*2.2. Mixture Proportion and Preparation*

The influence of glass powder on cement hydration was analyzed by preparing cement paste with 10% glass addition. To investigate the mechanical properties and microstructure of mortar, five mixtures were prepared, with different amounts of glass powder used as a partial cement substitution, i.e., 5%, 10%, 15% and 20% by cement mass. The composition of each mixture is presented in Table 3. The control mortar was marked as M0 (mortar without glass powder), and the experimental mortars were named, accordingly, M5, M10, M15 and M20, where the number indicates the cement replacement with the glass powder. All mixtures were prepared in accordance with European Standard EN 196-1, placed into 40 × 40 × 160 steel prim molds and consolidated by external vibration. The mortar samples after demolding were cured in water and at 20 ± 1 ◦C until the testing time.

**Table 3.** Mortar mixture proportions for one batch of laboratory mixer, [g].


#### *2.3. Test Methods*

The pozzolanic activity of glass powder was assessed by chemical and mechanical methods. The chemical method is based on the determination of the soluble silicon and aluminum oxides content in the glass powder in the NaOH solution. The physical method is based on the determination of the Strength Activity Index (SAI), which is the ratio of the strength of the experimental mortar (cement mortars with 25% cement replacement with glass powder) to that of the reference mortar, and it was conducted in accordance with EN 450-1.

The total heat of hydration after 72 h of hardening cements with the addition of glass waste was determined by the semi-adiabatic method, in accordance with the PN-EN 196- 9:2010 standard. The samples prepared with CEM I 42.5 and the addition of 10% waste and the reference sample of pure cement were used. To determine the compressive strength of the specimens after 28, 90 and 180 days of curing, EN 196-1 was employed. The compressive strength is the average value from six specimens tested at each age for each mixture. The porosity of each specimen was determined by the MIP method after 28 days of curing.

The microstructure analyses were carried out using an electron microscope, FESEM-EDX Carl Zeiss Sigma 300 VP (Carl Zeiss Microscopy GmbH, Jena, Germany), after sputtering the samples with graphite (Sputter Quorum Q150 from Quorum Technologies Ltd., East Sussex, UK).
