Rheological Behavior of Dry-Mix Shotcrete

Abstract

In this study three series of four test panels were molded varying the mortar content. In the three series, the dry-mix shooting process was regulated with three different conditions. In each test panel samples and cores were taken to determine shotcrete mix proportions and physical properties. The results show a good correlation between stiffness and W/C in accordance with the exponential model proposed by Powers, confirming the Proctor needle as a good instrument to dry-mix shotcrete workability control. The compaction and compressive strength were as high as the volume of paste incorporated in the shotcrete. This feature provides a typical dry rheological behavior to the dry-mix shotcrete, where Abram's Law is not valid. It occurs regardless of the fine and coarse aggregates proportion, although the influence of which on rebound is very clear. It is recommended that one should not fix a maximum W/C for a given compressive strength in the dry-mix shotcrete specifications. On the contrary, the consistency measurement by the Proctor needle appears to be a good instrument for dry-mix shotcrete workability control. The use of the aggregates gradation recommended by the ACI is a good way to achieve better shotcreting conditions with a minimum rebound.