Physical Properties of Rapid-Setting Concrete Using Ultra Fine Fly Ash

Generally, Ultra Fine Fly Ash (UFFA) has the advantage that it advances greater concrete workability and that it activates a greater pozzolanic reaction than common fly ash due to its ultra fine particle size. These properties enhance concrete durability by reducing permeability and increasing resistance to alkali silica reaction (ASR) and sulfate attack, etc. For these reasons, UFFA can be used in rapid setting concrete. The purpose of this study is to develop and evaluate the rapid setting concrete with UFFA as a repair material for early-opening-to-traffic. In previous studies, if only UFFA is added to the rapid setting concrete mixture, the pozzolanic reaction does not happen actively. In this study, the chemical and physical tests were performed for rapid setting concrete with a combination of UFFA and calcium hydroxide. This enabled the activity of pozzolanic reaction to be evaluated as well as the effectiveness of this mixture on enhancing concrete durability was investigated. This study found that adding UFFA decreased the water/cement ratio of concrete and compensated the reduced portion of the early strength of concrete. Additionally, rapid setting concrete with UFFA and calcium hydroxide activated a greater pozzolanic reaction than normal-UFFA concrete. As the calcium hydroxide increased, the electrical indication of the concrete's ability to resist chloride ion penetration was promoted significantly.