**1. Introduction**

Since the beginning of human civilization, construction and demolition wastes (CDW) had been becoming a global problem that affects the sustainable development of the resources and the environment [1]. To date, more than a hundred billion tons of CDW were generated in the world, while approximately 30% to 50% of them were waste concrete [2]. However, this considerable amount of waste concrete is mainly disposed of in landfills, resulting in a severe environmental problem [3–6]. In order to protect the ecological environment and achieve sustainable development, reducing, reusing, and recycling construction waste is a desirable approach to preserve the ecological environment [7–11]. Therefore, many countries have passed legislation to encourage the recycling of waste concrete for the resource utilization of recycled concrete.

Recycled concrete aggregates (RCA) can be obtained from waste concrete by crushing, screening, cleaning, and separating [12,13]. Previous studies have been conducted to characterize the potential advantages and drawbacks of RCA. Being different from natural aggregates (NA), RCA has a layer of old mortar attached to the surface, which has more loose pores at the interface [14]. The attached old mortar brings with it worse properties: a lower apparent density and higher water absorption [15,16]. Consequently, these properties cause the mechanical properties of RCA to be inferior to that of NA, which limits the application of recycled concrete in civil engineering. Although the mechanical properties of recycled aggregates are poor, different scholars, institutions, and countries have been applying recycled aggregates into structures through rational design and experiment in recent years, and in some cases, good results have been achieved [17–23].

To further promote the recycling of construction waste, growing studies on the production of recycled concrete blocks prepared by RCA have been conducted in years. Researchers proposed that the mechanical properties of recycled concrete blocks mainly depend on the substitution rate and qualities of RCA. Soutsos et al. [24] pointed out that the increase of recycled fine aggregates content has a more significant impact on the reduction of recycled concrete block strength. Therefore, the maximum replacement rate of recycled fine aggregates is recommended to be 20%. Bai et al. [25] also confirmed the findings through a similar experiment. A study conducted by Poon et al. [26] aimed to investigate the mechanical properties of recycled concrete blocks. They found that the substitution rate of RCA below 50% had little e ffect on the compressive strength of recycled concrete blocks. However, the compressive strength of recycled concrete hollow block (RCHB) decreases with the increase of the content of low-grade RCA (The content of soil or broken brick in aggregates being >10%) [27]. Guo et al. [28] investigated the influence of di fferent substitution rates of recycled concrete aggregates on the mechanical properties of recycled concrete blocks. The test results illustrated that with the substitution rate up to 75%, the strength of recycled concrete blocks slightly decreases but still complies with the standards. An experiment by Sabai et al. [29] showed that the compressive strength of recycled concrete blocks with 100% RCA can achieve the target of 7 MPa, and even the minimum strength requirement of construction.

Despite the fact that the compressive strength of the concrete block is the critical performance index about whether the block can be used in a masonry structure, the mechanical performance of a masonry prism is more reflective of the actual stress state of the masonry structure. Corinaldesi et al. [30] studied the compressive, shear, and bond strength of recycled mortar prisms, and found that the shear and compressive strength of recycled mortar prisms were close to or even better than that of ordinary mortar prisms. Guo et al. [28] conducted a study of recycled concrete block prisms, and the conclusions are consistent with that of Corinaldesi et al. [30]. In general, the shear strength of the recycled concrete prisms is close to that of the ordinary concrete prisms. However, the seismic performance of the masonry structure, especially the hysteretic characteristics and energy dissipation capacities of the masonry is unclear by the tests of the masonry prisms.

Through the analysis of the above examples, it can be proved that the mechanical properties of recycled blocks can satisfy the requirement of practical application, and the shear properties of masonry assemblages fabricated by recycled concrete blocks are close to those of ordinary masonry assemblages. However, there is still a lack of knowledge about the recycled concrete blocks, and whether they can be used to produce masonry structures with seismic requirements, especially regarding the research about the seismic performance of masonry structures, which is crucial for addressing the utilization problem of RCA. Therefore, if the waste concrete can be recycled to produce RCHB which can be used in the structures with seismic requirements, this type of RCHB will be popularized and further applied on a larger scale.

In view of this, RCA generated from waste concrete was used to produce a new type of RCHB which can be used for masonry structures. In this experiment, three RCHB masonry walls without structural columns constraint, one RCHB wall constrained by the recycled aggregate concrete structural columns, and other walls constrained by ordinary concrete structural columns were manufactured for seismic performance testing. The seismic behavior of the specimens, such as the failure pattern, the hysteresis curves, the skeleton curves, the ductility coe fficient, and the energy dissipation of the specimens was analyzed under cyclic loading. The influences of aspect ratio, vertical axial stress, and di fferent materials used for structural columns on the seismic performance of RCHB masonry walls were also studied. Finally, the seismic capacity of RCHB masonry structure under seismic loading was attained.
