International Concrete Abstracts Portal

Recent research data was evaluated with the aim of extending the applicability of using deformed steel fiber-reinforced concrete (SFRC) to enhance the shear strength of beams and one-way slabs. Experimental results were assessed for influences on the shear strength of SFRC members that do not contain stirrups of factors, including size effect, concrete density (normalweight and lightweight) and compressive strength, fiber-volume fraction (Vf), and the longitudinal steel reinforcement ratio. Estimates of steel stresses in longitudinal bars at the time of shear failure were carried out to identify differences in members with distinct longitudinal steel ratios and bar grades, consistent with the range of flexural design parameters in ACI 318-19. Results of these analyses and a reliability investigation of design equations applicable to members without fibers were used for proposing new provisions for the shear design of SFRC beams and one-way slabs based on the ACI 318-19 shear-strength model.

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.

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).

This study evaluates the potential to use shrinkage-reducing admixture (SRA) and pre-saturated lightweight sand (LWS) to shorten the external moist-curing requirement of ultra-high-performance concrete (UHPC), which is critical in some applications where continuous moist-curing is challenging. Key characteristics of UHPC prepared with and without SRA and LWS and under 3 days, 7 days, and continuous moist curing were investigated. Results indicate that the combined incorporation of 1% SRA and 17% LWS can shorten the required moist-curing duration because such a mixture under 3 days of moist curing exhibited low total shrinkage of 360 με and compressive strength of 135 MPa (19,580 psi) at 56 days, and flexural strength of 18 MPa (2610 psi) at 28 days. This mixture subjected to 3 days of moist curing had a similar hydration degree and 25% lower capillary porosity in paste compared to the Reference UHPC prepared without any SRA and LWS and under continuous moist curing. The incorporation of 17% LWS promoted cement hydration and silica fume pozzolanic reaction to a degree similar to extending the moist-curing duration from 3 to 28 days and offsetting the impact of SRA on reducing cement hydration. The lower capillary porosity in the paste compensated for the porosity induced by porous LWS to secure an acceptable level of total porosity of UHPC.