Viscosity Modifying Admixtures

Viscosity modifiers can be divided in several groups, taking into accoimt the type of chemical compound and the mechanism of their action [409]  

Class A—synthetic and natural organic polymers soluble in water, increasing the viscosity of mixing water these are the following groups of compounds cellulose ethers, poly(ethylene oxide), polyacrylamides, polyvinylalcohol and others. 

Class B—organic flocculants soluble in water, adsorbed on cement grains and increasing viscosity by electrostatic attraction. To class B belong styrene copolymers with carboxylate groups, synthetic polyelectrolytes and natural rabbets. 

Class C—emulsions of various organic substances, increasing the electrostatic attraction and introducing ultra-fine particles to cement paste. The following compounds, among many others, are in this group acryl emulsions and water dispersions of clay. 

Class D—inorganic materials dilnted with water, of very high specific surface area they improve the water retention of the paste. Typical examples bentonite, silica fume. 

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When these admixtures are added to concrete for rmder water works the resistance for washing-out is the key parameter, determining their applicability. In Fig. 6.109 the data relating to the two different viscosity modifying agents (VMA), used at various w/c ratios, are shown. As one can conclnde, even at addition on the level 0.10% by mass of cement, the cement paste washing-out is nearly 10 times lower. 

Ethylsilicate ETS-32 (ETS) (TU 6-02-895-78) being a mixture of tetraethoxysi-lane with geksaethoxydisiloxane with a small admixture of ethanol and oktaethoxy-trisiloxane was used as a modifier. The silicon content in terms of silicon dioxide is 30-34%, tetraethoxy silane—50-65%. Its density is 1.062 kg/m and viscosity is 1.6 cP. Ethylsihcate is manufactured by Production JSC Khimprom of Novocheboksarsk. 

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