One important factor affecting the resistance and durability loss of concrete structures is acid attack, and one common method of improving concrete properties against this attack is to use high-strength fiberreinforced concrete. In this study, high-strength concretes containing different percentages of fortaferro fibers (consisted of synthetic materials in the form of twisted bundle non-fibrillated monofilament and fibrillated polypropylene network) in the presence of silica fume and nano-silica pozzolans were made. After placing the specimens in 5% sulfuric acid for different days of immersion, the effect of adding fibers and pozzolans to the concrete mix on the strength and durability of the high-strength concrete was examined and the relationships between them were determined. Here, ultrasonic pulse velocity (UPV) test was also performed as a nondestructive test to evaluate the quality of high-strength fibrous concrete. The results indicated that as the volume fraction of fibers in the high-strength concrete exposed to sulfuric acid attack increased, less reduction in weight, crushing load, and ultrasonic pulse velocity occurred. In addition, using silica fume resulted in a greater improvement in the durability of the acid-exposed specimens relative to using nano-silica. Moreover, after 63 days immersion in acid, the specimen FF0.6SF10 had the lowest loss in the crushing load, UPV, and weight by demonstrating 4.7, 2.9, and 3.1%, respectively, variations relative to the corresponding reference specimen. Finally, an optimum solution for the design parameters where the crushing load of high-strength fibrous concrete is maximized, was found employing response surface method (RSM).
