness Brutally until rupture of the specimen.
The lifetime increases with decreasing load level.
In addition to these experimental results, it is well known that composite materials are resistant to cyclic loading, so the life of reinforced concrete increases in areas under load repeat
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