Application of R-curve, ANCOVA, and RSM techniques on fracture toughness enhancement in PET fiber-reinforced concrete

The present study focuses on evaluating the optimal mix-design parameters of waste PET-fiber reinforced concrete (PFRC), aiming to enhance its fracture toughness. This study is divided into three parts. To begin, an experimental examination is carried out to assess the fracture toughness of PFRC using crack mouth opening displacement (CMOD) and R-curve approaches. Secondly, the ANCOVA decomposition method is used which offers insights into the relative contributions of various parameters in resisting crack propagation. Finally, Response Surface Methodology (RSM) is employed to optimize the critical parameters. In this research, plain concrete samples were compared with PFRC samples to assess the impact of fiber reinforcement on fracture toughness. Waste PET fiber of 0.3%, 0.4%, and 0.5% was incorporated into conventional concrete to evaluate its fresh and mechanical properties. ANCOVA decomposition method was employed on the dataset comprised of both published literature and our research work. The results of the study revealed that PET-fiber reinforcement significantly improved the fracture toughness of the concrete. The R-curve analysis demonstrated a more gradual increase in crack resistance with crack extension for the PET-fiber reinforced samples compared to plain concrete. Concrete with 0.5% PET showed more ductility and more resistance to crack as observed from CMOD and R-curve. The ANCOVA decomposition analysis resulted in fiber aspect ratio, fiber volume fraction, fiber length, and W/B ratio as critical parameters. The resulting critical parameters are optimized using RSM with a primary focus on the enhancement of fracture toughness. The RSM optimization process yielded optimal values of 32.5 for aspect ratio, 1.5% for fiber volume fraction, 25 mm for fiber length, and a W/B ratio of 0.50 to maximize fracture toughness. The optimized result has the potential to enhance PFRC quality and performance, offering a more sustainable and cost-effective alternative to conventional concrete.