A new class of organosilane-modified polycarboxylate superplasticizers with low sulfate sensitivity

Abstract

It is well-established that a competitive adsorption exists between polycarboxylate superplasticizers (SP) with soluble sulfate ions solubilized in interstitial solution of cement paste, which may causes a loss of dispersing properties depending on the cement composition. Early reports suggested that this incompatibility is due to competitive weak ionic interaction between functional acrylate groups and solubilized sulfate ions with cement grains. In this study, SPs including trialkoxysilane functional groups have been synthesized via radical copolymerization of methacrylic acid, poly(ethylene glycol) methyl ether methacrylate and trimethoxysilyl propyl methacrylate. Adsorption and dispersing properties of these new SPs were evaluated in cement paste at different concentration of Na 2 SO 4 added in aqueous solution. Partial substitution of acrylate groups by trialkoxysilane in the polymer composition significantly enhances the compatibility with sulfate ions. We suggested that the high adsorption capacity of these SPs results from the formation of strong bonds between hydroxysilane groups and calcium silicate hydrate phases present at the surface of C 3 S. The improved compatibility of these new silylated SPs with cements more or less rich in sulfate alkaline has been demonstrated through the formulation of two different concrete equivalent mortars.

Fluidizing efficiency of comb-like superplasticizers: The effect of the anionic function, the side chain length and the grafting degree

“…The surface has not to be fully covered to have a high fluidity. As demonstrated by this study, previous results carried out with cement and superplasticizers have also shown a linear relationship between log(yield stress) [36][37][38] or the paste-flow [42][43][44] and the mass of adsorbed polymer on cement grains. More recently a similar linear relationship has been shown with a calcite suspension containing two PCEs which differ only by the repartition of the carboxylic monomer along the backbone [39].…”

“…5, the simplest way to link the yield stress with the adsorption for a defined paste formulation is the mass of adsorbed polymer. It is noteworthy that several experimental studies have already previously reported a linear relationship between the logarithm of the yield stress and the mass of adsorbed polymer [36][37][38][39]. Aside from the point without superplasticizer, the relationship is nearly linear until 0.3 mg/m 2 and diverges slightly after.…”

Advances in understanding hydration of Portland cement

“…layered calcium organosilicate hybrids with covalently linked organic functionalities [87,88]. The original observation that silylated hydrosoluble polymers can be covalently bonded to calcium silicate hydrate [89] led to a detailed study of polycarboxylate-based superplasticizers modified with trialkoxysilane functions synthesized by radical copolymerization [90]. The authors observed that that a partial substitution of carboxyl by trialkoxysilane groups enhances the adsorption; however, an excess of silylated functions can be detrimental for adsorption.…”

Molecular and submolecular scale effects of comb‐copolymers on tri‐calcium silicate reactivity: Toward molecular design

“…For example, it has been shown that the well-known sensitivity of PCEs to sulfates can be decreased by adding silyl functions in a methacrylic-based backbone. 72,73 Also, using totally different monomers in the backbone, as it is the case for amphoteric PCEs, is reported to improve the adsorption onto the negatively charged surfaces of silicates and/or onto special types of cement. 74,75 Such modifications that include introducing alternative monomers and/or macromonomers can clearly modify PCEs adsorption ability in three different ways.…”

“…They include, for example, the impact of overall PCE conformation both in the solution and on the surface. Finally, in the presence of other species PCEs may be sensitive to competitive adsorption, 22,72,73 a process in which both molecular and submolecular scale effects play a role. 53,67 These are simple examples of how the properties of a PCE may change with the chemical nature of its components and only represent a small insight into the broad range of possible modifications of PCEs.…”