Effect of processing variables on efficiency of eucalyptus pulps for internal curing Passarin Jongvisuttisun a , Camille Negrello a,b , Kimberly E. Kurtis a,⇑ a School of Civil and Environmental Engineering, Georgia Institute of Technology, 790 Atlantic Dr., Atlanta, GA 30332-0355, USA b Civil Engineering Department, Ecole Normale Superieure de Cachan, 94235 Cachan Cedex, France article info Article history: Received 9 August 2012 Received in revised form 16 November 2012 Accepted 20 November 2012 Available online 29 November 2012 Keywords: Autogenous shrinkage Cellulose Fiber reinforcement Wood-derived fibers Water entrainment abstract This study evaluates the effect of fiber composition and morphology, as altered by various papermaking processes, on internal curing performance of hardwood eucalyptus pulp fibers. The autogenous deforma- tions of cement pastes containing each of five different eucalyptus pulps—unbleached soda pulp, bleached soda pulp, unbleached kraft pulp, bleached kraft pulp, and semi-chemical pulp—were examined and analyzed in the context of the known relevant chemical composition and morphology, e.g., cellulose- to-hemicellulose ratio, cell wall thickness, and ‘‘hard to remove’’ (HR) water content. The results revealed that the internal curing efficiency of these pulps is related more strongly to their physical morphology than chemical composition, as measured by cellulose-to-hemicellulose ratio. The partial defiberization during mechanical treatment associated with semi-chemical pulping resulted in fiber fracture and also produced materials which were poorly dispersible; together, these factors limit internal curing capability of semi-chemical pulp. The soda fibers, both unbleached and bleached, with their thicker cell wall and higher HR water content were more effective for internal curing than kraft fibers. It is proposed that for hardwood pulp fibers a slower rate of entrained water release is beneficial for internal curing. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction The use of saturated lightweight aggregates and superabsorbent polymers (SAPs) as internal curing agents for the prevention of self-desiccation in high-performance concrete (HPC) has been examined because both materials can gradually release water to the surrounding hydrating paste [1–5]. Further, research has eluci- dated the key mechanisms controlling the effectiveness of both saturated lightweight aggregates and SAPs for this application. For saturated lightweight aggregates, capillary suction has been shown to be an important mechanism of water transport from the relatively larger pores in saturated lightweight aggregates to the surrounding and more finely porous cement paste, with vapor diffusion and capillary condensation also playing a role in moisture transport [6,7]. The key mechanisms controlling the internal curing capacity of SAPs are the combination of the swelling ratio, ion fil- tration, and the inter-particle spacing of the SAPs [6,8,9]. Cellulose or pulp fibers have also been studied as an alternative to saturated lightweight aggregates and SAPs for internal curing. These renewable materials have been shown to not only have the capacity to substantially reduce autogenous shrinkage but also to provide additional resistance to shrinkage-induced cracking by increasing tensile capacity [10]. While the abilities of different types of cellulose fibers (e.g., softwood thermomechanical pulp, softwood kraft pulp, and specialty cellulose fibers) to mitigate autogenous shrinkage in cement paste and mortar have been shown [10–12], the features of the fibers—both chemical and phys- ical—affecting their efficacy as internal curing agents remain rela- tively unexplored. In particular, the influence of fiber pulping on the internal curing capacity of fibers is an important topic because even in the same type of wood, the morphology and composition of its pulp can be altered by processing, and these alterations could have significant effects on the ability of the fibers to limit autoge- nous shrinkage. Therefore, an improvement in the understanding of the relationship between fiber properties and internal curing efficacy would make the selection, dosing, and even design of pulp fiber for internal curing in mortar and concrete more precise. More fundamentally, improved knowledge of the relationships between fiber parameters and changes in autogenous shrinkage should pro- vide new understanding of the mechanism(s) by which cellulosic materials function as internal curing agents. In pulp fibers, water can be held in the fiber lumen (or cavity enclosed by the cellulose-rich cell wall) or bound to and within the cell wall itself. The maximum amount of free water which can be held in the lumen could be related to the size of the lumen and its structure (e.g., open, closed, collapsed), which are in turn related to the type of wood and the processing of the fiber such as pulping, drying history, and refining. For example, fibers which have been dried after pulping may have collapsed lumens, which may limit their use for internal curing. The capacity to bind water 0958-9465/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.cemconcomp.2012.11.006 ⇑ Corresponding author. Tel.: +1 (404) 385 0825; fax: +1 (404) 894 2278. E-mail addresses: p.jongvisuttisun@gatech.edu (P. Jongvisuttisun), camille. negrello@ens-cachan.fr (C. Negrello), kimberly.kurtis@ce.gatech.edu (K.E. Kurtis). Cement & Concrete Composites 37 (2013) 126–135 Contents lists available at SciVerse ScienceDirect Cement & Concrete Composites journal homepage: www.elsevier.com/locate/cemconcomp