Three-dimensional (3D) concrete printing is a revolutionary technology in the construction industry. Here we show that climate-positive biochar is a carbon-negative additive for decreasing the carbon footprint of 3D printable concrete, while enhancing its performance. As biochar enhanced the effective water-to-binder ratio and served as a substrate for hydrates, the polymerization of hydrates increased in biochar-augmented concrete. The incorporation of 2 wt% biochar enhanced the structural build-up rate of fresh mixtures by 22% at 40 min. The 3D printing tests demonstrated that biochar improved the pumpability and extrudability of mixtures at the initial 20 min, and enhanced the buildability of 3D printed concretes at the after 40 min. The carbon footprint of 3D printable concrete was reduced by 8.3% through incorporating 2 wt% biochar. Thus, we developed a desirable biochar-augmented mixture for 3D concrete printing. Future field-scale application will make substantial contribution to the attainment of carbon emission reduction.

The creation of concrete shells from customized prefabricated modules is a novel approach that facilitates the construction of free-form surfaces considerably. In the framework of the Adaptive Concrete Diamond Construction (ACDC) project at TU Dresden, a material for 3D printing of the outer contours of such modules has been developed based on the principles of Strain Hardening Cementitious Composite (SHCC). In addition to its high ductility, the required material must also be suitable for 3D printing while enabling the achievement of high geometric accuracy in the manufacture of the modules. To gain the required performance, cellulose ether and starch ether were used specifically to extend the open time, for a longer period of maintaining initial workability, as well as for enhancing shape stability and surface quality. An extensive experimental program was carried out to evaluate the outcomes of the material modifications, including flow table tests, water retention tests, and several specific tests to determine the adhesiveness of the fresh SHCC. For hardened SHCC, surface roughness was assessed using a laser 3D scanner in addition to testing its mechanical properties.

3D concrete printing (3DCP) has all the chances to become the future of the construction industry, but this technology is not yet widely applicable. One of the main challenges still to be mastered is the difficulty of reinforcing printed structures. At this point, many reinforcement strategies have already been proposed, which are fully or partially capable of solving the problem. This publication provides first an overview of existing reinforcement strategies, classified according to the time of reinforcement introduction: before, during, or after 3D printing. Then the authors present the approaches developed at the TU Dresden and provide readers with information on new methods that still are in the development stage.