## 3 Results and Discussion
### Resistence to Chloride Ion Penetration  
The results of the rapid chloride penetration (RCP) test, Berke and Hicks [28] equation-calculated chloride diffusion (D) and the respective standard deviations for the 28 d and 90 d mixes are given in Table 5. The data show a steeper decline in Cl\({}^{-}\) penetration with curing age (\(\Delta\)RCP\({}_{\text{28d}\to\text{90d}}\)) in the mixes containing recycled materials (GRC and/or MRA) than in the OPC/NA concrete. Similarly, the absolute value of \(\Delta\)RCP\({}_{\text{28d}\to\text{90d}}\) was greater in both the GRC-NA (\(-\)13.7% in N10/0 and \(-\)14.3% in N25/0) and GRC-MRA (\(-\)14.9% in R10/50 and \(-\)16.5% in R25/50) families than the \(-\)9.3% in the reference NAC. Figure 3: (**a**) 28 d and 90 d oxygen permeability (error bars indicate the standard deviation associated with variability in results); and (**b**) variation in open porosity with oxygen permeability. According to Figure 4a, Cl\({}^{-}\) penetration rose linearly (R\({}^{2}\geq 0.949\)) with the GRC replacement ratio, irrespective of curing age (28 d or 90 d) and family (GRC-NA or GRC-MRA), with values 8.0% higher in mix N10/0 and 38.1% in N25/10 than in NAC, and 2.7% higher in R10/50 and 16.3% in R25/50 than in R0/50. The incorporation of 50% MRA (mix R0/50) also induced increases of 14.7% to 24.6%, relative to mix NAC. That behaviour can be directly associated with the higher porosity of the new cementitious matrices, given the presence of new recycled materials (GRC and/or MRA). It is also consistent with earlier observations for mixes with additions, such as 10% to 40% cement powder [44], 10% to 50% concrete powder [10], or 5% to 15% cement kiln dust [45] as OPC replacements, and materials containing 15% to 30% biomass bottom ash (BBA) to replace OPC, separately or in combination with 30% MRA as an NA substitute [46]. The 90 d mixes with 10% GRC, separately or in combination with 50% MRA, qualified for the same'moderate' corrosion risk class as mix NAC, given that all the rises were observed to lie within the 8% to 30% observed in earlier studies in mixes with 10% to 40% of other inert additions (marble powder and granite dust) [47]. Figure 4: (**a**) Variation in RCP with the inclusion of GRC in 28 d and 90 d mixes; and (**b**) relationship between the chloride diffusion and oxygen permeability coefficients. \begin{table}
\begin{tabular}{l c c c c c} \hline \hline \multirow{2}{*}{**Concrete Mix**} & \multicolumn{2}{c}{**28 d**} & \multicolumn{2}{c}{**90 d**} & \multirow{2}{*}{\(\Delta\)**RCP\({}_{\text{28d}\rightarrow\text{90d}}\)**} \\ \cline{2-2} \cline{4-6}  & **RCP (C) \({}^{*}\)** & & & **D (10\({}^{-12}\)m\({}^{2}\)/s)** & & \\ \hline NAC & 3480 \(\pm\) 258 & 9.72 \(\pm\) 0.72 & 3157 \(\pm\) 152 & 8.96 \(\pm\) 0.84 & \(-\)9.29 \\ N10/0 & 3950 \(\pm\) 245 & 10.81 \(\pm\) 0.94 & 3410 \(\pm\) 301 & 9.56 \(\pm\) 0.91 & \(-\)13.67 \\ N25/0 & 4806 \(\pm\) 453 & 12.75 \(\pm\) 1.01 & 4100 \(\pm\) 266 & 11.2 \(\pm\) 0.98 & \(-\)14.27 \\ R0/50 & 4336 \(\pm\) 361 & 11.7 \(\pm\) 0.95 & 3620 \(\pm\) 322 & 10.05 \(\pm\) 0.81 & \(-\)16.52 \\ R10/50 & 4454 \(\pm\) 284 & 11.96 \(\pm\) 1.04 & 3753 \(\pm\) 274 & 10.36 \(\pm\) 0.92 & \(-\)15.75 \\ R25/50 & 4950 \(\pm\) 181 & 13.07 \(\pm\) 0.87 & 4210 \(\pm\) 321 & 11.98 \(\pm\) 0.82 & \(-\)14.94 \\ \hline \hline \end{tabular}  
* \({}^{*}\)C: Coulomb.  
\end{table} 
Table 5: Rapid chloride penetration (RCP) and chloride diffusion in 28 d and 90 d mixes (\(\pm\), standard deviation). The close linear relationship (R\({}^{2}\) = 0.861 \(>\) 0.85 [48; 49]) between O\({}_{2}\) permeability and the chloride diffusion coefficient in the mixes studied (Figure 4b) is clear proof that both transport mechanisms depend on pore structure and pore interconnectivity alike [50].