Modification Mechanism of Glass Fibers on Ordinary Portland Cement and Sulphoaluminate Cement Composites

The problems of easy cracking, high brittleness, and low bond strength of ordinary Portland cement and sulphoaluminate cement (OPC-SAC) composites limit their application as rapid repair materials. In this study, glass fibers (GFs) were added to OPC-SAC composites with the content of 0.0–1.5% to improve their properties. Fluidity, mechanical properties, bond properties, and drying shrinkage properties were researched, and their microstructure was characterized by SEM and ICT. Hydration products at different curing ages were studied by XRD and FTIR. The results showed that GFs improved the mechanical properties of OPC-SAC composites. The 28 d flexural strength, compressive strength, and bond strength of specimens with 0.5% GFs reached maximum values, increasing by 22.1%, 12.1%, and 82.9%, respectively, compared with the control group without GFs.. GFs significantly inhibited the drying shrinkage of composites, and the inhibitory effect was magnified with the content of GFs. Adding 0.5% of GFs could reduce the porosity of specimens, decrease the volume proportion of pores (>10 mm3), and refine the pore structure. In summary, 0.5% is recommended as the optimal content of GFs to be added into the OPC-SAC composites.