Study on the Effects of Blending Basalt Fiber and Polyethylene Fiber on the Mechanical Properties and Microstructure of Mortars

Fiber reinforcement technology has become one of the effective ways to improve the mechanical properties and deformation capacity of concrete. This study investigated the effects of single-doped and blended-doped basalt fiber (BF) and polyethylene fiber (PEF) on the drying shrinkage and mechanical strength of mortars. Meanwhile, the microstructure and reinforcement mechanism of single-doped and blended-doped BF and PEF mortars were studied. The results show that the mortar with a single-doped 6 mm PEF has the strongest resistance to drying shrinkage, and that blended fibers also effectively enhance the resistance to drying shrinkage of mortars. The compressive strength and flexural strength of the blended-fiber mortars are both higher than those of the single-fiber mortar. When the fiber length was 12 mm and the BF/PEF was 1:1, the compressive strength and flexural strength of the mortar at 28 d were respectively 18.6% and 56.1% higher than those of the mortar without fiber. Furthermore, when the fiber lengths were both 12 mm and 18 mm, the splitting tensile strength of the blended-fiber mortar at 28 d was higher than that of the single-fiber mortar and the mortar without fiber. When the fiber length was 12 mm and the BF/PEF was 1:1, the splitting tensile strength of the blended-fiber mortar was 103.3% higher than that of the mortar without fiber. The BF is randomly distributed in the mortar in the form of single filaments, and it exhibits brittle fracture when the mortar fails. When the mortar is damaged, PEF exhibits the phenomenon that the fibers are pulled out, and its surface is covered with hydration products, demonstrating excellent interfacial bonding performance. BF and PEF can interlock and intertwin with each other, forming a three-dimensional network structure in mortar, and jointly exert a complementary reinforcing effect of rigidity and flexibility.