3D Printing of Concrete-Geopolymer Hybrids

Abstract

In recent years, 3D concrete printing technology has been developing dynamically. Intensive research is still being carried out on the composition of the materials dedicated to innovative 3D printing solutions. Here, for the first time, concrete-geopolymer hybrids produced with 3D printing technology and dedicated environmentally friendly building construction are presented. The concrete-geopolymer hybrids consisting of 95% concrete and 5% geopolymer based on fly ash or metakaolin were compared to standard concrete. Moreover, 3D printed samples were compared with the samples of the same composition but prepared by the conventional method of casting into molds. The phase composition, water leachability, compressive, and flexural strength in the parallel and perpendicular directions to the printing direction, and fire resistance followed by compressive strength were evaluated. Concrete-geopolymer hybrids were shown to contain a lower content of hazardous compounds in leaches than concrete samples. The concentration of toxic metals did not exceed the limit values indicated in the Council Decision 2003/33/EC; therefore, the materials were classified as environmentally neutral. The different forms of Si/Al in fly ash and metakaolin resulted in the various potentials for geopolymerization processes, and finally influenced the densification of the hybrids and the potential for immobilization of toxic elements. Although the compressive strength of concrete was approximately 40% higher for cast samples than for 3D printed ones, for the hybrids, the trend was the opposite. The addition of fly ash to concrete resulted in a 20% higher compressive strength compared to an analogous hybrid containing the addition of metakaolin. The compressive strength was 7–10% higher provided the samples were tested in the parallel direction to the Z-axis of the printout. The sample compressive strength of 24–43 MPa decreased to 8–19 MPa after the fire resistance tests as a result of moisture evaporation, weight loss, thermal deformation, and crack development. Importantly, the residual compressive strength of the hybrid samples was 1.5- to 2- fold higher than the concrete samples. Therefore, it can be concluded that the addition of geopolymer to the concrete improved the fire resistance of the samples.

A Scientometric Review on Mapping Research Knowledge for 3D Printing Concrete

“…It is revealed from the keyword analysis that 3D printing concrete has been mainly explored in terms of its mechanical and rheological properties [ 72 , 73 , 74 , 75 , 76 ]. Furthermore, 3D printing is also researched for manufacturing geopolymer concrete [ 76 , 77 , 78 ]. Three-dimensional printing has various benefits upon utilization as concrete.…”

A review of concrete 3D printed structural members

“…The decrease in strength is logarithmic for up to the first 5 min of gap time, and then the loss in strength is minimal (Tay et al, 2019b). The addition of flyash to a hybrid mix of 95% concrete and 5% geopolymer based on fly ash or metakaolin was found to increase the compressive strength of the mix by 20% (Ziejewska et al, 2022). But the cast concrete elements showed 40% higher compressive strength than printed elements.…”

Investigation of Mechanical Properties and Microstructure of Construction- and Demolition-Waste-Based Geopolymers

“…This type of fly ash contains many spherical particles [24]. Metakaolin contains many silicon oxides and aluminum oxides [25][26][27]. Qualitative analysis of the elemental composition of the examined surfaces showed elements in clay brick and concrete waste (rubble) such as oxygen, silicon, aluminum, iron and-in the case of concrete waste-calcium.…”