STUDY OF THE EFFECT OF REPLACING MICROSILICA
IN HEAT-RESISTANT CONCRETE WITH ADDITIVE
BASED ON METAKAOLIN
and E. Spudulis
Translated from Novye Ogneupory, No. 6, pp. 43 – 48, June, 2013.
Original article submitted January 9, 2013.
A comparative study is provided for the effect of microsilica additive and one based on metakaolin on
hydration of alumina cement and cement stone structure formation after hardening and firing. It is established
that in a composite with alumina cement an additive based on metakaolin promotes transfer of cement miner
als into solution more rapidly than microsilica additive, and also that composite hydration with additive based
on metakaolin proceeds more rapidly than a composite with microsilica. Additive based on metakaolin com
pared with microsilica improves mechanical properties of heat-resistant concrete based on a chamotte filler:
after hardening and firing the ultimate strength in compression for specimens with additive based on
metakaolin is higher by 5 – 27% than this index for specimens with microsilica additive,
Keywords: alumina cement, metakaolin, microsilica, heat-resistant concrete.
Currently in order to produce heat-resistant concretes the
active fine additives used mainly are microsilica  and re-
active alumina . Extensive use in heat-resistant concretes
of microsilica, i.e., waste from metallurgical production, is
based on its relatively low cost, and also on the well-known
advantage over other additives of the possibility (in combi
nation with deflocculants) of a significant reduction in the
amount of cement and water in concrete [1, 3 – 5]. Unfortu
nately, the amount of microsilica produced in the world de
pends on the metallurgical branch. In certain periods there
may not be enough of this material, since microsilica addi
tive is used extensively also for manufacturing other struc
tural materials. In view of this it is interesting to study of the
possibility of using metakaolin (or additives based upon it) in
heat-resistant concrete with the aim of replacing microsilica.
Metakaolin is amorphous aluminum silicate, which is
prepared by heat treatment of kaolin, used extensively in the
production of geopolymers [6, 7], and concretes based on
Portland cement. Studies of concrete based on Portland ce
ment have shown that addition of metakaolin develops
pozzolanic properties, (calcium hydrosilicates are formed)
and accelerates concrete hardening [8, 9], particularly in the
early period of hardening. It has been shown  that re-
placement of part of Portland cement by metakaolin reduces
concrete shrinkage and the number of cracks within it.
Data for application of metakaolin in heat-resistant com-
posites are not numerous. It has been established [11, 13]
that addition of microsilica and metakaolin to a composite
with alumina cement promotes formation of a hydration
product such as stratlingite. Formation of stratlingite in turn
limits the possibility of a “conversion” reaction (CAH
) for cement hydration products. It is also
indicated  that specially selected fraction of metakaolin
increases refractory composite thermal shock resistance.
In studying the possibility of replacing microsilica in
heat-resistant concrete with additive based on metakaolin
comparative analysis has been carried out for the properties
of two materials, cement suspensions, cement stone and con
cretes with chamotte filler.
MATERIALS AND RESEARCH METHODS
The following materials were used for the study:
microsilica (96.1% SiO
), additive based on metakaolin
, 45% Al
), alumina cement (AC, not less
than 40% Al
), chamotte filler (CF) fraction 0–5mm(not
Refractories and Industrial Ceramics Vol. 54, No. 3, September, 2013
1083-4877/13/05403-0232 © 2013 Springer Science+Business Media New York
Scientific Institute of Heat Insulation of Gediminas Vilnius Tech
nical University, Vilnius, Lithuania.