Sulfate Resistance of Mortars Containing Ground Granulated Blast-Furnace Slag With Variable Alumina Content
John P. H. Frearson and Denis D. Higgins
Appears on pages(s):
aluminum oxide; blast furnace slag; expansion; sulfate resistance; slags; mortars (material); water-cement ratio; Materials Research
Various researchers have reported that the sulfate resistance of portland blast-furnace slag cements was reduced when the slag contained a high alumina content. Much of this testing has used much higher water-cement ratios for the test specimens than are normally used in construction. In this study, the mixtures have been modified to assess mortars additionally at lower water-cement ratios. The test program used the German "Flat-Prism" test to assess blends of cement and various combinations of two slags: one slag of low alumina content, and the other slag with a higher alumina content. Results of expansion testing up to an age of 4 years are reported and indicate that when used at the replacement levels and water-cement ratios specified in current U.K. standards and codes of practice, both slags can provide resistance to sulfate expansion. At higher water-cement ratios and lower slag replacement levels, expansion does occur. Commercial blends of the two slags, when used to optimize other properties (e.g., strength), would not compromise the sulfate resistance properties. The greatest sulfate resistance, as represented by the lowest expansion, was not provided by the slag with the lowest alumina content, but by a composite slag sample with an alumina level of about 13 percent.