In Hawaii's coastal environment, what is the primary reason concrete structures require specific chloride ion protection measures?
Correct Answer
C) To resist salt spray corrosion of reinforcing steel
Salt spray from ocean environments contains chloride ions that penetrate concrete and cause corrosion of reinforcing steel, leading to structural deterioration.
Why This Is the Correct Answer
Option C is correct. Chloride ions from salt spray penetrate concrete over time and reach the reinforcing steel embedded within. Once chlorides accumulate at the steel surface above a threshold concentration, they disrupt the passive oxide layer protecting the steel and initiate corrosion. Corroding steel expands, creating internal pressure that cracks and spalls the surrounding concrete — a progressive failure called chloride-induced corrosion.
Why the Other Options Are Wrong
Option A: To reduce curing time in tropical heat
Curing time in tropical heat is a valid construction concern in Hawaii but has no direct relationship to chloride ion protection. Accelerating curing addresses workability and strength gain timing, not long-term corrosion resistance. These are separate material science topics.
Option B: To prevent thermal expansion cracking
Thermal expansion cracking relates to temperature differentials causing concrete to expand and contract. While Hawaii's tropical climate can cause thermal cycling, chloride protection measures specifically target electrochemical corrosion of steel, not thermal movement. Expansion joints address thermal cracking.
Option D: To improve workability in high humidity
Workability in high humidity is managed through mix design adjustments (water-cement ratio, admixtures) during fresh concrete placement. It has nothing to do with chloride ion protection, which addresses long-term durability of the hardened concrete structure.
Memory Technique
Chloride → Corrosion → Cracking. The salt spray delivers chloride ions that corrode the steel, and corroding steel expands and cracks the concrete from the inside out. Think of it as the ocean slowly 'eating' the steel hidden inside the concrete.
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