Study on Optimized Mix-Proportion and Crack Resistance of Modern Secondary Lining Concrete for High-Speed Railway Tunnel

Cracking is the most common damage in the secondary lining concrete because of its continuous thin-walled structure, potential surrounding rock pressure and poor curing conditions. In order to improve the crack resistance of concrete and to reduce the responding costs, seven series modern concretes including ultra-fine pozzolanic powder and different organic fibers are prepared and investigated. The optimized modern secondary lining concrete is determined as the concrete including 0.08% or 0.1% volume fractions of ultra-fine organic fiber (UF), based on the test results of segregation, air voids parameters, primary strengths and multi-factorial crack resistance. The spacing factor and average chord length of concretes including UF are less than 0.1mm, which is positive for mixing UF to enhance the crack resistance of concrete at micro- and meso-scale.