article · Construction and Building Materials
Metakaolin-based geopolymer concrete offers an alternative to Portland cement for 3D printing, but adoption has been limited by slow setting times and uncertain durability. This research evaluates standard metakaolin geopolymer concrete alongside a blend modified with a five percent slag addition, comparing printed specimens to traditional mould-cast samples. Adding slag substantially improved printing performance, reducing final setting times from seventeen hours to four hours and increasing buildability from 27 to 42 printed layers. At twenty-eight days, the slag-modified material displayed higher compressive and flexural strength, alongside reduced water absorption and drying shrinkage. Computed tomography revealed that printed geopolymer achieved a more compact pore structure and fewer large voids than cast concrete, though porosity varied across layer interfaces. Overall, durability indicators show that the printed material performs comparably to conventional cement concrete.
Construction 3D printing requires materials that set rapidly and resist environmental degradation without relying on carbon-intensive Portland cement. Demonstrating that slag-modified geopolymer concrete sets faster, holds its shape over dozens of layers, and matches conventional concrete in permeability supports the development of lower-carbon alternatives for automated construction.
This formulation could be used by automated construction companies and concrete manufacturers seeking low-carbon materials for additive manufacturing. By addressing slow setting times and demonstrating durability comparable to Portland cement, the formulation overcomes key operational barriers. The research remains at an applied, laboratory-tested stage, requiring full-scale structural testing before direct commercial deployment.
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An alternative to Portland cement concrete is metakaolin (MK)-based digitally fabricated geopolymer concrete. However, global adoption is sparse due to the prolonged setting time of a two-part geopolymer concrete (GPC) system and the uncertain long-term durability properties. The durability and pore structure of the MK-based 3DPGPC (M1) and slag-modified MK-based 3DPGPC (M2) are examined and juxtaposed with mould-cast specimens. Firstly, the fresh properties, rheological behaviour, compressive and flexural strength of 3DPGPC and cast specimens were characterised. Thereafter, the durability and pore structure are investigated by examining the drying shrinkage, water absorption, capillary and gel porosity, and oxygen permeability index (OPI) and X-ray computed tomography (X-CT) analysis. A 5% slag inclusion reduced workability and final setting time from 17 hours in M1 to 4 hours in M2. Also, slag inclusion increased the initial static and dynamic yield stresses by 0.1 and 2%, respectively, resulting in an increase in buildability from 27 of 42 layers. At the 28-day curing age, the average compressive strength of M2–3DPGPC is 11 and 21% higher than M1–3DPGPC in D1 and D3 specimens, while the flexural strength is 33 and 28% higher, respectively. Drying shrinkage and water absorption are mitigated with slag inclusion, and the OPI compares with OPC concrete. Specimens cored along the printing direction (D3) are less permeable compared to disc specimens’ core in the perpendicular to the printing direction (D1). The M1 and M2–3DPGPC specimens contain lower average CT scan macro pores of 2.98 and 1.81% in comparison to the mould-cast specimens having 4.48 and 4.07%. The porosity is position-dependent in 3DPGPC due to the presence of more voids at the interlayer region. 3DPGPC specimens depicted a more compact pore structure in the range of 0.1–1.7 mm, whereas pores in mould-cast are in the range of 0.1–2.5 mm. The durability index tests indicate that 3DPGPC is a potentially durable material.
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DOI: 10.1016/j.conbuildmat.2024.135847
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