Experimental determination of ammonia in fly ash for ready-mix concrete

Production of concrete with the addition of power plant fly ash created during selective non-catalytic reduction of nitrogen oxides (SNCR), (reaction of reducing agents such as urea or ammonia water), during which ammonia with nitric oxide (NO) and nitrogen dioxide (NO2) are split; manipulation with the concrete, its placement, and subsequent ammonia emissions into the interior environment of buildings raise the question of risk by exceeding the hygienic limits for ammonia concentration in the atmosphere (CSN EN 4502-1 states in Article 5.4.2 “The fly ash shall not contain substances which, when released from the concrete, would be hazardous to health, hygiene and the environment”, which ammonia is). The question is, how high the ammonia concentrations in the air are, whether they are “dangerous to health, hygiene and the environment”. In addition to these questions, there are also technological questions, i.e. the quality of such fly ash in terms of its impact on the properties of fresh and hardened concrete. This results in uncertainty regarding the safe use of such fly ash by the concrete manufacturer. Ultimately, the use of such fly ash is being reduced, because the potential risk (absence of limits) in using fly ash as a partial cement substitute outweighs the potential savings resulting from the lower price of this pozzolanic admixture (which contaminated fly ash certainly still is). In 2016, new legislative measures regulating emission limits of produced flue gases [1] were introduced. Demands on the quality of produced flue gases have been constantly tightened in recent years, which is why mainly producers of electricity in coal-fired power units are forced to introduce additional greening technologies. The new legislation tightens the inspection of the production of nitrogen oxide emissions the most, which was completely out of interest in recent times. Therefore, several methods of new greening technologies have been developed in order to improve the reduction of nitrogen oxides, which differ fundamentally in particular due to the need to intervene in the combustion process or in the construction of the entire combustion unit. However, due to economic reasons, most thermal power plants and incineration plants in the Czech and Slovak Republics follow a unified path by introducing selective non-catalytic reduction of nitrogen oxides (hereinafter referred to as SNCR).