Interface shear strength between soil and structural materials is dependent on the confining pressure. To increase the confining pressure, different methods of reinforcement and materials, such as carbon-fiber-reinforced polymer (CFRP) can be used. The shear strength of CFRP-improved soil is dependent on the interface properties of the soil and CFRP. The objective of this study is to investigate the interface properties (friction angle and adhesion) of sand and FRP experimentally using the direct shear test apparatus. To increase the surface roughness to improve the interface properties, a layer of sand was placed on saturated carbon fiber during the curing period [spark plasma sintering CFRP (SPSCFRP)] and normal stress was applied on the sand. More than 60 interface shear tests were conducted with different curing times, shear rates, and normal stresses on SPSCFRP during curing time. Tests showed that as normal stress on SPSCFRP during curing time increased, the friction angle increased; however, increasing the curing times and the rate of shearing had a small influence on interface properties.