# Performance Evaluation of Reinforced Recycled Aggregate Concrete Columns under Cyclic Loadings
## 3 Parametric Investigation
### Influences of \(r\) and of the Addition Water Method  
Previous experimental investigations (2014; 2015; 2016; 2017; 2018; 2019; 2020; 2021; 2022; 2023; 2024; 2025; 2026; 2027; 2028; 2029; 2029; 2030; 2040; 2051; 206; 2070; 2080; 2090; 2010; 2022; 2023; 2024; 2025; 2026; 2027; 2028; 2029; 2031; 2032; 20A careful inspection of compressive strength of RAC was carried out by examining the test results reported in [PERSON] et al. [56], [PERSON] and [PERSON] [76] (using AWM), as well as [PERSON] et al. [73] (using ETWM). Figure 7 displays the compressive strength ratio of RAC with respect to that of an equivalent NAC versus the RCA content in light of the above works. It shows that an increase in the RCA percentage reduces the compressive strength ratio between RAC and NAC when the AWM is employed, whereas an increase in the RCA percentage results in an overall increase in the strength of RAC when the ETWM is otherwise used. These experimental results ascertain the principles of the equivalent effective water method and the equivalent total water method based on the way the method affects the relationship between the strengths of NAC and RAC (Figure 6).  
In the present modeling, the RAC material properties were adopted from [PERSON] et al. [56] (in the case of the AWM) and [PERSON] et al. [73] (the ETWM). Figures 8 and 9 show the predicted horizontal load-displacement hysteresis loops and seismic performance using different concrete mixing methods. It can be seen from Figures 8 and 9 that: (i) An increase in \(r\) resulted in an up to 10% decrease in \(P_{\text{u}}\) of RRC columns using the AWM, whereas the opposite occurred when the ETWM was adopted. However, (ii) the variation in \(P_{\text{u}}\) was generally lower than that of the \(f_{\text{c}}\) of RAC, consistently true for the two types of mixing methods. This was because the impacts of RCAs (i.e., low strength of adhered mortar and crushing damage in RCAs (i.e., [63; 64; 65; 66; 67]) could be largely reduced in RRC columns  
Figure 6: The relationship between recycled concrete aggregate (RCA) characteristics and concrete compressive strength using: (**a**) the additional water method, and (**b**) the equivalent total water method.  
as a result of structural effects such as the confinement provided by transverse steel reinforcement. Despite the above detrimental effects, (iii) the ductility of RRC columns manufactured with the AWM increased slightly with an increase in the ratio of RCA percentage, whereas for the ETWM no such obvious dependency on the replacement ratio could be found. This can be explained as the AWM may have led to a lower \(f_{\rm c}\) compared to the ETWM, which in turn resulted in a decreasing brittleness [77].  
Figure 8: Effect of RCA percentage on hysteresis loops of RRC columns (\(n=0.3\)). (**a**) Additional water method ([PERSON] et al. [56]). (**b**) Equivalent total water method ([PERSON] et al. [72]).  
Figure 7: Effect of RCA percentage on 28-day compressive strength of recycled aggregate concrete (RAC) (Note: \(f_{\rm c,0}\) is the cylinder compressive strength when \(r=0\%\); \(f_{\rm c,r}\) is the cylinder compressive strength when \(r\
eq 0\%\)).  
Figure 9: Effect of RCA percentage on seismic performance of RRC columns (Note: \(P_{\rm c,0}\) is the ultimate lateral load when \(r=0\%\); \(P_{\rm c,r}\) is the ultimate lateral load when \(r\
eq 0\%\)). (**a**) Capacity. (**b**) Ductility.  
Due to the relatively pronounced and interesting effects caused by using the AWM, the numerical study in the following sections was based on the specimens (NAC-0.30-60, RAC50-0.30-60, and RAC100-0.30-60) reported in Yang [43], where the AWM was adopted.