Impact resistance is an outstanding characteristic of fiber-reinforced concrete (FRC). To evaluate this property, many methods have been designed. The most widespread test is the one proposed by ACI Committee 544. This test has stood out due to its speed and simplicity; nevertheless, the high dispersion in its results has made it unreliable. Recently, the authors have designed a new method based on the application of growing impact loads (GIL). It is simple, economical, and allows for the evaluation of FRC impact behavior at cracking and after cracking, with most of the resulting parameters expressed in terms of energy. In this paper, results obtained by both methods are compared. Two FRC materials were evaluated, the first incorporating 30 kg/m3 of steel fiber and the second 5 kg/m3 of a polymeric fiber. Results showed that the parameters from the GIL method were less variable (up to approximately 44%) and had acceptable coefficients of variation (<30%).

Experimental research performed on fiber-reinforced cement-based composites made with polymeric aggregate and reinforced with recycled steel fibers is presented in this paper. In total, 18 concrete prisms were cast with a two-stage procedure: first, the fibers from end-of-life tires were put in the molds and, subsequently, they were covered by a cementitious grout containing fine (recycled or virgin) aggregate. The two-stage composites showed more than one crack and a deflection-hardening behavior in the post-cracking regime by performing three-point bending tests. Moreover, both flexural and compressive strength increased with the fiber volume fraction. Thus, if the content of recycled materials is suitably selected, the ecological and mechanical performances of the two-stage composites improve and become similar to those of one-stage fiber-reinforced concrete made with only virgin components.

Fiber-reinforced high-strength grout (HSG) can secure exceptional mechanical properties; yet, case studies show that the interfacing layer to the existing substrate can be particularly vulnerable when used in specialty repair, precast, and retrofitting applications. Polymeric latex materials such as styrene-butadiene rubber (SBR) and acrylic ester (AE) are often incorporated to improve the bond properties and ensure monolithic behavior of the composite system. This paper assesses the concurrent effects of using steel fibers (SFs) and polymeric latexes on the flow and rheology of HSG, including their impact on mechanical properties and bond to existing concrete. The SF content varied from 0 to 5% by volume, while the mixing water was replaced by 10 to 20% of latex. Test results showed that the rheological properties of HSG increased with latex inclusion, given the coalescence of watersoluble polymers in the cementitious matrix that increased the viscosity of the interstitial liquid phase. The viscosity was aggravated with the addition of SF that accentuates the tendency of fiber grouping and interference between solid particles to hinder the ease of flow. The compressive strength slightly decreased when part of the mixing water was replaced by SBR or AE. Yet, in contrast, the flexural properties and pulloff bond strength were remarkably improved, which can be relevant to guarantee the integrity and monolithic behavior of the repair application.

This study aims at assessing the long-term bond behavior of headed-end glass fiber-reinforced polymer (GFRP) bars to basalt fiber-reinforced cementitious composite (BFRCC) exposed to 300 consecutive freezing-and-thawing cycles, followed by 75 cycles of wetting and drying, mimicking successive winter and summer seasons. A total of 85 pullout specimens reinforced with recently developed basalt fiber pellets and steel fibers were tested. The durability of the specimens was quantified in terms of visual analysis, residual compressive strength, relative dynamic modulus of elasticity, as well as the residual pullout capacity. The addition of fibers was capable of retaining approximately 90% of the pullout capacity for specimens exposed to harsh conditions owing to the restriction of cracks in the fiber-reinforced cementitious composites. Therefore, the results confirmed the suitability of steel-free reinforcement systems for long-term application under severe freezing-and-thawing and wetting-and-drying environments.

This paper presents the derivation as well as empirical verification of a compressive stress-strain model of concrete confined with fiber-reinforced concrete (FRC) jackets made using steel fibers. Both conventional (that is, strain-softening) FRC and high-performance (that is, strain-hardening) FRC (HPFRC) were considered. The model accounts for the tensile response of the jacket as a function of the fiber properties, fiber volume fraction, orientation, and the effects of fiber debonding, fiber pullout, and multiple cracking. Specific FRC and HPFRC materials used in this study include fiber-reinforced mortar (FRM), FRC, and slurry-infiltrated fiber-reinforced concrete (SIFCON), all made using steel fibers. Experimental behavior of model columns jacketed with FRC and HPFRC was compared to that of columns confined with conventional fiber-reinforced polymer (FRP) jackets. HPFRC jackets made with continuous aligned fibers exhibited fiber debonding and multiple cracking leading to the post-peak softening response. Varying the orientation of fibers in FRC and FRM jackets produces radial tensile stresses on the concrete core, thus reducing the strength of confined concrete. Concrete confined with FRC jackets exhibited post-peak softening response with lower ductilities than concrete confined with HPFRC jackets due to the random orientation and lower volume fraction of fibers within FRC jackets. HPFRC jackets with steel fibers are expected to sustain large rupture strains in the longitudinal and transverse directions, which translates into an improved ductility and energy absorption, making it a suitable retrofit option for existing columns.