1. Introduction to marine projects:
Marine structures are those structure built on sea or near it, properly designed to withstand internal, external loads and aggressive environmental exposures both physical and chemical in order to prolong service-life.
Reinforced concrete structures as part of marine structure are exposed to severe physical and chemical exposure such as wave impact, sulphate and chloride exposure. In tropical climates, the combination of above deleterious effects may cause severe defects in concrete structure only in very few years.
In order to delay these detrimental effects, high durability, chloride and sulphate resistant concrete become a necessity in constructing marine structure. The use of silica fume with a high water reducing admixture with retarding effect then become increasingly popular to produce a low permeability concrete and high sulphate resistant concrete.
2. Concrete Work in In Marine Structures
High strength concrete and durable concrete
b) Design Criteria:
• Sulphate and chloride resistance
• Low W/C ratio (splash & atmospheric zone < 0.40, submerged < 0.45) target 0.3 – 0.38 W/C
• High strength
• Abrasion resistance
• Low permeability
• Durability (High Performance Concrete = HPC)
c) Concrete Production:
• Objectives: Produce high strength concrete (HSC) & durable concrete (HPC)
• Targets: Maximization of concrete density
• Actions: Adherence to good construction practices
d) Concrete Mix Design:
• Performance for both fresh & hardened
• Maintenance – free during design life
• Re-orientation in the usual mixture design concepts and techniques
• Proper selection of material
• High cementing materials
• Use SilicaFume
• Use superplasticizer
e) Concrete Curing:
• For HSC and other concrete structures, proper curing is essential. In order to maintain a satisfactory moisture content and temperature in concrete during its early stages so that desired properties may develop. The strength and durability of concrete will be fully developed only if it is cured.
• Failure to prevent such excessive evaporation, frequently causes plastic shrinkage and loss of strength in the material near the concrete surface.