Additive manufacturing (also known as 3D printing) of concrete is able to enlarge the freedom of design and the building rate. At the same time, it reduces manual labor and resource consumption during construction. So far, however, the CO2 emissions related to additively manufactured concrete are–due to their high clinker content–rather high compared to conventional concrete mixes. Thus, in order to allow for a more sustainable construction with concrete, the replacement of the clinker with supplementary cementitious materials (SCMs) is essential, as the clinker is responsible for the major part of the CO2 emissions related to concrete production. For the use in conventional building techniques, the combination of calcined clays (CC) and limestone powder (LP) as partial replacement of clinker in concrete has shown promising results with regard to compressive strength and durability. However, the replacement of clinker by LP and CC affects the hydration rate of the cementitious binder and the workability of the concrete. To meet the requirements for 3D printing (i.e. pumpability and buildability) with concrete mixes using these composite binders adjustments of the dosages of the SCMs and special admixtures are needed. In this study, we want to investigate the impact of varying LP and CC dosages on the reactivity, including synergetic effects, and the rheological properties of selected model cements. Monitoring early hydration and the hydration phases forming enables us to assess the critical phases in 3D printing. By using R3-tests, calorimetry, XRD, TGA and rotational rheometry, we compare the suitability of different binder compositions for concrete extrusion and determine maximum building rates. Furthermore, the addition of admixtures at the concrete scale enables us to control and adjust the rheology as a function of time and thus to design the material for 3D printing. With the aim to serve as a proof-of-concept, the results are consequently validated by lab-scale demonstrators. We anticipate this study to be a starting point for further research within this field, in order to combine the material reduction enabled by additive manufacturing and the improvement of concrete mix designs in terms of related CO2 emissions by the replacement of clinker with SCMs.     «

Additive manufacturing (also known as 3D printing) of concrete is able to enlarge the freedom of design and the building rate. At the same time, it reduces manual labor and resource consumption during construction. So far, however, the CO2 emissions related to additively manufactured concrete are–due to their high clinker content–rather high compared to conventional concrete mixes. Thus, in order to allow for a more sustainable construction with concrete, the replacement of the clinker with sup...     »