Early age cracking potential of inner lining of coal mine frozen shaft

Abstract

Recently, the application of high performance concrete (HPC) is popular in inner lining of frozen shaft in water-rich stratum. The circular crack of inner lining concrete easily appears in the early age (0∼240 h) leading to water burst accidents in the service period. The early-age cracking potential of HPC in inner lining is investigated by Temperature Stress Test Machine (TSTM) in the laboratory. The complex boundary, temperature history and variable restraint degree, was performed simultaneously by TSTM in this study. The experimental analysis indicated that (1) The range of restraint degree is almost 40% to 89.3% under steel frame restrained condition which can almost realize actual constraint degree of inner lining; (2) The cracking potential increased slightly for Mixture C60, C70, and increased severely once the Mixture strength exceeded C70; (3) The integrated crack indicators of C60, C70 and C90 repeat such as cracking stress, crack age, cracking temperature and cracking thermal drop were fluctuant slightly with the concrete strength increased; (4) The increasing of concrete strength decreased the cracking potential of inner lining concrete under steel frame restrained condition, though the tensile strength is improved.

Keywords

• Early-age crack
• Inner lining
• High performance concrete
• Autogenous shrinkage
• Cracking potential