The concrete industry has long been adding discrete fibers to cementitious materials to compensate for their (relatively) low tensile strengths and control possible cracks. Extensive past studies have identified effective strategies to mix and utilize the discrete fibers, but as the fiber material properties advance, so do the properties of the cementitious composites made with them. Thus, it is critical to have a state-of-the-art understanding of not only the effects of individual fiber types on various properties of concrete, but also how those properties are influenced by changing the fiber type. For this purpose, the current study provides a detailed review of the relevant literature pertaining to different fiber types considered for fiber-reinforced concrete (FRC) applications with a focus on their capabilities, limitations, common uses, and most recent advances. To achieve this goal, the main fiber properties that are influential on the characteristics of cementitious composites in the fresh and hardened states are first investigated. The study is then extended to the stability of the identified fibers in alkaline environments and how they bond with cementitious matrices. The effects of fiber type on the workability, pre- and post-peak mechanical properties, shrinkage, and extreme temperature resistance of the FRC are explored as well. In offering holistic comparisons, the outcome of this study provides a comprehensive guide to properly choose and utilize the benefits of fibers in concrete, facilitating an informed design of various FRC products.

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Recent advances made in concrete fibers have made them one of the concrete's recommended ingredients, mainly to eliminate the drawbacks associated with the weakness of cementitious materials, such as concrete, in tension. The addition of fibers, however, introduces extra cost and labor requirements, while selecting an appropriate choice and dosage of fibers has still remained a standing question. To address the outlined issues, the current study investigates the development of fiber‐reinforced concrete (FRC) mixtures with a focus on achieving superior mechanical properties with a low dosage of synthetic fibers. For this purpose, three choices of macrofibers were examined. The investigations spanned four dosages of each macrofiber mixed with three dosages of a microfiber included to ensure adequate resistance to early‐age, shrinkage‐induced strains. The experiments conducted on the developed hybrid FRC mixtures systematically measured workability, as well as compressive, splitting tensile, and flexural strength properties. The test results were then paired with the micro‐scale monitoring of the bond between individual macrofibers and the concrete matrix through scanning electron microscope images. The outcome shed light on how each of the macrofibers of choice contributed to improving the FRC's mechanical properties. This paved the way to benefit from a minimum dosage of them to achieve the expected structural response, while avoiding crack formation and propagation in various applications.

With an increase in CO2 emission, corrosion of reinforcement as a result of carbonation has become more significant to researchers besides corrosion due to chloride ion ingress. Many structures are exposed to coupled effects of carbonation and chloride attack; therefore, investigating the effect of this combined attack on the durability of concrete is a vital subject. Also, the use of supplementary cementitious materials (SCMs) has become more common due to their contribution to concrete's properties. In this study, the combined effect of chloride attack and carbonation on the durability of mortars containing SCMs was studied. Two natural pozzolans (Pumice and Trass) were used as cement replacements in mortar mixtures with three w/b ratios of 0.485, 0.44, and 0.4. Four exposure conditions, namely normal (immersed in lime‐saturated water), chloride attack, carbonation, and cyclic carbonation and chloride attack were considered. Compressive strength, carbonation and chloride penetration depth, capillary water absorption, surface electrical resistivity, and chloride diffusion tests were performed. The results indicate that while carbonation depth is reduced in the combined attack environment, it imposed a more severe corrosive condition in comparison to pure immersion in saline water by increasing the diffusion coefficient up to 500%. Also, addition of pozzolans showed the potential to reduce the diffusion coefficient of the mortars as much as 76% pointing out that mortars without pozzolans were more vulnerable to this combined attack environment. Furthermore, cement replacement with Trass and reduction of w/b showed to be beneficial in reducing the destructive effects of the combined environment.