## 1 Introduction  
As the population of the world grows and living conditions improve, the number of construction and demolition activities around the world is increasing every year. It has been reported that the construction sector generated 1134 million tons of waste in 2014 in China [1]. The cyclic utilization of construction and demolition waste that produces recycled concrete (RC) and recycled aggregate infill wall materials (RAIW) can allow the sustainable development of the construction industry with good social, economic and environmental benefits. Construction and demolition waste is the primary solid waste and is generally composed of crushed clay brick, sand, concrete block, dust, mud and timber. The development and utilization of this construction waste is imminent; however, few existing studies of crushed clay brick and concrete blocks and analyses of the influential factors exist. This has become a prominent social and environmental problem recently. In order to study the main influential factors, the aggregate replacement rate, recycled coarse aggregate specification, raw concrete strength and aggregate flaw have been evaluated in regard to mechanical properties of the elastic modulus, compressive strength, splitting tensile strength, flexural strength and the flexural-compressive ratio. A series of factors affecting the recycled aggregate concrete was analyzed, which including the substitution rate [2; 3; 4; 5; 6; 7; 8], the interfacial transition zone [9; 10; 11], the aggregate particle size [12; 13], the type of aggregates [7; 8; 14; 15; 16] and aggregate combination [17; 18; 19; 20]. A series of tests were conducted to determine the optimum mix proportion of recycled concrete made from the crushed brick and concrete block. Numerous studies about recycled aggregate concrete (RAC) have been conducted, most of which have focused on the influence of the substitution rate of the recycled aggregate (RA) on the mechanical properties of the concrete. Compared to conventional aggregate concrete (CA), it has been reported that the compressive strength of RAC does not obviously decline at levels below a ratio of 30% ratio, but it is lower than that of the level at 100% [17; 21] which is different from other observations. [PERSON] et al. [4] found that the mechanical properties of four mix proportions in concrete were designed by 0%, 25%, 50% and 100% substitution levels of recycled coarse aggregate (RCA), respectively. The results showed that the 28-day compressive strength of the RAC with 100% of RCA decreased by 20-25% compared with the conventional concrete at the same water-cement ratio level. Moreover, the adhered mortar and the strength of the recycled aggregate (RC) effectively influenced the medium-high strength concrete made by the RC. [PERSON] et al. noticed that there was no significant degradation of the mechanical properties of concrete when the substitution rate varied from 0.25 to 0.50. In addition, there was no significant effect on the structure of concrete at the level of 25% replacement level of natural coarse aggregate (NCA) by recycled coarse aggregate (RCA) [6]. [PERSON] et al. [15] found that the maximum reduction of compressive strength at 100% substitution level with ceramic brick aggregates rose to 28%. Most of these investigations were aimed at the substitution rate of the RA; however, research about the influencing factors on the RAIW mechanical properties has been limited. The particle size and type of the recycled aggregate have effects on the mechanical properties of the RAC. [PERSON] et al. [7] reported that the substitution rate of the natural coarse aggregate (NCA) replaced by the industrial brick waste (RCA) was up to 75% in absolute volume fraction. The hardened concrete was evaluated in regard to its mechanical properties--compressive strength, flexural strength, tensile splitting strength and density. The results showed that the feasibility of using ceramic as the coarse aggregate is high.