The effect of polypropylene fibre and silica fume on the properties of tunnel slag shotcrete

The application of tunnel slag in shotcrete effectively addresses resource and environmental issues arising from the accumulation of excavated material. However, the high content of slag aggregate stone powder and the rough surface will lead to poor performance of shotcrete. In this paper, the effects of different dosages of silica fume (SF) and polypropylene fiber (PPF) on the workability, mechanical properties and impermeability of shotcrete were studied to determine the optimal dosage. The results showed that the incorporation of SF improves the mechanical properties of shotcrete, and the 28 d compressive strength and splitting tensile strength increase by 20.9 % and 21.4 %, respectively. The incorporation of PPF improves the workability of shotcrete mixture. However, too high fiber content will lead to fiber agglomeration, which affects the bonding between aggregates and has an adverse effect on strength. The optimum content of SF and PPF is 2.5 % and 2 kg/m 3 respectively. The synergistic effect of SF and PPF improves the performance of shotcrete. The 28 d compressive strength (CS) and splitting tensile strength (STS) of tunnel slag-based shotcrete (TSBS) increased by 21.9 % and 25 %, respectively, and the average water seepage height reduced by 41.4 %.