International Concrete Abstracts Portal

This experimental study investigates the influence of flexural cracks and punching shear failure inclination on double-headed studs anchorage within the critical perimeter. The research also explored the technical feasibility of using synthetic coarse aggregates from bauxite residue as a sustainable alternative in structural concrete production. The results showed that the overall structural integrity is impaired at 40 to 50% due to flexural cracks at the critical perimeter of 2‧d (30°), however, the perimeter of 1.2‧d (45°) enhanced the shear reinforcement activation and shear strength up 15%, providing a balanced failure within the strengthening zone. Thus, an internal equilibrium of the concrete capacity design (IECCD) method was proposed to calculate the contribution of double-headed studs and accurate the codes of punching shear strength predictions in serviceability and ultimate limits states. In addition, synthetic aggregates performed similarly to natural aggregates, offering environmental benefits such as reducing the carbon footprint and production stages.

Portland cement has played a significant role in the construction of major infrastructure and building structures. However, in light of the substantial CO₂ emissions associated with its production, there is a growing concern about environmental issues. Accordingly, the development of eco-friendly alternatives is actively underway. Geopolymer represents a class of inorganic polymers formed via a chemical interaction between solid aluminosilicate powder with alkali hydroxide and/or alkali silicate compounds. Concrete made with geopolymers, as an alternative to Portland cement, generally demonstrates comparable physical and durability characteristics to ordinary Portland cement concrete (OPC). Research on the material properties of geopolymer concrete (GPC) has made extensive progress. However, the number of large-scale tests that were conducted to assess its structural performance is still insufficient. Additionally, there is a shortage of comprehensive studies that compile and analyze all the structural experiments conducted thus far to evaluate the GPC’s potential. Therefore, this study aimed at compiling and analyzing a number of bond, flexural, shear, and axial strength tests of GPC to assess its potential as a substitute for OPC and to identify its distinctive characteristics compared to OPC. As a result, it is considered that GPC can be used as a substitute for OPC without any structural safety issues. However, caution is needed in terms of deflection and ductility, and additional experiments are deemed necessary in the aspect of compressive strength of large-scale members.

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.

Concrete, a highly energy-intensive material, contributes around 10% of global CO₂ emissions. To address this issue, incorporating industrial residues in concrete production has emerged as a viable solution, reducing natural resource consumption and lowering the CO₂ footprint. Using bauxite residues in concrete has proven to be an environmentally friendly and sustainable approach. In this study, cement mass was partially replaced with bauxite residues (at 5, 10, 15, and 20%), with variations in residue diameter (300 µm, 600 µm, and 2 mm) and in liquid form. The concrete's workability, air content, density, mechanical strength, elasticity, Poisson's ratio, and porosity were assessed with each replacement percentage. The study revealed that bauxite residues can effectively replace up to 20% of cement in the concrete mix. Although their use slightly affects the fresh properties of concrete, it significantly enhances its mechanical properties. With this approach, sustainable and eco-friendly concrete without compromising its performance can be created.

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.