주기적 염해 시험에 따른 소켓 타입 전극을 활용한 철근 콘크리트의 OCP 특성
Characteristics of OCP of Reinforced Concrete Using Socket-type Electrodes during Periodic Salt Damage Test
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초록
콘크리트 구조물의 내부의 매립된 철근은 부동태 피막으로 인해 부식으로부터 보호된다고 알려져 있다. 구조물의 경제적인 내구수명 산정을 위해 부식 발생 시기를 지연시키거나 초기 부식 시점을 평가하는 것은 매우 중요하다. 본 연구에서는 3 가지 수준의 피복두께(60 mm,45 mm, 30 mm), 물-시멘트 비(40.0%, 50.0%, 60.0%), 염화물 농도(0.0%, 3.5%, 7.0%)를 고려한 콘크리트 시편을 대상으로 부식 모니터링을 수행하였는데, 한천(Agar) 기반 소켓 형식 센서를 활용하여 OCP를 측정하였다. OCP 측정 시 습윤 조건에서는 전위가 감소하고 건조 조건에서는감소된 전위가 일부 회복하는 거동을 확인하였다. 모든 물-시멘트 비에서 피복두께가 30 mm의 경우 가장 낮은 OCP값이 측정되었으며, 피복두께가 30 mm에서 45 mm로 증가할 때 빠르게 OCP가 회복하였다. 이는 피복두께가 염화물 이온의 침투에 효과적인 방어기구로 작용하기 때문이다. 염화물 농도가 증가함에 따라 물-시멘트 비의 영향보다 피복두께에 대한 영향이 더 지배적인 경향을 보이는 것으로 도출되었다. 시편의해체 후 추가적인 모니터링과 염화물량의 평가를 수행하면 제안된 부식 모니터링 기법의 신뢰성을 높일 수 있을 것으로 판단된다.
Abstract
It is known that buried rebars inside concrete structures are protected from corrosion due to passive layer. It is very important to delay thetiming of corrosion or evaluate a detection of corrosion initiation for the purpose of cost-beneficiary service life of a structure. In this study, corrosionmonitoring was performed on concrete specimens considering 3 levels of cover depth(60 mm, 45 mm, and 30 mm), W/C(water to cement) ratio(40.0%,50.0%, and 60.0%) and chloride concentration(0.0%, 3.5%, and 7.0%). OCP(Open Circuit Potential) was measured using agar-based socket typesensors. The OCP measurement showed the consistent behavior where the potential was reduced in wet conditions and it was partially recovered indry conditions. In the case of 30 mm of cover depth for most W/C ratio cases, the lowest OCP value was measured and rapid OCP recovery was evaluatedin increasing cover depth from 30 mm to 45 mm, since cover depth was an effective protection against chloride ion ingress. As the chloride concentrationincreased, the effect on the cover depth tended to be more dominant than the that of W/C ratio. After additional monitoring and physical evaluationof chloride concentration after specimen dismantling, the proposed system can be improved with increasing reliability of the corrosion monitoring.
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