As a result, several process steps (spraying, extrusion, endless fibre
reinforcement) can be implemented in an automated process with the
spray-extrusion multi-tool nozzle without changing the tool or position
of the component. In this publication, reinforcement with endless fibres
for better comparability was not used.
2.2. Materials
The material composition bases on a complex of technological
restrictions and requirements of the precast concrete element. For
example, a high-strength and durable fine-grained concrete with
short-fibre reinforcement was developed, so these could be processed
using spraying and extrusion. When characterizing the material, the
green strength as well as the material and component-related strength
and failure behaviour under compressive and flexural stress were of
particular interest. In addition to high strength in the use state, the
concrete for this process combination of spraying and extrusion also
requires application-specific properties in the uncured state, such as
high green strength, thixotropy, low shrinkage, adjusted processing time
and good bonding behaviour of the individual layers as well as the
contact zone between the sprayed and extruded layers.
To evaluate the durability, crack and failure behaviour of the reference
components, climate change tests and angle-dependent insert pull-out
tests were also carried out. Furthermore, the influence of the recipe
and the process parameters on the material characteristics in the fresh
and hardened state was examined and described.
Another focus was on the exposed concrete properties of the sprayed
concrete shell for facade elements. For this purpose, the air void
content in the fresh concrete, the exposed concrete surface according to
the DBV/VDZ data sheet in porosity class and deviations from evenness
and colour requirements according to DIN 18202 were determined and
evaluated [7, 8].
The concrete recipe was determined empirically with constant testing of
the consistency and is summarized in table 3. The mixing process was
using an Eirich R05T.
Table 3. Concrete mixture