Mechanisms of placement in sprayed concrete

• The local placement of shotcrete impacting a receiving surface was investigated.
• Spatial distribution of sprayed concrete placement and composition were revealed.
• There is evidence of a Gaussian-type placement distribution around the spray axis.
• There is evidence of a rich binder layer in the impact peripheral zones.
• The measurements validity was confirmed using the mass conservation law.

Sprayed concrete is a well established application method for concrete repairs and ground supports; its popularity ever increasing in the past decades. In this field, the development of new fundamental and practical knowledge relies heavily on understanding the placement process, which controls the amount of rebound loss and consequently the in-place material composition and properties. In this context, an important experimental study investigating placement mechanisms at the process scale (spray scale) was undertaken and key findings are presented here. Indeed, the spatial distribution of the in-place sprayed material, around the spray axis, offers a unique view of the placement mechanisms; the effect of the spraying process is highlighted through the evaluation of the in-place material composition and distribution. In light of this study, a new approach is provided to initiate a thorough discussion on how shotcreting parameters and equipment can affect rebound losses and the quality of the in-place material.

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