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윤경구,Mohammad Shakhawat Hossain,김성권,한승연 대한토목학회 2022 KSCE JOURNAL OF CIVIL ENGINEERING Vol.26 No.5
Shotcrete is considered a substantial long-term product providing a sheltered working environment for tunneling engineering. However, multi-functional problems occur due to the sprayed concrete construction method. Moreover, the performance of the shotcrete placement into the wall of the tunnel is challenging to verify. Currently, accelerators are used in highway tunnels for improving the overall performance of shotcrete. This study evaluated the tunnel shotcrete performance for cement mineral, aluminate, and alkali-free accelerators, as well as steel fiber, which is the main constituent of shotcrete. The workability of concrete and shotcrete in situ has been measured for these combinations. Using 1-month samples, shotcretewas evaluated by means of accelerating agent, compressive strength, core compressive strength, flexural strength, and flexural toughness. In particular, 37 kg and 40 kg of steel fiber were included into the cement and aluminate mix and the alkali-free mix, respectively. Changes in strength and flexural performance of shotcrete were studied under Korean standard. Thus, concrete cylindrical molds were manufactured for the compressive strength test. After 28 days of curing, concrete and shotcrete test panels were manufactured for core compressive strength tests on cylindrical molds with diameters of 100 mm, 75 mm, and 55 mm. Furthermore, beam samples were produced for flexural strength and toughness tests to measure the shotcrete performance. Air void test and steel fiber remaining percentage after shooting were performed to ensure the performance image analysis. Alkali-free incorporated with steel fiber is the best combination for tunnel shotcrete premised on compressive strength, core compressive strength, flexural strength, and toughness test results, along with environmental and worker safety. Finally, the tunnel shotcrete performance was evaluated by regulating and improving the accelerator type with the steel fiber for shotcrete.