## 1 Introduction
### Cement-Based Material Containing Plastic Particles: The Effects of Gamma Irradiation  
In the previous section, the modification mechanism of plastics following gamma irradiation was analyzed. In this section, the effects of modified plastic materials on cementitious composites under various types of plastic aggregates and gamma irradiation doses are described, and a review of the literature is presented in Table 2.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Reference** & **Plastic Type** & **Application Type** & \
\begin{tabular}{c} **\(\gamma\) Irradiation** \\ **Dose Levels** \\ \end{tabular} &
\begin{tabular}{c} **Major Observations** \\ \end{tabular} \\ \hline
[40] & Nylon & Fiber & \
\begin{tabular}{c} 5, 10, 50, \\ and 100 KGy \\ \end{tabular} &
\begin{tabular}{c} \(\bullet\) \\ gamma-irradiated nylon fibers. \\ In the case of 50 KGy, yield tensile stress was 143.9\% higher than that of nonirradiated fiber specimen, and the compressive strength was increased by 292.3\% compared to the nonirradiated fiber specimen. \\ \end{tabular} \\ \hline
[41] & PET & \
\begin{tabular}{c} Binder \\ (cement \\ substitute) \\ \end{tabular} & 10 and 100 kGy &
\begin{tabular}{c} \(\bullet\) \\ gamma-irradiated plastic increased by 20\% compared to nonirradiated concrete. \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table}
Table 2: Literature studies related to properties of cementitious composites that contain gamma-irradiated plastics.  
Figure 4: Schematic diagram of crosslinking reaction according to gamma irradiation.  
Figure 5: Schematic diagram of chain scission reaction according to gamma irradiation.  
Based on the information contained in the reviewed literature, the mechanism behind the performance improvement in plastic materials by gamma irradiation is confirmed, and it can be concluded that the mechanical properties of cementitious composites are improved. One study reported that it was possible to modify the smooth surface of  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Reference** & **Plastic Type** & **Application Type** & \(\gamma\)**Irradiation Dose Levels** & **Major Observations** \\ \hline
[42] & PP & Fiber & \(5,10,50\), and 100 KGy & \(5,10,50\), irradiated fibers at 10 kGy & \(5,10,50\), and \(  
the plastic aggregate to a rough surface as the gamma irradiation dose increased, which improved the mechanical strength of concrete. This results from the fact that gamma irradiation leads to an improvement in bond strength between the cement paste and the plastic aggregate due to the rough particle surface formed by modifying the molecular structure of the polymer. From these observations, it can be concluded that gamma irradiation is a suitable technique for improving the performance of polymeric materials in composites and could be applied to mortar and concrete.  
However, in most cases, studies were mainly conducted on mortar or concrete with polymers added as fibers or fillers, and few studies were on cement composites with plastics added as aggregates. [PERSON] et al. [20; 36] conducted a study on mortar and concrete containing irradiated polymers as aggregates, but mostly high doses of gamma irradiation were used, and the types of polymers were also limited. Therefore, it is necessary to optimize the gamma irradiation dose for various plastic types by increasing the dose step by step from an initial low dose and to then analyze the changes in characteristics associated with the various dose levels that are tested.