The aim of this paper is to investigate effects of macromolecular structure and ionic competition phenomena induced by an increase of ionic strength on the dispersive action of new superplasticizers. These superplasticizers were synthesized and their structure is based on that of polycarboxylates. These superplasticizers are comb-like copolymers with phosphonic acids. Macromolecular parameters studied are the monomer repartition along the carbon backbone and the chain length. Ionic strength is increased either by adding sulfate or nitrate ions. The effects of these factors are then investigated using adsorption, stability and rheology results. It appears that statistical copolymers with phosphonic acids having the shortest chain length are the most efficient in terms of fluidity improvement even in the presence of sulfate or nitrate ions. (C) 2017 Elsevier B.V. All rights reserved.