Abstract

3D-printing could offer substantial benefits to the construction industry including the fabrication of customized/bespoke components, eliminating formwork, and reducing material waste. Despite these advantages, control of the pumpability, extrudability, and buildability of 3D-printed concrete (3DPC) remains challenging. This study demonstrates how the use of fly ash (FA) enables enhanced thermal stiffening, and rapid alkali-activation in the presence of portlandite (Ca(OH)2, CH). In general, blends of CH and FA exhibit less structural build-up at low temperatures, but upon reaching a trigger temperature of 75 °C, these blends achieve rapid stiffening, at rates of ∼800 Pa/s. The rapid stiffening arises from the flocculation of CH particles, and the onset of the pozzolanic/alkali-activation reactions between CH and FA, resulting in the formation of C-A-S-H and N-A-S-H during stiffening. Careful selection of the FA-CH blend ratio, which displays an optimum at ∼20 mass % CH, enables the composition of cement-free formulations for 3D-printing applications. The outcomes have important implications on alternate feedstock pathways to compose carbon-efficient formulations for construction.

Department(s)

Materials Science and Engineering

Second Department

Civil, Architectural and Environmental Engineering

Comments

Advanced Research Projects Agency - Energy, Grant 1922167

Keywords and Phrases

3D printing concrete; Alkaline activation; Fly ash; Portlandite; Stiffening control

International Standard Serial Number (ISSN)

0958-9465

Document Type

Article - Journal

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2025 Elsevier, All rights reserved.

Publication Date

01 Feb 2025

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