Tailoring high-strength SHCC

Multiple cracking and strain hardening can be achieved in cement-based specimens subjected to uniaxial tension by increasing the volume fraction of steel fibers with hooked ends, or by using plastic fibers with and without steel fibers, or by means of high bond steel fibers (e.g., twisted fibers or cords). To better understand why relevant mechanical performances are obtained in such situations, an analytical micro-mechanical model was proposed. The model, capable of predicting the average distance between cracks as measured in some experimental campaigns, is here used to tailor a high performance fiber-reinforced concrete. Specifically, a two High-Strength and Strain Hardening Cementitious Concrete (HS-SHCC), reinforced with different types of steel fibers, are introduced. By combining direct uniaxial tensile tests, performed on the so-called dumbbell-shaped specimens, and the results of the micro-mechanical model, the critical value of the fiber volume fraction can be evaluated. It should be considered as the minimum amount of long steel fibers which can lead to the formation of multiple cracking and strain hardening under tensile actions. The aim of the present paper is to reduce such volume as much as possible, in order to improve the workability and reduce the final cost of HS-SHCC.