Study of the Effects of Post-Combustion Ammonia Injection on Fly Ash Quality: Characterization of Ammonia Release from Concrete and Mortars Containing Fly Ash as a Pozzolanic Admixture. Semi-Annual Technical Progress Report for the Period 10/12/01 to 04/11/02.
Work completed in this reporting period focused primarily on continuing measurements of the rate of ammonia loss from concrete, and the measurement of ammonia gas in the air above concrete and flowable fill immediately after placement. Concrete slabs were prepared to monitor the loss of ammonia during mixing, the concentration in the airspace above the slabs soon after placement, and the total quantity of ammonia evolved over a longer time period. Variables tested include temperature, ventilation rate, water:cementitious (W:C) ratio, and fly ash source. Short-term data indicate that for concrete placed in areas with poor air ventilation the fly ash NH3 concentration should not exceed about 90 to 145 mg/kg ash, depending on the water:cement ratio and the fly ash replacement rate, if a concentration of 10 ppm NH(sub 3) in the air is assumed to be the maximum acceptable level. Longer-term experiments showed that the ammonia loss rate is dependent on ammonia source (that is ammoniated ash vs. non-ammoniated ash with ammonia added to the water), and is also dependent on W:C ratio and temperature. Experiments were also conducted to study the loss of ammonia from fresh concrete during mixing. It was found that a high water:cementitious mix lost a greater percentage of ammonia than a low W:C mix, with a medium W:C mix losing an amount intermediate between these two. However, a larger batch size resulted in a smaller percentage of ammonia lost. The data suggest that a significant quantity of ammonia could be lost from Ready Mix concrete during transit, depending on the transit time, batch size, and mix proportions.
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