Effects of Curing and Test Conditions on the Salt Scaling Durability of Fly Ash Concrete

Some specifications currently limit the amount of fly ash used in concrete exposed to de-icer salts and freezing conditions because of concerns over salt scaling durability. There is concern that the standard test method commonly used to assess concrete salt scaling performance, ASTM C672, is overly severe and not representative of field conditions. There is also concern that the use of fly ash as a mass replacement could lead to additional damage because of the higher paste volume that results from the lower specific gravity of fly ash relative to Portland cement. In this study, concrete mixtures with 40 % replacement by mass were tested according to ASTM C672 using a constant cementitious material mass and a constant paste volume. Specimens were tested at an outdoor field exposure site to test the severity of ASTM C672 and the effects of specimen size on salt scaling resistance. The experiments showed that the fly ash source has a large effect on the salt scaling resistance in laboratory testing, although the increase in cement paste volume from the mass replacement of cement did not correlate with decreased performance. Laboratory-size specimens showed much higher salt scaling than larger companion slabs cast from the same concrete batches.