Chloride Penetration and Water Absorption Into P.C., Fly Ash and Slag Concrete Under Different Curing Conditions

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Title: Chloride Penetration and Water Absorption Into P.C., Fly Ash and Slag Concrete Under Different Curing Conditions

Author(s): Z. Tian Chang and M. Marosszeky

Publication: Special Publication

Volume: 170

Issue:

Appears on pages(s): 349-362

Keywords: Absorption; chlorides; concrete; curing; fly ash; slags.

Date: 7/1/1997

Abstract:
The resistance to chloride penetration is one of the prime parameters in specifying concrete in marine applications and in a quality assurance scheme during construction. The aim of this research was to compare alternative accelerated laboratory test procedures for the assessment of chloride penetration into concrete containing supplementary cementitious materials. Three binder systems, a normal portland cement (PC), one with 30% fly ash and a third with 50% slag, were investigated under three curing conditions, 7 days water curing, air curing, and 12 hours 65 C water curing. Chlorides penetration was measured by static ponding (5% NaCl solution) and cyclic ponding (2%, 5% and 15% NaCl solutions with 12 hour wetting and drying cycles). The effect of the age at start of testing and the test duration were also investigated. The water absorption was tested by measuring weight gain, and the results were compared with that of the chloride penetration tests. It was found that the cyclic ponding test with 15% NaCl solution resulted in accelerated chloride penetration and a clearer chloride penetration front compared to the use of 2% and 5% NaCl solutions. Good correlation was found between the results from cyclic chloride ponding and static ponding. While the chloride penetration depth was found not vary significantly with test age from 7 to 56 days for all the three mixes, the increase of chloride penetration with the test duration from 3 to 14 days was much pronounced for the PC mix than the fly ash and slag mixes. The chloride penetration was highest in the air cured specimens and the lowest in the water cured specimens for all the three mixes, and the slag concrete had the lowest chloride penetration within the three mixes under each of the three curing conditions. It was also found that water absorption correlated poorly with chloride penetration.