**2. Experimental Program**

#### *2.1. Materials and Methods*

The fly ash used in the research came from the circulating fluidized bed combustion process in three Polish power stations: Katowice (K), Siersza (S) and Turów (T). Ashes were formed from the combustion of hard coal (K, S) and lignite (T). CFBC fly ash chemical analysis was carried out in accordance with European standards and is presented in Table 1.


**Table 1.** Chemical composition of circulating fluidized bed combustion (CFBC) fly ash determined by X-Ray Fluorescence Spectroscopy XRF method (wt %).

\* Loss on ignition at 1000 ◦C; \*\* Glycol method according to PN-EN 451-1.

Comparing the chemical composition to the requirements of PN EN 450-1, an excess of SO3 caused by anhydrite in the fly ash is shown. Ordinary Portland cement 32.5 R from "Małogoszcz" cement plant was used. The composition and physical properties are given in Table 2. Binders of the above ingredients were prepared by replacing 20% and 30% of the cement mass by fluidized fly ash K, S or T. For example, T20 corresponds to 20% fly ash from Turów (lignite burning), and K30 corresponds to 30% fly ash from Katowice (hard coal burning). The detailed composition of pastes is presented in Table 3. The difference in density between fly ash and cement was neglected. The cement paste with a constant water to binder ratio 0.5 was formed using prisms with dimensions 40 × 40 × 160 mm. Storage of the molds took place for 48 hours in a chamber with a humidity of 95%; after this period of time the specimens were kept in water and matured for 400 days at 20 ± 2 ◦C.


**Table 2.** Chemical composition and physical properties of cement, determined by XRF method (wt %).

\*\* Glycol method according to PN-EN 451-1.

**Table 3.** Composition of pastes prepared with CEM I and CFBC (g).

