Why is the primary sprayed concrete lining often referred to as 'sacrificial'?

The durability of the primary sprayed concrete lining has been traditionally questioned with various projects specifying even today a short-term design life. The main reasons behind this have been inferior material quality, poor workmanship, potential corrosion of rebar reinforcement if present, excessive lining deformations and aggressive ground/groundwater conditions.

The quality of modern sprayed concrete mixes is, however, comparable to that of cast in place concrete and the technological advancements allow for high standards of workmanship. The above combined with replacing the rebar reinforcement with fibres provide adequate arguments for considering at least partial structural contribution of the primary lining throughout a project’s life-cycle.