Preparation and characteristics of inorganic curing foam with large-volume fly ash in goaf

Air leakage in the goaf of coal mine is an important cause of coal fire disaster. The traditional filling and plugging materials are easy to crack, with poor fluidity and high cost. Therefore, it is necessary to develop new materials for effective filling and plugging of the air leakage channels. Herein, the new filling and plugging material of inorganic curing foam with large-volume fly ash was developed by optimizing the mix ratio based on material fluidity, initial setting time and compressive strength using the single factor variable method. Meanwhile, the material hydration process was characterized by the infrared spectroscopy, X-ray diffraction and scanning electron microscopy. The results show that the water based foam with sodium dodecyl sulfate (SDS)∶decyl glucoside (APG) of 1∶1 and xanthan gum (XG)∶guar gum (GG) of 1∶1 is selected based on the foam uniformity, foaming multiple, half-life and water separation rate. The initial setting time of the inorganic curing foam with large-volume fly ash is proportional to the amount of fly ash, water cement ratio and foam content. The fluidity is proportional to the water cement ratio water and iversely propotional to the amount of tlyash content based on the fluidity decreases with the increasing of fly ash content, and increases first and then decreases slowly with the increasing of foam content. The compressive strength of inorganic curing foam with large-volume fly ash increases first and then decreases with the increasing of fly ash content, but it is inversely proportional to the water cement ratio and foam content. According to the comprehensive evaluation indexes, the material fluidity is good at 15.9 cm, the initial setting time is moderate at 5 h, and the compressive strength is great, reaching 1.5 MPa at 28 d when the fly ash content was 60%, the water-ash ratio is 0.6, and the volume ratio of foam to composite slurry is 1:1. The hydration products of the material include ettringite (AFT) and C－S－H gel. The hydration reaction of cement first generates Ca(OH)₂, and then the Ca(OH)₂ reacts with fly ash to generate AFT and C－S－H gel, thereby improving the compressive strength of inorganic curing foam with high-volume fly ash, which is capable of satisfying the requirements leakage blocking in goaf.