Improving the sulfate resistance of Class C fly ash : a scientific approach to making bad ash concrete

Decades of research have shown that high calcium fly ash, when used as a partial replacement for portland cement, produces a binder that is susceptible to external sulfate attack. Previous research studies have shown that the external sulfate attack mechanism affecting these blends can be suppressed by using gypsum as an additive. In this research study, short-term expansion tests, calorimetry, and x-ray diffraction analysis have been used to show how gypsum affects the volumetric stability, hydration kinetics, and early age hydration products that form in these types of binders. Quantifying the hydration products that contribute to the external sulfate attack mechanism and correlating them to the amount of heat produced by the binder is a crucial step to determining the adequate amount of gypsum required to produce sulfate resistant cements containing high calcium fly ash. The use of these investigative techniques may allow for more widespread use of high calcium fly ashes as a replacement of portland cement.Civil, Architectural, and Environmental Engineerin