Use of wet cellulose to cure shotcrete repairs on bridge soffits. Part 1: Field trial and observations Medhat Shehata, Mike Navarra, Tom Klement, Mohamed Lachemi, and Hannah Schell Abstract: This paper presents the results obtained from a research project that focused on investigating the feasibility of using cellulose fibers to cure bridge soffit repairs. The use of cellulose as a curing method involves spraying wet cellulose on the freshly applied shotcrete. By adhering to the shotcrete, the wet cellulose maintains the relative humid- ity within the shotcrete above the level required to sustain hydration of the cementing materials. Twelve 1000 mm × 1000 mm × 130 mm panels were prepared using two types of shotcrete materials and cured using either air curing, curing compound, misting and curing compound, or cellulose. The results showed that the cellulose could be applied to shotcrete in an overhead position and remained adhered to the shotcrete for 28 days. At the end of the curing period, the cellulose was easily removed from the shotcrete surface by means of a hand shovel. Cellulose-cured panels showed the least evidence of surface cracking. Also, the use of cellulose did not have any negative effects on the temperature of the shotcrete. Key words: bridge repair, shotcrete, silica fume, accelerator, polypropylene fibers, curing, cellulose, heat of hydration, adhesion. Résumé : Le présent article présente les résultats d’un projet de recherche portant sur l’étude de la faisabilité d’utiliser des fibres de cellulose pour faire la cure des réparations des soffites des ponts. L’utilisation de cellulose comme mé- thode de cure implique la pulvérisation de cellulose humide sur du béton projeté fraîchement appliqué. En adhérant au béton projeté, la cellulose humide maintient l’humidité relative dans le béton au-dessus du niveau requis pour soutenir l’hydratation des liants hydrauliques. Douze panneaux mesurant 1000 x 1000 x 130 mm ont été préparés en utilisant deux types de béton projeté et durci soit à l’air, à l’aide d’un produit de cure, d’un brouillard et d’un produit de cure ou de la cellulose. Les résultats montrent que la cellulose pourrait être appliquée à du béton projeté sur une surface su- rélevée et qu’elle demeurerait fixée au béton projeté pour 28 jours. À la fin de la période de cure, la cellulose a été fa- cilement enlevée de la surface du béton projeté au moyen d’une pelle à main. Les panneaux durcis avec la cellulose ont montré moins de fissuration de surface. De plus, l’utilisation de cellulose n’a eu aucun impact négatif sur la tempé- rature du béton projeté. Mots clés : réparation des ponts, béton projeté, fumées de silice, accélérateur, fibres de polypropylène, cure, cellulose, chaleur d’hydratation, adhésion. [Traduit par la Rédaction] Shehata et al.: I 814 Introduction Durability is a major challenge facing authorities and own- ers of concrete bridges in many locations in North America (Faber et al. 2000). Many concrete bridges do not meet their designed service life due to various deterioration processes that are activated by deleterious substances, such as chlo- rides (from deicer salt), alkalis, and (or) carbon dioxide. Bridge soffits are subjected to chloride ions in the form of spray from the roadway below the bridge or leakage of water, with chlorides, from the deck through joints. This activates corrosion of the steel reinforcement which eventually causes cracking and spalling of the concrete cover. To restore the ser- viceability of the bridge, the deteriorated concrete cover is usually removed and replaced with a durable repair material that has high resistance to chloride or ion transport. Can. J. Civ. Eng. 33: 807–814 (2006) doi:10.1139/L06-023 © 2006 NRC Canada 807 Received 21 June 2005. Revision accepted 29 January 2006. Published on the NRC Research Press Web site at http://cjce.nrc.ca on 23 August 2006. M. Shehata 1 and M. Lachemi. Department of Civil Engineering, Ryerson University, 350 Victoria Street, Toronto, ON M5B 2K3, Canada. T. Klement and H. Schell. Materials Engineering and Research Office, Ontario Ministry of Transportation, 1201 Wilson Avenue, Downsview, ON M3M 1J8, Canada. M. Navarra. Golder Associates Limited, 100 Scotia Court, Whitby, ON L1N 8Y6, Canada. Written discussion of this article is welcomed and will be received by the Editor until 30 November 2006. 1 Corresponding author (e-mail: mshehata@ryerson.ca).