Influence of Accelerating Admixtures on the Durability of Dry-Mix Shotcrete Used for Repairs in a Marine Environment

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Title: Influence of Accelerating Admixtures on the Durability of Dry-Mix Shotcrete Used for Repairs in a Marine Environment

Author(s): Michel Pigeon, Ann Lamontagn, and Caroline Talbot

Publication: Special Publication

Volume: 163

Issue:

Appears on pages(s): 409-422

Keywords: accelerating agents; compressive strength; deicers; scaling; setting (hardening); shotcrete; silica fume; underwater structures; Materials Research

Date: 8/1/1996

Abstract:
The use of dry-mix shotcrete for the repair of structures in a marine environment was the subject of an investigation carried out for the Canadian Coast Guard. In addition to the control mixture, four different mixtures using two aluminate-based accelerating admixtures at two different dosages were prepared. All mixtures contained steel fibers and silica fume and were air- entrained. For each mixture, a panel of approximately 1.0 m x 1.0 m was shot on a wharf (in the St. Lawrence River north of Quebec City) to study the influence of freezing and thawing cycles in the presence of salt water, the influence of wetting and drying cycles, and the abrasion due to ice packs. Three panels were also shot with each mixture for laboratory testing purposes (mechanical strength, durability, and microstructure). The accelerating admixtures that were used were not found to have any adverse effects on any of the properties of the hardened shotcretes. The initial setting time was reduced to values below six minutes. For all five mixtures, the resistance to scaling due to freezing in the presence of deicer salts (ASTM C672) was found to be not very good. This confirms the results of previous tests which have also shown a negative influence of silica fume on the scaling resistance of dry-mix shotcrete measured in the laboratory.