The extensive use of Ordinary Portland cement (OPC) in foamed lightweight concrete (FLC) contributes significantly to its carbon footprint. Concurrently, the disposal of industrial by-products carbide residue slag (CRS) and ground granulated blast furnace slag (GGBS) poses challenges. This study developed a sustainable foamed lightweight concrete system employing CRS-activated GGBS as a complete OPC substitute to address both engineering performance and environmental concerns. An optimal CRS/GGBS ratio (10/90) was determined for achieving the maximum compressive strength in the binder system. Compared to OPC, the CRS/GGBS binder exhibits remarkably low heat of hydration, enabling safer large-volume placements and effectively mitigating the risk of early-age thermal cracking. The prepared CRS/GGBS foamed concrete has much higher compressive strength than those made with cement due to refined air void structure with increased sphericity and improved flexural strength of the solid matrix. The life cycle assessment demonstrated that CRS/GGBS foamed concrete has the ability to decrease carbon emissions by as much as 80 % when compared to cement foamed concrete. This work establishes CRS/GGBS as a technically viable and environmentally superior binder for foamed lightweight concrete, offering enhanced compressive strength, lower thermal cracking risk, and a reduced carbon footprint compared to conventional cement systems in civil engineering.

This study investigates the size effect on the compressive strength of foamed concrete at the mesoscale level combining X-ray computed tomography (X-CT) and a discrete lattice model. Image segmentation techniques and X-CT were employed to obtain virtual specimens comprising hydrated cement paste and air voids. The lineal-path function and pore size distribution was used to characterise the air void structure. A two-dimensional lattice fracture model of foamed concrete considering different wet densities was established. The model was verified experimentally at a wet density of 700 kg/m³ and then used to predict the strengths of specimens with wet densities of 600 and 800 kg/m³. Square and rectangular specimens (slenderness ratio = 2) with widths of 10, 20, 40, 70.7, and 100 mm were investigated. Results show that the air void structure significantly influences the observed size effect on the compressive strength in the investigated size range. A random forest regressor was used to predict the compressive strength of the foamed concrete; the regressor yielded satisfactory results. Finally, existing analytical size effect models were used to fit the simulated strength. Although good fitting was achieved, special attention should be given to the applicable range and physical meaning of fitted empirical parameters.