Title: Effects of Curing Conditions and Age on Chloride Permeability of Fly Ash Mortar

Author(s): Abdurahman Alhozaimy, Parviz Soroushian, and Faiz Mirza

Publication: Materials Journal

Volume: 93

Issue: 1

Appears on pages(s): 87-95

Keywords: drying; fly ash; moist-curing; permeability; statistical analysis.

DOI: 10.14359/9800

Date: 1/1/1996

Abstract:
Effects of fly ash type and content on the permeability characteristics of mortar materials subjected to two different curing conditions and two ages of testing were investigated. Three different fly ash contents (in addition to the control) and three different fly ash types were considered to provide suf-ficient data for statistical analysis of results. Fly ash was observed to be capable of reducing the permeability of mortar except for the Class C fly ash at lower cement substitution levels. Selection of fly ash type (Class F versus Class C), the level of cement substitution with fly ash, curing conditions, and age of testing had important effects on the permeability characteristics of fly ash mortar; the interactions between these factors were also generally important. Results showed that as the moist-curing duration increased the fly ash mortar became less permeable. The interruption of moist-curing and exposure to a low-humidity (interior) environment led to increased permeability, except for the Class F fly ashes after longer moist-curing durations, for which permeability stayed almost constant. One may attribute this effect of air-drying to the formation of shrinkage microcracks, with particularly adverse effects on permeability that more than compensate for any positive effects of the slow progress of hydration or pozzolanic reaction in an environment with low humidity. It may thus be concluded that assessment of mortar permeability based on a 28-day testing age after an initial moist-curing can be misleading.