Pore Structure and Chloride Permeability of Concretes Containing Fly Ash, Blast Furnace Slag and Silica Fume


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Title: Pore Structure and Chloride Permeability of Concretes Containing Fly Ash, Blast Furnace Slag and Silica Fume

Author(s): K. Trill and M. Kawamura

Publication: Special Publication

Volume: 132


Appears on pages(s): 135-150

Keywords: blast furnace slag; curing; environments; fly ash; hydration; mineral admixtures; permeability; porosity; silica fume; surface layers; Materials Research

Date: 5/1/1992

Report presents data on the effects of a mineral admixture such as fly ash, blast furnace slag, or silica fume on the pore structure and chloride permeability of concrete stored under various environmental conditions for a long time. Cubic concrete specimens with all surfaces coated with a polymer except for one surface were initially cured in water for 7 or 28 days, and then exposed to three environmental conditions for 1 year: in water at 20 C; in a room at 20 C, at 60 percent relative humidity; and outdoors. Cores from the specimens were investigated for the degree of hydration and the characteristics of pore structure of concretes both with and without mineral admixtures. The test involved ignition loss, mercury intrusion porosimetry, and scanning electron microscopy. The chloride permeability of exterior and interior portions of specimens was determined according to AASHTO T 277-831. The test results showed that, at the surface of concretes containing mineral admixtures, the hydration of portland cement and the pozzolanic reaction of mineral admixture were considerably depressed, and coarse pores were developed when the concrete specimens were exposed to dry environment for a long time; however, at 5 cm depth from the surface, there was little change in both the degree of hydration of cement and the pore structure. AASHTO T 277-831 data showed that both the surface layer and the interior concretes with mineral admixtures were much less permeable to chloride ions than the corresponding portland cement concrete specimens, irrespective of the curing and environmental conditions.