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).

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

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.

The objective of the present study is to assess the flexural residual strengths of lightweight aggregate concrete (LWAC) reinforced with micro-steel fibers. Further, the material class of such concrete was examined through comparison with the fiber-reinforced concrete classification specified in the provisions of fib 2010. Fourteen beam specimens were classified into L (21 MPa [3.05 ksi]) and H (40 MPa [5.80 ksi]) groups according to the design compressive strength of LWAC. The volume fraction of micro-steel fibers varied from 0 to 1.5% at a spacing of 0.25% in each beam group. From the beam test results under the three-point loading condition, flexural stress-crack mouth opening displacement (CMOD) curves were measured and then discussed as a function of the fiber reinforcing index (βf). The flexural residual strengths corresponding to four different CMOD values (0.5, 1.5, 2.5, and 3.5 mm [0.02, 0.06, 0.1, and 0.14 in.]) were compared with previous empirical equations and fib 2010 classification. The various analyses of the measured results indicate that βf can be regarded as a critical factor in directly determining the magnitude of flexural residual strengths and assessing material classification. The proposed refined equations improve the accuracy in predicting the flexural residual strengths of concrete beams with different densities and reinforced with different types of steel fibers. Consequently, microsteel fibers are a promising partial replacement for conventional steel reinforcing bars to enhance the ductility of LWAC elements.

The purpose of this study is to investigate the effect of steel fiber content and type on the compressive and flexural ductility capacities of lightweight aggregate concrete (LWAC). Fiber-reinforced LWAC specimens were divided into four groups according to the type of fibers, such as conventional macrosteel fibers (SFs) with hooked ends, straight copper-coated microsteel fibers (CMSFs), crimping-shaped CMSFs, and hooked-end CMSFs. The fibervolume fractions (Vf) were 0.5, 1.0, and 1.5%. This study also modifies the ASTM C1018 method by using the initial crack point calculated from the elastic theorem to save a tedious and elaborated effort in determining the reference point at the load-deflection curve, particularly for beams with a strong hardening response. The test results revealed that the hooked-end CMSFs were better than SFs and crimping-shaped CMSFs with the same shape and length at decreasing the slope of the applied loads at descending branches of the compressive stress-strain and flexural load deflection curves for the LWAC. Compressive and flexural toughness indexes were derived as functions of the fiber reinforcing index based on the regression analysis of test data to assess the ductility improvement of LWAC with steel fibers.