International Concrete Abstracts Portal

Experience and research have shown that reinforcement in submerged concrete appears to be well protected against corrosion. Questions have been raised as to whether this durability will be present in structures subject to dynamic loads and in structures spanning through several environment zones. To clarify the effect of loading, eight concrete beams were exposed dynamically loaded at a seawater laboratory. Four of the specimens were allowed to corrode freely, while the rest were cathodically protected. To study the corrosion behavior of multizone exposed concrete structures, eight concrete columns with a diameter of 0.6 m and a height of 5 m were installed in the sea. One of the main objectives was to study the cathodic current density demands of embedded steel exposed to different environmental zones and of multizone exposed embedded steel. This paper presents the results from the laboratory and field tests, and the main conclusion is that the corrosion conditions found on a multizone exposed concrete structure differ from those found on a completely submerged structure.

Composite steel/concrete sandwich elements are being given intensive research and development efforts because of their excellent structural performance under intense concentrated loads, such as those imposed by sea ice or icebergs. Since the initial applications are expected to be in Arctic and sub-Arctic environments, consideration must be given to thermal phenomena and to insuring long-term durability. Thermal problems addressed include the effects of heat of hydration, with subsequent cooling, freeze-thaw behavior, differential contraction and strain gradients, and low-temperature ductility under impact. Durability problems addressed are corrosion of plates and reinforcement, abrasion and abrasion-corrosion interaction, and fatigue under the continuous crushing of ice. After examining the particular aspects of these considerations in relation to composite elements, recommendations for long-term satisfactory performance are developed as a guide for practical application.

Many concrete structures, such as railways and highways, are constructed along the coastal lines or over the oceans in Japan. Most of these structures are deteriorated by corrosion of reinforcing bars. To prevent the corrosion in new structures, many methods are tested and several recommendations are already presented. Considering existing structures, the largest problem now is how to decide when to repair the deteriorated structure. This paper clarifies how the behavior of concrete beams and columns changes as corrosion of reinforcing bars increases and presents an idea as to when to repair the structures in marine environment. Results from the studies carried out indicate that the deterioration of marine concrete structures caused by corrosion of reinforcing steel bars is not always directly related to strength reduction of reinforcing bars. When corrosion of reinforcing bars takes place, crack formation in concrete could lead to a greater reduction in strength and ductility of the structure than expected. The repair of the structures must be done when cracks are formed along the reinforcing bars.

A new index has been suggested for controlling and protecting reinforced concrete from corrosion. This index, defined as the difference in the average strain between concrete and reinforcing bar, is tentatively called the cracking index. On the basis of the exposure tests, relationships between the cracking index and the rust thickness of reinforcing bars in concrete are evaluated under corrosive atmosphere. Cracking index could be used for the assessment of corrosion. The relationship between the critical rust, which is the rust thickness of reinforcing bars at the onset of longitudinal cracking, and cover thickness is obtained by rapid corrosion tests. It is concluded that the allowable stress for reinforcing bars--thus the corrosion--can be controlled by the required amount of concrete cover.

The Rodney Terminal is a 610 m long, 37 m wide, L-shaped container wharf of concrete construction. It was constructed during 1974-75 and utilized about 1750 24 in. (600 mm) hollow core octagonal precast piles. Soon after construction, pile distress began to be noted. Forty piles were repaired in 1978 and seven piles were replaced in 1982. Since the pile deterioration was rapid and progressive, extensive investigations were carried out to determine the causes of the pile deterioration and possible remedial measures. Later, studies were carried out to investigate whether the piles had met the contract specifications. These investigations revealed that distress was primarily vertical cracks in the outer half of the pile walls. Scouring and freezing and thawing spalling, over time, caused loss of the pile wall. The vertical cracks were related to thermal stresses during the winter months and possibly high thermal gradients during steam curing at the time of manufacture. The rapid freezing and thawing deterioration was due to inadequate air-entrainment of the concrete. The pile distress was also caused, in a few cases, by manufacturing defects. The investigations suggested that the following changes to the original design and specifications may have reduced the problems: 1) higher percentage of circumferential steel; 2) air-void system determinations on samples of the hardened concrete to insure that the specification intent was being met; and 3) use of solid instead of hollow core piles. Remedial steps at the Rodney Terminal have included epoxy-grouting (unsuccessful), pile replacement (expensive), fiberglass jacket over reinforced grouted annulus, insulated fiberglass jackets over reinforced grouted annulus, air-entrained and steel fiber reinforced concrete jackets, and insulated jackets.