Abstract
The performance of different natural fibers (hemp, kenaf and bamboo) used to formulate composites with an alkali-activated matrix based on metakaolin is evaluated. Short fibers were randomly dispersed up to about 3% of the binder weight, and the fresh and cured properties of the derived composites were determined. Up to the investigated fraction, it is still possible to obtain adequate workability without the supply of additional water or additives. Upon modification with fibers, the mechanical behavior changes from completely brittle to pseudoplastic with increased toughness. The flexural strength increases by up to 80% at the highest bamboo amount and up to 20% for kenaf. Hemp fibers have a negligible effect on flexural strength but strongly improve the materials’ toughness. Moreover, the addition of fibers does not change the manner in which the material interacts with moisture. Indeed, the water uptake of the modified samples was comparable to that of the unmodified samples, and the composites showed a decreased rate of water diffusion as the amount of fiber increased.
Highlights
Geopolymers represent a possible way to reduce the environmental impact caused by building materials based on traditional binders
While they possess promising mechanical properties, i.e., compressive strength, they suffer from extreme brittleness and from limited dimensional stability
Another problem related to the use of natural fibers as substitutes for synthetic fibers is the variability of the chemical composition, which affects the final mechanical properties
Summary
Geopolymers represent a possible way to reduce the environmental impact caused by building materials based on traditional binders While they possess promising mechanical properties, i.e., compressive strength, they suffer from extreme brittleness and from limited dimensional stability. Pretreatments have been made in order to overcome these problems, this increases the overall economic and environmental impact of the process [24,25,26,27,28] Another problem related to the use of natural fibers as substitutes for synthetic fibers is the variability of the chemical composition, which affects the final mechanical properties. For the first time, the effects of three different types of natural fibers inserted in an alkali-activated matrix based on metakaolin on fresh and cured properties have been compared.
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