Freezing and Thawing Durability of Air-Entrained Wet- and Dry-Mix Shotcrete Incorporating Silica Fume


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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

Volume: 145


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

Date: 5/1/1994

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.