Loess has poor engineering properties. Traditional cementitious solidifiers also cause high carbon emissions. To solve both problems, we processed waste foam concrete through mechanical grinding and thermal activation. This produced a composite-activated recycled micro-powder. We used this powder to prepare solidified loess with low strength and high flowability. The study included fluidity tests, viscosity measurements, and unconfined compressive strength tests. The results show that when preparing low-strength, high-flowability solidified loess using recycled micro-powder solidifier at dosages of 10%, 20%, and 30%, the flowability of the slurry decreases with higher micro-powder content, but improves upon adding a water-reducing agent. The rheological behavior of the slurry conformed to the Bingham plastic model, with both yield stress and plastic viscosity decreasing continuously as the recycled powder content increased. Flowability showed a positive correlation with yield stress. We have developed a rheological parameter prediction model based on the dosage of recycled micro-powder and water-reducing agent. The unconfined compressive strength of solidified loess specimens cured for 7 days exhibited an upward trend with increasing recycled micro-powder content, forming a damage constitutive model for solidified loess based on the dosage of recycled micro-powder. These findings indicate that the composite-activated recycled powder from waste foam concrete can be used to produce low-strength, high-flowability solidified loess with favorable engineering properties, offering useful insights for applying recycled powder in such materials.