Thesis by Sylvie Gérômey

Shotcrete is a material which adheres and develops resistance to the support without requiring formwork, which predisposes it to specific uses (temporary support of tunnels, repair of structures).

The projection technique remains closely linked to empiricism, as does the formulation of mixtures. Rules exist but do not make it possible to arrive at a composition guaranteeing the quality of the concrete.

To improve the state of knowledge on the subject, an experimental program has been established with the aim of obtaining information on the projection of mixtures and the characteristics of the concrete.

The results are comparable to those of worksites (conditions of realization). They corroborate or question certain ideas on the subject, specify certain trends.

They make it possible to obtain ranges of values ​​that can be expected from shotcrete, for common or more specific sizes, such as durability. Finally, some of the results obtained are used with the aim of proposing an optimization of the mixtures to be sprayed according to justified selection criteria.

Thesis by Julie Armengaud

Shotcrete is a placement method consisting of the pneumatic spraying of concrete over a surface at high speed. In the case of the dry method, the aggregate-cement mixture is introduced dry in the machine, water is added at the end of the transfer. This technique, which is widely used, nevertheless generates significant losses by rebound, which can amount to 40% of the projected mass.

The challenge of reducing losses is both economic and environmental. The factors influencing the rebound are related to the projection techniques and the formulation. The objective of this thesis is to optimize the formulation of concrete in order to reduce rebound losses, but also to improve durability. The study relates in particular to the influence on the rebound: of the granular skeleton, of the water content and of the use of additives and / or substitute additions.
A modeling approach of the rebound phenomenon is also discussed.