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Reactive powder concrete (RPC) represents a new generation of cement-based materials composed of cement, reactive ultrafine powders, siliceous fine aggregates, super plasticizers and fibers. Due to its microstructural properties, this concrete demonstrates specific properties including high compressive and flexural strength, superb durability. Since this is a novel type of concrete, a single design code containing multiple experimental results of high quality, together with reliable stress-strain models for the nonlinear analysis of the structural members made of this concrete type is lacking. Although some experimental equations to predict the strength of the RPC members can be found in the literature, note that there are shortcomings in the information provided specifically regarding the RPC containing synthetic and hybrid fibers. Hence, in this study, ten different mix designs of RPC, containing steel fibers at the volume fractions of 1, 2, and 3%, polyvinyl alcohol fibers at the volume fractions of 0.25, 0.5, and 0.75%, together with hybridizations of the two fiber types at the total fiber volume fraction of 1% were prepared, and then tested to obtain accurate and applicable equations as well as the compressive stress-strain curve with the purpose of estimating the mechanical properties and better predicting the behavior of this type of concrete. Then, the effect of the type and volume fraction of fibers, together with curing regime on the properties of RPC including the compressive strength, strain at peak stress, modulus of elasticity, and the shape of stress-strain curve was investigated. The obtained results indicate that as the volume fraction of steel and polyvinyl alcohol fibers increases, the compressive strength and strain at peak stress of the RPC specimens decreases; a trend which is also observed as the volume fraction of synthetic fibers in the concrete mix containing hybrid fibers increases.. The trend which is observed for the strain at peak stress in the RPC is very close to that for its compressive strength. The secant and tangential modulus of elasticity values of the RPC also demonstrate trends similar to each other, and the tangential modulus of elasticity in all the specimens has values higher than the corresponding secant modulus of elasticity. The RPC containing high volume fractions of steel fibers shows high modulus of elasticity values, due to the crimped shape of fibers as well as the strong cohesion they provide in the concrete. Heat treatment has a positive effect on the compressive strength and strain at peak stress of the RPC specimens, due to the acceleration of the hydration process of cementitious materials at high temperatures as well as the formation of a dense matrix. By using the nonlinear regression analysis of the data, experimental equations were developed for the parameters affecting the stress-strain curve of RPC. Finally, based on the experimental parameters obtained for all the RPC specimens, a model was proposed to predict the compressive stress-strain curve. By comparing the proposed model with the experimental results of the stress-strain curve of RPC, it can be said that the proposed model is capable of predicting the experimental results with a very good accuracy.

Keywords: Reactive Powder Concrete, Stress-strain diagrams, Fibers, Heat Treatment

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