Russian Journal of Applied Chemistry, 2012, Vol. 85, No. 12, pp. 1793−1799.
Pleiades Publishing, Ltd., 2012.
Original Russian Text © A.S. Brykov, A.S. Vasil’ev, M.V. Mokeev, 2012, published in Zhurnal Prikladnoi Khimii, 2012, Vol. 85, No. 12, pp. 1903−1909.
AND INDUSTRIAL INORGANIC CHEMISTRY
Hydration of Portland Cement
in the Presence of High Activity Aluminum Hydroxides
A. S. Brykov
, A. S. Vasil’ev
, and M. V. Mokeev
St. Petersburg State Technological University, St. Petersburg, Russia
Institute of High-Molecular Compounds, Russian Academy of Sciences,
St. Petersburg, Russia
Received July 26, 2012
Abstract—The effect of highly dispersed amorphous aluminum hydroxides on the hydration of Portland cement
was studied by the solid-state
Si NMR spectroscopy. It was established that in the presence of aluminum
hydroxides the decrease in the setting time of a cement paste is due to rapid formation of ettringite phase, with con-
tribution of admixture material the main and contribution of aluminum-containing phases at this stage insigniﬁ cant.
As known, the modern shotcrete technology of air
entrainment uses accelerating admixtures not contain-
ing alkalis and therefore having a number of advantages
instead of alkaline admixtures [1–3]. One component
of the accelerating admixtures of this type are highly
dispersed amorphous modiﬁ cations of aluminum hy-
droxides and oxides. These have high reactivity in
a cement paste and form with its components a number
of compounds, including high sulfate form of calcium
AFt, or ettringite), low sulfate form of calcium hydrosul-
O (phase AFm,
or monosulfoaluminate), and calcium hydroaluminates
such as 4CaO·Al
O, which also belong to the
AFm-like phases of layered structure. The diagram of the
conversion involving high-activity Al(OH)
by an example of the ettringite formation:
O) + 20H
Hydroxides and oxides may be main components of
such accelerators, whereas more often they are incorpo-
rated into aluminum hydroxosulfates of variable com-
position in combination with aluminum sulfates [4, 5].
Despite a considerable experience has been accumu-
lated in application of alkali-free accelerating admixtures,
the peculiar features of their interaction with components
of the cement are still unclear. In particular, there is no
clear understanding on the hydration of cement clinker
phases in the presence of aluminum-containing alkali-free
accelerators and on the contribution of clinker phases into
the mechanism of setting a cement paste in the presence
of the above admixtures.
In the study, the peculiar features of Portland cement
hydration in the presence of ﬁ ne particles of amorphous
aluminum hydroxides were determined by the solid-state
Si NMR spectroscopy.
We studied highly dispersed amorphous aluminum
hydroxides produced at two different plants. Their char-
acteristics are listed in Table. 1. Compared to product no.
2, product no. 1 consists of coarser particles. At the same
time, its speciﬁ c surface area, probably owing to more
developed surface structure, is larger. At the same time,
the mass loss by calcination for product no. 2 is larger
than for product no. 1, which may be indicative of its
larger amorphization and higher reactivity.
We used in the study a CEM I 42.5 N Portland ce-
ment. The cement has the phase composition (wt %):