The Effects of Supplementary Cementitious Materials and Exposure Temperature on External Sulfate Attack


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Title: The Effects of Supplementary Cementitious Materials and Exposure Temperature on External Sulfate Attack

Author(s): Ashlee Allison and Michael D.A. Thomas

Publication: Special Publication

Volume: 317


Appears on pages(s): 1-14

Keywords: ettringite, gypsum, limestone, portland limestone cement, sulfate, supplementary cementitious materials, temperature, thaumasite

Date: 6/1/2017

Synopsis: Mortar bars (CSA A3004-C8) were cast with portland and portland limestone cements in combination with various supplementary cementitious materials. The mortar bars were exposed to sodium sulfate solution at 1°C, 5°C, 10°C, and 23°C (34°F, 41°F, 50°F, 73°F); the length change due to external sulfate attack was monitored over time. Mortar cubes were also cast and stored in limewater at 5°C, 23°C, and 38°C (41°F, 73°F, 100°F). The compressive strengths of the mortar cubes were tested at regular intervals to determine the rates of compressive strength gain of the various mortars as a function of curing temperature. The results generally reveal that external sulfate attack is accelerated in cold temperature sulfate exposure, particularly among the mortars with higher supplementary cementitious material replacement levels. The results reveal that the hydration of supplementary cementitious materials is severely diminished upon early-age exposure to cold temperatures, leading to a more permeable pore structure and diminished resistance to sulfate attack. The compressive strength gain of the mortar cubes containing supplementary cementitious materials was retarded at cold temperatures; the impact was much less severe with control mortars. At temperatures ≥10°C (50°F) supplementary cementitious materials greatly enhance resistance to external sulfate attack relative to the control mortars.