V-notched rail shear test applied to geopolymer composites

This work presents a systematic study of the shear properties of a potassium-based geopolymer reinforced with distinct types of fibers. Chopped basalt reinforcements in lengths from 3 mm up to 50 mm and 13 μm in diameter were compared with thicker 20-mm length, basalt mini bars, sand-coated basalt mini rods, and steel fibers. The samples were tested under a V-notched rail shear tests (ASTM D7078), coupled with optical measurements, namely, digital image correlation, allowing a novel study of their crack patterns and failure modes under shear loading. In general, the use of chopped fibers resulted in shear strengths of up to 9 MPa and shear moduli of 4.3 GPa, with no significant variation with fiber length increments, neither in shear stress nor strain at peak load (0.1%). Mini bars and steel fiber reinforcements resulted in slightly lower shear stresses of 7.1 and 8.4 MPa, respectively. They exhibited greater strain values at peak loads, up to 2.1% which were attributed to fiber-matrix enhanced adhesions, thereby allowing gradual debonding and increased ductility. This effect was also recorded for mini rods, but at much lower strength levels, which did not contribute to their multiple cracking capacities. The alignment of the mini rods in 45° directions resulted in a 50% increase in shear stress, showing the feasibility of tailoring the manufacturing process to attend to distinct demands.