In recent years, fiber reinforced polymer (FRP) composites have been widely applied in civil engineering for retrofitting
or renewal of existing structures. Since FRP composite may degrade when exposed to severe outdoor environments, a
serious concern has been raised on its long term durability. In the present study, fiber Bragg grating (FBG) sensors were
embedded in glass-, carbon- and basalt-fiber reinforced epoxy based FRP plates with wet lay-up technology, to in-situ
monitor the stain changes in FRPs during the curing, and water immersion and freeze-thaw ageing processes. The study
demonstrates that the curing of epoxy resin brings in a slight tension strain (e.g., 10 ~ 30 με) along the fiber direction and a high contraction (e.g., ~ 1100με) in the direction perpendicular to the fibers, mainly due to the resin shrinkage. The
cured FRP strips were then subjected to distilled water immersion at 80oC and freeze-thaw cycles from -30°C to 30°C.
Remarkable strain changes of FRPs due to the variation of the temperatures during freeze-thaw cycles indicate the
potential property degradation from fatigue. The maximum strain change is dependent on the fiber types and directions
to the fiber. Based on the monitored strain values with temperature change and water uptake content, CTE (coefficient of thermal expansion) and CME (coefficient of moisture expansion) are exactly determined for the FRPs.