*2.1. Materials*

The materials used were the ordinary Portland cement type of CEM I 42.5R (PC) according to the PN-EN 197-1 standard [4], granulated blast furnace slag (GBFS), siliceous fly ash (SFA), and gypsum (G). The chemical composition and physical characteristics of these materials are presented in Table 1.


**Table 1.** Chemical composition and physical characteristics of the materials.

(1) D10, D50, D90: the portion of particles with diameters smaller than this value is 10, 50, and 90%, respectively; D50 is also known as the median diameter.

The XRD analysis of PC, GBFS and SFA (at 10–65◦2θ range) is presented in Figure 1. The GBFS is composed of a glassy phase (a background signal at 24–38◦2θ) with XRD peaks from the crystalline phases, such as akermanite and merwinite. For SFA, the identified phases were the glassy phase (a broad background signal at 16–38◦2θ), mullite, quartz and hematite.

The GBFS and SFA used meet the requirements according to the PN-EN 197-1 standard [4]. The chemical modulus of GBFS (CaO + MgO + SiO2) and ((CaO + MgO)/SiO2) were 87.2% and 1.4%, respectively. For SFA, the reactive SiO2 content was 38.87%, while the contents of MgO, SO3, and Na2Oe (Na2Oe = Na2O + 0.658K2O) were 8.22, 1.51, and 3.13%, respectively. SFA showed 0.013% chloride ion composition.
