Adsorption and Dispersion Mechanisms of Comb-type Superplasticizer Containing Grafted Polyethylene Oxide Chains

Abstract

Comb-type superplasticizers are used for producing self-compacting concrete and high strength concrete, and improving concrete durability. To establish the fluidity control technology for concrete with these polymers, it is necessary to clarify the relationship between the adsorption mechanisms, dispersion mechanisms and molecular structures of comb-type superplasticizers.
In a previous paper, we reported the influence of various types of inorganic electrolytes on the adsorption mechanism of comb-type polymers. When the dosage of inorganic electrolytes that form insoluble calcium salts increased, the apparent viscosity of CaCO₃ suspension rapidly rose, and the Ca²⁺ concentration in the liquid phase of suspension was rapidly decreased. Furthermore, the comb-type polymer with the larger content of carboxyl groups on the main chain may be adsorbed more, even though the adsorption sites decreased.
This paper discusses the influence of molecular structure and composition of copolymer for comb-type polymers on the fluidity of CaCO₃ suspension with K₂CO₃ or K₂SO₄. When a larger amount of functional groups (-SO^3-/-COO^-) was introduced onto the main chain, or when the distance between the grafted chains was extended, the influence of inorganic electrolytes on the fluidity of CaCO₃ suspension with comb-type polymer was decreased. These comb-type polymers can be adsorbed onto limestone powder even though the adsorption sites were decreased when inorganic electrolytes were added. In contrast to the case of CO₃ ^2-, the addition of SO₄ ^2- may possibly cause shrinking of the polymer chains as well as hindering the adsorption of the comb-type polymer. Comb-type polymers containing graft chains with some extent of chain length are effective for preventing the fluidity decrease when SO₄ ^2- is added. It is clear that the interval of the graft chain, the composition of copolymer, and the chain length of the grafted polymer for comb-type polymers is important for controlling the fluidity of the suspension with comb-type polymers.