Effect of interfacial properties between polyethylene and polyvinyl alcohol fiber/cement matrix on properties of mortar and ECC

To explore the influence of the interface properties between fiber/cement matrix on the performance of fiber‐modified cement‐based composite. Polyethylene (PE) and polyvinyl alcohol fiber (PVA) are brought in the cement‐based materials to prepare mortar and Engineered Cementitious Composite (ECC) samples. The mortar's mechanical, and ECC's tensile capacity, four‐point bending and porosity were tested to verify the interface's influence on samples' performance. Furthermore, the water contact angle was used to analyze the wettability of the fiber, and a scanning electron microscope (SEM) was used to observe the fiber/matrix interface on the microscopic scale. Molecular dynamics simulation was performed to calculate the interfacial paraments from an atomic scale. The results shows that fiber increases the toughness of the mortar and improved its flexural strength. Through SEM, it was found that PVA fiber can form tight adsorption with the hydration matrix. While there are many apparent cracks and pores at the PE/matrix interface, the poor bonding destroys the matrix's structure and reduces its compressive strength. By analyzing the performance of ECC samples, it was known that PVA‐ECC's strain rate can reach 5.73%, while PE‐ECC is 4.20%. PE fiber has higher mechanical strength and can bear more loads, it helps PE‐ECC to obtain a greater modulus of rapture. Nuclear magnetic resonance results showed that the porosity of PVA‐ECC is lower than PE‐ECC. The ability of PE‐ECC to resist external interference is weak, and the interface of PE/matrix is easily damaged. Molecule dynamics simulation results indicated the adsorption energy between PVA/CSH is 6.17 times that of PE/CSH. The PVA/C‐S‐H interface tends to form CaO and H‐bonds to strengthen the bonding, the bonding has limited the movement of atoms and making the PVA chains tightly adsorbed on the CSH surface. While the adsorption between PE and CSH is weak, the PE will detach from the CSH surface and form aggregates. Moreover, PVA and water molecules form a stable hydrogen bond network to promote the hydration production grows on the surface of PVA fiber. However, PE fiber is complex enough to adsorb water molecules and hardly encourage the development of pores at the interface. By analyzing the properties of the interface between different fibers and cement matrix can provide insights for strengthening the interface properties of fiber cement matrix, and then improve the properties of fiber cement‐based composites.