Stress and Strain Behavior of Confined Lightweight Concrete using Sand Coated Polypropylene Coarse Aggregate

Plastic waste greatly contributes to environmental pollution; therefore, using plastic waste in various applications, such as in concrete, is an important waste reduction strategy which could be contributed by the construction industry. This study presents the development of a concrete stress and strain model under compression for confined concrete specimens using polypropylene plastic as a substitution for coarse aggregate. Various short-column specimens were analyzed for stress and strain characteristics, effect of steel confinement, and compressive performance. Steel confinement increased the compressive strength and ductility of the section. The parametric identification of a stress-strain model defined for normal concrete was used in the experimental results to obtain new parameter values for the confinement coefficients k1  that are suitable for cylindrical and square lightweight concrete sections. The stress-strain diagrams for lightweight concrete of experimental cylinder and square column specimens, compared with the stress-strain modeled by the modified coefficients, indicate a fairly close agreement.

Compression; Confinement; Lightweight concrete; Polypropylene aggregate; Stress-strain

    Plastic wastes are almost non-degradable in the natural environment, even after a long period of exposure. The use of recycled plastic as fine and coarse aggregates in lightweight concrete has been studied by Choi et al. (2009), Frigione (2010), Al Bakri et al. (2011), and Islam et al. (2016) as part of an effort to reduce environmental pollution. The use of plastic aggregates in concrete has the additional benefit of providing a lighter weight of concrete than normal concrete containing natural aggregates. Inclusion of a plastic component as a substitution for natural coarse aggregate in concrete can therefore be a good solution to the environmental hazard posed by plastic wastes. However, a lack of information on the characteristics of lightweight concrete containing plastic aggregates is one of the main barriers hindering acceptance of this product in the construction industry. Polypropylene coarse aggregate, as shown in Figure 1, with or without sand coating, has been studied by Purnomo et al. (2017a) and Pamudji et al. (2018), who found a better bond between the coarse aggregate and hard matrix in the presence of the sand coating. Polypropylene has versatile physical characteristics and is inexpensive (Maddah, 2016; Jawaid and Khan, 2018); however, knowledge of the characteristics, strength, and stress and strain behaviors of lightweight concrete with plastic aggregate is still limited. In view of potential engineering problems, understanding the stress characteristics would provide insight into the structural element strength (Kurdi and Rahman, 2010; Purnomo et al., 2017b; Purnowidodo et al., 2018).

    Recent studies using confined concrete constitutive models have focused more on ultra-high performance concrete (UHPC) cases (Chang et al., 2020; Li et al., 2020). By contrast, stress-strain curves for lightweight concrete using recycled plastic aggregate have been studied only on a limited scale in the laboratory. The development of stress and strain models is important for further study of the behavior of this concrete type. This behavior depends largely on the concrete compressive strength and the stress-strain relationship. The main objective of the present study is to establish a stress-strain relationship under compression of confined concrete containing recycled polypropylene (PP) plastic as coarse aggregate. The expectation is that the determined relationship could represent the overall stress-strain behavior of strength with good control over the ascending and descending branches.

    The proposed procedure presented here provides satisfactory results for establishing a stress-strain relationship for confined lightweight concrete and is sufficient to cover the gap between experimental and analytical results. The reduced scale used in the experiment for cylindrical and square lightweight concrete specimens, which are one-third of the original dimensions, has provided satisfactory coefficients of confinement. In the future, full-scale experiments or reduced-scale rectangular column specimen experiments are required to validate the results obtained in this study using reduced-scale specimens.

    The authors express their gratitude to the Ministry of Education, Culture, Research and Technology, Republic Indonesia and Universitas Indonesia for facilitating this study with Prime Basic Research Grant 2020-2021, No. NKB-198/UN2.RST/HKP.05.00/2021.

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