CONCRETE

[:ru]Рояк Г. С.[:en]Royak, G.[:] [:ru]д.т.н., проф., АО ЦНИИС Научно-исследовательский институт транспортного строительства[:en]DSc in Engineering, Professor, SC TSNIIS Research Institute of Transport Construction[:]

[:ru]Грановская И. В.[:en]Granovskaya, I.[:] [:ru]к.т.н., АО ЦНИИС Научно-исследовательский институт транспортного строительства[:en]PhD in Engineering, JSC TSNIIS Research Institute of Transport Construction[:]

[:ru]Добкин В. С.[:en]Dobkin, V. S.[:] [:ru]инж., ОАО ЦНИИС[:en]engineer, OJSC “Central Scientific Research Institute of Construction”[:]

[:ru]Тарасова А. Ю.[:en]Tarasova, A. Yu.[:] [:ru]канд. техн. наук, ЦНИИС, Россия[:en]Cand. Eng. Sc., CSRIC, Russia[:]

[:ru]Миленин Д. А.[:en]Milenin, D. A.[:] [:ru]инж., Научно-исследовательский институт транспортного строительства, Москва, Россия[:en]Eng., Research Institute of Transport Construction, Moscow, Russia[:]

Alitinform №3-4 (04-05) 2008 г. 114-118 p.

Abstract

In the present report, authors summarize results of researches carried out during several years at the Research Institute of Transport Construction (TsNIIS) and other organizations. These researches concern study of properties of new class of polycarboxylate admixtures, their influence onto properties of concrete mixes, hardening of concrete, its physical and mechanical properties, and endurance.

The article [1] of year 2000, in which results of tests carried out by company Polimod and published abroad were summarized, points out a necessity to study a group of water-soluble carboxylated polymers as admixtures to concrete. Chemical modification of carboxyl polymers enables to introduce long side oligo alkylene oxide lateral chains into macromolecules through formation of corresponding polyester or amide groups. It was found that polycarboxylate additives were active superplasticizers having certain advantages for well-known plasticizing agents of SNF (sulfo-naphtalene-formaldehyde) type, and they could be used for production of both precast, and cast-in-place concrete.

According to report [2], however, there is no clear understanding of obtained results yet, based on theoretical conceptions of a role of adsorption of surfactants on cement grains and hydrate structures, forces of electrostatic and steric repulsive interaction, interrelation between macromolecules structure and adsorption layers composition and structure. Barrier mechanism, while the effect of liquefaction is still present, does not prevent hydration.
Polycarboxylates should be classified as a multipurpose modifying additives to concrete, that provide plastisizing and stabilizing effects [3]. According to the author, efficiency of such modifying additive comes from low optimal dosage rate, low sensitivity to type and composition of cement, long-term stability of initial consistency of concrete mix, and increased adhesion.

Detailed analysis of possible chemical processes going when polycarboxylate-based synthetic admixtures are added to concrete [4] led to a conclusion that a superplasticizer is non-reversibly fixed with products of Portland cement hydration. This was proved by numerous laboratory experiments
The author makes an interesting conclusion that mechanism of superplasticizers adsorption on products of cement hydration and on mineral filling is radically different. In the first case, non-resersible chemosorption takes place, in the second case – reversible physical adsorption.

In recent years, some producers of concrete mixes in co-operation with authors of the present article set up industrial production of concrete with polycarboxylate additive.

For monolithic construction, the most interesting are polycarboxylate additives with high water absorption ability that enables to transport concrete mix for a long distance without considerable loss of flowability. Polycarboxylate additives from several countries (Switzerland, Austria, Germany, and others) are available in construction market of Russia. They differ by a method of production, raw materials, and structure of core polymer component.