**2. Past Studies**

The constructability and mechanical properties of 3D printed concrete can be seen as the most significant issues at the moment. Therefore, many researchers have concentrated on mixture designs or the strength of 3D printed concrete. Paul et al. [7] introduced a

**Citation:** Arslan, V.; Dogan, Z. Three-Dimensional, Printable Paving Stone: A Preliminary Study. *Mater. Proc.* **2023**, *13*, 18. https://doi.org/ 10.3390/materproc2023013018

Academic Editors: Katarzyna Mróz, Tomasz Tracz, Tomasz Zdeb and Izabela Hager

Published: 14 February 2023

**Copyright:** © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

mixing ratio for 3D printing using cement, and the 28 day compressive strength of the produced concrete was measured, 36–57 MPa, and the bending strength was 10 MPa. Le et al. [8] designed a high-strength fiber-reinforced concrete with a compressive strength of 92 MPa and a flexural strength of 11 MPa. Ma et al. [5] utilized copper waste to develop a printable cementitious mix with good workability and 50 MPa compressive strength. Marais et al. [9] measured the thermal performance of 3D printed lightweight foam concrete and high-performance concrete elements. Ting et al. [10] analyzed the effects of the glass-to-binder ratio, fineness modulus, and nano-clay content on the extrudability and constructability of concrete. Gomaa et al. [11] and Alqenaee and Memari [3] developed a printable clay-based cob mix design in which the components have sufficient strength for construction. Hojati et al. [12] investigated ways to replace cement in the mixtures with other cementitious alternatives and to design sustainable mixtures suitable for 3D printing.

Most of the current literature in this field is focused on printing cement-based concrete. They aimed to analyze concrete mixture designs by utilizing different materials. In addition, most of the 3D printing research has been carried out at a laboratory scale. However, there are no studies in the literature on the mechanical or design properties of the 3D printed concrete paving stones. Concrete paving stones are popular around the world [13]. They are widely used in sidewalks, urban roads, etc. The most common grade of concrete paving stones is interlocking pacing stones [14]. Compared with concrete and asphalt pavements, interlocking paving stones offer numerous advantages such as minimal maintenance and economic benefits. Therefore, it can be stated that concrete paving stones deserve enough attention to be produced by utilizing advanced technology. The aim of this study was to develop a new method to produce 3D printed concrete paving stones. As a result, to the best of our knowledge, the present study is the first attempt to design a mixture for 3D printed concrete paving stones.
