Influence of Different Fiber Types in Geopolymer Mortars: Strength Development and Crack Formation

Geopolymers are a promising eco-friendly alternative to ordinary Portland cement because of their beneficial low-emission, mechanical, and durability properties. Nevertheless, these inorganic poly-mers show quasi-brittle behavior and possess low tensile strength which causes cracks under restraint shrinkage. This study aims at controlling drying shrinkage cracks in metakaolin-slag-based geopoly-mer mortar by means of adding fiber reinforcement up to 2% by volume. Polypropylene, glass, cellu-lose, uncoated basalt, and two different types of coated basalt fibers were used. The effect of fiber addition on the geopolymer composite behavior was investigated regarding workability, splitting ten-sile strength, and compressive strength. Moreover, the crack propagation was analysed on the cylin-dric disc samples. Results show that the strength characteristics of geopolymer mortar can be im-proved by fiber reinforcement, for instance, uncoated basalt fibers increased the splitting tensile strength and compressive strength of geopolymer mortar up to 33% and 17% respectively. Beyond that, cracks were distributed more uniformly, the crack widths were reduced to 20%, and crack prop-agation was limited by appropriate fiber reinforcement