Experimental study on the utilization of Fly ash solid waste in tunnel shotcrete materials

Fly ash has emerged as a prominent solid waste in China, leading to various environmental concerns and posing a threat to the health of living organisms, including humans. To enhance the industrial applicability of this waste material, a novel approach has been proposed wherein sand is replaced with fly ash as the primary raw material for wall grouting of coal mine roadways. To address the issue of low compressive strength and to improve the properties of fly ash shotcrete materials, a method employing an alkali activator to stimulate the chemical activity of fly ash has been put forward. The long-term effectiveness of the shotcrete material has been evaluated using compressive strength testing and scanning electron microscopy testing methods. The impact of replacing sand with fly ash on the compressive strength of shotcrete and the activation effect of sodium sulfate (Na₂SO₄), NaOH, and Na₂SiO₃ on fly ash shotcrete have been studied. The results indicate that the compressive strength of fly ash shotcrete shows optimal improvement when the content of Na₂SO₄ is 3%. The ideal ratio of cement to fly ash is 1:3. Therefore, incorporating an appropriate amount of alkaline activator could effectively address the compressive strength issues of fly ash shotcrete materials.