Optimizing polypropylene fiber and carbon nanotubes to reinforce concrete matrix: A response surface methodology

Polypropylene fiber (PPF)-based concrete incorporating carbon nanotubes (CNTs) has garnered significant attention in recent literature. However, determining the optimal content of PPF and CNTs remains crucial. Therefore, this study employed response surface methodology (RSM) to systematically optimize the ideal content and interaction between PPF and CNTs, with the aim to achieve the highest concrete strength and impact resistance. Following the recommendation of the ACI committee 544, the drop-weight impact test procedure was refined and utilized to assess the concrete's impact resistance. The study findings revealed that concrete incorporating optimal proportions of PPF (0.3 %) and CNTs (0.1 %) exhibited significantly enhanced strength properties and impact resistance compared to the control sample. The enhancements in compressive, tensile, and flexural strengths were measured at 29 %, 75 %, and 64 %, respectively. Furthermore, the impact energy consumption at the first and failure cracks was significantly higher, i.e., 1433.82 J and 2016.32 J, respectively, compared to 89.61 J for the control concrete. Scanning electron microscopy analysis revealed ribbed calcium silicate hydrate structures with CNTs, which were identified as the primary factor fortifying the stiffness and strength of the concrete matrix. This suggests that the inclusion of both CNTs and PPF holds promise for advancing the development of sustainable concrete materials with improved strength and impact resistance in the future.