Cellulose ethers and cement paste permeability Alexandre Pierre a, ⁎, Arnaud Perrot b , Vincent Picandet b , Yann Guevel b a University of Cergy-Pontoise, Laboratory of Mechanics and Materials of Civil Engineering, 5 mail Gay-Lussac, Neuville-sur-Oise, 95031 Cergy-Pontoise, France b UEB-LIMATB, ECOMATH, Université de Bretagne Sud, Centre de Recherche de St Maudé, 56321 Lorient, France abstract article info Article history: Received 20 July 2014 Accepted 6 February 2015 Available online 10 March 2015 Keywords: Permeability (C) Cement pastes (D) Rheology (A) Admixtures (D) Cellulose ethers Cellulose ether (CE) admixtures are used to improve the water retaining properties of cement-based materials in order to ensure their homogeneity during casting operations. Water permeation through concrete is usually quantified by permeability. In this study, an oedometric cell has been adapted to investigate the influence of CE dosage on the permeability of fresh cement pastes. The purpose-designed device has to allow the filtration of CE aggregates through the oedometric filters and retain cement particles. Simultaneous rheological shear flow measurements have been carried out to evaluate the viscosities of the initial interstitial liquid and the percolated fluid that has filtrated through the fresh cement paste. Comparison of both viscosities allows the evaluation of the amount of CE adsorbed by the cement particles over a wide range of CE dosage. Moreover, the analysis of experimental results confirms previous studies concerning the improvement of water retaining ability due to CE that in turn limits the amount of bleed water. Comparison of an apparent viscosity computed from permeability measurements and viscosity computed from rheological measurements shows that CE strongly modifies the particle networks above the overlap concentration. The results of this study suggest that CE aggregates are formed and plug part of the cement paste porosity. As a result, the apparent viscosity increases and leads to a strong decrease in the material's apparent permeability. Finally, apparent permeabilities are re- ported for CE dosages ranging from 0% to 0.5%. The results of the study show that combination of rheological and permeability measurements offers a promising method to analyze how CE acts on fresh cement pastes, that are subjected to a hydraulic gradient induced by casting processes. © 2015 Elsevier Ltd. All rights reserved. 1. Introduction Nowadays, stability of fresh concrete is a major concern in mix de- sign of highly fluid and self-compacting concrete (SCC). The freshly made mix has to remain homogeneous during the casting operation and the amount of bleed water has to be limited. It has recently been shown that cement grains in highly flowable concrete or SCC are not close enough to form a stable network that is able to sustain gravitation- al forces [1]. Consequently, these types of mixes are susceptible to bleeding. In order to slow down and prevent bleeding, viscosity modify- ing admixtures (VMA) are used, such as cellulose ether, superabsorbent polymer or welan gum [2–4]. These admixtures increase the water retaining properties of the freshly mixed concrete. It is worth noting that VMA are used for pre-cast processes such as extrusion, to prevent liquid drainage during production [5]. The improvement in material stability is due to different physical phenomena, which depend on the chemical nature of the admixtures. For all types of admixtures like VMA or superplasticizers [6], the viscos- ity of the interstitial liquid is largely increased and thus the bleeding or filtration rate is decreased. For cellulose ethers, another phenomenon is involved: the formation of aggregates of polymeric particles that plug part of the cement grain porosity [7]. Cellulose ethers tend to form ag- gregates during their dispersion due to hydrophobic interactions [7,8]. The particles' pore plugging induces a decrease in the water transport properties of the cement matrix. The size of these aggregates increases with the cellulose ether dosage and may reach more than a tenth of a micron [7–9]. It appears that this phenomenon predominates when the polymer dosage is higher than a critical dosage known as the overlap concentration [10,11]. This study focused on cellulose ethers and more precisely on the use of permeability measurements to assess their efficiency in improving the water retaining properties of fresh concrete. Permeability measure- ments were used to quantify the liquid filtration rate under a given pressure gradient. The device used to determine permeability consisted of a constant head measurement apparatus as described in Picandet et al. [12] and used in other studies [12,13]. This technique was used to estimate the hydraulic conductivity (here simply referred to as permeability) of fresh cement pastes. The permeability is very useful in evaluating the interstitial fluid transport properties as it links the liquid flow rate to the pressure gradient. This parameter is used to predict the amount of bleed water using consolida- tion theory [14–18] and to give drainage criteria for various concrete casting and pre-casting procedure [19]. Cement and Concrete Research 72 (2015) 117–127 ⁎ Corresponding author. Tel.: +33 2 97 87 45 20; fax: +33 2 97 87 45 72. E-mail address: alexandre.pierre@u-cergy.fr (A. Pierre). http://dx.doi.org/10.1016/j.cemconres.2015.02.013 0008-8846/© 2015 Elsevier Ltd. All rights reserved. Contents lists available at ScienceDirect Cement and Concrete Research journal homepage: http://ees.elsevier.com/CEMCON/default.asp