To address the shortcomings of oil well cement stone like high brittleness and susceptibility to cracking, basalt fiber (BF) can be incorporated to increase the toughness. However, the interfacial bonding between BF and the cement matrix is weak, which cannot give full play to the role of BF. Grafting graphite oxide (GO) onto BF surface enhances its hydrophilicity, increases surface roughness, and promotes interfacial interaction with the cement matrix. The role and mechanism of toughening of modified basalt fiber (MBF) were investigated by mechanical property tests and microscopic characterization. The results showed that: (1) MBF has superior hydrophilicity, a rougher surface, and higher interfacial shear strength compared to BF. (2) MBF can enhance the compressive strength of cement stone, when the MBF dosage is 0.4%, after 1, 3, 7 and 14 days of curing, the strength increased by 21.41%, 21.02%, 22.39% and 26.91%, respectively, compared with the blank sample. (3) According to microstructural characterisation, the addition of BF and MBF does not alter the hydration products of cement. The samples exhibited pore diameters predominantly ranging from 10 to 150 nm. The introduction of MBF resulted in a reduction of 11.01% in the porosity of the samples compared to the blank samples. The primary factor behind the improvement of cementite's mechanical characteristics by the fiber was the decrease in porosity.
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