The Effect of Biological Corrosion on the Hydration Processes of Synthetic Tricalcium Aluminate (C 3 A).

This paper presents a study related to the biological degradation of a tricalcium aluminate (C 3 A) phase treated with reactive media from the agricultural industry. During one month of setting and hardening, synthetic C 3 A was subjected to corrosion in corn silage, pig slurry and chicken manure. The hardening process of the C 3 A phase in water was used as a reference sample. The phase composition and microstructure of the hydrating tricalcium aluminate slurries were characterised by X-ray diffraction (XRD), thermal analysis (DTA/TG/DTG/EGA), scanning microscopy (SEM, EDS) and infrared spectroscopy (FT-IR). In the samples studied, it was observed that the qualitative and quantitative phase composition of the synthetic tricalcium aluminate preparations changed depending on the corrosion exposure conditions. The main crystalline phases formed by the hydration of the examined samples in water as well as in corrosive media were the catoite (Ca 3 Al 2 (OH) 12 ) and hydrocalumite (Ca 2 Al(OH) 7 ·3H 2 O) phases. Detailed analysis showed the occurrence of secondary crystallisation in hydrating samples and the phases were mainly calcium carbonates (CaCO 3 ) with different crystallite sizes. In the phase composition of the C 3 A pastes, varying amounts of aluminium hydroxides (Al(OH) 3 ) were also present. The crystalline phases formed as a result of secondary crystallisation represented biological corrosion products, probably resulting from the reaction of hydrates with secondary products resulting from the metabolic processes of anaerobic bacterial respiration (from living matter) associated with the presence of bacteria in the reaction medium. The results obtained contribute towards the development of fast-acting and bio-corrosion-resistant special cements for use in bioenergetics.