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.

Cenospheres are low-density and hollow microspheres derived from coal-fired power plant fly ash waste. This study aims to prepare ultra-light-weight (<1000 kg/m³ wet density) concrete using fly ash cenospheres (FAC). To begin with, FAC's shell thickness and the water absorption and desorption were characterized. A mixing procedure was designed to avoid the segregation between the FAC and cement slurry. FAC can affect the rheological properties of fresh mixture over time through absorption and desorption of free water. The presented ultra-light-weight concrete has several advantages compared to the ones prepared using foaming methods. First, shrinkage is significantly reduced due to FAC's internal restraint and curing effects. Secondly, it has good mechanical performance, especially in bending and is more environmentally friendly due to use of less cement. X-ray computed tomography illustrates that FAC ultra-light-weight concrete has smaller pores of more uniform size compared with those prepared using foaming methods. X-Ray diffraction, thermal gravimetry-derivative thermal gravimetry, fourier-transform infrared spectroscopy and scanning electron microscopy are employed for the hydration products and microstructure characterization. Outcomes prove that FAC can combine well with the cement matrix, and react with calcium hydroxide to produce C-A-S-H through pozzolanic reaction.