Title: Strength and Porosity ofHardened cement-Fly Ash Pastes in Hot Environment

Author(s): M. N. Haque and O. A. Kayyali

Publication: Materials Journal

Volume: 86

Issue: 2

Appears on pages(s): 128-134

Keywords: cement pastes; fly ash; hardened paste structure; sorption; high temperature; porosity; strength; water; Materials Research

DOI: 10.14359/2274

Date: 3/1/1989

Abstract:
The effects of hot-dry (45 C, 20 percent relative humidity) and temperate (23 C, 40 percent relative humidity) exposure conditions on the strength development, pore-size distribution, water sorptivity, and hydroxyl ion concentration of the hydrated cement paste, with and without fly ash, were studied. Plain cement and fly ash-cement paste specimens of 0.30 water-cementitious materials ratio and 0.30 fly ash-total cementitious ratio were cast. The specimens were cured in a fog room for differing periods varying from 1 to 112 days before exposure to the two regimes. The results indicate that given adequate initial curing of 7 days, the strength and strength-development characteristics of the fly ash-cement paste system are superior to those of the plain cement paste in both hot-dry and temperate exposure conditions. Further, exposure to hot-dry environment increases the total porosity of both the cement and cement-fly ash paste specimens as compared to the companion continuously moist-cured specimens. The decreased water sorptivity of the fly ash-cement paste specimens after 7 days of initial fog curing is also indicative of the beneficial effects of fly ash usage in hot-weather conditions where strength and permeability characteristics of concrete are most important for its durability.