ABSTRACT
Abstract In Québec, liquid air-entraining admixtures are commonly used to improve the durability of dry-mix shotcrete repairs exposed to severe winter conditions. The liquid airentraining admixture is mixed with the water that is added at the nozzle during the shooting operation, particularly in order to improve the resistance of shotcrete to scaling due to freezing in the presence of deicer salts. This procedure requires special equipment and may cause problems in the field. This paper presents the results of a study undertaken to verify the efficiency of powder air-entraining admixtures to entrain an adequate air void system in dry-mix shotcrete. Eleven mixtures were shot, using three powder and one liquid air-entraining admixtures. The test program included compressive strength, deicer salt scaling resistance, spacing factor and the volume of permeable voids tests. The results obtained show that powder air-entraining admixtures can improve both the quality of the air void system (i.e. lower the spacing factor), as well as the resistance to scaling due to freezing and thawing in presence of deicer salts. Keywords: compressive strength, dry-mix shotcrete, powder air-entraining admixture, scaling, spacing factor.
