مقاله انگلیسی رایگان در مورد عملکرد ضایعات پلاستیکی در تیرهای بتنی – الزویر ۲۰۱۸

The amount of synthetic plastic consumed annually has been steadily increasing. The intensifying synthetic plastic consumption can be ascribed to the practical features of synthetic plastic, namely, factory fabrication, lightness of plastic products and low production cost [1,2]. Plastic has been extensively used in bottles and food casings, industrial products, communication materials and housing, among other uses. Although several methods have been employed for the disposal of synthetic wastes, most treatments are inadequate because of excessive synthetic waste generation. Therefore, one of the alternatives is to recycle synthetic wastes and use them as fiber reinforcement for concrete. Synthetic fibers are popular for reinforcing lightweight precast concrete elements such as double walls, pipes and sleepers [3,4,5]. These applications can effectively control cracks [6] and prevent dry shrinkage cracks of concrete [7]. Besides, synthetic fibers have been used to improve the toughness of concrete with enhanced crack resistance [8]. Foti [9] studied the use of polyethylene terephthalate (PET) bottles as fiber to improve concrete ductility and found that the average tensile strength of the ring-shaped fibers is sufficiently high and comparable to the most commonly used carbon or steel fiber to reinforce concrete. The PP/PE blended fiber reinforced composites (HyFRCs) at fiber volume as 2.9% obtained mechanical enhancement of 38 ± ۲% on compressive and 40 ± ۱% flexural strengths compared to normal concrete [10]. Morphological observations show strong mechanical interactions between fibers and the cement matrix as similar to the chemical/mechanical interactions observed for polyacrylonitrile reinforced composites (PANFRCs). A comparison between steel fiber and synthetic fiber has been made. It shows that all types of fibers in concrete seem to yield better results for the same fiber content. In addition, the improvement appears to decrease when the total fiber content increases above a volume fraction of 1% [11]. The high fiber content can cause difficulty in mixing, which leads to poor compaction, non-uniform distribution of fibers, and an increase in void volume [11,12]. Foti [13] studied mechanical behavior of 3 types of possible structural reinforcing with rheoplastic mortar on reinforced concrete pillars. Foti [13] claimed that whole reinforcement (30 cm) of the concrete core obtains significant result compared to specimen with rheoplastic mortar covered at height of 28 cm. Many researchers claimed that the pullout fiber strength increases as the embedded length of the fibers increases in the concrete matrix [14,15]. The embedded length range of 45–۵۵ mm increased the fiber strength by 39.3%–۴۸٫۱% according to Richardson et al. [16]. This difference is related to the surface fiber area connected to surface concrete as this area determines the friction of the fiber and interfacial bond energy [17,18]. In their study, Ochi et al. [19] found that polyvinyl alcohol (PVA) fibers exhibited the highest tensile strength, whereas PET fibers had the lowest tensile strength (172 MPa) [19]. The smooth surface of fibers such as polypropylene (PP) fibers has a weak bond with concrete thereby preventing sufficient friction between concrete and fibers [20]. Compared to commercial plastic fibers, PET fibers exhibit adequate tensile strength.