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 used at the same fiber content, and different sets of single and hybrid fiber reinforced composites were fabricated and tested. Despite the fact that 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 (ECCs), 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 study investigates the behavior of recycled steel fibers recovered from waste tires (RSF) and industrial hooked-end steel fibers (ISF) in two single and hybrid reinforcing types with different volume content, incorporating microstructural and macrostructural analyses. Scanning electron microscopy (SEM) is used to study the microstructure and fractures, focusing on crack initiation in the fiber interface transition zone (FITZ). The macrostructural analysis involves using digital image correlation (DIC) software, Ncorr, to analyze the split tensile behavior of plain and FRC specimens, calculating strain distribution, and investigating crack initiation and propagation. The SEM study reveals that industrial fibers due to the presence of hooked ends promoted improved mechanical interlocking, anchors within the matrix, frictional resistance during crack propagation and significantly improved load transfer have better bonding, crack bridging, and crack deflection compared to recycled fibers. Recycled steel fibers significantly delay crack initiation and enhance strength in the pre-peak zone. The study suggests hybridizing recycled fibers from automobile tires with industrial fibers as an optimum strategy for improving tensile performance and utilizing environmentally friendly materials in FRC.

Corrosion of steel anchors in concrete poses a significant risk, leading to detachment, structural damage, and loss of anchor strength. To enhance the durability of structural elements involving anchors, using corrosion-resistant non-metallic inserts could be a feasible alternative. This study presents an experimental investigation of the tensile and shear concrete breakout capacity of a single cast-in Fine Ceramics Insert (FCI). The tensile tests were conducted with FCIs located at the center and edge of concrete blocks, while the shear tests were conducted with inserts positioned at varying distances from the concrete block's edge. The experimental program comprised 75 specimens with three different FCI diameters (FCI 1/2 in. [12.7 mm], FCI 5/8 in. [16.0 mm], FCI 1 in. [25.4 mm]) with two different embedment depths for each type. The experimental results showed that FCI anchors performed satisfactorily, providing bearing capacity conservatively satisfying the values calculated by ACI equations for the concrete breakout strength capacity.

An experimental study was conducted to evaluate the cyclic behavior of reinforced concrete (RC) flexural members with different design parameters. Twenty-five large-scale beam specimens were tested under lateral displacement reversals using a test setup intended to impose single-curvature deformation. Test parameters investigated include: 1) specimen aspect ratio, a/d; 2) designated shear stress demand, VMpr/bwd √fc′ ; 3) spacing of transverse reinforcement, s; 4) diameter of longitudinal reinforcement, db; and 5) tension-to-compression reinforcement ratio. All specimens were designed in compliance with ACI 318-19 using Grade 60 (fy = 60 ksi [414 MPa]) reinforcing steel and a specified concrete strength of 4 ksi (27.6 MPa). Test results indicated that specimen peak lateral strength, Vpeak, can be acceptably estimated by VMn, the shear corresponding to the development of the nominal flexural strength at the beam fixed end. The Vpeak/VMn ratio increased as the normalized peak shear stress, Vpeak/bwd √fc m , decreased, where bw, d, and fcm were the beam width, effective depth, and concrete cylinder strength, respectively. Specimen ultimate drift, du, was also found to be more sensitive to the normalized peak shear stress, Vpeak/bwd √fc m . Specimen ultimate drift, du, tended to increase as the Vpeak/bwd √fc m decreased. The average normalized energy dissipation capacity generally increased as the specimen normalized peak shear stress decreased, the aspect ratio increased, and the spacing of transverse reinforcement was reduced. Finally, specimen effective lateral stiffness increased as the shear span decreased or the reinforcement ratio on the tension side increased.

ACI 318-19 requires that prestressed concrete hollow-core slabswith depths exceeding 12.5 in. (320 mm) and subjected to a factored shear greater than half the design web-cracking shear strength be provided with at least minimum shear reinforcement. Because the use of bar-type shear reinforcement in hollow-core slabs is generally not possible, this requirement limits the use of these members in shear-critical cases. In this research, the use of hooked steelfibers as a means to increase the shear strength of deep hollowcore slabs was evaluated through 14 tests on extruded hollow-core slabs. Slab thickness was 16 in. (406 mm) and the shear span-effective depth ratio (a/d) was either 3.0 or 3.5. Two types of hooked steel fibers were evaluated at dosages between 40 and 62 lb/yd3 (24 and 37 kg/m3). Type 1 fibers had a single hook at each end and Type 2 fibers had double hooks at each end. The fiber-reinforced concrete slabs exhibited peak shear strengths that ranged between 0.94 and 1.29 times the ACI 318-19 calculated web-cracking shear strength Vcw, while the two slabs without fibers failed at shear forces corresponding to 0.93 and 0.87Vcw. Besides an increase in shear strength, the presence of fibers, particularly Type 2 fibers, led to a more gradual post-peak strength decay. Failure of the hollowcoreslabs without fibers occurred as soon as one web exhibitedweb-shear cracking. In the hollow-core slabs with fibers, on theother hand, fibers bridging the first web-shear crack preventedthis web from experiencing a sudden loss of shear capacity, which allowed the slabs to sustain additional shear until multiple webs had cracked in shear.