Issue 41

L. Zhang et alii, Frattura ed Integrità Strutturale, 41 (2017) 356-368; DOI: 10.3221/IGF-ESIS.41.47 356 Study on the effect of new type liquid accelerator on the performance of shotcrete Luchen Zhang, Shuchen Li, Qin Yan, Lin Zhu Geotechnical and Structural Engineering Research Center, Shandong University, Jinan, Shandong 250061, China 471263803@qq.com A BSTRACT . Shotcrete is an essential preliminary support means in New Austrian Tunneling Method (NATM) construction and plays a very important role in controlling the stability of surrounding rock. The accelerator is a necessary admixture in shotcrete and its quality can greatly affect shotcrete performance. This paper proposes a new liquid accelerator characterized by short initial and final setting time, small dosage, and good adaptability to cement. Laboratory tests and field tests are conducted to verify the influence of this liquid accelerator on performance of shotcrete. Numerical simulation is carried out to study the strength growth of shotcrete with time and interaction between the strength and stress release of surrounding rock. The results show that the initial and final setting time of this liquid accelerator is 2 minutes and 4 minutes respectively. Its dosage is just 1.5% to 4% of the cement quantity. Adding this liquid accelerator can effectively improve the early strength and reduce the later strength loss of shotcrete, and therefore enhance the supporting effects of shotcrete on surrounding rock. In the field application, it is an ideal liquid accelerator for shotcrete, characterized by little resilience, no slurry shedding, and low dust. K EYWORDS . Liquid accelerator; Shotcrete; Primary support; Stress release of surrounding rock; Numerical simulation. Citation: Zhang, L., Li, S., Yan, Q., Zhu, L. Study on the effect of new type liquid accelerator on the performance of shotcrete, Frattura ed Integrità Strutturale, 41 (2017) 356-368. Received: 22.03.2017 Accepted: 06.05.2017 Published: 01.07.2017 Copyright: © 2017 This is an open access article under the terms of the CC-BY 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. I NTRODUCTION ith the construction of large-scale underground engineering in China, shotcrete is widely used as a necessary support means. Shotcrete is a kind of concrete setting and hardening from a mix of cement, sand, stone, mineral materials, and admixtures in a proper proportion after being sprayed at high velocity onto a surface (such as the rock, soil layer, building structure or template) through the pipeline via compressed air. Shotcrete can be quickly hardened to support surrounding rock without manual vibration. The accelerator is a necessary admixture for shotcrete whose role is to quickly harden shotcrete, reduce resilience loss, prevent shotcrete from falling off due to the action of gravity, improve the adaptability of shotcrete to the aquifer, generate higher early strength, and increase the depth of single shotcrete layer [1-2]. The accelerator is classified into powdered and liquid accelerator. Their main types include alumina clinker-carbonate series, alumina clinker-alunite series, W