Abstract: This study selects polypropylene fibers (PP) and polyacrylonitrile fibers (PAN) as reinforcing contents of high-strength wear-resistant fly ash concrete (HF concrete) to improve its brittle damage characteristics. Combining digital image correlation technology (DIC) and ultrasonic detection (UT), we conduct experimental tests and examine the stress-strain characteristic parameters of this fiber-reinforced HF concrete under the condition of compression damage. The results show its damage and failure process can be divided into five stages－elasticity, plasticity, sudden damage, accelerated damage, and residual damage. PP inhibits the initiation of microcracks in elastoplastic stage, and PAN inhibits the propagation of microcracks in abrupt damage stage. With a PP content of 0.6 kg/m3 and PAN of 0.6 kg/m3, the concrete enjoys the best hybrid effect and a peak stress increase of 8.35% or 4.47% in comparison with that of the single PP or PAN respectively, and it manifests an increase of 23.74% or 9.87% respectively in its compressive toughness index. Finally, a stress-strain full curve model is developed for such fiber-reinforced HF concrete based on the CEB-FIP model and Guo Zhenhai model, and it is optimized using an improved differential evolution algorithm. It gives optimized stress-strain full curves in good agreement with the experimental curves. Our findings help engineering application of fiber-reinforced HF concrete and lay a basis for follow-up research.

Key words: HF concrete, fiber toughening, digital image correlation (DIC), ultrasonic detection, stress-strain, damage evolution