## 5 Energy Absorption Performance of Laminated Specimens under Confined Compression
### Energy Absorption Performance of Composite Specimen
This, in turn, is an indication of the energy absorption performance. Accordingly, from further research, the two curves obtained from the confined compression of the superimposed specimens were found to reflect the strain energy absorption and the strain energy output of the EPP concrete, respectively. Hence, the absorbed and the output strain energy density (\(W_{V}\) and \(W_{O}\)) were obtained by calculating the uniform rising section and the oscillating platform section of the two curves, respectively. Moreover, the difference between the two can be considered as the energy dissipated during the compression of the EPP concrete, the rate of which was calculated using Formula (14). \[D=\frac{W_{V}-W_{O}}{W_{V}} \tag{14}\]  
where \(D\) represents the energy dissipation rate (%), \(W_{V}\) stands for the strain energy density absorbed (kJ/m\({}^{3}\)) and \(W_{O}\) denotes the output strain energy density (kJ/m\({}^{3}\)). Table 7 shows the obtained results. As can be seen in Figure 25, the strain energy density of the laminated specimen is slightly larger than that of the cubic one. The application of the strain energy density formula and the analysis of the confined compressive strength of the two specimens show that this is caused by the larger confined compressive strength of the laminated specimen. Moreover, the changing trend of the strain energy density of B1-B6 containing the EPP particle content can be observed to be completely consistent with that of A1-A6, i.e., an increase in the EPP particle content led them both to increase as well, which is an indication of the energy absorption characteristics of the laminated specimen. As can also be observed in Figure 26, the higher content of the EPP particles resulted in a greater energy dissipation rate of the laminated specimen, which can be argued to be due to the increase in the pores of the specimen. Accordingly, it can be discussed that a larger amount of total energy is required to break the pores. Moreover, as can be seen, the energy dissipation rate increased in an approximately linear relationship with an increase in the EPP content, i.e., the linear relationship is established (see Figure 27 and Formula (15)). \[D=28+0.47V_{E} \tag{15}\]  
where \(D\) stands for the energy dissipation rate (%), and \(V_{E}\) represents the EPP particle volume content (%). By analyzing the results of lateral compression tests on six sets of composite specimens, including B1-B6, the buffering and energy absorption performance of the EPP concrete and C35 ordinary concrete under synergistic loading was investigated. The lateral compression test of EPP concrete and the C35 concrete laminated specimens showed that they are generally subjected to synchronous forces during compression, and when the EPP concrete layer was in the compression platform stage, the compressive stress of C35 concrete was at a lower level, indicating that the EPP concrete had a significant buffering effect on ordinary concrete. A constitutive model for calculating the energy dissipation rate of EPP concrete was proposed, and it was found that the higher the EPP particle content, the greater the energy dissipation rate of the composite specimen. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Number**} & \multirow{2}{*}{**EPP Volume Content \(V_{E}\)**} & \multicolumn{2}{c}{**Absorbed Strain Energy Density \(W_{V}\) (kJ/m\({}^{3}\))**} & \multirow{2}{*}{**Output Strain Energy Density \(W_{O}\) (kJ/m\({}^{3}\))**} & \multirow{2}{*}{**Energy Dissipation Rate \(D\)**} \\ \hline B1 & 28\% & 285.9 & 167.9 & 41.3\% \\ \hline B2 & 35\% & 1519.5 & 824.5 & 45.7\% \\ \hline B3 & 42\% & 1810.3 & 929.4 & 48.7\% \\ \hline B4 & 50\% & 3234.0 & 1587.6 & 50.9\% \\ \hline B5 & 57\% & 2445.2 & 1102.2 & 54.9\% \\ \hline B6 & 64\% & 2454.6 & 966.2 & 60.6\% \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Strain energy density of B1–B6 groups. Figure 25: Comparison diagram of strain energy density of two specimens.