# Mechanical Properties of Cement Composites Using Modified Plastics by Gamma Irradiation
## 3 Experimental Results and Consideration  
Flexural Strength of Cement Composites According to the Type of Plastic Pellet and Gamma Irradiation Dose  
Table 5 and Figure 5 show the flexural test results of specimens according to the type of plastic pellet and gamma irradiation dose. As a result of the flexural strength test, as the curing period increased, the strength increased. However, it seems that only some samples affected by gamma ray irradiation, and it presents a tendency such as showing high strength even when a plastic not irradiated with gamma ray is used as a substitute. From this point of view, it is determined that gamma irradiation does not have a significant effect on flexural strength.  
Compressive Strength of Cement Composites According to the Type of Plastic Pellet and Gamma Irradiation Dose  
Table 6 and Figure 6 show the compressive strength test results of cement composites according to the type of plastic pellets and the amount of gamma irradiation.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Specimen**} & \multirow{2}{*}{**Irradiation Dose (kGy)**} & \multirow{2}{*}{**Compressive Strength (MPa)**} & \multicolumn{2}{c}{**Increase Rate Compared to**} \\  & & & **Nonirradiated Specim (\%)** \\ \cline{3-6}  & & **7 Days** & **28 Days** & **7 Days** & **28 Days** \\ \hline Plain & - & 33.81 & 39.5 & - & - \\ \hline PP-50-0 & 0 & 16.15 & 20.48 & - & - \\ PP-50-25 &  
As a result of the compressive strength test, it was confirmed that the strength decreased in the plastic-substituted cement composite compared to the cement composite in which the sand was not replaced with plastic.  
In the case of the 7-day curing period, it was confirmed that the overall compressive strength increased moderately with the increase in the irradiation dose, and in the case of the 28-day curing period, the compressive strength of some specimens increased rapidly according to the increase in the irradiation dose.  
In addition, in the case of PP and PE aggregates, the compressive strength gradually increased up to the irradiation dose of 75 kGy, but it was found that the strength decreased at 100 kGy. Conversely, in the case of ABS, the overall compressive strength increased according to gamma irradiation, but it was found to increase randomly without any particular trend according to the increase in irradiation dose.  
In order to confirm the ductile behavior of specimens, Figure 7 describes the compressive stress-strain graph analyses. When the plastic aggregates irradiated with gamma ray is mixed into the specimen, it shows a lower strain rate and high compressive strength compared to the specimen substituted with the plastic aggregate that is not irradiated with gamma ray. In the case of PP, it was confirmed that the specimen substituted with modified plastic aggregate through 75 kGy gamma-ray irradiation exhibited the compressive strength of 30.02 MPa. There was an increase by about 15 MPa for the specimen substituted with PE modified plastic aggregate through 75 kGy gamma-ray. Moreover, the compressive strength reached to 31.76 MPa when the ABS modified plastic aggregate, which is irradiated with 75 kGy gamma-ray irradiation, was mixed into the specimen.  
Figure 7: _Cont_.  
Figure 7: _Cont._