The performance of bubble-mixed lightweight soil to relieve expansion of circulating fluidized-bed fly ash

Abstract

The treatment of circulating fluidized bed (CFB) fly ash with bubble-mixed lightweight soil (BMLS) was proposed. Artificial air bubbles in BMLS were used to restrict the dilatancy of CFB fly ash mixed with cement. The effects of CFB fly ash on pore structure of BMLS with CFB fly ash (BMLS-CF) were investigated. The material composition of BMLS was evaluated by X-ray diffractometry, and the pore structure was characterized by scanning electron microscope and mercury intrusion porosimetry. The results show that sulfur compounds in CFB fly ash react with cement in BMLS-CF to form ettringite and gypsum, which adhere to pore sizes of various sizes. The pore sizes of 50 nm to 50 μm are the most affected by expansive substances. The pores in BMLS-CF can accommodate the formation of expansive substances, and the effect of the accommodation increases with the increases in volume and number of bubbles. When the CFB fly ash content is between 50% and 66.7% with the same air-corbubble content, the effect of the accommodation is the best. The unconfined compressive strength of BMLS-CF first increases, then decreases with the increase of the CFB fly ash content, and the peak arises at a CFB fly ash content of 66.7%. It is therefore recommended that the CFB fly ash content in BMLS-CF be 66.7–75%.