Fiber-Matrix Bond Characteristics of Alkali-Activated Slag Cement–Based Composites Ahsanollah Beglarigale 1 ; Serdar Aydın 2 ; and Cengiz Kızılırmak 3 Abstract: Fiber-matrix bond properties of alkali-activated slag cements (AASC)–based composites have not been studied comprehensively in literature. Within the scope of this study, the effects of AASC matrix phase composition and the silicate modulus of activator solution on the pullout behavior of steel fiber were investigated under water- and steam-curing conditions. Test results showed that AASC have a superior bond strength compared to portland cement (PC). Bond strength of AASC mortars with a compressive strength greater than 18 MPa were found higher than that of PC mortar with a compressive strength of 55 MPa. When the compressive strength of AASCs is higher than 40 MPa, the bond strength of AASC exceeds the bond strength of PC mortars that have compressive strength of 120 MPa. Microstructural analysis revealed that the map cracking in the fiber-matrix transition zone, which was induced by high drying shrinkage of AASC, can be eliminated by incorporating pozzolans. Consequently, it is possible to produce much higher-performance fiber-reinforced composites by using AASC owing to its superior adherence to steel fiber. DOI: 10.1061/(ASCE)MT.1943-5533.0001642. © 2016 American Society of Civil Engineers. Author keywords: Steel fiber; Bond characteristics; Mechanical properties; Alkali-activated slag cement. Introduction Alkali-activated slag cements (AASC) composites can be catego- rized as new construction materials which are produced by the activation of ground-granulated blast furnace slag (GGBFS) by various alkali solutions. The main reaction product of AASC is Na-incorporated calcium-silicate-hydrate (C─S─H). The C─S─H gel of the AASC has a lower calcium:silicate (C∶S) ratio as compared to the portland cement (PC) binder. Except some drawbacks such as quick setting (Zivica 2007), high shrinkage with microcrack formations (Collins and Sanjayan 1999), and efflores- cence, the AASCs have many environmental, economical, and technical advantages. Recent studies showed that these deficiencies of AASCs can be reduced or completely eliminated by the partial replacement of GGBFS with silica fume, fly ash and metakaolin, and steam curing (Aydın 2010, 2013). The behavior of steel-fiber– reinforced AASC composites is directly related to fiber-bond char- acteristics. In spite of few studies on the flexural behavior of the steel-fiber–reinforced AASC composites presented in literature (Bernal et al. 2010; Aydın and Baradan 2013), the fiber-matrix bond (FMB) characteristic of AASCs have not been reported com- prehensively. Very limited information about the FMB property of an AASC mixture was reported by Bernal et al. (2010). The FMB characteristic, which provides the stress transferring between the fiber-matrix phases, is the key factor in the mechanical properties of fiber-reinforced composites. The findings from many research works that have dealt with PC composites can be summa- rized within three main questions: • How can the matrix properties affect the FMB performance? It is obvious that increasing the mechanical strength of cementitious composites leads to enhanced FMB properties (Shannag et al. 1997; Tuyan and Yazıcı 2012; Beglarigale and Yazıcı 2015). Most, if not all, factors that improve the mechanical strength can also increase the FMB strength. In other words, denser C─S─H structure, which can be provided by many factors such as the lower water-to-cement ratio or the incorporation of some of mineral admixtures (Tuyan and Yazıcı 2012), leads to denser fiber-matrix interface and better adhesion between them. Also, the aggregate size can affect the pullout behavior of fiber (Kim et al. 2012; Beglarigale and Yazıcı 2015). Aggregate coarser than 1 mm could have a frictional effect during the fiber pullout (Beglarigale and Yazıcı 2015). Kim et al. (2012) revealed that the bond strength of twisted fiber embedded in the concrete of nuclear power plants can be enhanced by increasing the sand-to- aggregate ratio. • How can the fiber-matrix transition zone (FMTZ) properties af- fect the bond characteristics? The FMTZ is one of the main fac- tors that affects the fiber-matrix bond properties. The FMTZ in the traditional cementitious materials is quite porous and also filled with CaðOHÞ 2 crystals (Bentur et al. 1985). The properties of FMTZ can be improved by supplementary cementitious ma- terials (Banthia et al. 1998; Bentur et al. 1995; Chan and Li 1997; Kayali 2004; Chan et al. 2004; Tuyan and Yazıcı 2012). Generally, any change in the properties of the FMTZ can affect the fiber-matrix bond characteristics. For example, microstructural investigation conducted by Beglarigale and Yazıcı (2015) revealed that the congestion of the tobermorite or other hydration products in the FMTZ of autoclaved cured cementitious composites leads to a major increase in the FMB strength. Also, some of the durability problems can affect the FMTZ and therefore the fiber-matrix bond properties. Beglarigale and Yazıcı (2013) reported that the alkali–silica reaction gel congestion in the fiber-matrix interface increased the bond strength significantly. • How can the fiber properties affect the bond characteristics? Fiber type, strength, diameter, embedded length, the end condi- tion of fiber (smooth and hooked-end), inclination angle, and 1 Ph.D. Candidate, Dept. of Civil Engineering, Dokuz Eylül Univ., Turkey (corresponding author). E-mail: ahsan.beglari@gmail.com 2 Associate Professor, Dept. of Civil Engineering, Dokuz Eylül Univ., Turkey. E-mail: serdar.aydin@deu.edu.tr 3 M.Sc. Candidate, Dept. of Civil Engineering, Dokuz Eylül Univ., Turkey. E-mail: cengiz_kizilirmak@hotmail.com Note. This manuscript was submitted on November 30, 2015; approved on March 4, 2016; published online on June 9, 2016. Discussion period open until November 9, 2016; separate discussions must be submitted for individual papers. This paper is part of the Journal of Materials in Civil Engineering, © ASCE, ISSN 0899-1561. © ASCE 04016133-1 J. Mater. Civ. Eng. J. Mater. Civ. Eng., 04016133 Downloaded from ascelibrary.org by Dokuz Eylul Universitesi Rektorlugu on 06/13/16. Copyright ASCE. For personal use only; all rights reserved. View publication stats View publication stats