Analytical Equation for Stress-Strain Relationship in compression for Reactive Powder Concrete

Abstract Concrete is an important construction material globally. Reactive Powder Concrete (RPC), also called Ultra-High-Performance Concrete (UHPC), represents a new type that differs significantly from traditional concrete. This new concrete was developed by Bouygues laboratory in France during the 1990s. It is characterized by its ultra-high strength and ductility composite material with advanced mechanical properties. This study conducted experimental investigations on different mixes of RPC to obtain the complete compressive stress–strain relationships. A general mathematical equation was derived to express this relationship theoretically. Two main variables were used to achieve different mixes of RPC. The variables were the type of pozzolanic materials used (metakaolin or silica fume) and the volumetric ratio of the fibers (1.25, 1, and 0.75). The results show that the increase in compressive stress for the mixtures of the first group G1, which contain metakaolin, is approximately 39% when the percentage of fiber is increased from 0.75 to 1%. The percentage becomes 50% when the fiber increases to 1.25. For the second group of mixtures with silica fume, increasing fiber percentage from 0.75% to 1% yields about a 20% rise in compressive stress, and 1.25% fiber increases it by 38%. For the compressive stress-compressive strain curve for RPC concrete, it was found that the two main variables in this research do not strongly affect the shape of the upward curve in this relationship. The downward curve is immensely affected by the quantity of fibers used. Furthermore, using steel fibers with a higher volume ratio leads to RPC concrete with higher ductility and toughness. The proposed analytical model for the stress-strain relationship of RPC mixes complies with experimental results.