Advancing the Field of 3D Concrete Printing by Exploring the Use of Eco-Friendly Mortars (2025-06)¶

Employing eco-friendly mortar for 3D concrete printing offers multiple benefits that align with environmental protection, cost reduction, and enhancing the longevity of the constructed structure. This type of mortar typically incorporates by-products from industrial processes, such as waste fly ash (WFA) or bottom ash (BA), as substitutes for traditional sand. WFA, a finer powder-like substance with the ability to undergo a pozzolanic reaction with lime and water, forms additional binding, adding benefits such as ease of mixing, lowered water consumption, and long-term strength. Its fine granularity can also lead to a more compact material structure and potentially superior structural strengths. Nonetheless, the composition of WFA can vary widely, which may influence the uniformity and reliability of the mortar’s characteristics. Excessive amounts of WFA might slow down the hardening process, posing challenges for the swift stacking (i.e., layer by layer construction) necessary in 3D printing. On the other hand, BA stands out due to its relatively larger grain size. It has the capacity to enhance the mortar’s resistance to heat and often entails less pre-use treatment than WFA. The inconsistent particle shape of BA, though, may lead to reduced mix fluidity, possibly necessitating more water or substances to modify the mixture for printing. In terms of sustainability, WFA and BA both limit the consumption of unprocessed resources and contribute to a decrease in overall greenhouse gas emissions from concrete manufacturing. Due to its reactive properties and minute particle size, WFA tends to produce a more robust and long-lasting mortar. When judged solely on strength, WFA tends to outperform due to its material-enhancing pozzolanic activities suitable for the demands of 3D-printed constructions. Nevertheless, the best option between WFA and BA depends on the application’s specific requirements, resource accessibility, financial considerations, and ecological policies. If a strong early development of strength is required to enable quick, undistorted layering, WFA would be the preferred option. Conversely, BA could be the preferred material if printing requires a rougher aggregate texture or if broader sustainability objectives demand a more comprehensive waste management approach. Both waste products contribute positively to the eco-friendliness of 3D-printed concrete structures.