Properties of Concrete after 30 yearsf Exposure under Marine Submerged Condition
Hidenori HAMADA, Tarek Uddin Mohammed, Toru YAMAJI
Abstract:A detailed investigation on 30-years old concrete specimens of 150 mm in diameter and 300 mm in height made with ordinary portland cement (OPC), high early strength portland cement (HES), moderate heat portland cement (MH), slag cement of type B (SCB), and alumina cement (AL) was carried out. In each specimen, steel bars were embedded at cover depths of 20, 40, and 70 mm. Mineralogy and microstructure of mortar portions at the inner and outer regions, coarse aggregate-mortar interface and steel-concrete interface were investigated. Carbonation depth, acid-soluble chloride contents, electro-chemical and corrosion condition of embedded steel bars were evaluated. It is concluded from the results that the microstructure of concrete at the outer region for SCB and AL becomes denser compared to the inner region. For AL, the inner region is relatively more porous and also a porous steel-concrete interface is found. Chloride ingress in concrete was lower for SCB and AL compared to OPC, HES and MH. However, more corrosion over the steel bars was found for AL. The surface condition of the steel bars embedded in concrete made with SCB remains as same as the initially polished condition. Utilization of SCB is concluded as one of the best choices to improve long-term durability of marine concrete structures. Key Words:Cement, Porosity, Mineralogy, Microstructure, Interface, Chloride, Corrosion, Marine