Examining the influence of post-mercury-control on properties of fly ash concrete

Activated carbon injections are the most mature technologies for mercury capture at coal-fired power plants. However the increased carbon content and concentrated toxic heavy metal elements (i.e. mercury, arsenic, lead etc.) in the fly ash may reduce the suitability of fly ash for use in concrete and call into question the safety of using this fly ash.This study examined the reuse potential of post-mercury-control fly ash in concrete. Specifically, the structural strength, durability, and environmental leaching of postmercury-control fly ash concrete were tested.Thirteen concrete mixtures containing post-mercury-control fly ashes derived from different technologies were designed and batched. This study confirmed the influence of the carbon on the air content of the concrete. However there was no difficulty in entraining air in activated carbon injection fly ash concretes within the recommended dosage range of air-entraining admixture. All air-entrained fly ash concretes exhibited excellent characteristics in compressive strength (&ge 32.0 MPa at 28 days), resistance to chloride-ion penetration (moderate to low at 28 days) and freeze-thaw (&ge90 average durability factor after 300 cycles).One fly ash was selected based on the structural performance of the fly ash concrete for the optimization phase of this study. Laboratory testing was completed to optimize the cementitious material and fly ash contents in the concrete. The cementitious materials content and the maximum possible cement replacement percentage by the tly ash can be selected to be 338 kg/m 3 (570 lbs/cy) and 50% respectively to yield a 28-day strength and a durability greater than that required by the Colorado Department of Transportation Class D structural concrete.The possible leaching of heavy metal elements was evaluated using the U.S. Environmental Protection Agency's Toxicity Characteristic Leaching Procedure for the selected fly ash and the optimized fly ash concrete mixture. The test results indicate that the leaching of only two toxic elements was higher than the reporting limits, but much lower than the maximum contamination level.The environmental impact of post-mercury-control fly ash concrete infrastructure in the Metropolitan-Denver Area was evaluated by calculating the embodied energy and GHG emission associated with one cubic meter fly ash concrete using a "Cradle-to-Grave" LCA model. The optimized concrete mixture has the lower embodied energy (2708 MJ/m3) and GHG emission (0.3696 MTCO 2E/m3) than other mixtures (control mixture: embodied energy 3936 MJ/m3 GHG 0.5562 MTCO2E/m3 ).