Russian Journal of Applied Chemistry, 2012, Vol. 85, No. 5, pp. 722−725.
Pleiades Publishing, Ltd., 2012.
Original Russian Text © A.S. Brykov, A.S. Panﬁ lov, M.V. Mokeev, 2012, published in Zhurnal Prikladnoi Khimii, 2012, Vol. 85, No. 5, pp. 718−722.
AND INDUSTRIAL INORGANIC CHEMISTRY
Effect of Metakaolin Structure on Its Binding Properties
in Alkaline Hydration
A. S. Brykov
A. S. Panﬁ lov
, and M. V. Mokeev
St. Petersburg State Technological Institute, St. Petersburg, Russia
Institute of Macromolecular Compounds, St. Petersburg, Russia
Received October 20, 2011
Abstract—Aluminum ion coordination to oxygen in metakaolin of different origin was studied by a solid-state
Al NMR spectroscopy, as well as changes in aluminum ion coordination in an interaction of metakaolins with
sodium silicate solution. At the same time a durability of structures resulting from this interaction was examined.
Based on the ﬁ ndings the relationship between the structure of metakaolin and its astringent properties in alkaline
environment was considered.
Metakaolin is formed in thermal processing of
monomineral kaolin clays (Al
O) in a tem-
perature range of 650–800°C. In the form of the high-dis-
persed powder or water suspension metakaolin is valuable
admixture for top-quality concrete possessing favorable
engineering properties including puzzolanic reaction
that occurs in aqueous environment forming non-water
soluble calcium silicate hydrate . The metakaolin as an
astringent has also an independent signiﬁ cance: in interac-
tion with solutions of alkali metal hydroxides and silicates
it forms a solid stone . Moreover, similar properties
are characteristics of other ﬁ ne aluminosilicate material:
various wastes of high-temperature industrial processes
(entrained ash, ground blast-furnace slag). In studying
the binding properties of these materials metakaolin is
often used as a model object, since in contrast to mineral
wastes and by-products of industry, it is characterized by
stability of the chemical composition and by not large
amounts of impurity components .
The thermal processing results in almost complete
removal of constitutional water, destroying primary crys-
talline structure of kaolinite, and formation of amorphous
product of an Al
composition. In the composi-
tion of kaolinite aluminum has a coordination number
VI to oxygen. The removal of hydroxyl groups from the
kaolinite structure results in transition of aluminum into
coordination IV and V. However, in this case coordination
VI can be preserved . Depending on the technologi-
cal parameters of processing of kaolinite in the industry
metakaolins from different manufacturers may vary by
microstructure. This allows the using metakaolin for the
study of the relationship between structural features of
aluminosilicate materials and their astringent properties
which are manifested under alkaline conditions or in
a Portland cement composition.
The purpose of the work is a study of binding proper-
ties of metakaolin of different origin together with the
study of the peculiarities of their structure by solid-state
Al NMR spectroscopy.
In the study we used three various metakaolins whose
characteristics were listed in Table 1.
It is known that the use of high alkaline silicate solu-
tions for hydration of metakaolin promotes formation of
a more stable structure than the use of NaOH solutions
. Therefore, aqueous solution of sodium silicate with
a molar ratio of SiO
O (silica modulus) 1.5, content
O, respectively, 17.5 and 12.0 wt %,