## 5 Conclusions  
The following conclusions could be drawn based on the results of the current investigation, considering the effects of recycled aggregate quality on the material properties, bond behavior, and the shear strength of RC members, using a recycled aggregate concrete. 1. Regarding the properties of fresh concrete with different recycled aggregate replacements and qualities, especially concrete with a recycled fine aggregate, the target workability could not be achieved easily, due to the various physical and mechanical properties of recycled aggregates. For instance, due to a higher fineness modulus of high- and medium-quality recycled fine aggregates, compared with the low-quality recycled fine aggregate, concrete requires approximately, a 3% greater mix of water, than concrete made by a low-quality recycled fine aggregate. As a result, a slump of fresh concrete made with a lower quality recycled fine aggregate has a lower slump, even though all coarse and fine aggregates are presoaked before the concrete mix. In contrast, concrete made with a lower quality recycled coarse aggregate has a comparatively higher slump. It might be due to the excessive water on the aggregate surface that could not be dried out completely by pieces of cloth. To overcome this, all coarse aggregates are dried out automatically one day before the concrete mix. As a result, the workability is almost the same, regardless of the effect of recycled aggregate qualities. However, all slump values are approximately 18 cm higher than the target value of 12 cm. 2. The compressive strength of concrete with different recycled aggregate replacements and qualities is normally lower than the strength of natural concrete, followed by the flexural strength,split tensile strength, static and dynamic elastic modulus, and the hardened concrete density. Even though the compressive strength of a high-quality recycled coarse aggregate concrete was 14% higher than that of natural concrete, only a little strength improvement could be observed for other material properties. In general, the strength of a high-quality recycled aggregate concrete is the highest followed by a medium- and low-quality recycled aggregate concrete. The dynamic elastic modulus is always lower for the lower quality recycled aggregate, irrespective of recycled aggregate replacements. Drying shrinkage of recycled concrete is generally higher than that of natural concrete. 3. Bond strength of both natural and recycled concrete increased with a decrease in water to cement ratio but there was no strength development, when water to cement ratio decreased from 0.60 to 0.45. It could be explained by a sharp drop in density increment, which has a tendency to increase, and almost the same drying shrinkage and dynamic elastic modulus of the concrete for a water to cement ratio of 0.60 and 0.45, even though the compressive strength, split tensile strength, static elastic modulus, and the compressive strength of mortar increased smoothly with a decrease in water to cement ratio. High- and medium-quality recycled coarse aggregate have a very little effect on the bond strength of concrete and are sometimes higher. However, the bond strength of low-quality recycled coarse aggregate was always the lowest one. The variation among specimens for bond stress was very large, compared with the material properties test. 4. Shear behavior of the RC beam with a natural and recycled concrete is very similar. The final beam failure due to shear occurs after the formation of a large diagonal crack. Just before, the maximum load, some beam specimens have several vertical cracks that form at the beam top or at the shear compression zone. The effects of recycled aggregate qualities could be revealed for the case of a small size beam. It might be due to a comparable effect of aggregate interlock mechanism and this effect is too small for the large-sized RC beams.