# Performance Evaluation of Reinforced Recycled Aggregate Concrete Columns under Cyclic Loadings
## 1 Introduction  
Recycled concrete aggregates (RCAs) generated from construction and demolition waste (CDW) have been deemed as a potential alternative to natural aggregates (NAs) with the advantage of minimizing the environmental impacts of CDW [1; 2; 3; 4], where the resulting concrete products, termed recycled aggregate concrete (RAC), are now received as a type of \"green concrete\" [5; 6; 7; 8; 9; 10]. Along this line, the reinforced recycled concrete (RRC) members (i.e., reinforced concrete slabs, beams, columns and shear walls manufactured with RCAs) have been developed and explored to promote the sustainable use of RAC at the structural level. Research efforts have been dedicated to characterizing the properties of RRC beams and columns in static loading conditions. The influence of RCAs on the monotonic shear [11; 12; 13; 14; 15; 16; 17; 18; 19; 20; 21; 22; 23] or flexural [24; 25; 26; 27; 28; 29; 30; 31; 32; 33; 34; 35] behaviors of RRC beams has also been extensively experimentally investigated, with the replacementratio (i.e., \(r\)) varied from 0% to 100%. The experimental outcomes indicate that: (i) in either shear or flexural failure, the presence of various RCA replacement ratios only has a limited influence on the damage process and failure pattern of RRC beams; (ii) an increased replacement ratio appears to reduce the load-carrying capacity of RRC beams. It should be highlighted that the RCAs used in the aforementioned studies were generally not treated before concreting. For the purpose of improving the performance of RCAs, [PERSON] and [PERSON] [36] adopted an acid treatment to eliminate the weak layer resulting from the adhesive mortar on RCAs so as to enhance the behavior of RRC beams. In the case of RRC columns, similar findings have been reported in a number of compression tests using untreated RCAs [37; 38; 39]: (i) RCA replacement ratio had no remarkable influence on the failure progression of the columns, and (ii) the compressive strength and the elastic stiffness of RRC columns were generally lower than those of conventional RC columns made with NAs, where the reductions in these properties depended on the RCA content. It is noteworthy that two thorough review studies by [PERSON] et al. [40] and [PERSON] et al. [41] have clearly shown that the design code Eurocode 2 can provide a good prediction for the load-carrying capacity of RRC beams without stirrups. However, for the beams with stirrups, which are more significant in practice--the predictions by Eurocode 2 showed a remarkable gap compared to the measurements, suggesting that the underlying mechanisms still needed to be revealed towards more reliable designs. Up to now, however, research is still scarce on the feasibility of using RAC in concrete elements designed with seismic-resistant purposes. Only a few experimental studies have been conducted aiming to clarify the effect of the incorporation of RCA on the seismic response of RRC columns. [PERSON] et al. [42] and [PERSON] [43] investigated the cyclic behaviors of RRC columns subjected to axial compression and lateral load reversals. They observed that an increased RCA replacement ratio tended to reduce the lateral load resistance of RRC columns. Moreover, both ductility and energy-dissipating capacities of RRC columns declined to an extent, owing to the incorporation of RCA. Seismic modeling is essential to generalize the experimental outcomes of RRC columns so as to gain the confidence of their structural use in seismic regions. Again, it is not surprising that only very few studies have been conducted on that important issue. [PERSON] et al. [44] have numerically modeled a three-dimensional RAC test frame in the OpenSees platform and validated that fiber-based finite elements can be used to approximate the seismic response of RRC frame structures. Still, the potential influences of the unique material properties of RAC on the RRC columns have not yet been numerically and systematically studied.