International Concrete Abstracts Portal

The production of carbonated aggregates from Class F fly ash (FA) is challenging due to its low calcium content, typically less than 10%. This study investigates the production of carbonated alkali-activated aggregates using FA and calcium carbide sludge (CCS). Sodium hydroxide was used as an activator and examined the effects of autoclave treatment on the properties of these aggregates. The optimal mixture, comprising 70% FA and 30% CCS, achieved a single aggregate strength of >5 MPa in autoclave carbonated (AC) aggregates, comparable to the strength obtained after 14 days of water curing in without autoclave carbonated (WAC) aggregates. Both AC and WAC aggregates exhibited a bulk density of 790 to 805 kg/m³ and CO₂ uptake of 12.5% and 13.3% in AC and WAC aggregates, respectively. FE-SEM and FT-IR analysis indicated the formation C-A-S-H gel in noncarbonated aggregates, while calcite and vaterite, along with N-A-S-H gel, formed in carbonated aggregate. Concrete incorporating AC and WAC aggregates exhibit compressive strengths of 39 and 38 MPa, with concrete density of 2065 kg/m³ and 2085 kg/m³, respectively. Furthermore, AC and WAC aggregate concrete showed a reduction in CO₂ emission of 18% and 31%, respectively, compared to autoclave noncarbonate (ANC) aggregate concrete. These findings highlight the potential of producing carbonated alkali-activated aggregates from FA and CCS as sustainable materials for construction applications.

Engineered cementitious composites (ECC) represent a significant innovation in construction materials due to their exceptional flexibility, tensile strength, and durability, surpassing traditional concrete. This review systematically examines the composition, mechanical behaviour, and real-world applications of ECC, with a focus on how fiber reinforcement, mineral additives, and micromechanical design improve its structural performance. The present study reports on the effects of various factors, including different types of mineral admixtures, aggregate sizes, fiber hybridization, and specimen dimensions. Key topics include ECC’s strain-hardening properties, its sustainability, and its capacity to resist crack development, making it ideal for high-performance infrastructure projects. Additionally, the review discusses recent advancements in ECC technology, such as hybrid fibre reinforcement and the material’s growing use in seismic structures. The paper also addresses the primary obstacles, including high initial costs and the absence of standardized specifications, while proposing future research paths aimed at optimizing ECC’s efficiency and economic viability.

This study investigates the behavior of recycled steel fibers (RSFs) recovered from waste tires and industrial hooked-end steel fibers (ISF) in two single and hybrid reinforcement 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 fiber reinforced concrete (FRC) specimens, calculating strain distribution and investigating crack initiation and propagation. The SEM study reveals that, due to the presence of hooked ends, industrial fibers promoted improved mechanical interlocking; created anchors within the matrix; added frictional resistance during crack propagation; significantly improved load transfer; and had better bonding, crack bridging, and crack deflection than recycled fibers. RSFs 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 using environmentally friendly materials in FRC.

Concrete, a highly energy-intensive material, contributes approximately 10% of global carbion dioxide (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 a concrete mixture. Although their use slightly affects the fresh properties of concrete, it significantly enhances its mechanical properties. With this approach, a sustainable and eco-friendly concrete without compromising its performance can be created.

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.