Numerical and analytical optimisation of functionally graded concrete incorporating steel fibres and recycled aggregate

Recent studies applied the concept of functionally graded material in fibre reinforced recycled aggregate concrete (FRRAC) to produce functionally graded concretes (FGC) with enhanced post-cracking flexural behaviour. In these studies, two-layered FGC were produced using plain cement concrete (PCC) and FRRAC in the top and bottom layers, respectively. It was found that a top layer of PCC as thin as 10% of the total height of the specimen (or h/H = 0.90) can enhance the post-cracking flexural behaviour of FGC. Based on these experimental results, this study aims to demonstrate the feasibility of using FGC in construction projects by estimating the ratio h/H that results in an optimal post-cracking flexural response of FGC beams produced with PCC and FRRAC. For this, the finite element analysis software ABAQUS, and the analytical model based on an analysis of evolutionary sections were used to estimate the flexural behaviour of homogeneous FRRAC and FGC beams considering different values of h/H. Then, the simulated results were compared with previous experimental results and the optimal h/H of FGC with FRRAC was evaluated considering its application in rigid pavements. In general, the simulated results indicate that the optimal post-cracking flexural performance is obtained for h/H between 0.80 and 0.90. Furthermore, the lowest slab thickness was achieved for h/H = 0.80.