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Home > Publications > International Concrete Abstracts Portal
The International Concrete Abstracts Portal is an ACI led collaboration with leading technical organizations from within the international concrete industry and offers the most comprehensive collection of published concrete abstracts.
Title: Freezing and Thawing Durability of Air-Entrained Wet- and Dry-Mix Shotcrete Incorporating Silica Fume
Author(s): B. Durano, J. Mirza, and P. Nguyen
Publication: Special Publication
Appears on pages(s): 623-642
Keywords: air-entrained concretes; air entrainment; bonding; durability; compressive strength; fibers; freeze-thaw durability; polypropylene fibers; portland cement; shotcrete; silica fume; slabs; superplasticizers; Materials Research
Abstract:Hydro=Quebec has undertaken a major study of shotcrete as a repair material for concrete dams. Six dry-mix shotcretes and one wet-mix shotcrete were shot on an old concrete slab and into sampling boxes using Types 10 and 30 portland cement, silica fume, superplasticizer, and polypropylene and steel fibers. An air-entraining agent (AEA) was added to all mixes except one to verify the effect of air entrainment on shotcrete. After wet-curing for 3 days at approximately 20 C and exposure to field conditions for 25 days, prisms and cylindrical specimens were taken from each of 600 x 600 x 150-mm shotcrete slabs. These specimens were then subjected to 500 freezing and thawing cycles, and tested for air-void parameters, compressive strength, and bond to old concrete. Freezing and thawing results showed that five of the six air-entrained mixtures yielded a durability factor (DF) over 100 after 500 freezing and thawing cycles, whereas one showed a DF of 84, although its spacing factor L was only 159 m. The one mixture with no AEA gave a DF of 64 with L of 272 m, although its corresponding air-entrained mix gave a DF of 102 and L of 234 m. The overall results showed that: 1) freeze- and thaw-resistant wet- and dry-mix shotcretes incorporating silica fume can be produced using proper proportioning and AEA; 2) silica fume shotcrete can be shot on a 70-deg inclined wall in thicknesses of up to 150 mm without sagging and can produce a good bond; 3) the wet-mix process produces better homogeneity than the dry-mix process.
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