Effect of confinement of steel tube on durability of concrete pier exposed to partial/full immersion sulfate attack solution

This study investigates the effect of confinement of steel tube on durability of concrete pier exposed to external sulfate attack (ESA). Two different dimension of concrete cylinder specimens by confinement of steel tube was placed in both partial and full immersion sodium sulfate solution, respectively. Expansion, compressive strength and sulfate profiles were tested, and chemical and microstructural analysis using microscopic tests were examined. Moreover, the confining compressive stress generated by confinement was calculated during the attack. Results indicate that confinement makes specimens superior resistance to both chemical sulfate attack (CSA) and physical sulfate attack (PSA). For partial immersion, steel tube creates a barrier between the external environment and drying parts of the concrete cylinder, which eliminates capillary rise on concrete surface and resulting salt crystallization damage, thus shifting from the dual actions of PSA and CSA to the sole CSA; Moreover, its confinement generates compressive stress inhibiting cracks of restrained specimens due to expansion force of attack products by the CSA, leading to reduction in penetration of sulfate (sulfate diffusion coefficient lower 30.3 % than unrestrained ones). For full immersion, confinement can restraint cracks of restrained specimens by the CSA, causing reduction in penetration of sulfate (diffusion coefficient of sulfate ion lower 104.6 % than unrestrained ones). Besides, confinement decreases the depth of chemical changes and the amount of sulfate attack products (ettringite and gypsum) compared to the unrestrained ones.