Basalt Fiber Surface Modification through Polydopamine Hydrophilic Coating for Oil Well Cements

Basalt fiber (BF) is a promising toughening material for oil well cement owing to its high mechanical strength and thermal stability; however, its smooth surface and poor dispersibility often result in weak interfacial bonding and limited toughening efficiency. To overcome these limitations, a mussel-inspired two-step surface modification strategy was developed. Dopamine hydrochloride (DA-HCl) was first introduced to enhance the surface hydrophilicity and reactivity of BF, followed by secondary modification using γ -glycidoxypropyltrimethoxysilane (KH560) and tetraethyl orthosilicate (TEOS) to further improve fiber dispersion and interfacial bonding with the cement matrix. Fourier transform infrared spectroscopy (FTIR) and energy dispersive spectroscopy (EDS) analyses confirmed the successful formation of the composite coating, while quantitative image analysis revealed a marked reduction in the dispersion coefficient from 191.59% to 19.47%. In addition, 3D optical surface profilometry was employed to quantitatively characterize the surface roughness evolution of the fibers, demonstrating a pronounced increase in nanoscale roughness after composite modification. Mechanical testing showed that cement reinforced with composite-modified BF exhibited increases of 14.9% in compressive strength and 20.3% in flexural strength compared with unmodified BF-reinforced cement. Single-fiber pull-out tests further indicated a 34.62% enhancement in interfacial bond strength. Moreover, microstructural observations after short-term high-temperature curing suggested that the composite-modified fibers maintained improved interfacial characteristics relative to unmodified fibers. Overall, the proposed modification strategy effectively enhances the interfacial adhesion of BF in cement-based systems and improves fiber dispersibility, providing a viable approach for enhancing the short-term mechanical performance of fiber-reinforced oil well cement.