Résumé Le béton projeté est un matériau de plus en plus utilisé, car il est très bien adapté à la réparation des dégradations d'ordre superficiel, dégradations de plus en plus présentes particulièrement dans les pays nordiques. Il existe deux procédés pour projeter le béton: le procédé par voie sèche et le procédé par voie humide. Les travaux à l'Université Laval ont permis de mieux connaître l'influence de plusieurs paramètres (ajout de fumée de silice, de fibres, d'adjuvants, etc.) sur les propriétés du béton projeté selon les deux procédés. Très souvent, les propriétés du béton projeté durci ressemblent de très près à celles d'un béton conventionnel de même composition et les résultats des essais ont bien montré qu'il est possible de fabriquer des bétons projetés durables, et qui résistent même au gel en présence de sels fondants. Ils ont aussi montré que la technique de préparation des surfaces à réparer a beaucoup d'influence sur la durabilité de l'adhérence des réparations minces en béton projeté. L'hydrodémolition semble être la technique qui donne les meilleurs résultats.

Summary The shotcrete technique is certainly one of the most suitable for repairing superficial damage to concrete structures. In certain cases, the use of dry or wet process shotcrete leads to economy in construction costs that are related to the reduction of the time required to realize the project. This paper summarizes various test results obtained at Laval University in recent years on this subject. In dry-mix shotcrete, the use of an air entraining admixture diluted in the water used for the shooting increases the deicer salt scaling resistance, because of a significant decrease in the air void spacing factor. The use of such admixtures, irrespective of the type or the dosage (between 10 and 40 ml l−1 water), does not modigy the properties of shotcrete significantly except for its compressive strength. A higher dosage leads to a reduction in strength. The use of a type 10 cement or a type 30 combined with the use of an air entraining admixture leads to excellent properties. For dry-mix shotcretes made with silica fume, the main advantage is a reduction in drying shrinkage and a low chloride ions permeability, but unfortunately these mixtures did not perform well in the deicer salt scaling tests. For wet-mix shotcrete, the use of silica fume seems to bring the same advantages as those obtained in conventional concrete. The advantages are a decrease in drying shrinkage, an increase in the resistance to freeze-thaw cycles, and a small increase in the compressive strength. Also, it seems clear that the spacing factor of the air bubbles in wet-mix shotcrete is very important for resistance to freeze-thaw cycles in the presence or absence of deicer salts. The test results indicate that it is more difficult to produce a durable wet-mix shotcrete that resists scaling in the presence of deicer salts. More research is needed to understand the mechanisms involved. The bonding between good quality shotcrete mixtures (with and without steel fibers) and concrete surfaces prepared by hydrodemolition or chipping with jackhammers followed by sandblasting was found to be generally strong and durable. The other types of surface preparation (grinding, chipping with jackhammers without sandblasting and sandblasting alone) resulted in either lower bonding strengths or a reduction in the bonding strength with time. No significant difference was observed between the bonding strength of dry or wet process shotcrete to a hydrodemolished surface.