NEW SAFETY CHALLENGES OF CEMENT-CONTAINING BUILDING MATERIALS AND PRODUCTS FROM THEM

The article considers a new problem of harmful effects of Portland cement on humans due to the possibility of releasing ammonia during hydration hardening of materials and products based on it. It notes the relationship between the analyzed problem and the intensification of energy and resource saving at modern cement plants, which allows nitrogen-containing materials to enter Portland cement: as part of raw materials; with materials utilized in high-temperature zones of rotary kilns and as part of additives introduced during grinding of cement clinker. Probable sources of ammonia release from Portland cement during its hydration are analyzed in a logical sequence and taking into account the chemical specificity of various groups of nitrogen-containing compounds. The most theoretically substantiated and experimentally confirmed hypothesis is chosen about the synthesis of iron nitrides in high-temperature zones of rotary kilns for burning cement clinker – the main sources of subsequent ammonia emission during hydration of Portland cement. A set of conditions necessary for the synthesis of iron nitrides is considered. The debatable nature of the issue of the stability of stoichiometric iron nitride Fe8N is indicated and it is proposed to consider it as a solid solution along with stoichiometric compounds Fe4N and Fe2N when analyzing chemical processes of hydration with the formation of ammonia. Possible solutions to the problem at the place of its occurrence - Portland cement plants – are discussed. The expediency of depleting sources of ammonia emission at the initial stages of hydration hardening of Portland cement is shown, which significantly reduces the risk of harmful effects on the human body. A method for eliminating the problem at large enterprises consuming Portland cement in significant quantities for the manufacture of dry building mixtures, concrete and products from them is selected. The essence of the method for proactively removing the main amount of ammonia emission sources at the initial stage of Portland cement hydration in the presence of the additive Ca(NO3)2 is described. Theoretical and practical arguments are presented about the positive effect of small amounts of Ca(NO3)2 on the formation of the microstructure and operational characteristics of cement stone, which additionally stimulates the implementation of the proposed method. The need for a comprehensive large-scale study of all possible manifestations of the analyzed problem with the involvement of specialists from sanitary and hygienic services is emphasized.