## 3 Results
### Mechanical Properties  
The 28-day mean compressive (f\({}_{\text{cm}}\)), mean splitting tensile (f\({}_{\text{st}}\)), relative compressive (\(\Delta\)f\({}_{\text{cm}}\)) and relative splitting tensile (\(\Delta\)f\({}_{\text{st}}\)) strengths are plotted in Figure 3. In terms of compressive strength, four of the recycled material mixes (R10/0, R25/0, R0/50 and R10/50), which exhibited f\({}_{\text{cm}}\) \(>\) 25 MPa, would be  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Component**} & \multicolumn{5}{c}{**Amount (kg/m\({}^{3}\))**} \\ \cline{2-7}  & **NAC** & **N10/0** & **N25/0** & **R0/50** & **R10/50** & **R25/50** \\ \hline
**Cement** & 300.0 & 270.0 & 225.0 & 300.0 & 270.0 & 225.0 \\
**GRC** & - & 30.0 & 75.0 & - & 30.0 & 75.0 \\
**Total water** & 171.3 & 177.1 & 183.3 & 205.2 & 211.2 & 217.2 \\
**NS-F** & 154.0 & 150.0 & 154.0 & 154.0 & 154.0 & 154.0 \\
**NS-C** & 754.5 & 754.5 & 754.5 & 754.5 & 754.5 & 754.5 \\
**NG-M** & 367.0 & 367.0 & 367.0 & 183.6 & 183.6 & 183.6 \\
**NG-G** & 653.0 & 653.0 & 653.0 & 326.5 & 326.5 & 326.5 \\
**MRA** & - & - & - & 449.0 & 449.0 & 449.0 \\ \hline \hline \end{tabular}
\end{table}
Table 6: Concrete mix design.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Agg. Group** & **Mix** & **w/b\({}_{\text{eff}}\)** & **Slump (mm)** & **Density (kg/m\({}^{3}\))** & **Air Content (vol\%)** \\ \hline
**NA** & NAC & 0.56 & 65 \(\pm\) 2.8 & 2367 \(\pm\) 8 & 2.6 \(\pm\) 0.2 \\  & N10/0 & 0.58 & 74 \(\pm\) 2.5 & 2340 \(\pm\) 9 & 2.7 \(\pm\) 0.2 \\  & N25/0 & 0.60 & 65 \(\pm\) 3.7 & 2309 \(\pm\) 10 & 2.9 \(\pm\) 0.1 \\  & R0/50 & 0.59 & 75 \(\pm\) 3.1 & 2251 \(\pm\) 11 & 3.2 \(\pm\) 0.1 \\
**MRA** & R10/50 & 0.61 & 61 \(\pm\) 3.7 & 2244 \(\pm\) 12 & 3.4 \(\pm\) 0.2 \\  & R25/50 & 0.63 & 63 \(\pm\) 4.2 & 2219 \(\pm\) 10 & 3.8 \(\pm\) 0.2 \\ \hline \hline \end{tabular}
\end{table}
Table 7: Fresh-state concrete properties (\(\pm\): standard deviation).  
apt for structural applications in building construction. A value under 25 MPa was found only in the mix with 25% GRC and 50% MRA (R25/50), whose use would be restricted to non-structural purposes.  
Figure 3 also shows that, irrespective of the GRC replacement ratio and the presence or absence of MRA, the experimental materials had lower compressive and splitting tensile strengths than those of the reference mix. [PERSON] et al. [44], studying concrete mixes with 10% or 15% ground brick and 30% RCA, found the incorporation of ground brick at both replacement ratios induced declines in 28-day compressive and flexural strength in the mixes, whether made with 100% NA or 30% RCA.  
Adding 10% GRC to the NA mix (R10/0) lowered compressive strength by 18.7% and tensile strength by 12.9%, whilst at a replacement ratio of 25% (R25/0) the decline was 38.1% in compressive and 19.4% in tensile strength relative to NAC, due to the lower reactivity of GRC relative to cement  
Figure 2: Fresh-state density and air content as a function of the w/b\({}_{\text{eff}}\) ratio.  
and the smaller amount of the latter in the mixes. In a study of the effect of replacing OPC with 15%, 30% or 45% ground crushed concrete, [PERSON] [22] attributed the declines in compressive and flexural strength observed to the lower reactivity of the addition.  
With the combined use of GRC and MRA, compressive strength was 33.4% and splitting tensile strength was 17.5% lower in R10/50 than in NAC, whilst in R25/50 compressive strength was 57.2% and splitting tensile strength was 48.2% lower. Those findings were the result of two factors: low GRC reactivity [22] and the lesser density and hardness of MRA than NA [45; 46; 47]. The declines recorded were steeper than the up to 20% reported for compressive strength and up to 24% for splitting tensile strength in a study [10] of concrete mixes with ground fired clay-based materials recycled from CDW, which were more reactive than the present GRC, and 50% of a harder MRA (LA \(<\) 36 wt%) than the one used here (LA = 46 wt%).