# Compressive Behaviors of Prisms Made of Demolished Concrete Lumps and Fresh Concrete
## 2 Materials and Methods  
### Specimen Design  
Demolished concrete used in this study was obtained from waste support beams from a deep foundation pit. Eighteen cylindrical cores (\(\Phi\)100 \(\times\) 100 mm) were drilled from these support beams, and their compressive strength was measured. The average compressive strength of all the cores was 40.8 MPa. According to European standard BS EN 13791 [35] and research conducted by [PERSON] and [PERSON] [36], the compressive strength of a concrete cylinder with a diameter of 100 mm and a height of 100 mm is almost the same as that of a concrete cube with an edge-length of 150 mm. On that assumption, the cubic compressive strength of the demolished concrete adopted in this study was taken to be 40.8 MPa. The fresh concrete used for all the specimens came from the same batch of ready-mix concrete. The mix proportions of the fresh concrete are listed in Table 1. Both the fresh concrete and the demolished concrete were made from ordinary Portland cement, water, river sand (fine aggregate), natural crushed basalt (coarse aggregate), and fly ash. As shown in Figure 2, the maximum aggregate size for the demolished concrete was about 25 mm, and for the fresh concrete was about 35 mm. The measured test-day cubic compressive strength and density of the fresh concrete were 53.0 MPa and 2314 kg/m\({}^{3}\), respectively. Figure 2: Maximum aggregate sizes for fresh concrete and demolished concrete. The waste support beams' concrete sheathing and steel reinforcements were removed using a high-frequency impact breaker. The waste beams were then broken into lumps using both the impact breaker and simple pneumatic picks and hammers. The demolished concrete lumps thus prepared were divided into five piles according their characteristic sizes (about 50 mm, 67 mm, 100 mm, 133 mm, and 167 mm), as shown in Figure 3.  
All of the specimens tested in this study were fabricated at the same time in the laboratory of the South China University of Technology, and were classified into six groups, labelled Group 1 to Group 6. Table 2 summarizes the specimens' details. In the table, each specimen is identified using the notation SHD-\(d\)-\(\eta\), where SH denotes the shape of the specimen (SH = CU for a cube, SH = CY for a cylinder, and SH = PR for a prism), \(D\) means the lateral dimension of the specimen (i.e., the edge-length of a cube, the diameter of a cylinder, or the length of a prism's shortest edge), \(d\) indicates the characteristic size of the DCLs, and \(\eta\) gives the replacement ratio of DCLs (i.e., the ratio of the weight of DCLs in the specimen to its total weight). For both the cylindrical and prismatic specimens tested, the ratio of the specimen's height to \(D\) was 2.0. For instance, \"PR400-133-0.3\" means that the specimen was a 400 \(\times\) 400 \(\times\) 800 mm prism with a characteristic DCL size of 133 mm and a replacement ratio of 30%. \begin{table}
\begin{tabular}{c c c c c c} \hline
**Water** & **Cement** & **Coarse Aggregate** & **Sand** & **Fly Ash** & **Water Reducer** \\ \hline
173 & 307 & 1052 & 672 & 86 & 7.06 \\ \hline \end{tabular} Note: The slump of the used fresh concrete was about 182 mm.  
\end{table} 
Table 1: Mix proportion of fresh concrete (kg/m\({}^{3}\)). Figure 3: Five piles of demolished concrete lumps (DCLs). In Group 1, the specimens with different shapes and sizes were made of FC alone, and these acted as control specimens. The specimens in Groups 2, 3, and 4 had the same lateral dimensions and lump size, but the replacement ratio varied. We tested the effect of the replacement ratio on the specimens' compressive strength, strain at peak stress, and modulus of elasticity. Comparing the test results of the specimens in Group 2 with those of the specimens in Groups 3 and 4, the shape effect on the specimens' mechanical behavior was highlighted.