Abstract: Grouting material is of crucial importance for the treatment of coal mine goaf by grouting. The physical and mechanical properties of fly ash cement grouting material with large volume ultra-fine fly ash are tested through orthogonal experiment. The influences of water-solid ratio, solid phase ratio, and dosage of sodium silicate on the setting time, water separating proportion, concretion rate, and unconfined compressive strength at different ages are also examined.Results showed that the performance of the slurry material is significantly affected by water-solid ratio, followed by solid phase ratio and dosage of sodium silicate. The 28-day compressive strength of grouting slurry with varying mix ratio is generally higher than 1 MPa and continues to grow; the strength at the 90^th day is larger than that at the 28^th day by over 60%. The regression formula of compressive strength along with mix proportion and the predictor formula of compressive strength along with age are obtained by curve fitting.

Key words: grouting material, ultra-fine fly ash, orthogonal experiment, strength prediction, coal mine goaf