*3.2. 27Al*

The 27Al NMR spectrum of the anhydrated cement (Figure 2 (top)) shows two isotropic signals. The signal at 85 ppm corresponds to aluminum atoms in tetrahedral environment of oxygen atoms Al(IV), which are in the form of impurities in alite and belite [18]. The signal at about 10 ppm corresponds to aluminum atoms in octahedral environment of oxygen atoms Al(VI). This signal consists of two spectral components: the narrow component at about 15 ppm corresponds to aluminum atoms in Ca3Al2O6 (C3A), and the broad one at about 10 ppm to C4AF [18].

**Figure 2.** 27Al NMR spectra of the (**top**) anhydrated Portland-limestone cement, and (**bottom**) cement paste sample with acetic acid addition at the 7th day of hydration.

In the 27Al NMR spectra of all studied hydrated samples (Figure 2 (bottom) shows the 27Al NMR spectrum from the **CAA07** sample; the rest of the spectra are shown in Supplementary Figures S4a–S6a), it can be seen that the signal from the aluminum atoms Al(IV) in anyhydrated alite and belite practically disappears already on the first day of hydration; there is only a weak signal at this age for the **CAA** and **CSA** samples. At the same time, a broad asymmetric signal appears at about 65 ppm that can be described as the sum of the two components at 60 and 75 ppm. Both correspond to aluminum atoms Al(IV) in the amorphous cement hydration gel. In fact, the line at about 75 ppm is typical for aluminum incorporation in the C–S–H gel, while the line at around 60 ppm for aluminum atoms in an unstable aluminum silicate hydrate (A–S–H) gel, forming near the surface of clinker grains at conditions of calcium shortage and excess aluminum [19]. In this case, the total relative integrated intensity of the signals in the given spectral region decreased with increasing the hydration time.

For the **C** and **CSA** samples, a broad asymmetric signal in the region of Al(VI) chemical shifts can be described also by two components: a narrow one at 15 ppm and a broad component, whose chemical shift decreased from 14 to 10.5 ppm from the 1st to the 7th day, and then increased to 14.5 ppm by the end of the investigated time interval. For the **CAA** sample, there is another narrow component, in this region of the spectrum, at about 11 ppm (see the example in Figure 2, bottom). The narrow intense line at about 15 ppm corresponds to aluminum atoms in ettringite [12]. The narrow line of weak intensity at about 11 ppm corresponds to calcium monocarboaluminate hydrate (AFm) [19]. The broad line, whose position varies in the range of about 10.5–14.5 ppm, corresponds to signals from several aluminum hydrates and calcium hydroaluminates of different compositions. According to the behavior of the chemical shift of the broad line under consideration, it can be assumed that redistribution of coexisting phases occurs, from aluminate hydrate (AH3) through

mono-(CAH10) and dicalcium hydroaluminate (C2AH8) to tricalcium hydroaluminate (C3AH6) [12].
