Synthesis and Properties of Geopolymers

The commercial cement CEM I 42.5R from the cement plant Górażdże Cement S.A. (Heidelberg Cement Group, Chorula, Poland) was used for the experiments. According to manufacturer protocol, in appropriate proportions, after very fine grinding and homogenization, the raw material was heated (cyclone heat exchangers) and then sintered (rotary furnace; raw material temperature 1450 °C, flame and gas temperatures 2000 °C). The material remained in the high-temperature zone for approx. 30 min. The temperature of cement clinker at the exit of the furnace was approx. 900–1300 °C. Then it was subjected to intensive cooling, down to a temperature of about 100 °C. As a result, the cement clinker (in the form of hard sintered lumps) was obtained. The product, with the addition of gypsum, was ground in a ball mill to a very fine powder (CEM I Portland cement). This cement meets the standard requirements according to PN-EN 197-1 [57 ], and the properties described in the Declaration of Performance No. 1487-CPR-027-02. Cement conforms to the IBDiM Technical Recommendation No. RT/2010-02-0060/1.
The fly ash (FA) from the combined heat and power plant in Skawina (Skawina CHP Coal Power Plant, Skawina, Poland) and metakaolin (MK) KM 60 (Keramost, Kadaň, Czech Republic) were used as raw materials for geopolymers production. The pulverization process of FA was used to uniform the chemical composition and particle size, as FA was collected from different mechanical and electrostatic precipitators and zones. MK was prepared via the dehydroxylation of kaolin to remove the chemically bonded hydroxyl ions, according to the procedure described earlier [58 (link),59 (link),60 (link)]. The raw materials were mixed with commercial quartz sand with a chemical composition: 90.0–90.3% SiO₂, max. 0.2% Fe₂O₃, 0.08–0.1% TiO₂, 0.4–0.7% Al₂O₃, 0.17% CaO, 0.01% MgO.