The Moisture Condition of Field Concrete Exhibiting Alkali-Silica Reactivity

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Title: The Moisture Condition of Field Concrete Exhibiting Alkali-Silica Reactivity

Author(s): David Stark

Publication: Special Publication

Volume: 126

Issue:

Appears on pages(s): 973-988

Keywords: alkali-silica reactions; climate; cracking; expansion; field concretes; humidity; wetting and drying tests; Materials Research

Date: 8/1/1991

Abstract:
The moisture condition of field concretes exhibiting evidence of alkali-silica reactivity was investigated utilizing relative humidity (RH) measurements. Prior determinations were made on laboratory mortar specimens to determine the threshold level required to sustain expansive reactivity. By comparing measurements of field concretes with the threshold level, environmental field conditions under which expansive reactivity is liable to occur were identified. Results indicated that RH values greater than 80 percent, referenced to 21 to 24 C, are required to support expansive alkali-silica reactivity. Field measurements revealed that most of the concrete in highways and dams in desert areas is sufficiently damp to sustain expansive ASR. Bridge decks and columns in dry climates are sufficiently damp on a seasonal basis to sustain expansive reactions. Massive concrete members indoors in controlled environments may remain sufficiently damp for more than 50 years to permit continued expansive reactivity. Both residual mixing water and external sources of moisture contribute to the moisture condition required for expansion to occur.