This thesis presents a proof-of-concept study on using biopolymer binders as cement replacement in 3D printing mortars to enable advanced flow properties and therefore, paving the way for the realization of highly optimized structures for minimum material consumption.
The construction sector is one of biggest polluters and emitters of CO2 worldwide. Therefore, recent research focuses on minimization of waste and emissions, and reducing, reusing and recycling. 3D printing of concrete shows the potential of increasing the productivity of the sector and, at the same time; enhancing its environmental performance by enabling the realization of optimized structures with a minimum of material use. In addition, no formwork is required for building, which significantly decreases the amount of waste for concrete structures.
Since the printing of concrete materials requires advanced rheological properties that let the material stiffen rapidly after extrusion, the printing of cementitious materials is usually connected with the use of a high share of Portland cement, presenting a drawback in its environmental performance. Its slow setting characteristics limit the placing of material to a, broadly seen, vertical build up. This restrains the possibilities of minimizing material use by realization of optimized structures.
This research project therefore investigates the potential of replacing the cementitious binders with biologically-based materials. The research focuses on natural polymers, which usually use low extraction temperatures. Some of the natural polymers showed thermoreversible properties, both in pure form, as well as in a concrete composite with mineral aggregates. This allowed for the use
within a temperature-controlled print-head and rapid stiffening after extrusion.
14 natural polymers are evaluated for the use as binder in printing concrete. Both polysaccharides and proteins prove elevated potential for the application. The materials are assessed for their mechanical strength, and rheological- and printing properties. Within a composite of biopolymer and mineral aggregates, gelatin showed the highest mean compression strength (37MPa and 59.5MPa, respectively for mammal and cold water fish gelatin), as well as the largest yield strength development in the fresh state under cooling from 50-20ºC (0.1kPa-106kPa).
The research proves that a concrete composite from biopolymers and mineral aggregates can be used as structural material and as filament in a temperature-controlled extrusion process. Its mechanical strength could be measured in the same order of magnitude as for cementitious printing materials. Its temperature controlled rheological stiffening as fresh material made it possible to print advanced free-form constructions up to an unsupported inclination of 80º. This enables the construction of freely shaped geometries and highly optimized structures without the use of CO2 intensive Portland cement.