The maximum post-cracking tensile strength (σpc) recorded in numerous investigations of ultra-high-performance fiber-reinforced concrete (UHP-FRC) remains mostly below 15 MPa, and the corresponding strain (εpc) below 4/1000. Both values are significantly reduced when the specimen size increases, as is needed for real structural applications. Test data on σpc and εpc from close to 100 series of direct tensile tests carried out in more than 20 investigations are analyzed. Factors influencing the strain capacity are identified. However, independently of the numerous parameters encountered, two observations emerged beyond all others: 1) the higher the post-cracking tensile strength (whichever way it is achieved), the higher the corresponding tensile strain; and 2) fibers mechanically deformed and/or with slip-hardening bond characteristics lead to an increase in strain capacity. A rational explanation for these observations is provided. The authors believe that achieving a large strain (εpc) at maximum stress is paramount for the successful applications of ultra-high-performance concrete in concrete structures not only for strength but, more critically, for ductility and energy absorption capacity improvements.

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.

The main focus of the current research is the development of high-performance fiber-reinforced cementitious composites with large amounts of coarse aggregates without risking deflection-hardening response, and the evaluation of the autogenous self-healing capability of these composites at different scales. The structural performance of cementitious composites exhibiting strain hardening should be known to be used in large-scale specimens. In addition to the studies carried out in small sizes, there is a need to examine the self-healing performances of large-scale specimens. Composite mixtures included different design parameters—namely Class F fly ash-to-portland cement ratio (FA/PC = 0.20, 0.70), aggregate-cementitious materials ratio (A/CM = 1.0, 2.0), addition/type of different fibers (for example, polyvinyl alcohol [P], nylon [N], and hooked-end steel [S] fibers), addition/type of nanomaterials (for example, nanosilica [NS] and nanoalumina [NA]) and inclusion of steel reinforcing bar in tested beams. Small-scale (80 x 75 x 400 mm [3.15 x 2.96 x 15.76 in.]) and large-scale beams (100 x 150 x 1000 mm [3.94 x 5.91 x 39.4 in.]) were produced and considered for performance comparison. Four-point bending tests were performed on different-scale beams loaded by considering different shear span-effective depth ratios (a/d) ranging between 0.67 and 2.00 and 0.67 and 2.96 for small- and large-scale beams, respectively. Autogenous self-healing evaluation was made using different-scale beam specimens subjected to 30-day further cyclic wetting-and-drying curing in terms of changes in microcrack characteristics and recovery in flexural parameters of preloaded beams. Experimental results showed that it is possible to successfully produce concrete with large amounts of coarse aggregates without jeopardizing the deflection-hardening response both at small and large scale. Autogenous self-healing is valid for small- and large-scale beams in terms of crack characteristics/flexural parameters and is found to improve with the increased FA/PC, decreased A/CM, in the presence of nanomaterials, and with the increased fiber amount (regardless of the type). Outcomes of this research are thought to be important because they show the manufacturability of deflection-hardening concrete with large amounts of coarse aggregates at large scale and validate their autogenous self-healing capabilities, which are important for the real-time applicability of such mixtures in actual field conditions.

The mechanical potential, the durability, and the most varied uses of structures have been studied and disclosed. However, there is still a gap regarding the determination of mixing ratios using a simple, accessible mixture design method that allows the determination of the ideal ratio of mixture constituents. Some studies on ultra-high-performance concrete (UHPC) mixtures did not present a method to define the mixing ratio with different materials and fiber contents, with high mechanical strength and no workability loss. To develop a method of mixing design from informational parameters of the materials, this paper presents a method of dosing UHPC. The proposed method is based on the packaging of particles through the previous evaluation of the percentages of each material according to its particle size distribution. Results showed that the proposed mixture design method can grant high potential compressive strength to the mixture. There was also a linear relation between higher matrix compacity and compressive strength. The composition with higher compacity—that is, the lowest void ratio of the mixture—presented an increase of 20% in compressive strength compared to the mixture with less compacity.

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.