Comparative Analysis on Use of Polymer Fibres from Recycled Polyethylene Terephthalate into Reinforced Concrete Solutions

Fibre–reinforced concrete cannot replace the ordinary reinforced concrete. However, there are areas of use in which fibre–reinforced concrete can be used alternatively or in addition to the ordinary reinforced concrete, offering several advantages, some of that being presented in this study. The basic idea is that reinforcements create a multi–directional “mesh” within the cementitious matrix that will make concrete stronger. In fact, adding the fibrous material to concrete will increase the strength. In this sense, the micro–fibres primarily work to prevent micro– or shrinkage cracking, which mostly occurs during the initial curing process of the concrete, or those critical first 28 days. By contrast, the macro–fibres provide load–bearing strength after the concrete cracks. But, in fact, the subject is more complex. The types and size of fibres, their distribution and orientation are a hugely complex topic. Fibres, of whatever nature, have been found to improve the properties of concrete. Fibre–reinforced concrete provides an alternative to conventional reinforcement, with the advantage of time and reduced costs of performing maintenance work. The complexity of various fibre use presents challenges for the construction sectors that may be beyond current levels of expertise. In this study, particularities of concrete reinforced with polymer fibres are presented. Also, a comparative study is presented, based on our previous works in area of the concrete reinforcing with recycled polyethylene terephthalate (PET).


Materials and methods
In view of the above, solutions are being sought for the creation of new types of concrete, including the dispersed ones. Therefore, different types of synthetic fibres are often used in concrete. At present, the objective is to identify and use alternative raw materials. Thus, fibres, of whatever nature, improve the properties of concrete ( Figure 6) [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25]. Our previous results presented in [7,8] indicate promising possibilities of using recycled polyethylene terephthalate (PET) in concrete products. At the same time, such applications would contribute to solving the problem of waste polyethylene terephthalate (PET) disposal. The present work refers to the concrete in which the dispersed reinforcement is made of polymeric materials. All the reinforcements used in this work to consolidate the ceramic composite materialsdispersed reinforced concrete typewere made from material from a mix of polyethylene terephthalate (PET) packages, of different types and characteristics, which are found daily in supermarkets and which then reach waste (Figure 7). Non-reinforced concrete (class C30/37) and reinforced concrete dispersed with reinforcements from polyethylene terephthalate (PET) waste were made in laboratory conditions. Non-reinforced concrete (class C30/37) is based on the following materials: water, Portland cement, sand (sort 0-4 mm) and gravel (sorts 4-8 mm and 8-16 mm) and additives, in proportion of about 77% aggregate, 15% cement and 8% water [7,8]. The concrete used in all the 5 samples (1 non-reinforced and 4 reinforced with recycled polyethylene terephthalate), was one and the same, with the same characteristics (class C30/37). In this way, the influence of the reinforcements on the compression characteristics was followed [7,8].
In the first of the reinforcement methods, the extraction of flat strips from polyethylene terephthalate (PET) packaging was chosen. (Figure 7a) The second reinforcement method uses reinforcements in the form of chips from polyethylene terephthalate (PET) packaging (Figure 7b). In the third of the concrete reinforcement methods, the extraction of yarns from polyethylene terephthalate (PET) packaging was chosen, followed by a mesh-shaped braiding process (Figure 7c). The fourth concrete reinforcement method uses reinforcements in the form of polymer rope, obtained from weaving the polyethylene terephthalate (PET) long yarns (Figure 7d).
The determination of the volumetric mass (density) is made according to [26]. The determination of the compressive strength of the reinforced concrete (at 28 days) is determined according to [27] and [28], based on the cubic strength test carried out on a minimum number of three samples of cubic form (Figure 8). The experimental steps of concrete casting and reinforcing and the test on reinforced concrete samples are presented in Figures 9 and 10 [7,8]. The compressive strength tests on concrete samples (1 non-reinforced concrete and 4 reinforced with PET fibres) are presented in Figure 11 [7,8].

Results and discussions
The experimental results presented in [7,8] indicated that the dosage and form of the reinforcements are the two most influential parameters in the concrete reinforcing process. For a given volume fraction of recycled polyethylene terephthalate (12 g), changing the fibre form (width, length, thickness) we experimented several reinforcing possibilities, large presented in [7,8]. Also, decreasing the fibre profile or equivalently increasing the number of fibres in the concrete mix significantly improves the compressive strength. At a volume fraction of 0.6%, most tested fine-diameter recycled polyethylene terephthalate (stripes and flakes) provided a reasonable increase of the reinforced concrete compressive strength ( Figure 12, Table 1), without unnecessarily adding to the density of concrete reinforced with recycled polyethylene terephthalate ( Figure 13, Table 1   The results in the 4 concretes reinforced with recycled polyethylene terephthalate in Figure 14 are presented. In interpreting the results, the comparative analysis followed the types of reinforcements used in experiments, the time of production of reinforcements from different polymer (PET) fibers, the increase in resistance obtained by the reinforcement method, and the complete feasibility of each reinforcement method. Figure 14. The interpretation of the results in the 4 concretes reinforced with recycled polyethylene terephthalate [7,8] Scores were awarded on a scale of 1 to 10 (1 being minimum and meaning weak and 10 being maximum and meaning very good). Scores for the preparation of recycled polyethylene terephthalate reinforcements represent the difficulties or ease in the making of the reinforcements, taking into account the need to manufacture special tools and working equipments, as well as the actual time to make the reinforcement types. The assembling/inserting score is the degree of difficulty with which the various recycled polyethylene terephthalate reinforcements are mounted and the time required to be made.
As can be seen from the comparative graph obtained on the base of the overall score presented in Figure 14, by far the most feasible and productive methods of reinforcement are those with dispersed reinforcement, namely flat fibre and chip reinforcements. These two reinforcement methods are carried out easily, without too many adjacent machines, in a relatively short time compared to the other two methods (both as the realization of the reinforcements and as their assembling/inserting). Moreover, this also represents the fact that these two reinforcement methods, in addition to being carried out easily and in relatively short time, are also the most productive when it comes to increasing the compressive strength of the cement matrix.
Regarding the relative poor results obtained by the braided mesh and the rope strands from recycled polyethylene terephthalate reinforcements, it should be noted that they lend themselves much better on stretching loads and thus compression loading does not show major improvements. For this reason, we will then analyse these two methods in a study on stretching load.

Conclusions
There are multiple reasons for adding polymer fibres in concrete, including the recycled polyethylene terephthalate reinforcements. In fact, choosing the right polymer fibre mostly depends on the type of application. Among the advantages of using polymer fibres into the concretes are the following, being perfectly aware that we can even include all: -one of the main benefits of polymer fibres are the homogenous distribution in the concrete. Other benefits include the better cohesion of the fresh concrete; also, thanks to extreme durability of polymers the fibre retain their full characteristics during entire concrete; the use of polymer fibres in the concrete composition increases its compressive strength; -addition of polymer fibres requires a lower processing costs, compared to steel reinforcements. The advantages of using reinforced concrete with polymer fibres are evident in the small prefabricated building materials, where the costs of reinforcement with bars are high; the addition of polymer fibres save time in the construction process and reduce costs; -the use of dispersed polymer fibres determine a reduced weight of prefabricated reinforced concrete, and therefore, traditional mesh and steel fibre reinforcement may be avoided. The polymer fibres replace or partially replace traditional reinforcing steel; The development of the construction sector, in particular the investments in infrastructure, remain the key factors of the economic growth. This implies a strong increase in the consumption of building materials in times of economic boom, and against the background of the significant increase in demand, the needs of raw materials also increase. Concrete is one of the main materials used in construction, therefore, the consumption of concrete is determined by the state of the construction industry. Being easy to use, dosed industrial or into a simply concrete mixer, the polymer fibres save time compared to traditional mesh application.