International Concrete Abstracts Portal

This paper investigates the mechanical characteristics (encompassing compressive strength, flexural strength, toughness, and impact resistance) of ultra-high performance fiber-reinforced concrete (UHPFRC) incorporating polypropylene (PP) and polyvinyl alcohol (PVA) fibers. An experimental program was conducted, based on which the polymer and metallic fibers were utilized at the same fiber content, and different sets of single and hybrid fiber-reinforced composites were fabricated and tested. Despite the fact it has been exhibited through previous research that the hybridized PVA-PP fibers do not result in the development of the mechanical characteristics of engineered cementitious composites (ECC), the UHPC composites incorporating such hybrid fibers show augmented levels of toughness, flexural strength, and resistance to impact loads. A comparison was also made to assess the potentiality of the used fibers in terms of environmental impact and cost. Based on the results, hybridization with PVA and PP fibers leads to remarkable improvement in technical performance and mitigation of the economic and environmental impact of UHPFRC composites.

This paper investigates the structural performance of lightweight self-consolidating concrete (LWSCC) and lightweight vibrated concrete (LWVC) beam-column joints (BCJs) reinforced with monofilament polyvinyl alcohol (PVA) fibers under quasistatic reversed cyclic loading. A total of eight exterior BCJs with different lightweight aggregate types (coarse and fine expanded slate aggregates), different PVA fiber lengths (8 and 12 mm [0.315 and 0.472 in.]), and different percentages of fiber (0.3 and 1%) were cast and tested. The structural performance of the tested joints was assessed in terms of failure mode, hysteretic response, stiffness degradation, ductility, brittleness index, and energy dissipation capacity. The results revealed that LWSCC specimens made with expanded slate lightweight fine aggregates (LF) appeared to have better structural performance under reversed cyclic loading than specimens containing expanded slate lightweight coarse aggregates (LC). Shortening the length of PVA fibers enhanced the structural performance of LWSCC BCJs in terms of initial stiffness, load-carrying capacity, ductility, cracking activity, and energy dissipation capacity compared to longer fibers. The results also indicated that using an optimized LWVC mixture with 1% PVA8 fibers and a high LC/LF aggregate ratio helped to develop joints with significantly enhanced load-carrying capacity, ductility, and energy dissipation while maintaining reduced self-weight of 28% lower than normalweight concrete (NWC).

External bonding with fiber-reinforced polymer (FRP) offers a potential solution to mitigate the detrimental effects caused by load impact and corrosion, which can weaken the bond strength of reinforced concrete structures. However, existing models need to be improved in addressing the FRP confinement mechanism and failure modes. As a solution, the proposed model employs stress intensity factor (SIF)-based criteria to determine the internal pressure exerted on the steel-concrete interface during various stages of comprehensive concrete cracking. Critical parameters are evaluated using weight function theory and a finite element model. A bond-slip model is introduced for the FRP-concrete interface and reasonable assumptions on failure plane characteristics. The internal pressure model employed demonstrates that FRP confinement has the ability to generate dual peaks in stress distribution and modify their magnitude as the confinement level increases. The proposed predictive model demonstrates superior performance in failure modes, test methods, and wrap methods for assessing bond strength with FRP confinement. The accuracy of this model is indicated by an integral absolute error (IAE) of 9.6% based on 125 experimental data, surpassing the performance of the other three existing models. Moreover, a new confinement parameter is introduced and validated, showing an upper bound of 0.44 for enhancing FRP bond strength. Additionally, a general expression validating the bond strength model with FRP confinement is established, allowing for the prediction of bond length.

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.