V

Small potential

Anode

Figure 3-42. Cathodic protection system potentials.

UNUttlMA Ittl insrtu hun procedures lar, the water-to-cement ratio. This ratio is one of the prime considerations in concrete mix design not only to provide adequate concrete strength, but, equally important, to provide long term durability of concrete in the harsh marine environment.

The performance of a concrete structure is most affected by the care taken in its construction and installation. Properly made concrete is highly durable in marine applications, exhibiting resistance to corrosion of reinforcing steel, chemical deterioration, weathering, erosion, and structural damage. Concrete is relatively strong under compressive loading, and with steel reinforcing resists bending and tensile forces. Concrete can be cast in place at the job site, precast into the required shape at a concrete plant and shipped to the site, or pre-stressed before installation to accept additional loading. With proper procedures (see Section 2.10), concrete can be rapidly placed underwater where it will harden into good quality concrete.

Circular or square concrete piles (Figure 3-6) are widely used to support piers, wharves, and other structures. Concrete is used as a decking material for many waterfront facilities and in retaining wall structures, such as those needed for closed piers and wharves, bulkheads, quay walls, dry-docks, and seawalls. It is also used in pavements, bridge foundations, boat loadings and ramps, breakwaters, undersea cable and pipeline stabilization, and offshore structures.

3.6.2 Deterioration of Marine Concrete Structures

The most common damage resulting from the premature deterioration of concrete structures in or near sea water is cracking and loss of material (or cross section). Softening of the concrete due to chemical action is another form of damage but less common than cracking. As shown in Table 3-5, the damage to concrete is generally most severe in the splash and tidal zones, but does occur in all zones. The different exposure zones are shown in Figure 3-11.

Table 3-5. Types of Damage in Marine Concrete

Description of Damage

Zone (Location)*

Common Causes of Damage

Observed

Reinforcement

Freeze-Thaw

Abrasion

Sulfate Attack

Chemical Reaction of Aggregates

Structural Overload

Cracking

All

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