Composite Retardants of Hydrophobic-Structuring Type
and Their Effect on Properties of Plasticized Concretes
N. Kh. Belous, V. D. Koshevar, and S. P. Rodtsevich
Institute of General and Inorganic Chemistry, National Academy of Sciences of Belarus, Minsk, Belarus
Received October 14, 2008
Abstract—Formulations of composite retardands of flowability loss, based on a polysiloxane emulsion and an
acid admixture, were developed. The influence of the content of the ingredients and of the sequence of
introducing the superplastricizer and retardant on the technological properties of concrete mixes and concretes
plasticized with Stachement-2000 polycarboxylate superplasticizer was examined.
AND POLYMERIC MATERIALS
ISSN 1070-4272, Russian Journal of Applied Chemistry, 2009, Vol. 82, No. 9, pp. 1669–1674. © Pleiades Publishing, Ltd., 2009.
Original Russian Text © N.Kh. Belous, V.D. Koshevar, S.P. Rodtsevich, 2009, published in Zhurnal Prikladnoi Khimii, 2009, Vol. 82, No. 9, pp. 1566–1570.
New kinds of polycarboxylate superplasticizers
(SPs) are widely used today in building industry.
These admixtures considerably decrease the water
demand of concrete mixes and enhance the strength of
concretes [1, 2]. However, introduction of such
plasticizing admixtures leads to rapid decrease in the
flowability , which gives rise to problems with
delivery of high-quality concrete mixes to remote
To prolong the pour life of plasticized concrete
mixes, retardants are included in SP formulations. The
retardant performance depends on the chemical and
mineralogical composition of cement, content of fillers
and admixtures, sequence of their introduction, water-
to-cement ratio, and other factors . Among
promising flowability loss retardants for Portland
cement systems are hydrophobic-structuring agents.
When introduced into the mix, these agents are
adsorbed on the solid phase surface to form a
hydrophobic film. This film ensures retarding and
plasticizing effects, and also uniformity and sedi-
mentation stability of concrete mixes. Representatives
of hydrophobic-structuring agents are organosilicon
emulsions (OSEs) which are characterized by low
hydrophilic–lipophilic balance and modify concrete
mixes by the bulk–adsorption mechanism [5, 6]. Such
emulsions clog pores of cement stone and fill its
volume on the level of the microstructure, and their
hydrophobizing components are tightly fixed on the
solid phase surface.
Effective flowability loss retardants are also hydro-
philic acid admixtures containing groups that tend to
form coordination bonds in the cement system .
These retardants react with calcium hydroxide to form
difficultly soluble compounds that affect air en-
trainment and thus additionally plasticize concrete mixes.
When admixtures of both types differing in the
mechanism of the effect on the Portland cement system
(adsorption of retardant component on clinker, filler,
and new formations in one case and chemical reaction
with calcium hydroxide in the other case) are mixed,
they show synergistic effect, and the influence of the
composite retardant is enhanced.
The behavior of a composite retarding admixture in
Portland cement systems with polycarboxylate
plasticizers is difficult to predict. The majority of
retardants in such systems exert a competing effect on
the adsorption of a plasticizer on clinker particles and
new formations . As a result, the performance of
both admixtures can decrease, and a problem of the
compatibility of the admixtures with each other and
with a particular kind of cement can arise. This may
lead to a decrease in the pourability and pour life of
concrete mixes, and also in the compression strength
of the resulting concretes.
The use of several separate admixtures in preparing
concrete mixes requires special dosing units and
separate feeding lines. Therefore, it is difficult to
ensure stability of the compositions. In this connection,