Numerical simulations of fracture resistance of functionally graded concrete materials

The concept of grading material composition in a predetermined direction to target multiple objectives and functionality is applicable to the layering and positioning of different materials at specified depths. From a fracture mechanics perspective, this study explores the advantages of using functionally graded concrete materials (FGCMs), that is, plain concrete and fiber-reinforced concrete (FRC), in two distinct layers. The fracture energy (G) and residual load capacity (Pδ) of two-layered concrete beams are investigated by means of numerical simulations with a cohesive zone model (CZM) implemented in a finite element framework. The required fracture parameters for defining the CZM are obtained from individual fracture tests of the plain concrete 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 Pδ-values at lower cost) than when it is placed in the top lift. 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 an FGCM beam has demonstrated its potential for also quantifying the effects of FGCMs on the fracture resistance of concrete pavements.