The Role of Surface Phenomena in Modified Cement Dispersions at Studying Poly-Functional Modifiers' Mechanism of Action

摘要

The research findings of colloid and chemical properties of poly-functional modifiers (PFM) with various chemical compositions and qualitative and quantitative proportions of polar organic substances with various molecular weights have been presented. The possibility of regulating the properties of PFM and concrete mixes, modified by them by means of not only changing the chemical composition of modifiers, but combining the types and quantity of active admixtures of polar organic substances with various molecular weights has been shown. It has been demonstrated that the modifiers under study possess the surface activity at solid-solution phase boundary, reducing the surface tension σ_(solid-liquid) (σ_(s-1)) At the same time the surface tension at the solution-air phase boundary can remain the same or reduce to a certain extent depending on the modifier's chemical composition. PFM and superplasticizer (SP) SB-3, which have, unlike SP S-3, the certain surface activity at solid-solution boundary, increase the air entrainment into concrete mix by 0.5÷1.5%, additionally increasing the freeze-thaw resistance of concretes of both fluid and equal-workable compositions without affecting their strength. The adsorption of modifiers on the disperse phase of suspension is conditioned by dispersion forces and, independently of its kind, is of monomolecular nature. For the localization of PFM molecules on the surface of a particle, its molecule should have a system of bonded aromatic rings or conjugated double bonds. The adsorbed modifier's molecules should make the disperse phase surface hydrophilic and for this purpose they should contain hydrophilic groups along the full length. All this predetermines the role of adsorption-solvation factor in modifiers' mechanism of action.