Fiber valorization in cementitious materials. Application in high performance structural concretes for the validation of Dynamic Interaction Tests

Abstract

This thesis investigates the impact of various fiber types on the mechanical properties, durability, and microstructural characteristics of High-Performance Concrete (HPC). The study aims to optimize fiber-reinforced HPC formulations for enhanced structural performance and sustainability. Nine concrete mixtures incorporating flax and polypropylene fibers were prepared and tested at different dosages and lengths. The mechanical properties, including compressive strength, flexural tensile strength, and split tensile strength, were evaluated alongside durability indicators such as porosity, capillary absorption, and thermal conductivity. Advanced techniques like Digital Image Correlation (DIC) and Scanning Electron Microscopy (SEM) were employed to analyze deformation behavior and microstructural integrity. Key findings indicate that fiber reinforcement significantly enhances the mechanical properties and durability of HPC, with optimal results observed at specific fiber dosages and lengths. For instance, including 0.3% flax fibers of 30 mm length (FF3030) improved compressive strength and reduced deformation under load. The study also highlights the importance of fiber surface treatment in enhancing matrix-fiber adhesion, as demonstrated by the alkaline treatment of flax fibers. While the research provides valuable insights into fiber-reinforced HPC optimization, limitations such as focusing on specific fiber types and the need for long-term durability studies are acknowledged. Future work should explore a broader range of fibers and investigate the long-term performance of fiber-reinforced HPC in real world applications.