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.

The attached cement paste in the recycled concrete aggregate leads to its potential reactivity against sulfate ions. Several test methods were evaluated to find a suitable, reliable, and accurate method to evaluate the potential reactivity of aggregates. Different quality recycled concrete aggregates were used to apply those methods. The studies include evaluations of concrete cores drilled from source concrete, recycled concrete aggregates, recycled mortar bars under different exposures, and recycled concrete prisms exposed to external sulfate attack. The concrete core test allowed qualifying source concrete as potentially reactive against sulfate in a short time. Tests on recycled aggregates and recycled mortar bars showed variable sensitivity levels. Results from concrete prisms showed an effective reactivity of recycled aggregates when the replacement is higher.

High cement content is often found in concrete mix designs to achieve the unique fresh-state behavior requirements of 3D Printable Concrete (3DPC), i.e., to ensure rapid stiffening of an extruded layer without collapsing under the stress applied by the following layers. Some materials with high water absorption, such as recycled concrete aggregates, have been incorporated in concrete mix designs to minimize environmental impact, nevertheless, the fine powder fraction that remains from the recycled aggregate processing still poses a challenge. In the case of 3DCP, few studies are available regarding mix designs using Recycled Concrete Powder (RCP) for 3D printing. In this context, this study presents the use of RCP as a filler to produce a printable mixture with low cement content. An RCP with 50 μm average particle size was obtained as a by-product from Recycled Concrete Aggregate production. Portland cement pastes were produced with 0%, 10%, 20%, 30%, 40% and 50% of cement mass replacement by RCP to evaluate its effects on the hydration reaction, rheology, and compressive strength. It was found that the studied RCP replacement was not detrimental for the hydration reaction of Portland cement during the initial hours, and at the same time it was capable of modifying the rheological parameters of the paste proportionally to the packing density of its solid fraction. The obtained results indicated the viability of 3DCP with up to 50% cement replacement by RCP. It was concluded that RCP presents good potential for decreasing the cement consumption of 3DPC, which in turn could decrease its associated environmental impact while providing a destination for a by-product from recycled concrete aggregate production.

This paper investigates the structural performance of lightweight self-consolidating concrete (LWSCC) and lightweight vibrated concrete (LWVC) beam-column joints reinforced with mono-filament polyvinyl alcohol (PVA) fibers under quasi-static reversed cyclic loading. A total of eight exterior beam-column joints with different lightweight aggregate types (coarse and fine expanded slate aggregates), different PVA fiber lengths (8-12 mm [0.315-0.472 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 fine aggregates (LF) appeared to have better structural performance under reversed cyclic load compared to specimens containing expanded slate coarse aggregates (LC). Shortening the length of PVA fibers enhanced the structural performance of LWSCC beam-column joints (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 normal-weight concrete.

A comprehensive laboratory testing program, field-testing program, numerical analysis, and life-cycle cost analysis were conducted to evaluate the beneficial effects of incorporating shrinkage-reducing admixture (SRA), polymeric microfibers (PMFs), and optimized aggregate gradation (OAG) into internally cured concrete (ICC) mixtures for rigid pavement applications. Results from the laboratory program indicate that all the ICC mixtures outperformed the standard concrete (SC) mixture. All the ICC mixtures showed a decrease in drying shrinkage compared to the SC mixture. Based on the laboratory program, three ICC mixtures and one SC mixture were selected for the full-scale test and subjected to a heavy vehicle simulator for accelerated fatigue testing. Extensive testing and analysis have shown that ICC mixtures incorporating SRA, PMFs, and OAG can be beneficially used in pavement applications to achieve increased pavement life.