The success of a refractory castable is largely due to the quality of its properties and ease
of application. Self-flow refractory castables (SFRC), with high flowability index (>130%), can be
easily accommodated in a mould without the application of external energy, being ideal for the
manufacture of monolithic linings. SFRC castables without cement require a matrix of very fine
particles, which guarantees improved rheological behaviour and performs the role of the binder in
the absence of the refractory cement. The presence of the aggregate (coarse particles) hinders the
flowability index, but improves the castable mechanical strength and reduces firing shrinkage, and
also contributes to the reduction of the castable costs. The control of the maximum paste thickness
(MPT) allows the reduction of the coarse particles interference, minimizing the number of contact
points among the grains and avoiding the formation of an aggregate skeleton that impairs the
flowability of the mixture.
In the present work, 100% alumina SFRCs without cement were produced with a fixed matrix of
fine particles, whose particle size distribution was optimized using statistical techniques (mixtures
design and triangular response surfaces). Different aggregate particle size distributions were used,
with several MPT values, with the objective of evaluating which was the mean distance that
maximized the flowability index, simultaneously ensuring good mechanical strength for the
refractory castable. Ensuring a minimum surface area of 2.22m2/g, the mixtures reach the self-flow
turning point with a minimum water content and the maximum flowability is obtained for an
aggregate particle size distribution modulus of q=0.22, and consequently an optimized MPT value.
SFRC with high mechanical strength (>60MPa) were obtained.
Aggregate Particle Size Calculation Based on Optimized Equivalent Ellipse
