## 5 Energy Absorption Performance of Laminated Specimens under Confined Compression
### Energy Absorption Performance of Composite Specimen  
The confined uniaxial compression test was carried out on the laminated specimen. While obtaining the compressive strength of the specimen, the vertical strain of ordinary C35 concrete was collected using the strain gauge and the static collector stuck on the ordinary concrete part of the laminated specimen. Moreover, it was converted into vertical stress so as to study the energy absorption performance of the EPP and the C35 concretes under cooperative stress. The comparison diagrams of the compressive stress of the specimen's top surface, as well as the compressive stress of the C35 concrete part, are shown in Figure 24.  
Figure 24: Comparison diagram of compressive stress on top surface of specimen and laminated stress of C35 concrete. (**a**) Group B1: EPP volume content of 28%. (**b**) Group B2: EPP volume content is 35%. (**c**) Group B3: EPP volume content of 42%. (**d**) Group B4: EPP volume content of 50%. (**e**) Group B5: EPP volume content of 57%. (**f**) Group B6: EPP volume content of 64%. As can be seen in Figure 24, the vertical deformation of the C35 concrete is micro-strain. Accordingly, the curve showing the relationship between the compressive stress on the top surface of the laminated specimen and the volume strain of the EPP concrete layer can be regarded as the compressive stress-volume strain curve of the EPP concrete layer. Consequently, it is in a three-stage form of 'elastic-plastic stage, compression platform stage, strain hardening stage'. The laminated specimen was observed to show good compression performance. The curve showing the relationship between the compressive stress measured by the C35 concrete layer and the volume strain of EPP concrete layer is also in a three-stage form, i.e., the uniform rising section, oscillating platform section, and accelerating rising section. The curve can generally be seen to be similar to the compression curve of the EPP concrete layer. In addition, the EPP concrete and the C35 concrete layer were observed to be basically stressed synchronously. Also, when the EPP concrete layer was in the compression platform stage, the compressive stress of the C35 concrete was at a low level, indicating the low level of the EPP concrete. However, the compressive stress of the C35 concrete was obviously less than the top pressure of the specimen. This is because a considerable part of the energy exerted by the external load was dissipated in the process of pore deformation and crushing volume compression in the EPP concrete layer, which could not be transmitted to the C35 concrete layer. In addition, the slopes, the starting points and the ending points of the two sections in the stress curve of the C35 concrete were found to be similar to those of the elastic-plastic and the compression platform sections of the stress curve of the EPP concrete layer. This is an indication of the elastic stress state, as well as the low level of compressive stress of the C35 concrete when the compression state of the EPP concrete was in the two stages. At this point, it is more reasonable to convert the stress value from the measured strain value. However, when the pores of the EPP concrete layer were compressed, compacted and reached the strain hardening stage, the buffering effect was essentially lost. Accordingly, the stress in the C35 concrete increased rapidly, which caused it to enter the plastic stage or even to break down. At this point, as can be observed by the accelerated rising in the third section of the curve, the converted compressive stress increased rapidly. As can be seen, it is quite different from the strain hardening stage of the EPP concrete layer, suggesting that the stress curve of this part does not correctly reflect the actual stress state of the C35 concrete. Moreover, the strain energy density of the EPP concrete can be obtained through the analysis of the elastic-plastic and the compression platform sections of the stress-volume strain curve of the EPP concrete cube.