On the Cementitious Mixtures Reinforced with Waste Polyethylene Terephthalate

Abstract

The last decade was dominated by a serious problem that now affects all the planet's natural ecosystems: the increasing growth of plastics and microplastics that are difficult to dispose of. One strategy to mitigate this problem is to close the life cycle of one of them-polyethylene terephthalate (PET)-by reusing it within the most common building materials, such as mortars and concretes. The reuse of PET waste as aggregates also allows us to limit the CO₂ emissions released during the production of natural aggregates. This paper analyzes the outcomes of many studies carried out on the characteristics of cementitious mixtures reinforced with waste PET material. Many researchers have demonstrated how PET used as reinforcement of mortars and concretes can produce an increase in the mechanical strengths of the corresponding cementitious mixtures without PET. The tensile strength of this resin is higher than that of concrete; so, by combining the two materials it is possible to obtain a mixture with an overall higher tensile strength, resulting in increased flexural strength and reduced cracking. Using an effective size of PET fibers, it is possible to achieve an increase in the ductility and toughness of the cementitious mixture. Several studies reveal that PET reinforcement reduces the density with a consequent decrease in weight and structural loads, while the workability increases using spherical and smoother PET aggregates.

Keywords: PET fibers and aggregates; PET-reinforced cementitious mixtures; concrete; mortar; recycling; strengthened mechanical properties.

Figure 4

PET fiber examples of width 20 mm, thickness 0.5 mm, length 50 mm (a), and length 50 mm (b) [95].

Figure 5

Screening of the different types of PET reinforcement in the cementitious matrix.

Figure 12

Schematic diagram of the bridging stress for multiple cracking and the resulting high ductility behavior. (a) Bridging stress—single crack opening; (b) fiber bridging stress transfer; and (c) composite tensile stress–strain [172].

Figure 1

Overview flow-chart.

Figure 2

Example of a reinforced concrete structure with 10 columns, 26 beams, and 11 load-bearing walls of 5 floors.

Figure 3

Types of PET aggregates used in some research: (a) lamellar and irregular larger than (b); (c) regular and cylindrical [50]; (d) shredded irregular shape [53]; (e) 300–150 μm flaky shape [54]; (f) angular shape [55]; (g) smooth sphere shape [56]; and (h) 2.36–1.18 mm flaky shape [54].

Figure 6

Fiber dimensions of different geometries: (a) straight slit sheet, (b) flattened end slit, (c) deformed slit sheet, and (d) crimped end sheet [101].

Figure 7

Hydrolysis of PET.

Figure 8

Deformed fiber-reinforced cube after failure [82].

Figure 9

Compressive strength of concrete versus incorporation of PET aggregate to replace natural aggregate [52].

Figure 10

Values of μ_d (=ductility) for the three different fiber contents. Laminated fibrous reinforcement [164].

Figure 11

Comparison of toughness for mortar mixtures with increasing percentage of volume fraction of PET fibers [95].