Effect of PCs superplasticizers on the rheological properties and hydration process of slag-blended cement pastes M. Palacios Æ F. Puertas Æ P. Bowen Æ Y. F. Houst Received: 29 December 2008 / Accepted: 17 February 2009 / Published online: 13 March 2009 Ó Springer Science+Business Media, LLC 2009 Abstract The effect of polycarboxylate (PC) superplast- icizers with different structure on the rheological properties and hydration process of slag-blended cement pastes with a slag content between 0 and 75% has been studied. Fluid- izing properties of PCs admixtures are significantly higher in slag-blended cement with respect to non-blended Port- land cement. Also, it has been observed that the rise of the fluidity induced by the PCs on the cement pastes increases with the slag content. This effect is mainly attributed to a decrease in the amount of C 3 A available to adsorb and consume admixture to form an organo-mineral phase. Consequently, the PC admixtures are absorbed onto the silicate phases of the clinker and onto the slag particles, inducing a repulsion and the concomitant reduction in yield stress despite a reduction in the zeta potential. The rheo- logical results allow us to conclude that the highest increase of the fluidity is caused by the admixtures with highest molecular weight due to the higher steric repulsion induced. As a consequence of the adsorption of the PCs, a delay of the hydration process of the pastes has been observed. Introduction The use of mineral additions, as a partial substitution of Portland cement clinker, has become one of the chief ways of obtaining more eco-efficient cements, whose manufac- ture entails lower energy demands and lower emission of greenhouse gas into the atmosphere than ordinary Portland cement (OPC). Both natural additions such as volcanic ash or limestone and industrial by-products such as fly ash or blast furnace slag are appropriate for these purposes. The advantages of slag-blended cements include not only the energy savings and lower pollution compared to clinker production, but also greater mechanical strength at longer ages [1] and higher durability than non-blended Portland cement due to their finer pore structure [2]. More specifically, these cements are highly sulphate- [3] and alkali-aggregate reaction- [4] resistant, while exhibiting a lower chloride diffusion rate [2] than OPC. However, slag- blended cements also show poor early strength and lower resistance against carbonation than non-blended Portland cements. Slag cements also have lower heat of hydration values than OPC and the reaction processes involved in their hydration are more complex [5, 6]. In these cements, the Ca(OH) 2 released as a result of C 3 S hydration activates the slag hydration. Superplasticizers are nowadays an essential component of concrete. These admixtures reduce the amount of water needed in the preparation of concrete, enhancing its mechanical strength and durability. The use of the latest generation polycarboxylate (PC)-based superplasticizers, which induces the highest reduction of water content, has become imperative in high performance and self-com- pacting concretes. These PC admixtures are characterized by a ‘‘comb’’ type structure [7] in which the backbone is a linear hydrocarbonate chain and carboxylate and ether groups form the lateral chains. In a process mediated by the carboxylate groups, these admixtures are adsorbed onto the cement particles, which are subsequently dispersed due to the electrosteric repulsion generated [8, 9]. A number of M. Palacios (&)  F. Puertas Eduardo Torroja Institute for Construction Science (CSIC), Box 19002, 28080 Madrid, Spain e-mail: martapalacios@ietcc.csic.es P. Bowen  Y. F. Houst Laboratoire de technologie des poudres, E ´ cole Polytechnique Fe ´de ´rale de Lausanne (EPFL), 1015 Lausanne, Switzerland 123 J Mater Sci (2009) 44:2714–2723 DOI 10.1007/s10853-009-3356-4