Impact of the pumping process on the properties of lightweight concrete

The distinctive characteristic of lightweight concrete lies in its combination of load-bearing and insulating properties. In order to produce this material using modern manufacturing processes such as spraying or printing, certain hurdles must be overcome. For example, a multi-component concrete has to be developed that is not only optimized concerning its rheological properties, but also takes into account the influence of the pumping process on its characteristics. Especially concerning the objective of a heat-insulating concrete, the pumping process has a decisive influence on the range of properties. For pumping applications, the system technology limits the largest grain size of the concrete mixture. This leads to very fine concretes or mortars, which react sensitively to the applied pressure. The occurring pressure-induced compaction leads to an increase in strength due to an increment in bulk density and the damage of lightweight aggregates. This, in turn, affects the thermal conductivity of the material. Based on a lightweight concrete developed at the Institute of Construction Materials at the University of Stuttgart, these challenges are highlighted and discussed in the following paper. The concrete was utilized for pumping and spraying experiments at a testing facility in collaboration with the Institute for System Dynamics, and the resulting thermal properties were examined at the Material Testing Institute, University of Stuttgart. Furthermore, the interaction between the employed system technology and the properties of the pumped lightweight concrete, such as consistency, strength, bulk density, and thermal conductivity was examined and analyzed. Results showed that the concrete properties reacted sensitively to different configuration setups of the pumping system and the conveyance line. Hence, a clear interdependency between the mix design and the employed machinery could be observed and has to be considered in future endeavours.