Method of Optimisation for Ambient Temperature Cured Sustainable Geopolymers for 3D Printing Construction Applications

Abstract

Since the initial introduction of geopolymers, these materials have been characterised as environmentally-friendly sustainable substitutes for ordinary Portland cement (OPC). There is a routine increase in the application of geopolymers, especially in advanced technologies. Because of its better rheological characteristics compared to OPC, geopolymers are appropriate materials for extrusion-based 3D printing technologies. This paper focuses on the optimisation of an ambient temperature cured geopolymer for 3D printing construction applications. The effects of mixture parameters, including the type of hydroxide solution (HS), the type of silicate solution (SS) and the mass ratio of SS to HS on the workability, extrudability, shape retention ability and mechanical performance of different geopolymer mixtures were investigated. Accordingly, an optimum mixture was identified for geopolymers cured at ambient temperatures. Mechanical properties of the optimised mixture, including flexural and compressive strengths, were measured in different directions with respect to the printed layers. Further, uniaxial tension tests were also conducted on the optimised mixture to measure its interlayer bond strength. The results showed that among the activators investigated, the sodium-based activator composed of sodium hydroxide and sodium silicate solutions, with a SiO2/Na2O ratio of 3.22, was the most effective activator, providing appropriate workability and extrudability, along with reasonable strength and a high shape retention ability. The acquired mechanical properties exhibited anisotropic behaviour in different testing direction. The strength of the interlayer bond was found to be adequate to avoid interfacial shear failure.

Development of a 3D-Printable Ultra-High Performance Fiber-Reinforced Concrete for Digital Construction

“…It should be noted that the observed significantly higher inter-layer bond strength in the printed UHPFRC composite as compared to that of the printed UHPFRC matrix shall be investigated comprehensively in our future research. The inter-layer bond strength of the UHPFRC observed in this study is significantly higher than the values reported in the literature for normal strength concrete [35], geopolymer concrete [8,36], fiber- reinforced concrete [12], fiber-reinforced geopolymer concrete [13] due to the superior mechanical properties of the UHPFRC. Figure 19 shows the apparent porosities of the UHPFRC matrix and composite.…”

“…including printing configurations and printing materials [30]. Similar anisotropic behavior has been reported in the literature for normal strength concrete [7], high performance concrete [12] and geopolymers [8,13].…”

“…Each of the five layers was at least 250 mm long with a cross-section of 30 mm (W) × 15 mm (H) extruded using the small-scale printer with a piston type extruder (described in section 3.2). Similar approaches were used elsewhere [8,11] to evaluate extrudability.…”

“…At the same time, the material should set quickly to withstand the weight of the subsequent layers deposited above [6]. Few printable concretes with the above combination of properties have been reported in the literature -for example, normal strength concrete [7], geopolymer concrete [8,9], earth-based mortar [10], and high-performance fiber-reinforced cementitious composite (HPFRCC) [11,12]. These materials were designed for a specific printer with particular printing configurations (nozzle type and size, flow rate, pumping specifications, etc.)…”

Performance Indicators of Printed Construction Materials: a Durability-Based Approach

“…The AFGC guide summarizes the different methods available for determining durability indicators as shown in Table 1. Example of research projects on tensile strength of 3D printed materials for construction [22][23][24]. The concept of printability was also investigated in literature research, and linked to some indicators, such as the shear rate, viscosity, and thixotropy [6,25].…”