Title: Effects of Microsilica and Class F Fly Ash on Resistance of Concrete to Rapid Freezing and Thawing and Scaling in the Presence of Deicing Agents

Author(s): Colin D. Johnston

Publication: Symposium Paper

Volume: 100

Issue:

Appears on pages(s): 1183-1204

Keywords: air-entrained concretes; concrete durability; deicers; fly ash; freeze-thaw durability; reviews; scaling; silica; tests; Materials Research

DOI: 10.14359/2082

Date: 4/1/1987

Abstract:
The freeze-thaw durability of concretes containing up to 42 percent Class C fly ash or 15 percent microsilica by weight of cement with ratios of water to cementitious material of 0.53 to 0.88 is examined to establish the extent to which such relatively lean mixtures can yield good durability along with the satisfactory levels of strength already known to be achievable, particularly with microsilica. The results show that, while the inclusion of fly ash or microsilica does not detract from performance in rapid freezing and thawing (Procedure A of ASTM C 666), performance with respect to scaling (ASTM C 672) may not be satisfactory, even with an apparently adequate air-void spacing factor. When spacing factors are adequate, the 300-cycle durability factors consistently exceed 85 percent, even for the leanest mixtures, while scaling of some of the mixtures with fly ash or microsilica is severe. Concretes with microsilica can be durable in both ASTM C 666 and C 672 at w/c + ratios up to a limit of 0.70, where strengths of 25 MPa at 28 days can be reached with as little as 225 kg/m3 of cement. For concretes with Class C fly ash, the corresponding limit for w/c + f appears to be no higher than the 0.45 recommended for normal concrete when exposed to deicing agents.