Mechanical behavior of K‐geopolymers reinforced with silane‐coated basalt fibers

Abstract

AbstractA potassium‐based geopolymer (KGP) was produced through the combination of metakaolin and a K‐based alkali metasilicate solution (K2O•Al2O3•4SiO2•11H2O). Two types of silane‐coated chopped basalt fibers, manufactured for cement or epoxy‐based applications, were used in order to compare their effects. The fibers had a 12.7 mm (½ inch) length and were incorporated initially in 10 wt % contents, due to the limited fluidity of the matrix. The effect of the addition of Sapetin® superplasticizer in varying weight percentages was examined through consistency tests. 0.5% by weight of the matrix was established to be an adequate amount to improve the geopolymer workability, allowing a greater incorporation of both types of fibers into the matrix (20 wt%). The mechanical properties were analyzed through compression and 4‐point flexural tests. Pull‐out and direct tensile tests were also performed. Additionally, X‐ray diffraction (XRD) was conducted with the KGP material and scanning electron microscopy (SEM) was used to measure the fiber cross sections. Both composites manufactured with 10 wt % of fibers reached similar high flexural strengths (~30 MPa), suggesting a suitable crack propagation at higher stresses due to strong fiber‐matrix adhesions. The fibers manufactured for epoxy applications presented a greater compatibility in 20 wt % contents, reaching 37.8 MPa in flexural tests. This was attributed to a better dispersion of such fibers in a fresh mix with reduced friction, such as KGP with the addition of superplasticizer, suggesting an improved use of this reinforcement in such contents.