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10ARCHITECTURE AND CONSTRUCTION
CARRYING CAPACITY OF BENDING CONCRETE ELEMENTS REINFORCED BY FIBRO AND STRIPES TAKEN
FROM USED POLYETHYLENE TEREPHTHALATE BOTTLES
Ph.D. in Technical Sciences, Associate Professor Roman Shmyh, Ph.D. in Technical Sciences, Associate Professor Vitaliy Bilozir,
senior Lecturer Andriy Vysochenko, student Volodymyr Bilozir
Ukraine, Lviv National Agrarian University
Abstract. The results of prisms tests from fine-grained concrete in the sizes 400 mm x 100 mm x 100 mm on compression and three-point bend for a run 350 mm are submitted. The average cubic strength of the concrete was 31.21 MPa, of the prism - 23.23 MPa. The average flexural strength of the prism without a fibre is 58.54 kN • cm, with a PET fabric of 50 mm x 3 mm x 0.2 mm - 64 kN • cm and 71, 84 kN • cm for the percentage of reinforcement 1 and 1.5 respectively. The average flexural strength of the prism, reinforced with strips, made of 4 glued fragments of PET bottles in the sizes 200x80x0.25 mm - 79, 80 kN • cm. The destruction offibrous concrete prisms was viscous, and prisms, reinforced with stripes, were fragile. The necessity of developing a deformation method for calculating PET-fiber-reinforced concrete bending elements, as well as the need to find ways to improve the adhesion of PET strips with concrete is shown.
Keywords: PET bottles, recycling, fibers, strip valves, concrete, bending elements, bearing capacity.
Polyethylene terephthalate (PET or PETF) is a complex thermoplastic polyester of teraphthalic acid and ethylene glycol, which is made on the basis of resins obtained from petroleum. The physical and mechanical characteristics of PET allow this material to be used for the packaging of mineral water, carbonated beverages, juices, beer, oil, mayonnaise, household chemicals, cosmetics, films, fibers, structural elements, etc. The scientists from the KPI consider that it is necessary and possible to recycle the used raw materials into the new PET products[1]. The product obtained by recycling almost does not differ by the physical, mechanical and thermophysical properties from the primary PET. There are 6 enterprises in Ukraine that collect and process the used packaging into PET granules and flakes.
According to the information provided by trade and industrial group "GALPET", more than 10 thousand tons of PET granulate are imported to Ukraine every month. The main volume of this material is used for making bottles, that should be disposed of after use. Domestic enterprises of PET recycling is still capable of processing only 1 thousand tons per month [2].
One of the promising areas where raw materials from used PET bottles could be used is construction. The conducted analysis has shown that in Ukraine the study of bearing capacity, deformability and fracture resistance of concrete elements reinforced with fibrous, striped or other reinforcement of used PET bottles has not been carried out yet. The same concerns the technology of manufacturing both fiber-concrete mix and structures.
Japanese researchers studied the technology of manufacturing fiber-concrete mixture with PET fibers in length of 20 mm [3]. In this paper, it is indicated that such fibers, even in content of 3 % of the volume of the mixture, is easy to mix, without getting caught in the cuffs. This fiber is used for the production of sidewalk tiles and mine structures.
It has been shown in the paper [4] that the fibrobone on the PET fibre has a long compressive strength and tensile strength for multiple freeze-thawing; the action of various chemical media is not lower than that of ordinary concrete.
The results of studies [5] indicate that the compressive strength and the modulus of elasticity of fibrobone on PET fibers decreased with an increase in the percentage of fibrous concrete reinforcement by volume. Obviously, this issue needs further research. However, this paper draws attention to positive influence of fibers on the frictional resistance to bending, the reduction of the width of the opening of shrinkage cracks, the viscous nature of the destruction. The small (up to 3.6 %) decrease in the compressive strength of fibrobone on PET fibrils in the sizes of 50x1,2x0,3 mm
in terms of a volume percentage of 1,5 % reinforcement is indicated in the papers [6, 7]. A similar effect was observed for the reinforcement of fine-grained concrete by PET flakes [8].
In recent years, Dora Foti systematically conduted the studies of mechanical properties of fibrobone on a fiber from PET bottles [8, 9]. Prisms 400x100x100 mm, reinforced with PET fibers in the size of 32x2x0,1 mm and rings with a diameter of 30-50 mm and width of about 5 mm, were tested according to the scheme of three-point bend for a run of 350 mm. The percentage of reinforcement by weight was 0.5 and 0.75 (in volume - 0.78 and 1.16 respectively). It turned out that the bending strength of such prisms did not always exacerbate the strength of concrete prisms [8].
The abovementioned brief survey of the research allows us to draw the following conclusions:
1. The reasons for a slight decrease in the compressive strength of fibrobone on a fiber made of PET bottles are not explained, in comparison with usual fine-grained concrete.
2. There is no minimum percentage of reinforcement with such a fiber, which would give a stable increase in flexural strength compared to concrete.
3. The question of the optimal size of fiber reinforcement of used PET bottles has not been studied, including experiments on the removal of fibers from concrete of different classes
4. No studies were carried out concerning the using of PET bottles walls for the manufacture of strip reinforcement.
5. The technology of manufacturing of fittings made of used PET bottles is not developed in the finished form.
On the basis of the analysis presented above, for the purpose of this stage, we shall test the strength of the bend of prism, reinforced with fiber and strip reinforcement of used PET bottles.
According to the goal of this article, the following primary tasks are under consideration: the study of the impact on the flexural strength of concrete reinforced prisms, the percentage of fiber reinforcement in volume (1 % and 1.5 %), and the possibility of using bandgap reinforcement from used PET bottles for bending concrete elements.
The research program involved the production of prisms of 400x100x100 mm in fine-grained concrete, testing them according to the scheme of three-point bending for a 350 mm run (Table 1), analysis of the results of experiments and the development of proposals. To determine the strength of concrete on compression cubes of 150h150h150 mm were made.
As a disperse reinforcement, a pre-fabricated fiber from PET bottles of 50x3x0.2 mm. dimensions, which are designed in such a way that the required length of annealing in concrete is not longer than half the length of the fibers (Fig. 1) were used [11]. Strip fittings are made of 4 fragments of PET bottles in the size of 200x80x0.25 mm, glued with cyanacrylate adhesive with each other, and 2 fragments of 120x80x0.2 mm in size, which glued on both ends to 4 glued sheets for a length of up to 30 mm (Fig. 1). Thus, the total length of the reinforcing strip is 380 mm. At the final sections of the tapes, 6 holes with a diameter of 5 mm were punched to improve the anchoring. The reinforcing strips were placed in forms at a distance of 10 mm from the bottom edge.
a 6
Fig. 1. Fiber (a) and strip (b) fittings made of used PET bottles
For the production of samples, in order to obtain concrete of 020/25 class, the cost of materials per 1m was: cement of the brand 400 - 549 kg, sand - 1647 kg, water - 285.5 l, fiber per p = 1% ; per p = 1,5 % - 14,2 kg, for - 21,3 kg. After preparation, application and sealing of the
mixture, the test specimens were stored under a layer of moist filings for 28 days in a room with a temperature of 180 ... 200 C (Fig. 2). Tests were conducted within one week, starting 29 days after the preparation of samples. At first, the cubes and compressions were tested (Fig. 3).
Table 1. Prism test program
Samples code Sample sizes Type of test Pv,% Pi,% Type of PET fitting Mass of fibers, strips - grams
P 1.1 400x100x100 Compression 0 - -
P 1.2
B 1.1 Bending - -
B 1.2
B 2.1 1,0 fiber 57 57
B 2.2
B 3.1 1,5 «1 00 00
B 3.2
B 4.1 1,0 strip 31 31
B 4.2
p- percentage of fibrous reinforcement in volume; - 3ercentage of reinforcement with strip reinforcement in area.
The strength ofthe cubes fcube according to the test results is 31.33 MPa, 30, 61 MPa and 31,
70 MPa (average value 31.21 MPa). The average experimental values for prisms are as follows: prism strength fc,prism,m = 23.23 MPa, initial deformation module Ecm = 28,02T03 MPa, Poisson's coefficient vm = 0.202, boundary deformations corresponding to prism strength £ci,c,m = 1,98- 10-3 (Table 2).
Table 2. Results of prism tests on axial compression
Samples code fcfripris MPa fc,pripnsm, MPa Er, MPa •10-3 Erm, MPa •10-3 V Vm Sri,r-10i ^r^rm 10
P 1.1 P 1.2 22,95 23,51 23,23 28,76 27,28 28,02 0,208 0,196 0,202 2,01 1,95 1,98
The rest of the prism were tested according to the scheme of a three-point bend for a working run of 350 mm (Fig. 4, 5). During loading samples, deflections, strains of extreme stretched and compressed fibers, destructive forces were controlled. The test results presented in Table. 3, indicate that the bearing capacity concerning pfv = 1% on the average increased by 9.9 %, and in relation to
p = 1,5 % by - 15 % compared with concrete samples.
Fig. 2. Fiber-concrete mixture (a) and concrete prisms and prisms, reinforced with a ribbon ofPET
bottles, after manufacturing (b)
Table 3. Results of bending elements-prisms tests
Samples code Pv,% Pi,% Destructive effort Pu, kN Average value of the destructive effort Pum, kN Average value of maximum bending moment Mu, kN •cm
B 1.1 B 1.2 0 6,57 6,80 6,69 58,54
B B 2 1 1,0 7,45 7,25 7,35 64,31
B 3.1 B 3.2 1,5 7,59 7,81 7,70 71,84
B 4.1 B 4.2 1,0 9,68 8,55 9,12 79,80
Fig. 4. Prism test according to the three-point bending scheme
Fig. 5. Bending elements-prisms, reinforced with fibers and ribbons after tests
In the paper [9], the excess of the load-carrying capacity to the bend of the fiber-reinforced concrete prism over the concrete for reinforcing with p = 0,88 % - 3.9 % was obtained. Obviously,
an additional substantiation and setting of the minimum percentage of reinforcement of PET fibers by volume is required.
According to the triangular calculation diagram of stresses in the compressed zone and rectangular - in the stretched, bearing capacity of samples B 1.1 and B1.2 can be calculated according to the known formula:
bh2
Mu = 1,75/.--, (1)
6
where / - the strength of concrete on tension;
b=h=10 cm - the size of the base of the prism.
Substituting in the formula (1) the average torque of 58.54 kN • cm (Table 3), we obtain / =2.01 MPa, which may well correspond to the class of concrete C20 / 25.
The bearing capacity of bending fiber-concrete elements B1.1, B 1.2, B 1.1 and B 2.2 for rectangular scenes in stretched and compressed zones [11] can be calculated by the formula:
M = /diL- • ^, (2)
u /+L 2 ' ()
where / - prism strength of concrete in compression;
/ - s trength of fiber reinforced concrete on tension.
From this formula, using the data from tab. 3, we find / . It turned out that for p = 1%
f = 1,37 Mna , and for p = 1,5 % f = 1,54 Mna which indicates the necessity of improving the
methodology for calculating bearing capacity using full diagrams of deformation of fibrobone for stretching, given that the strength of the fiber concrete, calculated using the formula (2), was less than the strength of concrete for tension.
The average value of the maximum bending moment Mu for samples B 4.1 and B 4.2, reinforced with PET strips, is 79.8 kN • cm. This bending moment is equal in effort in the concrete of the compressed zone, multiplied by a pair of internal forces on the shoulder:
Mu = /-(Ax)(d -A) , (3)
where Ax - the estimated value of the height of the compressed zone of concrete;
d - working height (90 mm).
Solving this quadratic equation, we find that Ax = 0,39 cm
Since the internal effort in the concrete of the compressed zone is equal to the effort in the strip reinforcement, we can write:
/-(Ax) = /yApei, (4)
where /y - the estimated value of the strength of the PET stripe;
Apet - cross-sectional area of the PET stripe (4-0,25-80=80 mm2)
From this equation we obtain f =113.25 MPa. The temporal resistance value of a ring-shaped
PET tape has been experimentally obtained - 160 MPa [9]. Thus, the tensile strength of the PET stripe is not used enough and the internal stress for the destruction of samples is about 71 %. Samples B 4.1 and B 4.2 collapsed brittle with exfoliation of the protective layer of concrete and the loss of adhesion of the tape with concrete. This indicates the necessity of finding tools that would ensure the consistent operation of the tape with concrete until it reaches stresses close to temporary resistance.
Conclusions.
1. In Ukraine, there is an acute problem with the disposal of used PET bottles. Existing capacities of six Ukrainian enterprises provide processing of only 1 thousand tons of recycled PET raw material from 10 thousand tons of granulate imported from abroad. Construction is one of the areas where fibers and reinforcing tapes from used PET bottles can be used.
2. In Ukraine, experimental research on concrete reinforced elements with fibers and reinforcing strips from used PET bottles has not been carried out - as the results of patent search demonstrated.
3. Foreign studies of the problems raised in this paper are insignificant and indicate the necessity to study both the issues of calculation and design, as well as, the technology of fabrication of fittings for used PET bottles.
4. The increase in the percentage of fiber reinforcement in the volume of concrete to 1.5 % led to an increase in the carrying capacity of concrete reinforced bending elements by 15 %.
5. The greatest force effect (36.3 %) has been reinforced by tapes made of PET bottles, compared with concrete elements. However, the nature of the destruction of samples, under-utilization of the strength characteristics of PET bottles, indicates the necessity of finding ways to increase the anchoring capacity of these tapes.
6. Further research concerning the designation of optimal geometric parameters of the fibers, it's anchoring in concrete, bearing capacity at larger volumetric percentages of reinforcement, the technology of fabrication of fibers and the technology of manufacturing fiber-concrete mix - should be carried out.
7. The method of calculating the bearing capacity of fiber-reinforced concrete elements using simplified rectangular stresses is imperfect and should be changed to deformation, which uses full deformation diagrams of the material.
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