Alkali Silica Reaction Mitigation Using High Volume Class C Fly Ash

Alkali-Silica Reaction (ASR) is a neutralization reaction that occurs between an acid (silicic acid) and a basic pH pore solution (Calcium Oxide, Potassium Oxide, and Sodium Oxide). ASR causes deleterious expansion within concrete, which can cause durability issues decreasing the life span of concrete. ASR in concrete has been found in increasing quantities since its discovery in 1940 by Stanton. Several cases of ASR have occurred in Arkansas near Fayetteville, Pine Bluff, and Little Rock. The purpose of this research was to develop preventative measures using Class C fly ash in concrete, which contains the moderately reactive aggregates found in the Arkansas River. The research used locally available fly ashes in order to represent the materials used in conjunction with the Arkansas River fine aggregates. The research includes three regional, Class C fly ashes. Two fine aggregate (sand) sources are included in order to evaluate the ability of Class C fly ashes in preventing ASR. The first fine aggregate evaluated was Arkansas River sand from Van Buren, AR. This is a moderately reactive aggregate that was used and is currently used in concrete throughout the region. In addition to the river sand, a highly reactive fine aggregate (Jobe-Newman), was evaluated to determine the ability of Class C fly ashes in preventing ASR when aggregates of different levels of reactivity are used. Jobe-Newman aggregate has been documented by many researchers as a highly reactive source of silica. Class F fly ashes have been previously prescribed for preventing ASR when there is a source of reactive aggregates (ACI Committee 221 1998). However, the availability of Class F fly ash in regions, such as Arkansas, is somewhat limited compared to the availability of Class C fly ash. This research examines the use Class C fly ash for preventing ASR in concretes containing moderately reactive aggregates. Based upon the AMBT results for Arkansas River sand Class C fly ash was found to be able to impede alkali silica reaction to the point of making concrete non-reactive based upon the accelerated mortar bar test as defined by ASTM C1260 and ASTM C1567. Also, based on the accelerated mortar bar test results recommendations were made as to how to better classify fly ashes compared to the current ASTM C618 including placing limits on MgO content and analyzing fly ashes by a ratio of sum of alkalis: sum of oxides instead of simply classifying a fly ash based upon sum of oxides