The combination of multiple layers to produce functionally graded concretes (FGC) creates an interfacial zone between layers named here as layer transition zone (LTZ). The LTZ can be considered similar to the overlay transition zone found in concrete overlays used to repair concrete structure. As the weakest link between concretes, the properties of LTZ can significantly influence the bond quality and mechanical behaviour of FGC. Thus, in this research, the effect of several factors in the bond quality of FGC incorporating steel fibres and recycled aggregates was studied. The experimental results indicate that the effect of type of aggregate and casting delay between each layer in the quality of the LTZ in the FGC studied is higher than the effect of the content of fibre. In addition, the FGC studied can be produced with a casting delay shorter than 24 h between layers without loss of mechanical performance, increasing the potential of large-scale production of lower loading capacity structures.

多层组合以生产功能梯度混凝土 (FGC)，在此处命名为层过渡区 (LTZ) 的层之间形成界面区域。可以认为 LTZ 类似于用于修复混凝土结构的混凝土覆盖层中的覆盖过渡区。作为混凝土之间最薄弱的环节，LTZ 的性能会显着影响 FGC 的粘结质量和力学性能。因此，在这项研究中，研究了几个因素对结合钢纤维和再生骨料的 FGC 粘结质量的影响。实验结果表明，在所研究的FGC中，骨料类型和每层之间的浇注延迟对LTZ质量的影响大于纤维含量的影响。此外，