Effect of thixotropy enhancing agents on extrudability of lightweight concrete

Lightweight concrete enables the production of monolithic exterior wall components with sufficient thermal insulation even under Central European climatic conditions. If, in addition, additive manufacturing by extrusion is used for production, these components can be further improved by installing air chambers to increase thermal insulation of the component or varying wall thicknesses to reduce material demand. Furthermore, it is beneficial to use lightweight aggregate concrete (LAC) instead of e.g. aerated concrete due to its higher robustness with regard to the pumping process. Nevertheless, the water absorption of the lightweight aggregates changes the behaviour of the fresh concrete compared to normal concrete, especially taking into account the pumping pressure. In previous studies we were able to show that materials with a lower viscosity and a higher proportion of limestone powder are better pumpable. However, for extrusion it is necessary that the deposited strands have as good green strength as possible in order to bear their own weight and the weight of subsequent layers. In order to meet both contracting requirements, this paper focuses on the simultaneous fulfilment of pumpability and green strength requirements for LAC through the use of thixotropy enhancing agents. Based on rheological investigations, a correlation between the structural build-up rate Athix and the achievable component height (number of layers) was investigated. Simultaneously, dynamic rheological examinations (evaluated by Herschel Bulkley) were carried out. This provided information on the shear rate dependent behaviour of the materials. The pumping behaviour (in an eccentric screw mortar pump) was analysed taking those properties into consideration. Despite high viscosities at rest, the thixotropy enhancing agents allowed the development of well pumpable mixtures with higher green strength than the reference material. With our results, we contribute to the development of a lightweight, 3D printable concrete.      «

Lightweight concrete enables the production of monolithic exterior wall components with sufficient thermal insulation even under Central European climatic conditions. If, in addition, additive manufacturing by extrusion is used for production, these components can be further improved by installing air chambers to increase thermal insulation of the component or varying wall thicknesses to reduce material demand. Furthermore, it is beneficial to use lightweight aggregate concrete (LAC) instead of...     »