Russian Journal of Applied Chemistry, 2013, Vol. 86, No. 6, pp. 942−944.
Pleiades Publishing, Ltd., 2013.
Original Russian Text © V.E. Akhrimenko, N.V. Pashchevskaya, 2013, published in Zhurnal Prikladnoi Khimii, 2013, Vol. 86, No. 6, pp. 1001−1003.
Problem of Controlling the Gypsum Setting Time
V. E. Akhrimenko
and N. V. Pashchevskaya
Kuban State Agricultural University, Krasnodar, Russia
Kuban Socio-Economic Institute, Krasnodar, Russia
Received February 7, 2013
Abstract—Effect of molasses, a waste formed in manufacture of sugar, on the gypsum setting time was studied.
It is shown that molasses solutions can be used to control the hardening time of the gypsum paste.
Gypsum plaster belongs to rapidly hardening air-
setting binders. The hardening of a gypsum paste begins
already in 3–5 min after its tempering with water. The
gypsum setting time (GST) largely depends on the start-
ing raw material, technology of its manufacture, storage
duration, and presence of additives. The rapid setting of
gypsum in numerous industrial processes is a positive
factor that enables fast extraction of articles from molds
and their higher turnover rate in assembly-line production
However, the rapid setting of gypsum gives no way
of preparing its paste in substantial amounts. That is why
various additives are used to control the GST . A search
for effective additives for controlling the GST and rais-
ing the mechanical strength of gypsum casts is a most
important practical task to whose solution the authors of
 have made a signiﬁ cant contribution. In , the inﬂ u-
ence exerted on the hardening of gypsum hemihydrate by
complexonates of Ba
, and Cr
, synthesized on
the basis of their salts with a doubly charged anion of eth-
ylenediaminetetraacetic acid, was considered.
The goal of this study was to seek for an effective
GST-controlling agent whose application would make it
possible to prepare substantial amounts of gypsum paste,
necessary in building and ﬁ nishing procedures.
As objects of study were chosen gypsum plaster
from Khabezskii gypsum plant [GOST (State Standard)
125–79, G-5, G-6] and additives: an organic electrolyte
(molasses), an inorganic electrolyte (hydrated lime), and
a neutral substance (beet sugar).
Molasses is a water-soluble waste formed in
manufacture of sugar, 80% composed of calcium
saccharates. The gypsum paste was prepared by vigorous
agitation of a gypsum powder with a tempering ﬂ uid
whose role was player by potable water and solutions
of the above additives in this water. The GST was
determined using the Vick’s instrument. For this purpose,
the gypsum paste was placed in the ring of this device
and its needle was dropped into the paste after a certain
interval of time. The depth to which the needle penetrated
into the paste after this interval of time was used to ﬁ nd
the beginning and end of its setting. To determine the
strength of the stone being formed, the gypsum paste
was placed in 20 × 20 × 100 mm dismountable metallic
molds and the gypsum beams obtained were subjected
to compressive strength tests.
The manner in which the setting time of the gypsum
under study varies with the water-to-gypsum ratio (W/G)
in the case when drinking water served as the tempering
ﬂ uid can be seen in Fig. 1, curve 1.With increasing W/G,
the gypsum setting process becomes slower. The process
is decelerated to an even greater extent in the presence
of molasses in the gypsum paste (curve 2). It follows
from Fig. 1 that, with the gypsum paste containing 2%