Coupled effect of time and temperature on variations of plastic viscosity of highly flowable mortar Jean-Yves Petit a, ⁎, Kamal H. Khayat b , Eric Wirquin a a Université d'Artois, LAMTI, Technoparc Futura, F62400 Béthune, France b Université de Sherbrooke, 2500 Bd Université, Sherbrooke, Qc, Canada J1K 2R1 abstract article info Article history: Received 30 November 2007 Accepted 11 December 2008 Keywords: Temperature (A) Fresh concrete (A) High-range water reducers (D) Rheology (A) Plastic viscosity Self-consolidating concrete (SCC) is being increasingly used as construction material for its workability. However, the rheological properties of such concrete, which is made with significant concentration of high- range water-reducing admixture (HRWRA), depend in most cases on the casting temperature of the material. The study presented herein aimed at evaluating the coupled influence of time and temperature on the variations of plastic viscosity (μ) of micro mortar made with polymelamine (PMS), polynaphtalene (PNS) and polycarboxylate (PCP) polymer. In total, seven micro mortar mixtures proportioned with various binder compositions and water-to-binder ratios of 0.42 and 0.53 were prepared at 10 to 33 °C. Test results show that the plastic viscosity varies linearly with the coupled effect of time and temperature for mixtures made with PNS or PMS HRWRA. However, for mixtures made with PCP-HRWRA, both temperature and mixture proportioning have influence on the variation of viscosity with time. © 2008 Elsevier Ltd. All rights reserved. 1. Introduction In order to improve workability of concrete, high-range water- reducing admixtures (HRWRAs) are incorporated into the cement mixture. The most commonly used HRWRAs are polynaphtalene sulfonate (PNS) and polymelamine sulfonate (PMS). New classes of long-chained polymers with significant molecular weights have been recently developed to further enhance water reduction and its retention with time through a more effective steric dispersing mech- anism. Polycarboxylate polymers (PCPs) constitute a new family of these newly-used admixtures. The dispersion properties of PCPs on cement particles is especially noted in mixtures made with low water- to-binder ratios (W/B), compared to PNS- or PMS-based HRWRA that can exhibit sharper drops in fluidity with time and, in some cases, delay in setting [1]. The mixture composition and mixing procedure have some impact on the efficiency of PCP-based HRWRA in improving fluidity of cement paste [2,3]. A relatively high concentration of sulfate-ion in the interstitial solution can lead to some incompatibility between the binder and HRWRA, thus affecting the adsorption behavior of the PCP onto cement particles, resulting in a loss of workability [4–8]. The cement hydration process was also shown to reduce dispersion efficiency of the HRWRA due to some intercalation of the HRWRA into the hydration products [7–9]. Interaction between cement, viscosity- enhancing agents (VEA) and HRWRA can also lead to loss in fluidity or delay in set time; this depends on the concentration and type of the admixtures [10–12]. Leeman and Winnefeld [12] reported that a reduction of W/B from 0.48 to 0.38 can lead to an increase in plastic viscosity from 5 to 22 Pa s in mortar systems made with PCP-HRWRA. Such observation was also reported for mortars containing natural polysaccharide VMA at dosages of 0.2%, 0.4%, and 0.8% by mass of binder, for mortar mixtures with 0.38 to 0.48 W/B. In some cases, the reduction of W/B can cause sharper increase of plastic viscosity than an increase in VMA at an equivalent yield stress [12]. Temperature also affects the level of incompatibility between the cementitious materials and various admixtures [13–18]. Golaszewki and Szwabowski [15] showed that the rheological properties of mortar mixtures made with PNS and PCP HRWRAs are strongly influenced by mixture temperature. An increase in mixture temper- ature can lead to an increase in yield value and decrease in initial plastic viscosity. For mortars prepared at a W/B of 0.40 to 0.50 and 1% to 2.25% HRWRA dosage, by mass of binder, the increase in temperature from 10 to 30 °C was found to decrease the plastic viscosity (μ with time; this behavior was found to depend on the binder type. Similar results were found on micro mortars prepared with W/B of 0.42 to 0.53 and either PNS or PMS HRWRA at dosage rates ranging between 0.28% and 0.8%, by mass of binder [16]. The increase in mixture temperature from 10 to 30 °C resulted in a linear increase in plastic viscosity with time, but a decrease in the initial μ value. A decrease in temperature of the micro mortar resulted in reducing the rate of cement hydration and HRWRA adsorption, thus prolonging the dormant period [16,17]. For example, Jolicoeur et al. [17] showed that the concentration of adsorbed and residual PNS- HRWRA can vary with paste temperature, resulting in direct impli- cation on rheological properties of the paste. Cement and Concrete Research 39 (2009) 165–170 ⁎ Corresponding author. Fax: +33 3 21 63 71 23. E-mail address: jyves.petit@univ-artois.fr (J.-Y. Petit). 0008-8846/$ – see front matter © 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.cemconres.2008.12.007 Contents lists available at ScienceDirect Cement and Concrete Research journal homepage: http://ees.elsevier.com/CEMCON/default.asp