Issue 41

L. Zhang et alii, Frattura ed Integrità Strutturale, 41 (2017) 356-368; DOI: 10.3221/IGF-ESIS.41.47 367 Specimen SN Age/d Bearing area/mm 2 Compressive strength f cu /MPa Single block value Group value 1 1 22500 13.4 12.6 2 22500 12.5 3 22500 11.9 1 7 22500 27.8 27.1 2 22500 26.9 3 22500 26.6 1 28 22500 33.5 32.4 2 22500 31.6 3 22500 32.2 Table 9 : Compressive strength of shotcrete. C ONCLUSIONS (1) The dosage of this liquid accelerator is small, only from 1.5% to 4%, and it is an effective compound liquid accelerator. When the dosage is 2%, the effects of coagulation are optimal. The initial and final setting time of neat cement paste is 2 minutes and 4 minutes respectively. It is also a kind of uniform and stable liquid without crystals and precipitate, and it is slightly affected by the ambient and well adaptive to cement. (2) This liquid accelerator contains the thickening components, which increase the cohesiveness of shotcrete and can effectively reduce resilience and dust during spraying concrete. Meanwhile, it increases the adhesion strength between shotcrete and surrounding rock, be adhered to the sprayed surface comprehensively and solidly, and achieve better supporting effects. (3) This liquid accelerator can effectively reduce the later strength loss of shotcrete and ensure that the strength loss is controlled within 10%. Adding this liquid accelerator can improve the strength of shotcrete at each age and effectively inhibit the development of displacement and plastic zones of surrounding rock. In the numerical simulation analysis of the relationship between shotcrete and surrounding rock support, the strength growth of shotcrete and stress release of surrounding rock with the passage of time should be considered. (4) The new liquid accelerator and its matching spraying technology can effectively reduce resilience and dust in the construction, the resilience rate is less than 10%, save the cost, improve the environment, enhance the shotcrete strength, have good popularization using value. A CKNOWLEDGEMENTS he authors would like to thank the National Natural Science Foundation of China (Grant No. 51179098 、 51379113), the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20120131110031). R EFERENCES [1] Guan, B., Technique of shotcrete support for tunnel and underground works[M]. Beijing: China Communications Press, (2009). [2] Zhu, G., Progress of the research for shotcrete, Concrete, 258(4) (2011) 105-109. [3] Cheng, L., Shotcrete, Beijing: China Architecture and Building Press, (1990). [4] Feng, H., Zhu, Q., Handbook of engineering application of concrete admixture, Beijing: China Architecture & T