Circulating fluidized bed fly ash (CFBFA) is a by-product from the combustion in circulating fluidized bed boiler in power plants. Herein, to resourcefully utilize CFBFA and reduce cement consumption, the CFBFA was ground (GCFBFA) and used to prepare low-carbon lightweight foamed concrete (LFC) for subgrade filling. The effect of GCFBFA substitution ratio on the blended cement binder and LFC was investigated. It was found that incorporation of 30 wt% GCFBFA stimulated cement hydration and produced more hydration products including C-S-H and AFt, thus enhancing the performance of binder. For LFC, GCFBFA improved the stability of fresh LFC slurry and the air-void structure by increasing the rheological properties of binder, thus improving the mechanical properties and durability including water stability and freeze-thaw resistance. The extension of setting time and reduction in hydration heat due to GCFBFA can be beneficial for transportation and massive construction. For subgrade filling, the GCFBFA content is limited to 50 wt% for LFC with wet density of 600 kg/m3 (D600) and up to 70 wt% for D700 and D800. Life cycle assessment (LCA) showed that a reduction of 52.3% in global warming potential and 43.2% in total cumulative energy consumption for the production of LFC was achieved when GCFBFA replaced 70% of cement.@en

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.

@en