Title:
Long-Term Durability of Blended Cement Against Sulfate Attack
Author(s):
Medhat H. Shehata, Giri Adhikari, and Shaun Radomski
Publication:
Materials Journal
Volume:
105
Issue:
6
Appears on pages(s):
594-602
Keywords:
calcium content; permeability; sulfate attack; X-ray diffraction
DOI:
10.14359/20201
Date:
11/1/2008
Abstract:
Five different supplementary cementing materials (SCM) were investigated for their resistance to sodium sulfate attack using ASTM C1012. The results showed high-calcium fly ash (HCFA) to have the lowest resistance, which was attributable to its calcium-aluminate glass. The performance of HCFA was improved when the ash was blended with an optimum amount of gypsum or 5% silica fume (SF), however, blending with SF produced better results. The X-ray diffraction patterns confirmed that blending HCFA with gypsum sustained early formation of stable ettringite rather than monosulfate. Low ion migration and reduced calcium hydroxide (CH) were behind the enhanced performance of the sample with HCFA and 5% SF. The observed differences in the sulfate resistance of the three tested fly ashes could not be attributed, even partly, to their differences in CH consumption, which were insignificant. Compared with samples with only portland cement, however, all samples with SCM showed a significant reduction in CH.