Comb copolymers with an adsorbing backbone and nonadsorbing side chains can be very effective dispersants, particularly when a high ionic strength strongly penalizes electrostatic stabilization. For this reason, they have become essential components of concrete over the past decade. This article examines the steric hindrance characteristics of such polymers through the use of atomic force microscopy (AFM) on calcium silicate hydrate, the main hydration product of Portland cement. It is found that solution and surface properties (hydrodynamic radius, radius of gyration, surface coverage, steric layer thickness) and force-distance curves obtained during AFM measurements can be well described by a scaling approach derived in this paper. This represents the first real quantitative step in relating these properties directly to the molecular structure of such comb copolymer dispersants.

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During the last few years, polycarboxylate based polymers have become very popular. They contain a polycarboxylic backbone onto which ethyleneoxide side chains have been grafted. However its dispersing and slump keeping properties vary significantly, depending on the chemical structure. The dispersing properties of two polymers having a different number of polyoxyethlene (PEO) graft chains relative to the length of the backbone were evaluated in cement paste by measuring adsorption on cement paste and flow properties in different mortar compositions. The effects of the polymers on the fluidity and the retention of flow of the cementitious systems are significantly different. While one polymer gives a very strong initial water reduction, the second one shows excellent flow retaining properties. When combined, the two polymers are well suited for the production of RMC and self-consolidating concrete mixes with different cements and in different climate zones.