Influence of steel slag on the properties of alkali-activated fly ash and blast-furnace slag based fiber reinforced composites

This work focuses on studying the alkali-activated fiber reinforced composites (AAFRCs) with steel slag (SS) as a precursor material. Apart from finding a sustainable way to reuse the enormous amount of industrial by-product SS, it is also the aim to develop material systems with excellent ductility that may be used in a variety of applications. Using SS as a partial replacement (0%–25%) for fly ash (FA) and ground granulated blast-furnace slag (GGBS), the influence on the alkaline activated system was carefully studied. Tensile and compressive properties of the composites were tested. Cracking characteristics under tensile tests were carefully analyzed. Meso-scale studies were performed, including three-point bending test and single crack tensile test, aiming to understand the mechanisms of the high ductility. Scanning electron microscopy (SEM) was adopted to study the microstructure. Based on the results of the mechanical properties, the optimum mix is with 15% SS replacement, where the tensile strength, tensile strain capacity and the compressive strength are 4.86 MPa, 3.94% and 93 MPa, respectively. SS replacement ratio higher than 15% leads to the deterioration of all the studied mechanical properties. The SS replacement has limited impact on the cracking characteristics of the concerned composite system. The results of the meso-scale studies help to explain the mechanism(s) accounting for the high ductility of the studied mixes. Especially, the influence of the SS replacement on the tensile strain capacity of the studied system is well reflected by the energy index. The SS replacement with a ratio of 15% showed no significant impact on the microstructure in comparison with that of the control mix, while it appears that the SS replacement modifies (weakens) the fiber-matrix interfacial bonding to some extent, leading to the improvement of the ductility.