Fracture response of concrete containing carbon nanotubes under various loading conditions

The demand for high-performance cementitious materials capable of sustaining extreme mechanical loads has intensified in recent years, as conventional concrete often suffers from brittle fracture and limited durability under dynamic actions. Nanomaterials such as carbon nanotubes (CNTs) have emerged as promising additives owing to their remarkable mechanical and interfacial properties, offering the potential to enhance the fracture resistance of ultra-high-performance fiber-reinforced concretes (UHPFRCs). This study explores the fracture durability of UHPFRCs incorporating CNTs under both static and impact loading conditions. Mixtures were prepared with CNT dosages ranging from 0% to 1.5% by cement weight, and fracture behavior was evaluated through fracture strength (ft), specific work of fracture (WS), total fracture energy (WE), and softening fracture energy (WF). The experimental results indicated that CNT addition substantially improved fracture resistance, particularly tensile strength, across all loading rates. The mixture containing 1.0% CNTs achieved the highest fracture strength and exhibited the maximum dynamic increase factor (DIF) compared with the control and other CNT dosages. Furthermore, fracture parameters ft, WS, and WE demonstrated pronounced sensitivity to loading rate, with DIF values ranging from 1.21 to 4.50, while WF remained nearly unchanged, with DIF values between 0.90 and 0.98. These outcomes confirm that CNTs strengthen the fiber–matrix interfacial zone, leading to more efficient stress transfer and improved durability. The findings provide valuable insights for the design of UHPFRCs with superior performance under both static and impact loads, contributing to the development of resilient structural materials