Degradation Characteristics of Glass Fiber Reinforced Plastics Using Unsaturated Polyester as Matrix in Weak Alkaline Aqueous Solution

To verify the applicability of glass -fiber reinforced plastic (GFRP) with an unsaturated polyester matrix in manhole environments, we conducted solution immersion tests in a weak alkaline aqueous solution to evaluate degradation characteristics. The test results clarify the effect of accelerated deterioration due to alkali remaining on the sample surface, that diffusion of alkaline ions is slower than that of water, and that the resin -fiber interface preferentially deteriorates due to the diffusion of water. If water diffusion is the dominant factor in the degradation of the flexural strength of a sample, the degradation of the flexural strength can be extrapolated using a power law equation; however, under conditions where the degradation is also accelerated by alkali, it is appropriate to extrapolate by the degree of degradation using a logarithmic equation that fits the measurement results well. The results showed that the flexural strength of hand -layered GFRP with a thickness of 5 mm and 7 layers in an alkaline solution of pH 10 was estimated to decrease by half in 16.3 to 21 years.