Rin KASAI

Inhibition of Deterioration in Polymer Concrete Manholes using Surface Protection Methods

Takumi Shimomura

Polymer concrete has been widely used for underground structures such as manholes due to its high strength and durability. However, reports of unexpected strength degradation in long-term service have necessitated the establishment of rational maintenance strategies. Since moisture penetration is the primary cause of deterioration, this study evaluated the efficacy of surface protection methods, analyzed the mechanical behavior of large-scale specimens, and performed numerical simulations to predict service life.
Initial performance evaluations using small-scale specimens under 40°C hot water immersion and 20°C high-humidity conditions revealed that impregnation-type agents were ineffective because they could not penetrate the dense structure of polymer concrete. For coating-type agents, such as epoxy resins, weight-change metrics failed to confirm clear inhibition effects. This was attributed to the coating itself absorbing water and swelling, which offset the weight-gain inhibition of the substrate. These findings suggest that traditional evaluation methods based solely on mass change are insufficient for strictly judging the water-sealing performance of coatings applied to polymer concrete.
Subsequently, large-scale specimens with thicknesses of 100 mm and 150 mm—matching actual manhole wall dimensions—were tested under 60°C immersion. These results were compared with a numerical model developed from small-scale data that correlates moisture penetration depth with bending strength. The model successfully reproduced the mass increase and bending strength degradation, demonstrating high applicability across different specimen dimensions and moisture penetration directions. Furthermore, temperature dependency was evaluated using the Arrhenius law, determining that 40°C and 60°C environments represent acceleration factors of 5.6 and 31.4, respectively, relative to a 20°C ground environment.
This study proposes a shift from relying on surface protection methods, which are currently difficult to evaluate accurately, toward "preventive maintenance." This approach utilizes numerical analysis to predict the deterioration of the polymer concrete substrate itself, allowing for the determination of optimal inspection timings.