Ammonia Release from Concrete Containing Ammoniated Fly Ash

摘要

The presence of ammonia in fly ash, resulting from the injection of ammonia to controlNO_x emissions, could create a major barrier to the utilization of fly ash in concrete.Practical guidelines for the handling and utilization of ammoniated fly ash are needed tohelp maintain the existing concrete and cement markets, which is the overall goal of thisproject. Specifically, the objective of our work is to determine the amount of ammoniathat is released, over the short- and long-term, from concrete that contains ammoniatedfly ash. The technical approach has been to prepare mortar and concrete slabs andmonitor the loss of ammonia during mixing, the concentration in the air-space above theslabs soon after placement, and the total quantity of ammonia evolved over a longertime period. Variables tested include temperature, ventilation rate, water:cementitiousmaterial (W:C) ratio, and fly ash source. The data indicate that for concrete placed inareas with poor air ventilation the fly ash NH3 concentration should not exceed 110 to170 mg/kg, depending on the water:cement ratio and the fly ash replacement rate, if anexposure limit of 10 ppm is not to be exceeded. Longer-term experiments showed thatthe ammonia loss rate is independent of fly ash source and W:C ratio.