Does an air-entraining agent serve any purpose in wet-mix shotcrete? I believe shotcrete is placed with such force that any air-entraining effect is negated. Should we use air-entraining agents in concrete that will be placed by wet-mix shotcreting?
The ACI 506 "Guide to Shotcrete" recommends entraining air in wet-mix shotcrete. Section 2.7.2 of that document says: "Wet-mix shotcrete that will be exposed to freeze-thaw cycles should be air entrained. Air entrainment tends to make some mixes more workable and may reduce rebound. Data are available to show that a significant quantity of the entrained air in wet mixtures is lost in gunning, but this may be offset by increasing the amount of air-entraining agent." Section 2.4 of ACI 506.2 "Specification for Materials, Proportioning, and Application of Shotcrete" also states that for wet-mix shotcrete exposed to freezing and thawing, an air-entraining admixture should be specified.