Shrinkage crack inhibiting of cast in situ tunnel concrete by double regulation on temperature and deformation of concrete at early age

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The temperature difference between peak temperature due to the hydration of concrete and its surrounding is the key factor that leads to early age cracking in main structure of tunnel concrete, and autogenous shrinkage will increase the crack risk. Given this, a temperature rise inhibited and slight expansion mixture (HME) was adopted in a large scale cast in situ tunnel under water. Results indicate that HME decreased the hydration rate of cement in the acceleration period and prolonged the main heat release peak. The early age rate of adiabatic temperature rise was decreased with a negligible level effect on the final value after using HME. In this case, the peak temperature could be decreased under a certain heat dissipation condition. Meanwhile, HME could reduce shrinkage deformation not only in the temperature rise stage but also in the entire process. The reduction of compressive strength affected by using HME instead of cement and its regulation on cement hydration could be further reduced to a negligible level at later ages. The first sidewall and roof have been casted more than five months and no penetrating crack and leakage were observed, which means that the double regulation on temperature and deformation technology provides a feasible and effective approach to prevent the penetrating crack of cast in situ tunnel concrete at early age.