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 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.

In light of the effort for decarbonization of the energy sector, it is believed that common geopolymer binding materials such as fly ash may eventually become scarce and new geological aluminosilicate materials should be explored as alternative binders in geopolymer concrete. A novel, tension-hardening geopolymer concrete (THGC) that incorporates high amounts of semi-reactive quarry wastes (metagabbro) as a precursor, and coarse quarry sand (granite) was developed in this study using geopolymer formulations. The material was optimized based on the particle packing theory and was characterized in terms of mechanical, physical, and durability properties (that is, compressive, tensile, and flexural resistance; Young’s modulus; Poisson’s ratio; absorption; drying shrinkage; abrasion; coefficient of thermal expansion; and chloride-ion penetration, sulfate, and salt-scaling resistance). The developed THGC, with an air-dry density of 1940 kg/m3 (121 lb/ft3), incorporates short steel fibers at a volume ratio of 2%, and is highly ductile in both uniaxial tension and compression (uniaxial tensile strain capacity of 0.6% at an 80% post-peak residual tensile strength). Using digital image correlation (DIC), multiple crack formation was observed in the strain-hardening phase of the tension response. In compression, the material maintained its integrity beyond the peak load, having attained 1.8% compressive strain at 80% postpeak residual strength, whereas upon further reduction to 50% residual strength, the sustained axial and lateral strains were 2.5% and 3.5%, respectively. The material exhibited low permeability to chloride ions and significant abrasion resistance due to the high contents of metagabbro powder and granite sand. The enhanced properties of the material, combined with the complete elimination of ordinary portland cement from the mixture, hold promise for the development of sustainable and resilient structural materials with low CO2 emissions, while also enabling the innovative disposal of wastes as active binding components.

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.

As one of the key factors influencing the hydration process, as well as the microstructure formation and evolution of ultra-highperformance concrete (UHPC), the action mechanism of different curing regimes have been studied to some extent. However, the current knowledge of the underlying mechanisms that control the different effects of different curing regimes is limited. In this study, the composition of hydration products, micromorphology, and migration and evolution of aluminum-phase hydration products of UHPC under three combined curing regimes (standard curing, steam curing + standard curing, and autoclave curing + standard curing) were investigated in depth. Micromorphology observation shows that heat treatment promoted the formation of higher-stiffness hydration products (tobermorite and xonotlite) in UHPC, and the higher the polymerization degree, the higher the Si/Ca ratio of the hydration product. Meanwhile, 29Si and 27Al nuclear magnetic resonance (NMR) spectroscopy shows that specimens with higher strength had higher Al[4]/Si and a lower amount of ettringite and AFm at the early curing stage. The elevated curing temperature reduced the formation of ettringite and AFm and allowed more Al3+ to replace Si4+ into the structure and interlayer of the calcium- (alumino)silicate-hydrate (C-(A)-S-H) gel, which increased the mean chain length (MCL) and polymerization degree of the C-(A)-S-H gel. However, the polymerization effect of Al ions is limited, so the provision of the silicon source to improve the Si/Ca ratio of the system is important.