Shotcrete: early strength and re-entry revisited – practices and technology

Abstract

Shotcrete, a globally employed support system of choice in underground mining, is required to perform its support function not only over the expected life of underground openings, but also from a safety and productivity perspective, at a very early age. The balance between placement ability, early strength and longterm performance is a delicate one which has been repeatedly improved upon as shotcrete has proliferated in mining and tunnelling. Early strength is particularly important in safeguarding the integrity of underground openings and the people and machinery which need to return to them as quickly as safety doctrine allows. This paper covers the state-of-the-art with respect to practices and technology which forms the basis for the safest, earliest re-entry policies. Technologies discussed include the examination of strength development via thermal imagery, infrared analysis, fibre performance, admixture and accelerator formulation, and robotic placement. Practices discussed cover approaches in both mining and tunnelling, early re-entry times and policies, and lessons learned anecdotally from contemporary case studies. Preservation of people and assets, the environment and cost savings are co-drivers of industry advances.