| Abstract [eng] |
Mayenite (Ca12Al14O33) is a highly interesting functional material not only in view of its unique crystal structure but also for its variety of possible applications: catalysis (oxidation and reduction, ammonia synthesis), environmental sensors and CO2 sorbent materials [1,2]. In addition to the aforementioned possibilities of using mayenite, it is also constituent part of compounds in calcium aluminate and calcium sulfoaluminate cement clinkers [3]. It should be noted that, mayenite additives accelerates ettringite formation and change Portland cement hydration mechanism [4]. For this reason, the hydration experiments of mayenite and gypsum mixture samples were performed. Mayenite synthesis was carried out in two stages: hydrothermal synthesis (4 h, 130 °C) and calcined (1 h, at 350 °C). Dry primary mixtures with differences mass ratio of gypsum and mayenite: 1.755 (labelled: CA1_2.5); 0.855 (labelled: CA1_5) and 0.555 (labelled: CA1_7.5) were mixed. These ratios were calculation, which corresponds to the mentioned compounds mass ratio in OPC with mayenite additives (a partial replacement of the OPC at 2.5; 5 and 7.5 % by weight of the total cementitious material). The heat release kinetics of the samples was investigated with an isothermal calorimeter at 25 °C for 60 h when the ratio of the primary water/solid mixtures was equal to 0.75. It was determined that in all samples initial reaction start slowly because maximum heat evolution rate was observed after 40 min of hydration. It should be emphasized that hydration at this stage is accelerated by mayenite because this effect grows as the mayenite level increases (Fig. 1). Besides, the accelerating effect began after 4-5 h of hydration in all samples and the maximum values of heat flow of the second exothermic reaction were determined, when mayenite amount decrease, i.e. 0.08 W/g at 8 h, 0.085 W/g at 10 h and 0.047 W/g at 13 h. After 72 h of hydration, the highest quantity of the total heat (~460 J/g) was obtained in the CA1_5 mixture, while in the CA1_7.5 and CA1_2.5 samples, were slightly lower and reached very similar values (>450 J/g). In order to determine the mineralogical composition of hydration products, CA1_2.5, CA1_5, CA1_7.5 mixture was hydrated using ratio of water/cementitious mixtures 0.75 at 25 °C, which were characterized by XRD, STA, and FT-IR analysis. [...]. |
