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• application notes & technical articles
Wet-Shotcrete of Refractory Castables
construction & building
industries
mining industries
In recent years, the refractory
industry has focused much
effort on discovering novel
techniques for castable
installation that combine
high placing rate and low cost
while maintaining final material
properties.
The use of versatile and automated placing
methods such as pumping of self-flowing
castables and shotcrete has been encouraged to
replace the traditional vibration moulding
technique.
Based on these aspects, wet shotcrete is highly
interesting from a technological standpoint,
particularly for the lining of large areas and/or for
the repair of damaged surfaces.
The technique consists of pumping the castable
from the miser to the pipeline nozzle, where
high-pressure compressed air is injected so as to
project the pumped castable onto the surface to
• application notes & technical articles
Rheological Behaviour of Automotive
Paint Systems
surface coatings industries
Modern Characterisation
Methods Show Good
Correlations to Observable
Effects
biennial 07-08
be covered. This promotes a spray flow that
ensures a high installation rate and the formation
of a thick layer.
The difficulties involved in the shotcrete technique
relate mainly to the bonding of the material on the
area to be lined. The primary condition for a
successful operation is that the projected material
does not flow over the back lining refractory
surface, and this requires a sudden loss of the
castable’s fluidity. Traditionally, this effect is
achieved by the controlled use of cement settling
accelerators, which are also injected into the
nozzle.
Although they ensure the material’s cohesion,
conventional accelerators such as sodium silicate
and aluminium sulfate usually deteriorate the
mechanical properties of castables at high
temperatures. Therefore, proposals have been
made for novel additives based on distinct
concepts to promote the rapid reduction of
castable fluidity.
In most bases, material waste is generated during
shotcrete application due to the so-called rebound
effect. This wastage occurs when a portion of the
sprayed castables, which may amount to as much
as 30%, fails to adhere to the applied surface. The
rebound effect, which is also enhanced by the use
of accelerators, can be minimised by selecting
additives that simultaneously impart adhesive and
In this paper the most important measuring
methods for studying the rheological behaviour of
modern paint systems (oscillation tests,
determination of low yield points) are described.
These methods were at first used to describe the
rheological/physical properties of model
polyurethane micro gels. The measured values for
storage modulus, phase shift and yield point in
waterborne Pearle scent/coloured pigment
systems were compared with flop-index values.
The results show good correlations between the
plastic characteristics to the castable, resulting in
homogeneous and cohesive linings, even when
successive layers are applied
In addition to the intrinsically complex pumping
operation, wet-shotcrete applications must also
take into account: (a) an abrupt increase in the
castable shearing rate and the injection of
additives, controlled by the air rate supplied in the
nozzle, and (b) the material’s adhesion and
consolidation on the surface.
The conventional testing techniques, however do
not properly evaluate shotcrete castables, given
the rheological behaviour of these castables under
similar shearing conditions during their installation
is not analysed. The traditional approaches focus
mainly on the influence of additives on the
castable’s consistency (fluidity measurements) and
on post-setting properties.
The main objective of the present study was to
develop a novel shotcrete characterisation
technique based on castable rheometry that
simulates the material’s application. Commercial
wet-shotcrete additives and other compounds with
a high potential for this application were also
evaluated using the new testing procedure.
A complete copy of this article is available on
request by quoting Rf-290802-BR-02.
observable effect and the rheological parameters
of the liquid paint.
Also measurements of powder and electrode
position coatings and clear coats with the
oscillation technique to determine the viscositytemperature
behaviour correlate well with
technical properties of the final films.
A complete copy of this article is available on
request by quoting Rheo008TP.
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