While this situation can occur, it is rarely due to an inappropriate use of shotcrete. Usually, shotcrete is chosen in situations that demand its superior compressive strength, excellent bond, prevention of corrosive agents, or ability to be applied under severe access and environmental conditions. If a shotcrete project begins to “fall apart” in a few years, it is most likely due to poor workmanship.
Potential causes are:
1) surface preparation (i.e. the corroded rebar and/or steel was not sufficiently removed, and/or the deteriorated concrete was not completely removed prior to applying shotcrete)
2) inappropriate aggregate was used which allowed for undesired water penetration (ASTM C-33 concrete sand should be used for the correct gradation of aggregate)
3) poor placement of shotcrete (inappropriate technique used to place shotcrete and/or inexperienced nozzleman)