Tests to characterise properties of fresh dry-mix shotcrete

Abstract

The intent of this project is to study the fundamental characteristic properties of dry-mix shotcrete. Although several factors are known empirically to influence the shooting properties of the dry process shotcrete, it is generally not clear how and why these variables are important, particularly with regard to the maximum buildup thickness. With this in mind, different dry-mix shotcrete mixtures were shot, and rebound and maximum buildup thickness were evaluated for each. In particular each mixture was shot at a different consistency, which was evaluated from the force required to push a needle into the fresh shotcrete. Relationships were found between the penetration resistance of a fresh mixture and its fresh tensile strength or maximum buildup thickness (cohesiveness). However, distinct relationships were obtained for the different mixtures tested, which implies that consistency (penetration stress) is not sufficient by itself to characterise fresh dry-mix shotcrete. The addition of silica fume or air-entraining admixture allowed one to shoot better quality shotcretes. However, these additions had an opposite effect on the fresh tensile strength.