## 3 Results and Discussion
### Recycled Concrete Aggregates (HR and CR)
#### 3.1.2 Concrete Test Results  
The results of the fresh concrete tests are shown in Table 4. Slump values increased as the rate of recycled aggregate increased, which can be attributed to the method of achieving the SSD condition of the aggregates, with HR aggregates showing better results. The recycled aggregates have been soaked with the amount of water required to reach the SSD state; however, it is not certain if the aggregates have actually absorbed all the water in the presoaking process or if they produced free water during the mixing process, mainly due to their porous nature. It is very probable that they did not remain completely saturated and that an amount of free water was released from the aggregates, resulting in an increased w/c ratio and increased workability. Of course, there is a reduction in the strength of the concrete with recycled aggregates, which is attributable to this excess water. The air content of all mixtures was around 2%, regardless of the type of aggregates used. The density seemed to decrease as  
Figure 8: XRD diagram of HR, where C: calcite, Q: quartz and P: portlandite. Figure 9: Resistance to freezing and thawing expressed by mass loss. the rate of recycled aggregates in the mixture increased, but the reduction is greater, as expected, when the fine recycled aggregates are used. The results of the tests that were conducted on hardened concrete are given in Table 5, while in Figure 10, various mechanical properties of the recycled-base mixtures (Xi) are compared to the corresponding ones of reference concrete (X\({}_{\rm LL}\)). HR-based mixtures showed increased mechanical properties compared to those with CR aggregates and were lower compared to reference concrete. The open porosity was similar to that of the reference concrete when coarse recycled aggregates were used, but it increased considerably when the fine recycled aggregate was used. Compared to LL, HR 55 and HR100 showed a reduction of compressive strength of only 11% and 15%, respectively, which indicates that even the finer fraction of HR does not reduce the compressive strength of the produced concrete considerably. The flexural strength and elastic modulus, on the other hand, rely more on the quality of the interfacial transition zone between the aggregate and the cement paste, and the reduction in these values is in the range of 9-13% and 28-38% for HR55 and HR100, respectively. This implies that the bond between the fine aggregates and the cement paste was weaker when fine HR was used. Regarding CR, however, CR 55 and CR100 showed a reduction of compressive strength by 26% and 47%, respectively, which corresponds with the lower properties of CR measured earlier and the same trend applied for flexural strength and elastic modulus. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & **LL** & **CR55** & **CR100** & **HR55** & **HR100** \\ \hline Air content (\%) & 2 & 2 & 2.3 & 2.2 & 2 \\ Slump (cm) & 6.5 & 11 & 17 & 15 & 18 \\ Density (kg/m\({}^{3}\)) & 2418 & 2318 & 2165 & 2378 & 2157 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Fresh concrete properties. Figure 10: Comparison of various properties of mixtures (X) with the reference concrete (X\({}_{\rm LL}\)). Regarding the durability tests, as shown in Table 5, the concretes with coarse CR and HR showed similar chloride ion penetrability to the reference concrete, while the mixtures with both fine and coarse recycled aggregates showed considerably higher penetrability. This can be attributed to the increased porosity of CR100 and HR100, which allowed the chloride ions to enter the concrete mass. Freeze-thaw results serve only as an indication of durability, since more cycles are usually required; however, the tested concretes with only coarse recycled aggregates seem to perform in a similar way to the reference concrete. The drying shrinkage results, as shown in Figure 11, show that HR aggregates, regardless of size, perform better than CR aggregates.