Promotion Mechanism of Setting and Hardening of High-Volume Phosphogypsum Foamed Concrete

The preparation of foamed concrete using phosphogypsum can effectively consume industrial solid waste. However, PO₄^3- in phosphogypsum retards cement hydration, causing foam collapse and preventing foamed concrete from forming. Therefore, this paper investigated the effects of water washing treatment, alkaline activators, and sulphoaluminate cement on the setting time and compressive strength of phosphogypsum foamed concrete. The results show that soluble substances in phosphogypsum retard cement hydration and slow down the early strength development of foamed concrete. Water washing pretreatment has almost no effect on the setting time of foamed concrete. When calcium hydroxide and water glass are used as activators, the low solubility of calcium hydroxide fails to activate the reactivity of slag powder in the paste, leading to insufficient strength and mold collapse of the specimens. In contrast, the excessively high alkalinity of water glass results in poor fluidity of the paste and powder agglomeration, which damages the matrix strength. Sodiumaluminate as an activator can produce specimens with good forming performance, but an excessive dosage of sodium aluminate reduces fluidity; the fluidity of foamed concrete meets the requirements at a sodium aluminate dosage of 0.5%. Sulphoaluminate cement as an activator can effectively prevent mold collapse of foamed concrete, and its strength and setting time increase with the increase in dosage. The foamed concrete achieves the optimal performance at a sulphoaluminate cement content of 6%.This research provides a theoretical basis for the engineering applications of phosphogypsum foam concrete.