# Compressive Behaviors of Prisms Made of Demolished Concrete Lumps and Fresh Concrete
## 3 Results and Discussion
### Mechanical Properties of the Specimens Made of Fresh Concrete Alone
\begin{table}
\begin{tabular}{l c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Notation**} & \multirow{2}{*}{**Serial No.**} & \multicolumn{3}{c}{\(f\)**-**,D,FC (MPa)**} & \multicolumn{3}{c}{\(\widetilde{\epsilon}\)*,D,FC (\(\times 10^{-6}\))**} & \multicolumn{3}{c}{\(E_{\star,\text{D,FC}}\) (GPa)**} \\ \cline{3-11}  & & _Mea._ & _Avg._ & _Std._ & _Mea._ & _Avg._ & _Std._ & _Mea._ & _Avg._ & _Std._ \\ \hline \multirow{3}{*}{CU150} & 1 & 53.2 & & & — & & — & — & — & — & — \\  & 2 & 54.0 & 53.0 & 0.9 & — & — & — & — & — & — \\  & 3 & 51.8 & & & — & & — & — & — & — \\ \hline \multirow{3}{*}{CY150} & 1 & 43.7 & & & & 2487 & & & 26.9 & & \\  & 2 & 43.3 & 42.4 & 1.6 & 2637 & 2605 & 86 & 27.3 & 26.4 & 1.0 \\  & 3 & 40.2 & & & 2691 & & & 25.1 & & \\ \hline \multirow{3}{*}{PR150} & 1 & 41.9 & & & & 2377 & & & 27.9 & & \\  & 2 & 44.8 & 41.9 & 2.4 & 2266 & 2220 & 150 & 27.4 & 28.8 & 1.6 \\  & 3 & 39.0 & & & 2018 & & & 31.1 & & \\ \hline \multirow{3}{*}{CU300} & 1 & 45.2 & & & — & — & — & — & — & — \\  & 2 & 43.1 & 43.6 & 1.2 & — & — & — & — & — & — \\  & 3 & 42.5 & & & — & & — & — & \\ \hline \multirow{3}{*}{CY300} & 1 & 38.2 & & & 2011 & & & 28.3 & & \\  & 2 & 37.0 & 37.5 & 0.5 & 2033 & 2067 & 65 & 23.9 & 27.1 & 2.3 \\  & 3 & 37.2 & & & 2158 & & & 29.2 & & \\ \hline \multirow{3}{*}{PR300} & 1 & 36.2 & & & 2090 & & & 26.4 & & \\  & 2 & 38.7 & 37.4 & 1.0 & 2010 & 2060 & 36 & 29.6 & 27.1 & 1.8 \\ \cline{1-1}  & 3 & 37.4 & & & 2080 & & & 25.3 & & \\ \hline \hline \end{tabular} Note: _Mea._, measured value; _Avg._, average value; _Std._, standard deviation.  
\end{table} 
Table 3: Experimental results of specimens in Group 1. * For the specimens made of FC alone, the variations in elastic modulus with the specimens' size and shape were also limited. This is consistent with previously published findings [29; 48] for normal-strength and high-strength concrete [51]. Based on extensive test data, [PERSON] et al. [52] developed a quantitative relationship between cylindrical compressive strength (\(f_{\mathrm{cy,150}}\), in MPa) and elastic modulus (\(E_{\mathrm{cy,150}}\), in MPa) for conventional concrete as:  
\[E_{\mathrm{cy,150}}=k_{1}k_{2}\alpha\gamma^{2}(f_{\mathrm{cy,150}})^{1/3} \tag{1}\]  
where \(k_{1}\) and \(k_{2}\) are, respectively, modification factors related to the type of coarse aggregates and mineral admixtures; \(\alpha\) is a constant with a value of 1.486 \(\times\) 10\({}^{-3}\); and \(\gamma\) (in kg/m\({}^{3}\)) denotes the density of concrete. In this study, the measured density of the fresh concrete was 2314 kg/m\({}^{3}\), and the values of \(k_{1}\) and \(k_{2}\) recommended by [PERSON] were 0.922 and 1.087, respectively. For specimen CY150 listed in Table 3, the elastic modulus predicted using Equation (1) would be 27.8 GPa, which agrees well with the measured result of 26.4 GPa. Since the influences of a specimen's size and shape on its elastic modulus are limited, \(E_{\mathrm{cy,150}}\) in Equation (1) may be extended to \(E_{\mathrm{\star,D}}\); here the subscript \(D\) is within the range of 150 to 300 mm, and the subscript * only refers to a prism or a cylinder. On the other hand, the prismatic and cylindrical compressive strengths were almost the same (\(f_{\mathrm{cy,150}}\approx f_{\mathrm{pr,150}}\)), so \(f_{\mathrm{cy,150}}\) in Equation (1) can be extended to \(f_{\mathrm{\star,150}}\). In this way, Equation (1) is rewritten as the following:  
\[E_{\mathrm{\star,D}}=k_{1}k_{2}\alpha\gamma^{2}(f_{\mathrm{\star,150}})^{1/3}=1.04\times k_{1}k_{2}\alpha\gamma^{2}(f_{\mathrm{\star,300}})^{1/3} \tag{2}\]  
where the constant 1.04 = (1.13)\({}^{1/3}\); here 1.13 is an approximate value of the ratio of \(f_{\mathrm{pr,150}}\) to \(f_{\mathrm{pr,300}}\) or \(f_{\mathrm{cy,150}}\) to \(f_{\mathrm{cy,300}}\), as has been discussed.