The concept of grading material composition in a pre-determined directionto target multiple objectives and functionality is applicable to layeringand positioning different materials at specified depths. From a fracture mechanics perspective, this paper explores the advantages of using a two-layered functionally graded concrete materials (FGCM), i.e., plain and fiber reinforced concrete (FRC). The fracture energy (G) and residual load capacity (Pd) of two-layered concrete beams are investigated by means of numerical simulations using a cohesive zone model (CZM) implemented in a finite element framework. The required fracture parameters for defining the cohesive zone model are obtained from individual fracture tests of the plain and FRC materials. The numerical simulations analyzed the effects of FRC thickness and position (whether at the top or bottom of the beam) on the fracture resistance of the two-layered concrete beam. A cost-benefit analysis showed that the FRC placed in the bottom lift is more fracture efficient(higher G and Pd values at lower costs) than when it is placed in the toplift. There is also an optimal FRC thickness in which the benefit in fracture resistance is reduced as the FRC layer is increased. The application of a CZM to predict the fracture behavior of a FGCM beam has demonstrated its potential for also quantifying the effects of FGCM on the fracture resistance of rigid concrete pavements.
Abstract