The use of fly ash or silica fume to enhancethe durability of HPC

Freeze-thaw-, scaling- and chloride-resistance

Two common features of high performance concrete (HPC) are low w/cm ratios and use of supplementary cementing materials. In Canada, as elsewhere, concrete structures are frequently exposed to severe freezing and thawing cycles, extended periods at low temperatures and large quantities of deicing salts. In a majority of project specifications for HPC, the use of silica fume is made a requirement. The focus of this study was to determine if high quality/high performance concrete can be produced using available sources of aggregate and fly ash, without silica fume. The properties of fly ash concretes and silica fume concretes were compared in terms of strength, dimensional stability, freezing and thawing resistance and migration rates of chloride ion. The study shows that both fly ash concrete and silica fume concrete can satisfy high performance expectations and produce an extended service life. The quality of aggregates and SCMs as well as the consistency of commercially produced concrete mixes is also important.

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