*4.2. Results of the Compressive Strength Test*

The 3D printed paving stones are also required to meet specific mechanical strength parameters in accordance with TS EN 12390-3. The compressive strength of the 3D printed materials was measured 1, 7, and 28 day ages to monitor the strength development over time. To conduct a compressive strength test, the printed samples were placed in the moist cabinet for proper curing. After that, the mechanical properties of hardened 3D printed paving stones were measured according to TS EN 12390-3.

Although the primary findings of the study show promising results to obtain suitable cement-based mortar for 3D printing, the 3D printing process of concrete paving stones was successfully completed. Therefore, the immature results of the compressive strength tests have not been presented in this paper. It should be noted that there is no study which revealed the mechanical properties of 3D printed concrete paving stones. Therefore, the results of the study will be compared to compressive strength of the paving stones produced with conventional construction methods.

### **5. Conclusions**

The goal of this study was to produce 3D printed concrete paving stones. To do this, a unique 3D printer was developed, and a digitally controlled printing process which can build 3D printed paving stones without formwork was designed. As soon as the suitable cement-based mortar was obtained, the 3D printed paving stones were produced. Thereafter, the mechanical results of compressive strength tests were published. Threedimensional printing could be used instead of a conventional production machines to achieve real, rapid manufacturing. Further research will be conducted to assess the structural behavior of 3D printed construction materials under the provided conditions to improve the mechanical and architectural properties of these materials.

**Author Contributions:** Conceptualization, V.A. and Z.D.; methodology, V.A.; software, Z.D. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by Zonguldak Bulent Ecevit University Scientific Research Projects (BAP) Coordination Unit, grant number 2022-37891158-01.

**Institutional Review Board Statement:** Study did not require approval.

**Informed Consent Statement:** We did not need any consent in the study.

**Data Availability Statement:** The study did not report any data.

**Acknowledgments:** The authors thank the technical support provided by Zonguldak Bulent Ecevit University. The publication cost of this paper was covered by the funds of the Polish National Agency for Academic Exchange (NAWA): "MATBUD'2023—Developing international scientific cooperation in the field of building materials engineering" BPI/WTP/2021/1/00002, MATBUD'2023.

**Conflicts of Interest:** The authors declare no conflict of interest.
