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Fresh and hardened properties of self-compacting concrete containing plastic bag waste fibers (WFSCC)
Construction and Building Materials 82 (2015) 89–100
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Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Fresh and hardened properties of self-compacting concrete containing plastic bag waste fibers (WFSCC) Youcef Ghernouti a,⇑, Bahia Rabehi a, Tayeb Bouziani b, Hicham Ghezraoui c, Abdelhadi Makhloufi c a
Research Unit: Materials, Processes and Environment, University M’Hamed Bougara of Boumerdes, Algeria Structures Rehabilitation and Materials Laboratory (SREML), University Amar Telidji of Laghouat, Algeria c Materials Engineering Department, Faculty of Engineering Science, Boumerdes University, Algeria b
h i g h l i g h t s Recycling plastic bag waste fibers as reinforcement of SCC. Effects of length and fiber contents on fresh and hardened properties of SCC. Stress–strain behavior of SCC reinforced by plastic bag waste fibers. Load–deflection behavior of SCC reinforced by plastic bag waste fibers.
a r t i c l e
i n f o
Article history: Received 20 November 2014 Received in revised form 2 February 2015 Accepted 20 February 2015
Keywords: Self-compacting concrete Plastics bag waste fiber Workability Compressive strength Flexural strength Split tensile
a b s t r a c t This paper presents the fresh and hardened properties of self-compacting concrete (SCC) containing plastic bag waste fibers (PBWF). Fibers were prepared by recycling waste material such as, plastic bag. Fourteen mixtures of SCC with 0.40 of water/cement ratio were studied, twelve SCC mixtures with plastic bag waste fiber (WFSCC) by varying the length of fibers (2, 4 and 6 cm) with different levels of incorporation (1, 3, 5 and 7 kg/m3) and two other mixtures, one with 1 kg/m3 of polypropylene fibers (PFSCC) and another without fiber as reference (RSCC). Slump flow, L-box, and sieve stability were performed to assess the fresh properties of the prepared mixtures. Compressive strength, splitting tensile strength and flexural strength of the concrete were determined for the hardened properties Test results show that mixtures based on PBWF with a length of 2 cm, met the criteria of self-compactability (evaluated by slump flow diameter, L-box and sieve stability test) regardless of the fibers content. The obtained results are very interesting, suggesting a possible use of PBWF for structural reinforcement of SCC, the presence of this fibers in concrete delaying the location of microcracks. Although, the incorporation of PBWF has not a significant effect on the compressive and flexural strengths, it has a important effect on the split tensile strength value at 28 days. The improvement varies from 4% to 74%, it depends on the amount of fibers, and it is not affected by the length of PBWF. Ó 2015 Elsevier Ltd. All rights reserved.
1. Introduction The reuse of plastic wastes plays an important role in sustainable solid waste management. From different points of view, it helps to save natural resources that are not replenished, it decreases the pollution of the environment and it also helps to save and recycle energy production processes. Wastes and industrial byproducts should be considered as potentially valuable resources merely awaiting appropriate treatment and application. Plastic wastes are among these wastes; their disposal has harmful effects ⇑ Corresponding author. Tel.: +213 555478419; fax: +213 24913866. E-mail addresses: [email protected], [email protected] (Y. Ghernouti). http://dx.doi.org/10.1016/j.conbuildmat.2015.02.059 0950-0618/Ó 2015 Elsevier Ltd. All rights reserved.
on the environment due to their long biodegradation period, and therefore one of the logical methods for reduction of their negative effects is the application of these materials in other industries. Much research effort has focused on reusing waste materials from plastic industries in concrete. The addition of plastic waste to concrete corresponds to a new perspective in research activities, integrating the areas of concrete technology and environmental technology. Numerous studies on fiber reinforced concrete have been performed. The research results show that concrete reinforced with short plastic fibers drastically improves the performance of concrete and negates its disadvantages such as low tensile strength, low ductility, and low energy absorption capacity [1–10].
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Polypropylene, polyethylene, nylon, and polyesters are commonly used short plastic fibers in concrete members [10–12]. Among these materials, polypropylene fibers are one of the most widely used for construction applications such as blast resistant concrete and pavements [13,14]. Different works, have analyzed the effect of addition of recycled polyethylene terephthalate (PET) to the properties of concrete [15– 17]. The fibers of recycled PET easily mix in the concrete, giving new properties to the material [18]. Another author has observed that the addition of tire rubber particles provided the concrete with higher ductility in compressive strength testing, if compared with concrete without addition [19]. Soroushian et al. [20] stated that polypropylene can be used as synthetic fibers to increase the toughness of concrete. The study carried out by Kou et al. [21] revealed that the workability, compressive strength, and tensile splitting strength of lightweight aggregate concretes prepared with recycled plastic waste were reduced. Foti [22] analyzed the reinforced concrete with PET bottles waste fibers and found that adding little amount of recycled fibers from PET bottle wastes can have a great influence on postcracking performance of simple concrete elements. As well, these fibers improve the toughness of samples and increase the plasticity of concrete. Pereira de Oliveira et al. [23], used fibers made from recycled PET bottles in reinforced mortar. Their results showed that using PET fibers makes a significant improvement on compressive strength of mortars, in addition to a noticeable effect on their flexural strength along with increase in their toughness. The work realized by Foti [24] is to explore the possibility of recycling PET fibers, obtained from waste bottles with different shapes. The tests showed that PET fibers in a concrete mixture are likely to increase the ductility of concrete. Meddah and Bencheikh [25], studied the influence of volume and length of waste metallic fibers and polypropylene fibers on the compressive and flexural strengths, and toughness of fibers reinforced concretes. The results obtained have shown that the polypropylene fibers decrease the compressive strength, especially when using long fibers with high volume fraction. A slight decrease of the compressive strength was also observed with the composites containing more than 2% of the waste metallic fibers. However, adding the polypropylene fibers and the hybrid fibers increases the flexural strength of fibers reinforced concretes. An experimental investigation was performed by Khaloo et al. [26], to study the rheological and mechanical behavior of two strength classes (medium and high strength) of the self-compacting concrete reinforced with steel fibers, using four different volume fractions (0.5%, 1%, 1.5%, and 2%), the workability of all SCC classes is reduced by increasing the steel fiber volume fraction, and using high percentages of fibers led to decrease of other rheological characteristics. On the contrary, splitting tensile strength, flexural strength, and flexural toughness are increased by increasing the percentage of fibers; however compressive strength is decreased by increasing the percentage of fibers. Mazaheripour et al. [27], investigate the effect of polypropylene fibers inclusion on fresh and hardened properties of lightweight self-compacting concrete (with a density of 1700–2000 kg/m3). The results obtained have shown that the polypropylene fibers did not influence the compressive strength and elastic modulus, however applying these fibers at their maximum percentage volume determined through this study, increased the tensile strength by 14.4% in the splitting tensile strength test, and 10.7% in the flexural strength. In the study of Kim et al. [28], the basic material properties and drying shrinkage resistance of concrete reinforced with recycled PET fibers are evaluated. These recycled PET fibers are produced from waste PET bottles. Based on the study results, which include comparisons with specimens containing polypropylene fibers
reinforcement, PET fiber reinforced concrete exhibited a slight decrease in compressive strength and elastic modulus as the fiber volume fraction increased. The recycled PET and polypropylene fiber-reinforced specimens showed a decrease in compressive strength about 1–9% and 1–10%, respectively, compared to specimens without fiber reinforcement. In this study, fresh and hardened properties of self-compacting concrete containing plastic bag waste fibers (WFSCC) are evaluated. Recycled plastic bag waste fibers (PBWF) are produced from plastic bag waste, as described later in this paper. A comparison with non-confined self-compacting concrete (RSCC) and SCC containing polypropylene fiber (PFSCC) were also performed. 2. Experimental program and test procedures 2.1. Materials 2.1.1. Concrete mix Ordinary Portland cement CEM II/A 42.5 NA, from Algeria cement factories, with a density of 3.1 g/cm3 was used. Continuously graded coarse aggregates 3/8 and 8/ 15 were used in this study with specific gravity and water absorption of 2.58 g/cm3 and 1.03% respectively. Natural sand of 3 mm maximum size was used as fine aggregate, with a specific gravity of 2.5 g/cm3 and a fineness modulus of 2.4. The limestone fillers used in this work, were issued from the crashing plant of Boumerdes (Algeria). A polycarboxylate-based superplasticizer named MEDAFLUID-104 was used to achieve the appropriate workability of the concrete mixes. 2.1.2. Polypropylene fiber (PF) The used polypropylene fibers, named GRANIFIBRE are shown in Fig. 1, these fibers have a length of 12 mm, a diameter of 30 lm, a modulus elasticity of 3kN/ mm2 and a density of 0.9. 2.1.3. Recycled plastic bag waste fiber (PBWF) The used recycled PBWF are produced from plastic bag waste (as seen in Fig. 2). The plastic bags waste are introduced into a regenerating at a temperature around 250 °C, and then exits as a fibrous pulp that passes through a tank of water for cooling and hardening. Then they will be cut in fibers. The recycled PBWF has a diameter of 1.6–2 mm and a specific gravity of 0.87 g/cm3. Tensile test was performed on two samples of recycled PBWF with 50 mm length and 1.6 mm in diameter, using ZWICK/Z010 machine, with a capacity of 10kN and a loading speed of 50 mm/min (Fig. 3). The results of tensile test are represented in the Fig. 4 and shown in Table 1. 2.2. Mixture proportions Based on self-compacting concrete mix design japanese method [29], fourteen mixes were produced: a reference self compacting concrete (coded RSCC) and thirteen mixtures of fibers reinforced self compacting concrete. For all the mixtures, the total amounts of cement, fillers, coarse aggregates, sand, water and superplasticizer were all kept constant (430, 30, 350, 314, 174 and 6.6 kg/m3 respectively). Twelve mixtures of reinforced concrete containing PBWF (coded WFSCC), indicating the different values of fiber length (2, 4 and 6 cm), and different values of fiber content (1, 3, 5 and 7 kg/m3). For comparison a mixture concrete based on polypropylene fiber (coded PFSCC) is also prepared with a fiber length of 1.2 cm and a fiber content of 1 kg/m3.
Fig. 1. Polypropulene fiber (GRANIFIBRE).
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Fig. 2. Stages of recycling plastic bag waste fiber (PBWF).
Fig. 3. Experimental setup of tensile test.
2.3. Preparation and casting of test specimens The mixing procedure and time are very important, thus the mixing process was kept constant for all concrete mixtures. All the ingredients were first mixed under dry condition in the concrete mixer for one minute. Then 70% of calculating amount of water was added to the dry mix and mixed thoroughly for one minute. The remaining amount of water was mixed with the superplasticizer and was poured into the mixer and mixed for five minutes. Later, required quantities of fiber were sprinkled over the concrete mix and mixed for one minute to get a uniform mix. Thus, the total mixing time was 8 min. After this sequence of preparation, flowability, passing ability and resistance to segregation of prepared mixtures are measured. For each concrete mixture three prisms of 70 * 70 * 280 mm and three cylinders 110 * 220 mm specimens were cast. Therefore, the total number of specimens considered in this experimental investigation was forty two cylinders and forty two beams. The specimens were demolded after one day and then placed in a curing room with an humidity of 90% and a temperatutre of 20 ± 2 °C until the testing days.
Fig. 4. Stress–strain curves of PBWFsamples.
2.4. Tests on fresh concretes The flowability was evaluated by slump flow diameter, the passing ability was measured by L-box and the resistance to segregation was measured by sieve stability test, according to the specification and guidelines for SCC prepared by the European project group [30]. The slump flow is used to evaluate the horizontal free flow (deformability) in the absence of obstructions. The test method is very similar to that for determining the slump of concrete. The difference is that, instead of the loss in height, the diameter of the spread concrete is measured in two perpendicular directions and recorded as slump flow. The higher the slump flow is, the larger is concrete’s ability to fill formwork. According to Nagataki and Fujiwara [31], a slump flow diameter ranging from 500 to 700 mm is considered as the slump required for
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Table 1 Tensile test results of recycled plastic bag waste fiber (PBWF). Sample
Maximal stress (N/mm2)
Breaking stress (N/mm2)
Elongation (%)
Elastic modulus (GPa)
1 2 Average
31.17 31.90 31.5
9.39 12.04 10.7
13.20 14.43 13.8
0.03 0.03 0.03
a concrete to be classified as SCC. According to the recommandations of the European project group [30], a slump flow diameter ranging from 650 to 800 mm can be accepted for SCC. In addition to the slump flow test, L-box and sieve stability tests are also performed to assess the passing ability and stability of SCC. L-box test measures the fresh SCC passing ability and self-leveling. The test apparatus made from two prisms and set as L form box with three bars and opening slide at bottom box connector. As the vertical box is fully filled, the slid then is opened that allows the fresh SCC flow passing the steel bar. The self-leveling ratio is measured as the ratio between the highs of fresh concrete surface at the beginning (h1) and at the end (h2). For acceptable SCC, L-box ratio must be in the range of 0.8–1.0 and the sieve stability values must be in the range of 0–15% (see Fig. 5).
Fig. 6. Compressive strength test.
2.5. Tests on hardened concrete Tests on hardened concrete have been performed to determine compressive strength, splitting tensile strength and flexural strength. The test results were reported as the average of three tested specimens in the respective testing. From each concrete mixture, 70 * 70 * 280 mm beams has been casted for the determination of flexural strength, and 110 * 220 mm cylinders for the determination of compressive strength and splitting tensile strength tests.
Fig. 7. Flexural strength test.
2.5.1. Compressive strength test Compressive strength have been determined at 28 days in accordance with NF EN 12390-3 standard. The specimens were loaded under a monotonic uni-axial compressive load up to failure by using an MATEST hydraulic testing machine with a capacity of 3000 kN (Fig. 6). The loading rate was approximately 0.4 MPa/s. The higher tray is fixed and the lower support is mobile. Before testing, the faces of the specimen were suffered with a surfacing machine, to ensure parallelism and flatness of the faces of support. An extensometric comparator is fixed to the side face of the specimen at mid-height. The value of the vertical force and the corresponding displacement is recorded simultaneously.
2.5.2. Flexural strength test Flexural strength test was carried out using a three-point loading method at 28 days of curing age, conforming to NF EN 12390-5 standard. The specimens were subjected to bending tests with a concentrated load at the centerline in order to verify their behavior. The bending tests were performed by an ZWICK/Roell test machine of 60 kN maximum load, with a loading rate of 0.05 MPa/s (Fig. 7), using a comparator to measure the elongation of the specimen to view in real-time the load–displacement curves and record, moment by moment, the values of load and displacement.
Fig. 8. Splitting tensile strength test.
3. Results and discussions 3.1. Fresh concrete properties
2.5.3. Splitting tensile strength test Splitting tensile strength has been determined at 28 days in accordance with ASTM C496 standard. The cylindrical sample with dimensions of 110 ⁄ 220 mm is horizontally placed in a special ring of the compressive machine with the capacity of 3000 kN (Fig. 8). The force is applied along the cylinder’s vertical axis constantly, until the fracture happens. The loading rate was approximately 0.05 MPa/s.
(a) Slump flow test
As a first part of this study, the objective is to know the influence of the plastic bag waste fibers (PBWF) on the workability of concrete. The obtained results of the slump flow diameter, L-box and sieve stability test of different mixtures are given in Table 2.
(b) L-box test Fig. 5. Tests on fresh concretes.
(c) Seive stability test
Y. Ghernouti et al. / Construction and Building Materials 82 (2015) 89–100 Table 2 Fresh properties of self-compacting concretes. Mix ID
Slump flow (mm)
L-box ratio (%)
Sieve stability (%)
RSCC WFSCC1(2) WFSCC3(2) WFSCC5(2) WFSCC7(2) WFSCC1(4) WFSCC3(4) WFSCC5(4) WFSCC7(4) WFSCC1(6) WFSCC3(6) WFSCC5(6) WFSCC7(6) PFSCC
660 660 680 690 690 660 680 695 700 660 685 705 710 621
0.9 0.9 0.88 0.85 0.82 0.81 0.72 0.67 0.59 0.57 0.48 0.41 0.34 0.64
7.64 8 9 10 13 8 13 14 18 8 14 21 28 5.7
From the obtained results it can be seen that the incorporation of PBWF in the SCC, improves the slump flow diameter, regardless the dosage and the length of the fibers. This is may be due to the smooth surface of these fibers, which facilitates the flow of the fresh concrete. It can be also seen that all WFSCC meet the criterion of slump flow (slump flow values between 650 and 800 mm) [30]. However, PFSCC (with polypropylene fibers) does not meets this criterion due to the negative effect of polypropylene fibers, which can be attributed to the increase of SCC viscosity in the presence of polypropylene fibers. This result was confirmed by the majority of reinforced concrete researches Hashem et al. [32], Salih and ALAzaawee [33]. It can also be noted that the addition of polypropylene fibers in mortars and flowable concretes present a large reduction in the workability and increase the viscosity [34], however, it can be also reported that the effect of the ratio (l/d) of plastic waste fibers on the slump flow is less important than the effect of their content percentage [35].
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During the L-box test, it is important to note that the concrete flows through the frames properly and no blocage has been observed for WFSCC mixes with a fiber length of 2 cm regardless of the dosage of fibers (1, 3, 5 and 7 kg), since all the WFSCC mixes present an L-box ratio higher than 0.80 (see Fig. 9). However, the increase of fiber length of PBWF above 4 cm causes immobility of WFSCC mixes in confined environment. This may be attributed to the fact that the length of fibers (4 cm) exceeds the spacing between the reinforcement of the L-box which is the order of 3.5 cm. The polypropylene fibers influential adversely on mobility of SCC in a confined concrete (blocking of concrete in L-box), this is due to the significant amount of fiber added during mixing (1 kg/m3). All WFSCC containing plastic fibers with a length of 2–4 cm have a segregation rate lower than 15% which indicate a good stability. By increasing the length and the dosage of the fibers the segregation ratio of WFSCC increase. For PFSCC mix which contain 1% of polypropylene fibers, the sieve stability test value indicates that is conform up to the standard of segregation. Finally, it can be concluded from the three tests on fresh concrete (slump flow diameter, L-box and sieve stability tests) that the best formulation satisfying the criteria of self-compactability is that the concrete containing a plastic bag waste fiber with a length of 2 cm, regardless of the fiber content.
3.2. Hardened concrete properties 3.2.1. Compressive strength Fig. 10 presents the results of compressive strength at 28 days, performed on cylindrical specimens (110 * 220 mm) for all studied mixtures. By examining the Fig. 10, it can be found that the compressive strength at 28 days is an increasing function with the increase amount of PBWF whatever the length of these fibers.
Fig. 9. Evolution of L-box ratio depending on the length and the content of PBWF.
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Fig. 10. Compressive strength values for all mixtures at 28 days.
The incorporation of short PBWF, with 2 cm length in SCC causes approximately the same variation of compressive strength as that caused by the incorporation the fibers with 4 and 6 cm length, whatever the amount of fiber used. Therefore, the length/diameter ratio (l/d) of PBWF does not affect the compressive strength at 28 days. Other studies have found lower 28-day compressive strength values prepared with short synthetic polypropylene fiber, compared to compressive strength of unreinforced concretes [36]. The concrete based on polypropylene fibers (PFSCC), has the same compressive strength value at 28 days that the reference concrete (SCC). In this study, the increase of compressive strength of specimens concrete based on plastic bag waste fiber (WFSCC) is about 13% maximum, compared to the reference SCC and PFSCC in the case of the mix containing a large amount of fibers (7 kg/m3). The slight increase in compressive strength with the incorporation of plastic fibers is confirmed by several authors who show a negligible effect of these fibers on the compressive strength [37]. The compressive strength of the nylon fiber concrete and the polypropylene fiber concrete was improved by 12.4% and 5.8% respectively for a fibers concentration of 0.6 kg/m3. Nevertheless, the majority of the researches realized on reinforced concretes indicated that plastic fiber reinforced concretes have a negligible evolution of the compressive strength [38,39]. The possible reason for this behavior is the bad homogeneity of the concrete, the high ratio of water or the weak compactness of the concrete caused by the excess of fibers content.
The Figs. 11–13 show the behavior laws stress–strain of WFSCC prepared with 2, 4 and 6 cm respectively, compared to RSCC (reference concrete). The comparison of WFSCC with RSCC allows assessing the gains in strength and deformability of concrete. From these figures, it can be seen that SCC contain a large amount of PBWF (5 or 7 kg/m3) with a fiber length of 6 cm, gain about 7% and 10% in compressive strength respectively (see Fig. 10) and more are characterized with a large phase of plastic deformation. This can be explained by the effect of fiber length which prevent and retard the propagation of cracks. Typically, all stress–strain curves exhibit an initial slope up to an inflection point, followed by a large deformation zone. Depending on the dosage and the length of fiber, the stress level and the plastic zone varies considerably from one variant to another. We find that all specimens of WFSCC have suffered a behavior divided into three phases: (1) A linear phase: happening before micro cracking of concrete, similar to the control concrete up to 50% of the breaking load. (2) A curved phase: in this ascending part, the concrete shows a microcracks and the fibers are put under tension. (3) Descending phase: the effort is taken up by the fibers that assemble the cracked concrete until rupture. In general, the different types of fibers can change the axial behavior of concrete by improving its strength and ductility. The
Fig. 11. Stress–strain curves of WFSCC with a length of 2 cm, compared to RSCC.
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Fig. 12. Stress–strain curves of WFSCC with a length of 4 cm, compared to RSCC.
Fig. 13. Stress–strain curves of WFSCC with a length of 6 cm, compared to RSCC.
Fig. 14. Stress–strain curves of WFSCC with a length of 2 cm and a content of 5 kg/m3 compared to PFSCC and RSCC.
same findings are observed in the behavior of studied WFSCC specimens. However, the ultimate values of the corresponding strain at failure of these specimens are much higher. It can be also observed that the mechanical behaviors of specimens are different. The rigidity of WFSCC specimens is higher than
that of RSCC specimen. The plastic zone of these specimens is also greater than that of RSCC specimens. It is very clear that the improve in the maximum deformation is considerable in the case of WFSCC specimens containing a higher amount of PBWF. As can be expected from Figs. 11–13, for the values 5 and 7 kg/m3
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has been also confirmed in a recent study performed on the use of plastic waste as fine aggregate in self-compacting mortars [40].
Fig. 15. Physical adhesion between PBWF and cement paste.
of PBWF contents, the strain in the specimens WFSCC exceeds 50% of that in the RSCC specimen. The maximum value of the strain is 4660 lm/m (observed for WFSCC5(2)). Fig. 14 shows a comparison between the stress–strain curves of WFSCC5(2), PFSCC and RSCC mixtures. According to this figure, it can observed that WFSCC5(2) has shown a better behavior in terms of strength and deformability. The improvement in compressive strength of concrete containing PBWF is about 11% and 13% compared to RSCC and PFSCC, respectively. The gain in strain for WFSCC is about 58% compared to RSCC. However, the fracture surface of WFSCC shows that most of PBWF are not pulled out and remain stuck in the concrete specimens. The good adhesion of PBWF can be reported to their annular and cylindrical forms which promote the physical bond with cement paste (Fig. 15). This finding
3.2.2. Flexural tensile strength The test results of 28 days flexural load for all studied mixtures are shown in Fig. 16. As a first result, it can be observed that the flexural load of all reinforced fiber concrete mixtures is higher than that of the control concrete. This improvement varies from 0% to 14%, and it depends on the type, the amount and the length of fibers. The incorporation of short PBWF with 2 cm length in SCC does not affect the flexural strength whatever the amount of fiber used. In general, the incorporation of plastic bag waste fibers in the SCC has not a significant effect on flexural strength. For a PBWF amount of 7 kg/m3, the flexural load is improved about 14% and 11% for mixtures with 4 cm and 6 cm in PBWF length, respectively (Fig. 17), compared to the reference concrete (RSCC). This can be explained by the strong bond between the fibers and the cementitious matrix and the local constraints given by the presence of these fibers which occur in an oblique and vertical way against the microcracks. Figs. 18–20 show the obtained load–deflection curves for WFSCC mixtures made with 2, 4 and 6 cm length of PBWF. The results show that the elastic behavior of all specimens before cracking was approximately similar whatever the fiber content. The initiation of cracks occurred earlier in the specimens without fibers than in the fiber reinforced concrete specimens. From these figures, it can be observed a loss in deflection values for all mixtures containing PBWF with 2 cm length; this is may be due to the limited length of fibers that cannot prevent the propagation of cracks.
Fig. 16. Values of flexural load at 28 days for all mixtures.
Fig. 17. Gain of flexural Load for WFSCC in comparison with RSCC and PFSCC.
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Fig. 18. Load–deflection curves of WFSCC(2) and RSCC specimens at 28 days.
Fig. 19. Load–deflection curves of WFSCC(4) and RSCC specimens at 28 days.
Fig. 20. Load–deflection curves of WFSCC(6) and RSCC specimens at 28 days.
However, the mixtures with 4 and 6 cm PBWF length show a better crack resistance and strain–hardening capacities than the specimens without fibers. Due to the increase in crack resistance, the macro-crack propagation in the material is delayed, which stabilizes the overall behavior of the structural member. Fig. 21 shows the load–deflection curves of the mixture WFSCC7(4) in terms of flexural load and deformability
compared to PFSCC and RSCC. From this figure, it can be found that the specimens of concrete reinforced by PBWF have shown a better behavior in terms of strength and deformability. The flexural load of the mixture WFSCC7(4) is approximately similar to PFSCC and RSCC. However, the deflection in WFSCC7(4) is higher about 21% and 16% compared to RSCC and PFSCC respectively.
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Fig. 21. Load–deflection curves of WFSCC with a length of 4 cm and a content of 7 kg/m3 compared to PFSCC and RSCC.
Fig. 22. Splitting tensile strength value of all mixtures at 28 days.
Fig. 23. Gain in splitting tensile strength of WFSCC in comparison with RSCC and PFSCC.
3.2.3. Splitting tensile strength Split tensile test of WFSCC, RSCC and PFSCC is shown in Fig. 22. The results clearly indicate that the split tensile strength of all WFSCC mixtures is higher than that of the control concrete, and evolves with the increase of PBWF content. The incorporation
of PBWF in SCC has a significant effect on the split tensile strength value at 28 days. The recorded improvement of WFSCC in comparison to RSCC varies from 4% to 74%, it depends on the amount of PBWF, and it is not affected by the length of these fibers (Fig. 23).
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The maximum gains are obtained for the WFSCC containing the maximum dosages of PBWF. For example as can be seen from Fig. 22, for a PBWF content of 7 kg/m3, the splitting tensile strength was improved by 67, 74 and by 70% for WFSCC mixtures with fibers length of 2, 4 and 6 cm, respectively, compared to RSCC. This improvement can be explained by the large amount of PBWF and the action of these fibers in preventing the propagation of cracks. The enhancement of the splitting tensile strength with the increase of fibers content is also confirmed by Salih and ALAzaawee [33].
4. Conclusions This experimental investigation focuses on the effect of reused plastic bags waste fibers (PBWF) on fresh and hardened properties of SCC. The ecological benefit of effectively utilizing this waste material is another prime motivation for this work. From the obtained results of this study, the following conclusions can be drawn: – The incorporation of PBWF in the concrete, improves the slump flow spreading and facilitates the flow of the fresh concrete. All plastic reinforced SCC meet the criterion of slump flow recommendations, except for SCC made with polypropylene fibers. The effect of the length/diameter ratio (l/d) of PBWF on the slump flow diameter is less important than the effect of their content percentage. – Plastic waste fiber self-compacting concrete (WFSCC) made with PBWFof 2 cm in length present an L-box ratio higher than 0.80 and show an easy passing through L-box bars. While the increase in PBWF length above 4 cm causes the blocage of WFSCC flow. – WFSCC made with PBWF of 2–4 cm have a segregation rate lower than 15% stands for a good stability. However, the increase in fibers length and content, decreased the stability. – The length/diameter ratio (l/d) of PBWF does not affect the 28day compressive strength. The increase in compressive strength is about 7–13%, compared to the reference concrete (RSCC). For WFSCC containing a large amount of fibers, the strain exceeds 50% compared to RSCC. – The incorporation of PBWF in the SCC has a negligible effect in the flexural strength. The flexural load of WFSCC is improved if compared to the RSCC. The incorporation of short plastic bag waste fiber with 2 cm length does not affect the flexural strength whatever the amount of fiber used. – The incorporation of PBWF in SCC has a positive effect on the split tensile strength value at 28 days. The improvement can reach 74%, it depends on the amount of PBWF, and it is not affected by the length of fibers. – The presence of PBWF in SCC prevents the sudden break and increases the fracture toughness of the material; this property can be interesting in terms of security, since even after breaking, the parts of concrete remain attached to each other. Finally, it can be said that the use of PBWF in the SCC brings two major advantages: The first one regards the protection of the environment through the recycling of this harmful waste. Second, the recycled PBWF can be used successfully in structural SCC for improving their fresh and hardened properties.
Acknowledgement This research was supported by the General Directorate for Scientific Research and Technological Development of Algeria.
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The effect of polypropylene fibers on the properties of fresh and hardened lightweight selfcompacting concrete. Constr Build Mater 2011;25:351–8. [28] Kim SB, Yi NH, Kim HY, Kim J-HJ, Song Y-C. Material and structural performance evaluation of recycled PET fiber reinforced concrete. Cement Concr Comp 2010;32:232–40. [29] Okamura H, Ozawa K. Mix design for self-compacting concrete. Concrete Lib JSCE 1995;25:107–20. [30] EFNARC. The European Guidelines for Self-Compacting Concrete. 2005. [31] Nagataki S, Fujiwara H. Self-compacting property of highly flowable concrete. ACI Special Publ 1995;154:301–14. [32] Hashem M, Al-Mattarneh A, Zakiah A. Characterization of Natural Fibre Concrete using Destructive and Non-Destructive Testing Methods. Proceeding of the 6th International Conference on Concrete Technology for Developing Countries, Amman, Jordan, 2002; 551–560. [33] Salih SA, AL-Azaawee ME. Effect of polypropylene fibers on properties of mortar containing crushed bricks as aggregate. 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Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Fresh and hardened properties of self-compacting concrete containing plastic bag waste fibers (WFSCC) Youcef Ghernouti a,⇑, Bahia Rabehi a, Tayeb Bouziani b, Hicham Ghezraoui c, Abdelhadi Makhloufi c a
Research Unit: Materials, Processes and Environment, University M’Hamed Bougara of Boumerdes, Algeria Structures Rehabilitation and Materials Laboratory (SREML), University Amar Telidji of Laghouat, Algeria c Materials Engineering Department, Faculty of Engineering Science, Boumerdes University, Algeria b
h i g h l i g h t s Recycling plastic bag waste fibers as reinforcement of SCC. Effects of length and fiber contents on fresh and hardened properties of SCC. Stress–strain behavior of SCC reinforced by plastic bag waste fibers. Load–deflection behavior of SCC reinforced by plastic bag waste fibers.
a r t i c l e
i n f o
Article history: Received 20 November 2014 Received in revised form 2 February 2015 Accepted 20 February 2015
Keywords: Self-compacting concrete Plastics bag waste fiber Workability Compressive strength Flexural strength Split tensile
a b s t r a c t This paper presents the fresh and hardened properties of self-compacting concrete (SCC) containing plastic bag waste fibers (PBWF). Fibers were prepared by recycling waste material such as, plastic bag. Fourteen mixtures of SCC with 0.40 of water/cement ratio were studied, twelve SCC mixtures with plastic bag waste fiber (WFSCC) by varying the length of fibers (2, 4 and 6 cm) with different levels of incorporation (1, 3, 5 and 7 kg/m3) and two other mixtures, one with 1 kg/m3 of polypropylene fibers (PFSCC) and another without fiber as reference (RSCC). Slump flow, L-box, and sieve stability were performed to assess the fresh properties of the prepared mixtures. Compressive strength, splitting tensile strength and flexural strength of the concrete were determined for the hardened properties Test results show that mixtures based on PBWF with a length of 2 cm, met the criteria of self-compactability (evaluated by slump flow diameter, L-box and sieve stability test) regardless of the fibers content. The obtained results are very interesting, suggesting a possible use of PBWF for structural reinforcement of SCC, the presence of this fibers in concrete delaying the location of microcracks. Although, the incorporation of PBWF has not a significant effect on the compressive and flexural strengths, it has a important effect on the split tensile strength value at 28 days. The improvement varies from 4% to 74%, it depends on the amount of fibers, and it is not affected by the length of PBWF. Ó 2015 Elsevier Ltd. All rights reserved.
1. Introduction The reuse of plastic wastes plays an important role in sustainable solid waste management. From different points of view, it helps to save natural resources that are not replenished, it decreases the pollution of the environment and it also helps to save and recycle energy production processes. Wastes and industrial byproducts should be considered as potentially valuable resources merely awaiting appropriate treatment and application. Plastic wastes are among these wastes; their disposal has harmful effects ⇑ Corresponding author. Tel.: +213 555478419; fax: +213 24913866. E-mail addresses: [email protected], [email protected] (Y. Ghernouti). http://dx.doi.org/10.1016/j.conbuildmat.2015.02.059 0950-0618/Ó 2015 Elsevier Ltd. All rights reserved.
on the environment due to their long biodegradation period, and therefore one of the logical methods for reduction of their negative effects is the application of these materials in other industries. Much research effort has focused on reusing waste materials from plastic industries in concrete. The addition of plastic waste to concrete corresponds to a new perspective in research activities, integrating the areas of concrete technology and environmental technology. Numerous studies on fiber reinforced concrete have been performed. The research results show that concrete reinforced with short plastic fibers drastically improves the performance of concrete and negates its disadvantages such as low tensile strength, low ductility, and low energy absorption capacity [1–10].
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Polypropylene, polyethylene, nylon, and polyesters are commonly used short plastic fibers in concrete members [10–12]. Among these materials, polypropylene fibers are one of the most widely used for construction applications such as blast resistant concrete and pavements [13,14]. Different works, have analyzed the effect of addition of recycled polyethylene terephthalate (PET) to the properties of concrete [15– 17]. The fibers of recycled PET easily mix in the concrete, giving new properties to the material [18]. Another author has observed that the addition of tire rubber particles provided the concrete with higher ductility in compressive strength testing, if compared with concrete without addition [19]. Soroushian et al. [20] stated that polypropylene can be used as synthetic fibers to increase the toughness of concrete. The study carried out by Kou et al. [21] revealed that the workability, compressive strength, and tensile splitting strength of lightweight aggregate concretes prepared with recycled plastic waste were reduced. Foti [22] analyzed the reinforced concrete with PET bottles waste fibers and found that adding little amount of recycled fibers from PET bottle wastes can have a great influence on postcracking performance of simple concrete elements. As well, these fibers improve the toughness of samples and increase the plasticity of concrete. Pereira de Oliveira et al. [23], used fibers made from recycled PET bottles in reinforced mortar. Their results showed that using PET fibers makes a significant improvement on compressive strength of mortars, in addition to a noticeable effect on their flexural strength along with increase in their toughness. The work realized by Foti [24] is to explore the possibility of recycling PET fibers, obtained from waste bottles with different shapes. The tests showed that PET fibers in a concrete mixture are likely to increase the ductility of concrete. Meddah and Bencheikh [25], studied the influence of volume and length of waste metallic fibers and polypropylene fibers on the compressive and flexural strengths, and toughness of fibers reinforced concretes. The results obtained have shown that the polypropylene fibers decrease the compressive strength, especially when using long fibers with high volume fraction. A slight decrease of the compressive strength was also observed with the composites containing more than 2% of the waste metallic fibers. However, adding the polypropylene fibers and the hybrid fibers increases the flexural strength of fibers reinforced concretes. An experimental investigation was performed by Khaloo et al. [26], to study the rheological and mechanical behavior of two strength classes (medium and high strength) of the self-compacting concrete reinforced with steel fibers, using four different volume fractions (0.5%, 1%, 1.5%, and 2%), the workability of all SCC classes is reduced by increasing the steel fiber volume fraction, and using high percentages of fibers led to decrease of other rheological characteristics. On the contrary, splitting tensile strength, flexural strength, and flexural toughness are increased by increasing the percentage of fibers; however compressive strength is decreased by increasing the percentage of fibers. Mazaheripour et al. [27], investigate the effect of polypropylene fibers inclusion on fresh and hardened properties of lightweight self-compacting concrete (with a density of 1700–2000 kg/m3). The results obtained have shown that the polypropylene fibers did not influence the compressive strength and elastic modulus, however applying these fibers at their maximum percentage volume determined through this study, increased the tensile strength by 14.4% in the splitting tensile strength test, and 10.7% in the flexural strength. In the study of Kim et al. [28], the basic material properties and drying shrinkage resistance of concrete reinforced with recycled PET fibers are evaluated. These recycled PET fibers are produced from waste PET bottles. Based on the study results, which include comparisons with specimens containing polypropylene fibers
reinforcement, PET fiber reinforced concrete exhibited a slight decrease in compressive strength and elastic modulus as the fiber volume fraction increased. The recycled PET and polypropylene fiber-reinforced specimens showed a decrease in compressive strength about 1–9% and 1–10%, respectively, compared to specimens without fiber reinforcement. In this study, fresh and hardened properties of self-compacting concrete containing plastic bag waste fibers (WFSCC) are evaluated. Recycled plastic bag waste fibers (PBWF) are produced from plastic bag waste, as described later in this paper. A comparison with non-confined self-compacting concrete (RSCC) and SCC containing polypropylene fiber (PFSCC) were also performed. 2. Experimental program and test procedures 2.1. Materials 2.1.1. Concrete mix Ordinary Portland cement CEM II/A 42.5 NA, from Algeria cement factories, with a density of 3.1 g/cm3 was used. Continuously graded coarse aggregates 3/8 and 8/ 15 were used in this study with specific gravity and water absorption of 2.58 g/cm3 and 1.03% respectively. Natural sand of 3 mm maximum size was used as fine aggregate, with a specific gravity of 2.5 g/cm3 and a fineness modulus of 2.4. The limestone fillers used in this work, were issued from the crashing plant of Boumerdes (Algeria). A polycarboxylate-based superplasticizer named MEDAFLUID-104 was used to achieve the appropriate workability of the concrete mixes. 2.1.2. Polypropylene fiber (PF) The used polypropylene fibers, named GRANIFIBRE are shown in Fig. 1, these fibers have a length of 12 mm, a diameter of 30 lm, a modulus elasticity of 3kN/ mm2 and a density of 0.9. 2.1.3. Recycled plastic bag waste fiber (PBWF) The used recycled PBWF are produced from plastic bag waste (as seen in Fig. 2). The plastic bags waste are introduced into a regenerating at a temperature around 250 °C, and then exits as a fibrous pulp that passes through a tank of water for cooling and hardening. Then they will be cut in fibers. The recycled PBWF has a diameter of 1.6–2 mm and a specific gravity of 0.87 g/cm3. Tensile test was performed on two samples of recycled PBWF with 50 mm length and 1.6 mm in diameter, using ZWICK/Z010 machine, with a capacity of 10kN and a loading speed of 50 mm/min (Fig. 3). The results of tensile test are represented in the Fig. 4 and shown in Table 1. 2.2. Mixture proportions Based on self-compacting concrete mix design japanese method [29], fourteen mixes were produced: a reference self compacting concrete (coded RSCC) and thirteen mixtures of fibers reinforced self compacting concrete. For all the mixtures, the total amounts of cement, fillers, coarse aggregates, sand, water and superplasticizer were all kept constant (430, 30, 350, 314, 174 and 6.6 kg/m3 respectively). Twelve mixtures of reinforced concrete containing PBWF (coded WFSCC), indicating the different values of fiber length (2, 4 and 6 cm), and different values of fiber content (1, 3, 5 and 7 kg/m3). For comparison a mixture concrete based on polypropylene fiber (coded PFSCC) is also prepared with a fiber length of 1.2 cm and a fiber content of 1 kg/m3.
Fig. 1. Polypropulene fiber (GRANIFIBRE).
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Fig. 2. Stages of recycling plastic bag waste fiber (PBWF).
Fig. 3. Experimental setup of tensile test.
2.3. Preparation and casting of test specimens The mixing procedure and time are very important, thus the mixing process was kept constant for all concrete mixtures. All the ingredients were first mixed under dry condition in the concrete mixer for one minute. Then 70% of calculating amount of water was added to the dry mix and mixed thoroughly for one minute. The remaining amount of water was mixed with the superplasticizer and was poured into the mixer and mixed for five minutes. Later, required quantities of fiber were sprinkled over the concrete mix and mixed for one minute to get a uniform mix. Thus, the total mixing time was 8 min. After this sequence of preparation, flowability, passing ability and resistance to segregation of prepared mixtures are measured. For each concrete mixture three prisms of 70 * 70 * 280 mm and three cylinders 110 * 220 mm specimens were cast. Therefore, the total number of specimens considered in this experimental investigation was forty two cylinders and forty two beams. The specimens were demolded after one day and then placed in a curing room with an humidity of 90% and a temperatutre of 20 ± 2 °C until the testing days.
Fig. 4. Stress–strain curves of PBWFsamples.
2.4. Tests on fresh concretes The flowability was evaluated by slump flow diameter, the passing ability was measured by L-box and the resistance to segregation was measured by sieve stability test, according to the specification and guidelines for SCC prepared by the European project group [30]. The slump flow is used to evaluate the horizontal free flow (deformability) in the absence of obstructions. The test method is very similar to that for determining the slump of concrete. The difference is that, instead of the loss in height, the diameter of the spread concrete is measured in two perpendicular directions and recorded as slump flow. The higher the slump flow is, the larger is concrete’s ability to fill formwork. According to Nagataki and Fujiwara [31], a slump flow diameter ranging from 500 to 700 mm is considered as the slump required for
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Table 1 Tensile test results of recycled plastic bag waste fiber (PBWF). Sample
Maximal stress (N/mm2)
Breaking stress (N/mm2)
Elongation (%)
Elastic modulus (GPa)
1 2 Average
31.17 31.90 31.5
9.39 12.04 10.7
13.20 14.43 13.8
0.03 0.03 0.03
a concrete to be classified as SCC. According to the recommandations of the European project group [30], a slump flow diameter ranging from 650 to 800 mm can be accepted for SCC. In addition to the slump flow test, L-box and sieve stability tests are also performed to assess the passing ability and stability of SCC. L-box test measures the fresh SCC passing ability and self-leveling. The test apparatus made from two prisms and set as L form box with three bars and opening slide at bottom box connector. As the vertical box is fully filled, the slid then is opened that allows the fresh SCC flow passing the steel bar. The self-leveling ratio is measured as the ratio between the highs of fresh concrete surface at the beginning (h1) and at the end (h2). For acceptable SCC, L-box ratio must be in the range of 0.8–1.0 and the sieve stability values must be in the range of 0–15% (see Fig. 5).
Fig. 6. Compressive strength test.
2.5. Tests on hardened concrete Tests on hardened concrete have been performed to determine compressive strength, splitting tensile strength and flexural strength. The test results were reported as the average of three tested specimens in the respective testing. From each concrete mixture, 70 * 70 * 280 mm beams has been casted for the determination of flexural strength, and 110 * 220 mm cylinders for the determination of compressive strength and splitting tensile strength tests.
Fig. 7. Flexural strength test.
2.5.1. Compressive strength test Compressive strength have been determined at 28 days in accordance with NF EN 12390-3 standard. The specimens were loaded under a monotonic uni-axial compressive load up to failure by using an MATEST hydraulic testing machine with a capacity of 3000 kN (Fig. 6). The loading rate was approximately 0.4 MPa/s. The higher tray is fixed and the lower support is mobile. Before testing, the faces of the specimen were suffered with a surfacing machine, to ensure parallelism and flatness of the faces of support. An extensometric comparator is fixed to the side face of the specimen at mid-height. The value of the vertical force and the corresponding displacement is recorded simultaneously.
2.5.2. Flexural strength test Flexural strength test was carried out using a three-point loading method at 28 days of curing age, conforming to NF EN 12390-5 standard. The specimens were subjected to bending tests with a concentrated load at the centerline in order to verify their behavior. The bending tests were performed by an ZWICK/Roell test machine of 60 kN maximum load, with a loading rate of 0.05 MPa/s (Fig. 7), using a comparator to measure the elongation of the specimen to view in real-time the load–displacement curves and record, moment by moment, the values of load and displacement.
Fig. 8. Splitting tensile strength test.
3. Results and discussions 3.1. Fresh concrete properties
2.5.3. Splitting tensile strength test Splitting tensile strength has been determined at 28 days in accordance with ASTM C496 standard. The cylindrical sample with dimensions of 110 ⁄ 220 mm is horizontally placed in a special ring of the compressive machine with the capacity of 3000 kN (Fig. 8). The force is applied along the cylinder’s vertical axis constantly, until the fracture happens. The loading rate was approximately 0.05 MPa/s.
(a) Slump flow test
As a first part of this study, the objective is to know the influence of the plastic bag waste fibers (PBWF) on the workability of concrete. The obtained results of the slump flow diameter, L-box and sieve stability test of different mixtures are given in Table 2.
(b) L-box test Fig. 5. Tests on fresh concretes.
(c) Seive stability test
Y. Ghernouti et al. / Construction and Building Materials 82 (2015) 89–100 Table 2 Fresh properties of self-compacting concretes. Mix ID
Slump flow (mm)
L-box ratio (%)
Sieve stability (%)
RSCC WFSCC1(2) WFSCC3(2) WFSCC5(2) WFSCC7(2) WFSCC1(4) WFSCC3(4) WFSCC5(4) WFSCC7(4) WFSCC1(6) WFSCC3(6) WFSCC5(6) WFSCC7(6) PFSCC
660 660 680 690 690 660 680 695 700 660 685 705 710 621
0.9 0.9 0.88 0.85 0.82 0.81 0.72 0.67 0.59 0.57 0.48 0.41 0.34 0.64
7.64 8 9 10 13 8 13 14 18 8 14 21 28 5.7
From the obtained results it can be seen that the incorporation of PBWF in the SCC, improves the slump flow diameter, regardless the dosage and the length of the fibers. This is may be due to the smooth surface of these fibers, which facilitates the flow of the fresh concrete. It can be also seen that all WFSCC meet the criterion of slump flow (slump flow values between 650 and 800 mm) [30]. However, PFSCC (with polypropylene fibers) does not meets this criterion due to the negative effect of polypropylene fibers, which can be attributed to the increase of SCC viscosity in the presence of polypropylene fibers. This result was confirmed by the majority of reinforced concrete researches Hashem et al. [32], Salih and ALAzaawee [33]. It can also be noted that the addition of polypropylene fibers in mortars and flowable concretes present a large reduction in the workability and increase the viscosity [34], however, it can be also reported that the effect of the ratio (l/d) of plastic waste fibers on the slump flow is less important than the effect of their content percentage [35].
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During the L-box test, it is important to note that the concrete flows through the frames properly and no blocage has been observed for WFSCC mixes with a fiber length of 2 cm regardless of the dosage of fibers (1, 3, 5 and 7 kg), since all the WFSCC mixes present an L-box ratio higher than 0.80 (see Fig. 9). However, the increase of fiber length of PBWF above 4 cm causes immobility of WFSCC mixes in confined environment. This may be attributed to the fact that the length of fibers (4 cm) exceeds the spacing between the reinforcement of the L-box which is the order of 3.5 cm. The polypropylene fibers influential adversely on mobility of SCC in a confined concrete (blocking of concrete in L-box), this is due to the significant amount of fiber added during mixing (1 kg/m3). All WFSCC containing plastic fibers with a length of 2–4 cm have a segregation rate lower than 15% which indicate a good stability. By increasing the length and the dosage of the fibers the segregation ratio of WFSCC increase. For PFSCC mix which contain 1% of polypropylene fibers, the sieve stability test value indicates that is conform up to the standard of segregation. Finally, it can be concluded from the three tests on fresh concrete (slump flow diameter, L-box and sieve stability tests) that the best formulation satisfying the criteria of self-compactability is that the concrete containing a plastic bag waste fiber with a length of 2 cm, regardless of the fiber content.
3.2. Hardened concrete properties 3.2.1. Compressive strength Fig. 10 presents the results of compressive strength at 28 days, performed on cylindrical specimens (110 * 220 mm) for all studied mixtures. By examining the Fig. 10, it can be found that the compressive strength at 28 days is an increasing function with the increase amount of PBWF whatever the length of these fibers.
Fig. 9. Evolution of L-box ratio depending on the length and the content of PBWF.
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Fig. 10. Compressive strength values for all mixtures at 28 days.
The incorporation of short PBWF, with 2 cm length in SCC causes approximately the same variation of compressive strength as that caused by the incorporation the fibers with 4 and 6 cm length, whatever the amount of fiber used. Therefore, the length/diameter ratio (l/d) of PBWF does not affect the compressive strength at 28 days. Other studies have found lower 28-day compressive strength values prepared with short synthetic polypropylene fiber, compared to compressive strength of unreinforced concretes [36]. The concrete based on polypropylene fibers (PFSCC), has the same compressive strength value at 28 days that the reference concrete (SCC). In this study, the increase of compressive strength of specimens concrete based on plastic bag waste fiber (WFSCC) is about 13% maximum, compared to the reference SCC and PFSCC in the case of the mix containing a large amount of fibers (7 kg/m3). The slight increase in compressive strength with the incorporation of plastic fibers is confirmed by several authors who show a negligible effect of these fibers on the compressive strength [37]. The compressive strength of the nylon fiber concrete and the polypropylene fiber concrete was improved by 12.4% and 5.8% respectively for a fibers concentration of 0.6 kg/m3. Nevertheless, the majority of the researches realized on reinforced concretes indicated that plastic fiber reinforced concretes have a negligible evolution of the compressive strength [38,39]. The possible reason for this behavior is the bad homogeneity of the concrete, the high ratio of water or the weak compactness of the concrete caused by the excess of fibers content.
The Figs. 11–13 show the behavior laws stress–strain of WFSCC prepared with 2, 4 and 6 cm respectively, compared to RSCC (reference concrete). The comparison of WFSCC with RSCC allows assessing the gains in strength and deformability of concrete. From these figures, it can be seen that SCC contain a large amount of PBWF (5 or 7 kg/m3) with a fiber length of 6 cm, gain about 7% and 10% in compressive strength respectively (see Fig. 10) and more are characterized with a large phase of plastic deformation. This can be explained by the effect of fiber length which prevent and retard the propagation of cracks. Typically, all stress–strain curves exhibit an initial slope up to an inflection point, followed by a large deformation zone. Depending on the dosage and the length of fiber, the stress level and the plastic zone varies considerably from one variant to another. We find that all specimens of WFSCC have suffered a behavior divided into three phases: (1) A linear phase: happening before micro cracking of concrete, similar to the control concrete up to 50% of the breaking load. (2) A curved phase: in this ascending part, the concrete shows a microcracks and the fibers are put under tension. (3) Descending phase: the effort is taken up by the fibers that assemble the cracked concrete until rupture. In general, the different types of fibers can change the axial behavior of concrete by improving its strength and ductility. The
Fig. 11. Stress–strain curves of WFSCC with a length of 2 cm, compared to RSCC.
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Fig. 12. Stress–strain curves of WFSCC with a length of 4 cm, compared to RSCC.
Fig. 13. Stress–strain curves of WFSCC with a length of 6 cm, compared to RSCC.
Fig. 14. Stress–strain curves of WFSCC with a length of 2 cm and a content of 5 kg/m3 compared to PFSCC and RSCC.
same findings are observed in the behavior of studied WFSCC specimens. However, the ultimate values of the corresponding strain at failure of these specimens are much higher. It can be also observed that the mechanical behaviors of specimens are different. The rigidity of WFSCC specimens is higher than
that of RSCC specimen. The plastic zone of these specimens is also greater than that of RSCC specimens. It is very clear that the improve in the maximum deformation is considerable in the case of WFSCC specimens containing a higher amount of PBWF. As can be expected from Figs. 11–13, for the values 5 and 7 kg/m3
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has been also confirmed in a recent study performed on the use of plastic waste as fine aggregate in self-compacting mortars [40].
Fig. 15. Physical adhesion between PBWF and cement paste.
of PBWF contents, the strain in the specimens WFSCC exceeds 50% of that in the RSCC specimen. The maximum value of the strain is 4660 lm/m (observed for WFSCC5(2)). Fig. 14 shows a comparison between the stress–strain curves of WFSCC5(2), PFSCC and RSCC mixtures. According to this figure, it can observed that WFSCC5(2) has shown a better behavior in terms of strength and deformability. The improvement in compressive strength of concrete containing PBWF is about 11% and 13% compared to RSCC and PFSCC, respectively. The gain in strain for WFSCC is about 58% compared to RSCC. However, the fracture surface of WFSCC shows that most of PBWF are not pulled out and remain stuck in the concrete specimens. The good adhesion of PBWF can be reported to their annular and cylindrical forms which promote the physical bond with cement paste (Fig. 15). This finding
3.2.2. Flexural tensile strength The test results of 28 days flexural load for all studied mixtures are shown in Fig. 16. As a first result, it can be observed that the flexural load of all reinforced fiber concrete mixtures is higher than that of the control concrete. This improvement varies from 0% to 14%, and it depends on the type, the amount and the length of fibers. The incorporation of short PBWF with 2 cm length in SCC does not affect the flexural strength whatever the amount of fiber used. In general, the incorporation of plastic bag waste fibers in the SCC has not a significant effect on flexural strength. For a PBWF amount of 7 kg/m3, the flexural load is improved about 14% and 11% for mixtures with 4 cm and 6 cm in PBWF length, respectively (Fig. 17), compared to the reference concrete (RSCC). This can be explained by the strong bond between the fibers and the cementitious matrix and the local constraints given by the presence of these fibers which occur in an oblique and vertical way against the microcracks. Figs. 18–20 show the obtained load–deflection curves for WFSCC mixtures made with 2, 4 and 6 cm length of PBWF. The results show that the elastic behavior of all specimens before cracking was approximately similar whatever the fiber content. The initiation of cracks occurred earlier in the specimens without fibers than in the fiber reinforced concrete specimens. From these figures, it can be observed a loss in deflection values for all mixtures containing PBWF with 2 cm length; this is may be due to the limited length of fibers that cannot prevent the propagation of cracks.
Fig. 16. Values of flexural load at 28 days for all mixtures.
Fig. 17. Gain of flexural Load for WFSCC in comparison with RSCC and PFSCC.
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Fig. 18. Load–deflection curves of WFSCC(2) and RSCC specimens at 28 days.
Fig. 19. Load–deflection curves of WFSCC(4) and RSCC specimens at 28 days.
Fig. 20. Load–deflection curves of WFSCC(6) and RSCC specimens at 28 days.
However, the mixtures with 4 and 6 cm PBWF length show a better crack resistance and strain–hardening capacities than the specimens without fibers. Due to the increase in crack resistance, the macro-crack propagation in the material is delayed, which stabilizes the overall behavior of the structural member. Fig. 21 shows the load–deflection curves of the mixture WFSCC7(4) in terms of flexural load and deformability
compared to PFSCC and RSCC. From this figure, it can be found that the specimens of concrete reinforced by PBWF have shown a better behavior in terms of strength and deformability. The flexural load of the mixture WFSCC7(4) is approximately similar to PFSCC and RSCC. However, the deflection in WFSCC7(4) is higher about 21% and 16% compared to RSCC and PFSCC respectively.
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Fig. 21. Load–deflection curves of WFSCC with a length of 4 cm and a content of 7 kg/m3 compared to PFSCC and RSCC.
Fig. 22. Splitting tensile strength value of all mixtures at 28 days.
Fig. 23. Gain in splitting tensile strength of WFSCC in comparison with RSCC and PFSCC.
3.2.3. Splitting tensile strength Split tensile test of WFSCC, RSCC and PFSCC is shown in Fig. 22. The results clearly indicate that the split tensile strength of all WFSCC mixtures is higher than that of the control concrete, and evolves with the increase of PBWF content. The incorporation
of PBWF in SCC has a significant effect on the split tensile strength value at 28 days. The recorded improvement of WFSCC in comparison to RSCC varies from 4% to 74%, it depends on the amount of PBWF, and it is not affected by the length of these fibers (Fig. 23).
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The maximum gains are obtained for the WFSCC containing the maximum dosages of PBWF. For example as can be seen from Fig. 22, for a PBWF content of 7 kg/m3, the splitting tensile strength was improved by 67, 74 and by 70% for WFSCC mixtures with fibers length of 2, 4 and 6 cm, respectively, compared to RSCC. This improvement can be explained by the large amount of PBWF and the action of these fibers in preventing the propagation of cracks. The enhancement of the splitting tensile strength with the increase of fibers content is also confirmed by Salih and ALAzaawee [33].
4. Conclusions This experimental investigation focuses on the effect of reused plastic bags waste fibers (PBWF) on fresh and hardened properties of SCC. The ecological benefit of effectively utilizing this waste material is another prime motivation for this work. From the obtained results of this study, the following conclusions can be drawn: – The incorporation of PBWF in the concrete, improves the slump flow spreading and facilitates the flow of the fresh concrete. All plastic reinforced SCC meet the criterion of slump flow recommendations, except for SCC made with polypropylene fibers. The effect of the length/diameter ratio (l/d) of PBWF on the slump flow diameter is less important than the effect of their content percentage. – Plastic waste fiber self-compacting concrete (WFSCC) made with PBWFof 2 cm in length present an L-box ratio higher than 0.80 and show an easy passing through L-box bars. While the increase in PBWF length above 4 cm causes the blocage of WFSCC flow. – WFSCC made with PBWF of 2–4 cm have a segregation rate lower than 15% stands for a good stability. However, the increase in fibers length and content, decreased the stability. – The length/diameter ratio (l/d) of PBWF does not affect the 28day compressive strength. The increase in compressive strength is about 7–13%, compared to the reference concrete (RSCC). For WFSCC containing a large amount of fibers, the strain exceeds 50% compared to RSCC. – The incorporation of PBWF in the SCC has a negligible effect in the flexural strength. The flexural load of WFSCC is improved if compared to the RSCC. The incorporation of short plastic bag waste fiber with 2 cm length does not affect the flexural strength whatever the amount of fiber used. – The incorporation of PBWF in SCC has a positive effect on the split tensile strength value at 28 days. The improvement can reach 74%, it depends on the amount of PBWF, and it is not affected by the length of fibers. – The presence of PBWF in SCC prevents the sudden break and increases the fracture toughness of the material; this property can be interesting in terms of security, since even after breaking, the parts of concrete remain attached to each other. Finally, it can be said that the use of PBWF in the SCC brings two major advantages: The first one regards the protection of the environment through the recycling of this harmful waste. Second, the recycled PBWF can be used successfully in structural SCC for improving their fresh and hardened properties.
Acknowledgement This research was supported by the General Directorate for Scientific Research and Technological Development of Algeria.
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