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Three types of binders were investigated by combining a water granulated fayalite slag and three different activating solutions (NaOH, SH; Na-silicate, SS; and a 1:1 mixture of the two, SH + SS). A reactivity test proved that the slag dissolves in the alkaline environment, releasing both Si and Al. Through rheological measurements it was found that the most alkaline solution (SH) led to a very fast structure build-up, followed by the activating solution SS+SH; when SS was used, the storage modulus did not increase even after 2 h. A similar trend was observed by calorimetry, where the paste with SH resulted in heat release within minutes, followed by SH + SS. These transformations were also followed by in situ ATR-FTIR, indicating changes in the vibrational bands attributed to asymmetric stretching vibration of [SiO 4 ] with 3 or 4 NBO/Si. In the case of the sample activated with SH, a new band appeared after 96 h and continued to increase in intensity at later times. For SS + SH activating solution, a new band appeared after 96 h, increasing over time, whereas the originally present band at 940 cm -1 became more distinct. For the sample with only SS, no vibrational changes were detected after 24 h. In conclusion, the fayalite slag is a reactive material that can undergo microstructural changes toward new reaction products, with the choice of the activating solution being a crucial factor in the process.

The science of rheology is increasingly used to describe the properties of fresh cement paste. Compared to standard workability tests, rheological properties allow for more fundamental investigation, more precise phenomenological description of flow properties and serve as input for numerical simulations. Standard commercially available rheometers are typically used to perform those measurements. However, the results of the measurement depend on the geometry, testing procedure and a number of potential artefacts. This technical letter describes the most common techniques and procedures used to assess the rheological properties of cement paste, as well as challenges during measurements and actions to counter these challenges.

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