Tomoya Nishiwaki

Development of Ultra-high-performance Hybrid Fiber-reinforced Cement-based Composites

A new ultra-high-performance hybrid fiber-reinforced cement-based composite (UHP-HFRCC) was developed in this study. The UHP-HFRCC exhibited a tensile strength of 20.1 MPa (2.9 ksi), a strain capacity of 1.06%, and energy-absorption capacity of 153 kJ/m³ (1356 lb-ft/ft³). The multi-scale fiber-reinforcement system employed herein effectively improves the mechanical properties of the UHP-HFRCCs under tension. Determining the appropriate volume fraction of the longer fibers is crucial for enhancing a variety of mechanical properties, including the tensile strength, strain capacity, and energy-absorption capacity. Besides the significant improvement in the mechanical properties of UHP-HFRCC, the cost was reduced, and the workability of the material was improved by using relatively low-volume fractions of fibers (total volume fraction = 2.5 to 3%).

Tailoring Hybrid Strain-Hardening Cementitious Composites

A class of fiber-reinforced concrete, commonly called strain-hardening cementitious composite (SHCC), can show very ductile behavior under tension. In the post-cracking stage, several cracks develop before complete failure, which occurs when tensile strains finally localize in one of the formed cracks. To predict the mechanical performances of monofiber SHCC, a cohesive model has been proposed. Such a model is used herein to tailor hybrid SHCC, made with long and short fibers. By combining uniaxial tensile tests and the theoretical results of the model, the critical value of the fiber-volume fraction can be evaluated. It should be considered as the minimum amount of long fibers that can lead to the formation of multiple cracking and strain hardening under tensile actions. The aim of the present research is to reduce such volume as much as possible, to improve the workability and reduce the final cost of SHCC.