## 1 Introduction
### Modification of Plastic Materials Using Gamma Irradiation  
The focus of research in the literature described in the previous section was on recycling plastic wastes, rather than treating virgin plastics, to achieve optimal performance before and after mixing them into cementitious composites. Therefore, there is a need for a review that examines potential innovative methods of treating waste plastic before and/or after inclusion within cementitious composites. One literature review has reported that various treatments are used to improve the properties of cementitious composites containing plastics [20]. Plastic aggregates are inherently smooth and hydrophobic and characterized by poor bond formation in the interfacial transition zone (ITZ) between plastic aggregates and cement paste, dissimilarly to natural aggregates; consequently, the inclusion of plastic aggregates in cementitious composites results in decreased compressive strength [4; 14; 17; 21; 22; 23; 24; 25; 26; 27]. Therefore, the properties of cementitious composites with the incorporation of plastic aggregates depend significantly upon the treatment applied to the plastic particles [21; 28; 29]. The type, shape, and surface texture of the plastic used in the cementitious composite are important in relation to the performance of cementitious composites containing plastics. Therefore, it may be hypothesized that the poor bond strength and higher air content between the aggregate and cement paste within cementitious composites containing plastic aggregates are key factors determining their lower performance. Commonly, chemical surface modifications such as the use of mineral admixtures along with alkaline bleaching (bleaching with NaOH) have been reported to improve the bond properties between plastic particles and the cement matrix [21; 30]. It is hypothesized that the reaction between plastics and oxidizing chemicals creates certain chemical substances that modify the polymer surfaces of functional groups that may eventually be involved in the cementitious reaction. Thus, a partial chemical bond between cement paste and plastic particles could be possible. Gamma-ray treatment is attracting attention as a new method to modify the physical and chemical properties of plastic materials without adding or heating special additives and without the release of harmful chemical byproducts. In recent decades, interest in polymer \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Reference** & **Plastic Type** & **Shape** & **Replacement Types and Ratio** & **Studied Properties** \\ \hline
[14] & PET & Pellet /Flake & FA: 5, 10, and 15 vol.\% & Compressive, tensile and flexural strength \\
[15] & Various plastic mixed waste & Powder & Cement: 5, 10, 15, & Compressive, tensile \\
[16] & LDPE + red & & 20, and 25 vol.\% & and flexural strength \\
[17] & dune sand & Irregular & CA: 25, 50, 75, & Density, compressive, tensile \\  & & & and 100 vol.\% & and flexural strength \\
[17] & PET & Flake & FA: 5, 10, and 15 vol.\% & Density, compressive, tensile \\  & & & & and flexural strength \\
[18] & PS and LDPE & Pellet & FA: 10, 30, and 50 vol.\% & Density, compressive strength \\  & & & Mixed in concrete: & Density, compressive, tensile \\
[19] & PET & Fiber & 0.25 vol.\% & and flexural strength \\ \hline \hline \end{tabular}  
* \({}^{1}\) FA: fine aggregate; \({}^{2}\) CA: coarse aggregate.  
\end{table} 
Table 1: Cont. treatment through gamma irradiation has steadily increased as polymer materials have been modified and improved with respect to their chemical, physical, structural, and optical properties. Research related to the improvement of durability and corrosion resistance and the surface hardening of plastics through crosslinking, curing, grafting, and decomposition, including the processing of polymer materials using gamma irradiation emitted from cobalt-60, has been reported. Upon gamma-ray irradiation, chemical reactions occur, as shown in Figures 1 and 2; these reactions change the physical and chemical properties of the plastic.