Rheological Properties of Metakaolin-Based Geopolymers for Three-Dimensional Printing of Structures

The use of geopolymers as binders in three-dimensional (3D) printing processes has great potential due to their fast strength development, high durability, and lower environmental impact compared to portland cement matrixes. Metakaolin-based geopolymers are a viable solution for a Brazilian-based additive manufacturing application due to the widespread availability of kaolinitic clays, which minimizes transportation costs and reduces the associated CO₂ emissions. Nevertheless, it is necessary to identify the rheological behavior of this type of binder to evaluate its suitability in an extrusion process. This work presents a calorimetric and rheological characterization of pastes and mortars produced with a metakaolin-based geopolymer as the binder, exploring the influence of the nature of the activator, the water-solids ratio, and the aggregate on the rheological parameters that describe a 3D printing process, and on their evolution in time. Two types of metakaolin-based geopolymers were characterized: one activated with a mixture of potassium hydroxide (KOH) and potassium silicate (K₂SiO₃), and one activated with a mixture of sodium hydroxide (NaOH) and sodium silicate (NaSiO₃). The water-solids ratio of each geopolymer paste varied between 0.40 and 0.50, and natural sand was added in a 40% volume per volume percent (v/v) fixed proportion to produce mortars. The yield stress of each sample was measured after different resting times using a vane rheometer. Isothermal heat flow curves were acquired in the same time scale to connect the reaction kinetics to the rheological measurements. The water-solids ratio and the presence of aggregate are able to modify the initial yield stress and the thixotropic buildup of the matrix. The sodium-based activator is correlated with a rapid structural buildup because of faster precursor dissolution and gel formation. The presence of sand increased the shear stress values and generated stiffer systems compared to the pure geopolymer pastes.

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    • Abstract reprinted with permission from the American Concrete Institute.
  • Authors:
    • Paiva, M D M
    • Rocha, L D Fonseca
    • Fernandez, L I Castrillon
    • Filho, R D Toledo
    • Silva, E C C M
    • Neumann, R
    • Mendoza Reales, O A
  • Publication Date: 2021-11

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  • English

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  • Accession Number: 01851723
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Jul 18 2022 11:25AM