A review of cement–superplasticizer interactions and their models

Abstract

This paper presents a focused review of cement±superplasticizer interactions. It has been concluded from the survey of the literature that cement±superplasticizer interactions are generally preceded by the adsorption of superplasticizers on the hydrating cement particles. However, the mechanisms of such adsorptive interactions have not been adequately addressed experimentally or discussed in the literature. The reason for this appears to be the lack of a conceptual model that can delineate the results to date and project needed experiments. A chargecontrolled-reaction mechanism model involving Ca 2 ions from initial hydration is proposed to explain the adsorption characteristics of superplasticizers and other organic additives and their effects. The calcium ions released by hydration form a bilayer immediately upon contact of water with the cement, which is followed by adsorption of superplasticizer anions on the Ca 2 ion side of the bilayer. The interfacial structures and their influence on electrical characteristics, hydration reactions and phase growth in the hydrating cement are discussed in terms of the proposed model.

Early Age Hydration, Microstructure and Micromechanical Properties of Cement Paste Modified with Polymeric Vesicles

“…Because the mechanical properties of the LD CSH and HD CSH are intrinsic to cement paste (Constantinides and Ulm 2004;Constantinides et al 2003;Zhu et al 2007), the most plausible reason for the lower modulus value of LD CSH for specimen OPC is related to a more porous microstructure of the cement matrix. As afore-mentioned in the "Introduction" section, the PEO-containing polymers influence the properties of fresh cement paste: they can hinder the coagulation and sedimentation of un-hydrated cement particles by increasing the electrostatic and/or steric repulsive forces (Jansen et al 2012;Mollah et al 2000). This effect would influence the distribution of hydration products in the hardened cement paste.…”

“…Additionally, some reports on retardation of early hydration of cement paste due to admixed PEO-containing polymers (normally used as superplasticizers for cement-based materials) need to be also considered (Sakai et al 2006;Winnefeld et al 2007) as contributing factors. The retardation effects are reported to be mainly relevant to the hydration of C 3 S (Lothenbach et al 2007;Pourchet et al ;Winnefeld et al 2007) and the proposed mechanisms (Gu et al 1994;Jansen et al 2012;Mollah et al 2000) can be summarized as: (1) polymers adsorption on the surface of cement grains, hindering the diffusion of water and Ca 2+ ions at the cement grain/solution interface; (2) impeded growth of hydrate phases due to the presence of polymers; (3) dispersive ability and effect of the polymers which alter the growth kinetics and morphology of the hydration products. These effects are not necessarily [Hu et al 2012a] relevant for the present investigation, mainly because of: 1) the type and size of the hereby PEO-b-PS -based vesicles, being in the nano-range; 2) these self-assembled architectures are in a minimal concentration of 0.025 wt.% per cement weight.…”

“…workability, setting time, water requirement and mechanical strength (Aitcin and Neville 2003;Jansen et al 2012;Young 1972), consequently producing high-strength and high-performance concretes (Jansen et al 2012;Li et al 2005;Neville and Aitcin 1998). The influence of admixed polymers on the properties of cement-based materials is reported to be mainly related to their dispersion ability via increasing repulsive forces and hindering the coagulation and sedimentation of the cement particles by introducing electrostatic and/or steric repulsion (Jansen et al 2012;Mollah et al 2000). The reported mechanisms are generally commented with regard to the molecular structure and adsorption characteristics of the investigated polymeric additions (Uchikawa et al 1997).…”

“…The reported mechanisms are generally commented with regard to the molecular structure and adsorption characteristics of the investigated polymeric additions (Uchikawa et al 1997). It is also known that admixed polymers generally influence cement hydration to a significant extent, consequently affect the morphology and microstructure of cement-based materials (Chandra and Flodin 1987;Mollah et al 2000;Young 1972). …”

Adsorption of superplasticizer admixtures on alkali-activated slag pastes

“…Such admixtures not only improve the in situ placement of concrete, but lower the water demand by up to 40%, improving mechanical and durable properties [6,7]. The mechanisms involved and the superplasticizer compatibility with Portland cement have been studied and described in numerous articles [8][9][10]. These papers report that such admixtures adsorb onto the surface of cement particles, causing inter-particle electrostatic and electrosteric repulsion.…”