Interfacial Bond Quality in Functionally Graded Concretes Incorporating Steel Fibres and Recycled Aggregates

Abstract

A functionally graded material (FGM) is a material presenting gradation in composition and structure, designed to attend to specific functions. FGM produced with concrete, known as functionally graded concrete (FGC), has been studied for several applications by combining layers of distinct types of concrete showing technical benefits. Due to the material discontinuity, an interfacial zone is created between layers, named as layer transition zone (LTZ). As the weakest link between different concrete layers, the bond quality of LTZ may influence the mechanical behaviour of FGC. In this paper, the quality of LTZ in FGC was assessed considering the type of aggregate, content of steel fibres and casting delay between layers. FGC were produced with a top layer of plain cement concrete (PCC) and a bottom layer of conventional fibre reinforced concrete (FRC) or fibre reinforced recycled aggregate concrete (FRRAC). The FGC were assessed for compressive strength and bond strength between layers. The results indicate that the bond quality of LTZ is affected by casting delay and compressive strength of each layer. Moreover, it was noticed that the impact of adding steel fibres was not significant to alter the bond quality in FGC. Overall, adequate bond strengths were obtained in FGCs with casting delays of up to 24 h.