Multiple cracking response of plasma treated polyethylene fiber reinforced cementitious composites under flexural loading Kamile Tosun ⇑ , Burak Felekog ˘lu 1 , Bülent Baradan 2 Department of Civil Engineering, Dokuz Eylul University, _ Izmir, Turkey article info Article history: Received 22 February 2011 Received in revised form 1 December 2011 Accepted 3 December 2011 Available online 9 December 2011 Keywords: Polyethylene Plasma Fiber reinforced cementitious composites Multiple cracking behavior abstract The effects of low frequency cold plasma treatments on the microstructure and chemistry of Polyethylene (PE) have been investigated. PE plates and fibers were exposed to plasmas of argon and oxygen gases. The surface wettabilities of plasma-treated plates were monitored. Possible physical changes on fiber surfaces were observed by a scanning electron microscope (SEM) at micrometer scale and by an atomic force microscope (AFM) at nanometer scale after this process. The effects of plasma treatment on surface chemistry of PE fibers have been analyzed by using an X-ray photoemission spectroscope (XPS). The fibers modified by plasma treatments were used in prismatic cementitious composites. The flexural per- formance of samples were characterized at two different ages (28 days and 8 months). Results showed that plasma treatment caused significant modifications on fibers’ surface structure and composites’ per- formance. Proper plasma treatment conditions significantly leads to improvement of multiple cracking behavior of fiber reinforced composites. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Fiber reinforcement is a preferred way of improving the toughness and reducing the cracking susceptibility of cementitious composites [1,2]. High-strength polyvinyl alcohol (PVA) and poly- ethylene (PE) fibers can be accepted as favorable examples of polymeric fibers for fiber reinforced composite (FRC) production. Among these fibers, PE fibers can be produced with variable densi- ties and called as high density polyethylene (HDPE), ultra high molecular weight polyethylene (UHMWPE) depending on fibers’ manufacturing procedure and polymerization degree [3]. Commercial examples of ultrahigh molecular weight polyethyl- ene (Spectra Ò , Dyneema Ò ) fibers have been previously produced with excellent tensile and shear strength properties and intensively being used in special applications like weapon armors, high strength ropes, etc. These fibers were recently employed in FRC applications, and found significantly effective in terms of toughness improvement. It was also reported that incorporation of PE fibers at dosages in the order of 1–1.5% by volume resulted with composites presenting multiple cracking behavior [4–6]. Furthermore, signifi- cant strength and toughness improvements were recently reported when PE fibers used in hybrid fiber applications with steel fibers [7–9]. Despite their high-performance in cementitious composites, the activated capacity of high-strength PE fibers limited due to their surface structure. These polyolefin group fibers have smooth and hydrophobic surface that may be susceptible to slipping when used as reinforcement in cementitious composites. Their potential can be further improved and activated if the surface structure of PE fibers properly changed and optimized by means of chemical bonding and mechanical interlocking capacity. Cold plasma treatment can be a suitable pre-processing method to modify the surface properties of PE fibers without causing any significant change in their bulk properties [10–12]. Unlike other wet chemical etching methods, cold plasma treatment is an envi- ronmentally friendly alternative for polymer surface modification purposes. While the selection of plasma composition brings the controlled application of treatment, if appropriate gas composition is selected, no problematic waste will be disposed to nature after the treatment. A comprehensive literature survey on the compari- son of cold plasma treatment of polymers can be found in Morent et al. [13]. The main changes on polymer surface by the application of cold plasma treatment can be listed as plasma deposition or polymerization, surface energy change due to additional bonding or bond breaking and physical etching [13,14]. All these modifica- tions can be observed instantaneously. The resultant effect depends on the competition between etching and redeposition rate. If etching is more significant than redeposition, the resultant situation called plasma etching. If redeposition is dominant, plasma polymerization takes place [14–16]. While the former is usually observed in gas plasmas, the latter can be seen mostly in case of monomer plasma applications. In this study, gas plasma treatments have been implemented and the dominant 0958-9465/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.cemconcomp.2011.12.001 ⇑ Corresponding author. Tel.: +90 232 4127059. E-mail addresses: kamile.tosun@deu.edu.tr (K. Tosun), burak.felekoglu@deu. edu.tr (B. Felekog ˘lu), bulent.baradan@deu.edu.tr (B. Baradan). 1 Tel.: +90 232 4127041. 2 Tel.: +90 232 4127011. Cement & Concrete Composites 34 (2012) 508–520 Contents lists available at SciVerse ScienceDirect Cement & Concrete Composites journal homepage: www.elsevier.com/locate/cemconcomp