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July 10, 2024

Eco-Friendly 3D-Printed Concrete Innovations

A recent article published in Materials presented three eco-friendly alternatives for creating artificial aggregates (AAs) including organic hemp shives (HSs), pyrolyzed coal (charcoal), and solid waste incinerator bottom slag (BS). The usage of the aggregates prepared from these was investigated in 3D-printed concrete (3DPC).

Eco-Friendly 3D-Printed Concrete Innovations
Study: Eco-Friendly 3D-Printed Concrete Innovations. Image Credit: sergey kolesnikov /Shutterstock.com


Using sustainable building materials has become necessary to achieve the 2050 goal of a carbon-neutral building industry. Consequently, 3DPC is prepared using sustainable mixing materials such as rice husk ash, marble dust, and burnt ashes from municipal solid waste incinerators.

Widely popular cogeneration power plants generate large amounts of waste and BS, the accumulation of which in landfills poses significant waste management challenges. Alternatively, BS is applicable as a replacement in mortar and recycled fine/coarse lightweight aggregate in green concrete. Moreover, granules made from BS can replace all of the natural gravel in concrete.

Among different agricultural organic wastes used in 3DPC manufacturing, hemp is the most popular. It is well known for its insulating properties and environmental friendliness.

Another frequently used organic material in grilling today is charcoal. Its lightweight, insulating, and absorption properties are attractive in lightweight concrete or concrete bricks as a sand replacement. Thus, this study combined AAs made from, organic HSs and charcoal, and BS to produce eco-friendly 3DPC.


The main binder materials for 3DPC production included ordinary Portland cement (OPC; 30%). hydrated lime (HL; 2%), and burnt fly ash (BFA; 9%). Additionally, differing amounts of natural aggregate (55% to 41%) and sand were used in 3DPC apart from BS, HS, and charcoal AAs.

Before granulation, HS and charcoal were milled in a cutting mill. The size of all AAs was ensured to be less than 4 mm by sieving. Moreover, sugars present in HS could affect the properties of the concrete. Thus, a sugar refractometer was used for measuring the sucrose content in investigated organic components.

Agitation granulation was performed to produce AAs with nine different compositions mechanically. The granule diameter was ensured to be under 4 mm for comparison with the natural aggregate-containing 3DPC. From each type of AA, 10 most-rounded granules were selected and heated at 105 °C until constant weight was reached.

Subsequently, a thin layer of wax was applied to each granule and weighed using hydrostatic scales. Additionally, the bulk density of the granules was measured through free fall in a one-liter bowl. Next, the strength of different granules was compared in 3DPC composites in the fresh state.

Energy dispersive spectroscopy (EDS) and scanning electron microscopy (SEM) were used to investigate the microscopic structure of AAs and 3DPC elements. The flow of newly mixed composites was assessed following the standard flow table test. Additionally, the flexural and compressive strength and freeze-thaw resistance of the 3DPC composites were examined by fabricating prism samples.

Results and Discussion

The parameters for mechanical agitation granulation were optimized to obtain granules acceptable for printing. Approximately 80% of the total mass of these granules was achieved with slow water spray and 35 rounds per minute rotation speed.

The SEM images of AAs revealed absorption of the moist and dry mass of the binders in both organic materials, forming spherical or round granules. In contrast to charcoal, HS AAs became more brittle after sieving with weaker bonding with the binder layer. However, loose granulated BS exhibited the most favorable strength of 3DPC.

Widely used burnt oil shale ash and lime exhibited weaker strength than the AAs proposed in this study. In addition, the concrete with BS had the same performance as the reference concrete comprising natural aggregates. Furthermore, the reference mix performed poorly in the deformation tests compared to the 3DPC compositions containing BS and HS granules. This was attributed to the BS’s high stability and the fibrous nature of HS.

Irrespective of the relative strength, these results exhibit the benefit of granulation of materials to obtain particles of similar dimensions, making them appropriate for 3D printing. Additionally, the processed organic aggregates made 3DPC more stable (smaller deformations) than the non-granulated organic aggregates.

Furthermore, the specimens without granulated organic AAs exhibited inferior accession (only 2.2-2.7%) in the freeze-thaw resistance test. The deformation graphic depicted that the expansion regulator could regulate deformations in concrete only when the organic components were granulated.  Otherwise, the regulator slows the reactivity of organic materials in a concrete mix.


Overall, the researchers successfully demonstrated the potential of mechanically-produced AAs in manufacturing low-carbon 3DPC with enhanced properties. Specifically, the lightweight aggregates of HS, charcoal, and BS could constitute up to 14 wt.% in concrete without compromising performance.

The comparison between 3DPC comprising unprocessed and granulated HS, charcoal, and BS after 28 days of curing indicated the high performance of the latter. However, analysis of the granulation process indicated that organic materials like HS need to be safeguarded from the negative effects of humid environments.

Journal Reference

Butkutė, K., Vaitkevičius, V., & Adomaitytė, F. (2024). Eco-Friendly 3D-Printed Concrete Made with Waste and Organic Artificial Aggregates. Materials17(13), 3290. DOI: 10.3390/ma17133290, https://www.mdpi.com/1996-1944/17/13/3290

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