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CAER Seminars

The Development of a Blended SCM containing Silica Fume and Class C Fly Ash

Phil Zacarias
Mineral Solutions, Inc.

Friday, June 17, 2005, 10:30 am
Ben Bandy Conference Center
Center for Applied Energy Research

This presentation will highlight data from laboratory studies aimed at the development of a blended supplementary cement material (SCM) containing silica fume and high-lime fly ash. High-lime fly ashes (meeting CSA A 23.5 Type CH with more than 20% CaO) are generally not effective in controlling alkali-silica reaction (ASR) in concrete unless they are used at high replacement rates. Further, such ashes show highly variable performances when tested for sulphate resistance in ASTM C 1012. Blends of high-lime fly ash and silica fume were evaluated using a range of tests (ASTM C 1260, C 441, C 1293 and C 1012) and reactive aggregates to determine the viability of using the blend as an alternative to Class F fly ash, slag or silica fume for controlling ASR and sulphate attack. The results indicate that blends in the range of 80 parts high-lime fly ash to 20 parts silica fume are effective in this role.

This presentation will discuss data from concrete tests including setting time, strength, chloride permeability, chloride diffusivity and de-icer salt scaling resistance. The data indicate that the use of the blended SCM results in improvements to the concrete properties beyond those that would normally be expected using either high-lime fly ash or silica fume on their own. In other words there is a certain synergy when these two materials are combined and this effect is discussed.