## 6 Conclusions  
Based on the presented experimental research campaign, the following conclusions can be drawn:  
1. The compressive strength of porous concrete made with granite screenings (2.5-5 mm) was found to be higher than that of concrete made with granite crushed stone (5-10 mm). For instance, at a water/cement ratio (W/C) of 0.45 and cement paste layer thickness (CPLT) of 150 microns, the strength of concrete with granite screenings was 11.4 MPa, while with granite crushed stone, it was 7.6 MPa. The finer fraction (2.5-5 mm) resulted in a higher concrete density due to the reduced void content, enhancing strength and structural quality.
2. There is an optimum W/C ratio for each aggregate type and fraction. Any deviation from this optimum ratio, whether increasing or decreasing, has been shown to result in a reduction in compressive strength. For example, the highest strength for both granite screenings and crushed stone was achieved at a W/C of 0.45, with notable decreases in strength observed at both lower and higher ratios.
3. The compressive strength of porous concrete was observed to increase with CPLT; however, an excess cement paste was found to have the potential to fill the voids between grains, acting as a ballast rather than contributing to grain bonding. The study determined that a CPLT of 150 microns was optimal for achieving the highest strength for both granite screenings and crushed stones.
4. A clear relationship was established between the density and strength of porous concrete, with higher strength corresponding to higher densities. This was particularly evident with the use of finer aggregates, which resulted in concrete with higher compressive strengths and densities.
5. The coefficient of structural quality (CSQ), defined as the ratio of compressive strength to the relative density of concrete, was found to be higher for concrete produced with granite screenings in comparison to concrete produced with granite crushed stone. This suggests that the quality of porous concrete with finer aggregates is increased.
6. The study put forward a method for the design of porous concrete compositions based on the optimal combination of cement paste volume, W/C ratio, and aggregate type and size. This method allows for the creation of tailored concrete mixes to efficiently achieve desired strength and density properties.  
The findings provide valuable insights for the practical application of porous concrete in construction, particularly for low-rise buildings and other structures where both permeability and strength are critical. The research confirms that appropriate selection and proportioning of materials can significantly enhance the performance of porous concrete.  
Conceptualization, L.D.; methodology, L.D. and O.B.; software, O.B.; validation, L.D. and T.T.; formal analysis, O.B. and T.T.; investigation, L.D. and O.B.; resources, K.M.; data curation, O.B.; writing--original draft preparation, L.D., O.B., T.T. and K.M.; writing--review and editing, T.T. and K.M.; visualization, O.B. and T.T.; supervision, L.D.; project administration, K.M.; funding acquisition, K.M. All authors have read and agreed to the published version of the manuscript.  
The research was supported by the Polish National Agency for Academic Exchange under activities complementary to those undertaken by the University as part of the European University alliance initiative entitled STARS EU, an academic cooperation with Ukrainian universities, grant no. BNI-UE-2023-8. This research was co-funded by the Polish National Centre for Research and Development in Poland, under the M-ERA.NET 3 program, grant number M-ERA.NET3/2021/144/3D-FOAM/2022.  
Not applicable.  
Data availability Statement: Data are contained within the article.  
Author [PERSON] is supported by the Foundation for Polish Science (FNP).  
The authors declare no conflicts of interest.