Innovative high-technology concrete mix design method integrating rheological properties and Fracture Mechanics

Abstract

This article presents an innovative approach to concrete mix design, introducing the concept of high-technology concrete (HTC) and incorporating both the rheological and fracture behavior of the material in its fresh and hardened states. Traditionally, the design of concrete mixtures for reinforced structures has prioritized consistency and compressive strength, assuming that tensile capacity is solely provided by steel reinforcement. However, the inclusion of dispersed steel fibers has led to the development of specific guidelines, such as Annex L in the new Eurocode 2, which considers flexural strength classes, allowing for a more comprehensive evaluation of the composite’s behavior. This approach not only assesses compressive strength but also flexural capacity, including aspects such as energy absorption and ductility. The new mix design methodology proposed in this study aims to align the actual behavior of the concrete with structural requirements, enabling the optimization of more efficient structural elements. In its fresh state, the desired consistency is defined through rheological parameters, while in its hardened state, target compressive and flexural strength classes are established, which are interrelated through equations derived from statistical techniques applied to a large experimental database. These equations allow for the calculation of the required volume fraction of steel fibers to achieve the target flexural strength classes, considering fiber geometric properties such as length, diameter, and aspect ratio. Additionally, the granular skeleton composition is optimized for compactness, directly impacting the modulus of elasticity and compressive strength. The experimental results validate the relevance and feasibility of this approach for designing structural elements using HTC, representing a valuable contribution to concrete technology.