## 2 Materials and Methods
The following types of concrete mixes have been prepared for laboratory tests:  
* BZ--reference concrete without additives,
* 1M--concrete with 10% glass flour and 4% polypropylene fibers,
* 2M--concrete with 20% glass flour and 4% polypropylene fibers,
* 3M--concrete with 30% glass flour and 4% polypropylene fibers. Table 4 shows the composition of individual concrete mixes. Figure 3: Polypropylene fibers and their characteristics. Figure 2: Glass flour grain size curve (manufacturer’s data). The following tests of fresh concrete mixes were carried out:  
* consistency, in accordance with EN 12350-2:2019-08, reflow table method,
* density, in accordance with EN 12350-6:2019-08,
* air content, in accordance with EN 12350-7:2019-08, pressure method [38; 39; 40]. The following concrete tests were carried out:  
* compressive strength, according to EN 12390-3:2019-07,
* density, in accordance with EN 12390-7:2019-08,
* frost resistance, according to 88/B-06250:2004 [41; 42; 43],
* evaluation of the effect of the addition of glass flour and polypropylene fibers on the microstructure of concrete. The research was carried out in the Building Laboratory at the Faculty of Civil and Civil Engineering, in the Laboratory of Physical Processes at the Water Centre of the Warsaw University of Life Sciences, and in the Concrete Laboratory at the Building Research Institute in Warsaw. The compressive strength test fc was performed after 28, 56, and 90 days of maturation in the hydraulic testing machine H011 Matset (Italy). Based on the obtained average strengths, the result was converted into cubic samples with a side of 15 cm, and the concrete class was determined. \[f_{c,cub~{}15}=0.95\cdot f_{c,cub~{}10}\]  
The frost resistance test was performed on samples measuring 10 \(\times\) 10 \(\times\) 10 cm after 28 days of concrete maturation for 150 freeze and thaw cycles. Three criteria were adopted to assess the degree of frost resistance, the fulfilment of which determines the degree of frost resistance achieved:  
* no cracks on the samples after all freezing and thawing cycles,
* not exceeding the value of a 5% difference in the weight of the samples soaked in water before and after the frost resistance test,
* a decrease in compressive strength between witness and frozen samples of not more than 20%. Three types of concrete containing polymer fibers and various amounts of glass flour (samples M1, M2, and M3) were prepared for Scanning Electron Microscope (SEM) examinations. At the first stage, from 10 \(\times\) 10 \(\times\) 10 cm concrete cubes, a thick slice from the middle section was cut perpendicular to the twroelling surface for each type of material. In this way, surfaces were grinded and polished. Cut and pre-polished sections of polymer composites are presented in Figure 4.  
In the next step for SEM examinations, a chosen region from the pre-polished sections of each sample was cut with surface dimensions of about 20 \(\times\) 20 mm. After cutting, they were dried in the oven and put into epoxy resin in a vacuum chamber. Microscopic sections were prepared in the same way as in previously published papers [44]. Figure 5 presents images of prepared samples made using an optical microscope. Before SEM examinations, samples were gold-evaporated. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{3}{*}{**Specification**} & \multicolumn{5}{c}{**Components of the Concrete Mix**} \\ \cline{2-6}  & \multirow{2}{*}{**Water**} & \multicolumn{2}{c}{**Aggregate**} & \multirow{2}{*}{**Cement**} & \multirow{2}{*}{**Glass Flour**} \\ \cline{3-3} \cline{5-6}  & & **Sand** & & **Gravel** \\ \hline BZ concrete & 287.08 & 488.34 & 831.49 & 666.03 & - \\ \hline Concrete with 10\% M1 flour & 287.08 & 488.34 & 831.49 & 599.43 & 66.60 \\ \hline Concrete with 20\% flour M2 & 287.08 & 488.34 & 831.49 & 532.82 & 133.21 \\ \hline Concrete with 30\% M3 flour & 287.08 & 488.34 & 831.49 & 466.22 & 199.81 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Concrete mix proportions by weight.