Traditional Ordinary Portland cement (OPC)-based concrete consumes large quantities of natural resources for its production, which is highly energy intensive and has high CO2 emission. Therefore, development of the geopolymer concrete, based on use of industrial byproducts, can provide an environmentally friendly and low-carbon alternative to OPC concrete. Geopolymer concrete characterized with low permeability, mechanical properties and excellent heat resistance, has been receiving increasing attention in building industry nowadays. However, there are some challenges regarding the structural application, such as adjusting the fast setting time, tailoring the workability, and controlling the shrinkage of blast furnace slag based geopolymer concrete. The main aim of this study is to design and optimize geopolymer concrete mixture for manufacturing a reinforced cantilever bench. This is accomplished by testing rheological and mechanical properties, and the drying shrinkage of geopolymer concrete. The geopolymer binder consisted of fly ash (FA), blast furnace slag (BFS) and activator. The activator was made by mixing sodium hydroxide and waterglass solutions. The prolonged setting time of the studied mixture was achieved by using proper type and amount of chemical admixture in order to achieve enough time for casting but not to affect mechanical properties of the hardened concrete. The compressive strength, elastic modulus, flexural strength, drying shrinkage and the effects of curing duration were evaluated. The application of the optimized geopolymer mixture in the complex structural element such as cantilever bench has shown promising results. Such small scale application and low risk project was suitable to gain the experience and confidence with this innovative type of material for which no international codes or regulations are available. Furthermore, this project has proven to be encouraging for further upscaling of geopolymer concrete for larger scale structural applications, like bridges and/or other structural elements in the building industry.

In spite of the fact that there are many advantages of alkali activated materials (also called geopolymers) over the cement-based materials, geopolymer concrete has been used in the past for construction purposes on a very limited level. Among the many advantages of geopolymers compared with the cement-based materials is less CO2 emission, it uses byproducts as a binder, less energy consumption during its production, more durable as a material, fast setting time and high strength development. This work is an attempt to exert some light on the usability and applicability of geopolymers in the field of construction with concentration on its use in the 3D printing. The main aim of this study is to propose a design methodology for geopolymer paste mixture to be used in 3D printing process. For achieving this goal, one paste mixture design was selected among six ones on the bases of longer workability/flowability, suitable extrudability and specific setting time. These six designs have different binder ratios. The selected mixture design, named S20, was tested further to find out its suitability for 3D printing process. This S20 mixture was tested on compressive strength, setting time, rheological properties, open time, buildability and 28 days tensile bonding strength of two layers. To find the best suitable design, modifications were done on the S20 mixture by changing the ratios between the used alkaline solutions Na2SiO3 and NaOH (0.25 was selected). These alkaline solutions played a major role in delaying the initial setting time for rheological tests (90 minutes were selected) and the extrudability for the 3D printing process. Another factor for the best design is the Acti-gel as an additive. This additive has a direct link with the buildability, extrudability and viscosity when added with different percentages. The best selected percentage of the Acti-gel was 0.75% for this mixture design. The open time and the 28 days tensile bonding strength tests were selected to be 33 minutes and 1.32 MPa respectively. Comparing the measured plastic viscosity to the open time test, the extrudability of the mixture is not anymore valid beyond 8.8 Pa.s plastic viscosity. This short open time of 33 minutes for such geopolymer mixture design needs a fast-performing 3D printer. This might help in achieving construction projects within short time.