Effects of blast induced vibrations on the fresh concrete lining of a shaft

During shaft excavation, blast induced vibrations can cause micro-cracks in the fresh concrete lining and decrease its strength. The traditional method to reduce the vibration effect is to control the scale of blasting and apply temporary support to protect the fresh concrete. Recent research was conducted to study the effects of the blast induced vibration on the fresh concrete. Shaft sinking operations (drilling, blasting and concrete lining) were simulated in a laboratory model. Additives of triethanolamine - TEA (N(C2H4OH)3) and sodium chloride (NaCL) in varying proportions were added to the concrete lining to increase the early strength. Vibration was generated by small scale blasting. The experimental results show that the blast induced vibration has negative and positive effects on the strength of the fresh concrete depending on the curing time at blasting. Vibration can increase the strength within the first 1-2 days. After that period, vibration can cause cracks in the fresh concrete and reduce the strength. Still later, it has no more effect. The time windows vary with the magnitude of vibration and the strength of the concrete at the time of blasting. It was also found that both additives increased the early strength of concrete lining and expanded the time windows. These results indicate that proper timing of blasting and use of additives can change the negative effect of the blast induced vibration into a positive effect and increase the strength of a concrete lining.