International Concrete Abstracts Portal

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.

Compared to external curing, internal curing enables the judicious use of available water to provide additional moisture in concrete for more effective hydration and improvement in the performance of concrete structures. However, certain challenges with the incorporation of internal curing materials (ICMs) still need to be addressed, as their effectiveness depends on several factors. Furthermore, sustainable construction demands the use of recycled materials, and this paper discusses the comparative evaluation of recycled aggregate (RA) as an ICM, along with two other types of ICMs, on various properties of high-performance concrete in the hardened state under two curing conditions. Concrete mixtures were prepared with pre-wetted RAs, superabsorbent polymers (SAPs), and pre-wetted lightweight volcanic aggregates (LWVAs) as ICMs. Concrete performance was compared through the investigation of the strength development, shrinkage, mass loss, and volumetric water absorption. In addition, the change in internal humidity of concrete with time at different stages of hardening was determined. The compressive strength results showed that RA and LWVA are more efficient in early days, and the performance of SAP is better in the later age due to its slow water releasing capabilities. Compared to the control mixture, the least reduction in strength of 4% and 8% at 28 days and 90 days, respectively, could be observed for the mixtures containing RA under both air and water curing.

Lightweight concrete (LWC) finds wide-ranging applications inthe construction industry due to its reduced dead load, good fireresistance, and low thermal and acoustic conductivity. Lightweightgeopolymer concrete (LWGC) is an emerging type ofconcrete that is garnering attention in the construction industryfor its sustainable and eco-friendly properties. LWGC is producedusing geopolymer binders instead of cement, thereby reducing thecarbon footprint associated with conventional concrete production.However, the absence of standard codes for geopolymer concreterestricts its widespread application. To address this limitation,an investigation focused on developing a new mixture design forLWGC by modifying the existing ACI 211.2-98 provisions has beencarried out. In this study, crucial parameters of LWGC, such asalkaline-binder ratio (A/B), molarity, silicate/hydroxide ratio, andcuring temperature, were established using machine learning techniques. As a result, a simple and efficient method for determining the mixture proportions for LWGC has been proposed.