ACI - SP-326
Durability and Sustainability of Concrete Structures (DSCS-2018)
|Publication Date:||1 August 2018|
In recent years, internal curing whereby water pre-saturated materials such as lightweight aggregates (LWAs), superabsorbent polymers (SAP), and etc. are used not only to enhance the hydration of cement-based materials, but also to minimize self-desiccation routinely observed in low water-to-cement (w/c) ratio cement composites have generated enormous attention in the cement research community. Studies by Henkensiefken et al. (2009, 2010) reported improved drying shrinkage and plastic shrinkage resistance of cement mixtures containing presaturated LWAs. Related study by Bentz (2009) indicated that internal curing by LWAs enhanced the chloride penetration resistance of cement mortar. These aforementioned studies have conspicuously indicated that internal curing could play a major role in the quest to achieve durable high-performance cement composites. However, sustainability considerations make it imperative that renewable and readily available materials should be explored for use as internal curing agents.
Wood fibers are in abundant supply all over the world, and they have several advantages such as being lightweight and renewable. Moreover, given that the ability to retain and release water is an essential attribute of internal curing agents, porous and hydrophilic cellulose fibers seems to meet this fundamental requirement. However, compared to LWAs and SAP, just a few studies (Kawashima & Shah, 2011; Mezencevova et al., 2012; Jongvisuttisun et al., 2013) have investigated the possibility of using wood fibers as internal curing agents in cement composites. Kawashima & Shah (2011) observed that while autogenous shrinkage test result indicate that cellulose fibers have internal curing potential, poor fiber dispersion induced by reduced matrix consistency hampers the effectiveness of cellulose fibers. Mezencevova et al. (2012) reported that treated thermomechanical pulps were more efficient in reducing autogenous shrinkage of cement paste. Related study by Jongvisuttisun et al. (2013) revealed that the internal curing potential of hardwood fibers is greatly influenced by the physical morphology of fibers.
Mechanical refinement is one of the established process of modifying the physical morphology of cellulose fibers in the paper industry. According to Roux and Mayade (1999), pulp refinement enhances inter-particle bonding of fibers. And this is traceable to refinement induced changes in fiber structure and chemical components on fiber surface (Fardim and Duran, 2003). For cement composites, Coutts (2005) suggested that refining softens fibers thereby enhancing fiber-matrix bonding. In a related study, Tonoli et al. (2007) observed improved mechanical properties in cement composites containing moderately refined fibers. From the foregoing it is apparent that refinement has some positive influence on the behavior of fibers as reinforcement in composites. However, it is unclear whether this influence could be extended to, and relevant to the performance of cellulose fibers as internal curing agent in cement-based materials.
Therefore, the present study investigates the effect of refinement induced physical changes of cellulose pulp on their potential as internal curing agent in cement composites. Specifically, how the degree of fiber refinement influences the physical morphology of fibers, water retention-desorption