Effect of Cement-Type and Limestone-Powder-Content on Extrudability of Lightweight Concrete (2020-07)¶

Extruded lightweight aggregate concrete (LAC) enables to unite static and building physics properties within monolithic structures. Besides, material demand can be reduced according to necessity. However, the contradicting requirements in extrusion for pumpability and buildability are intensified compared to normal concrete due to the change of LAC fresh properties during pumping. This paper focusses on the effect of cement type and amount of limestone powder on the pumpability of LAC at comparable buildability. We show that the pumping performance enhances with increasing limestone powder content. Furthermore, we find that the increase in density during the pumping process is affected by the water retention of the material, which in turn correlates with the limestone powder content. The resulting strength can thus be consciously improved. The amount of limestone powder has only a minor effect on structural build-up and static yield stress and thus, on buildability. However, we find a general strong increase in static yield stress during pumping of LAC, which further facilitates the buildability in addition to the positive effect of the low density of LAC resulting in reduced weight loads to bear during extrusion. Another advantage is that reasonable replacement of cement by limestone powder leads to less drying shrinkage without significantly reducing the strength. Concluding, the requirements for extrusion of LAC – for both pumpability as well as buildability – can be fulfilled and adjusted to necessity by partly substitution of the cement with limestone powder.