For buildings in Hawaii subject to salt air exposure, what is the maximum allowable chloride content in concrete mix water?
Correct Answer
C) 500 ppm
Concrete exposed to chloride environments in Hawaii requires mix water with maximum 500 ppm chloride content to prevent accelerated corrosion of reinforcement steel.
Why This Is the Correct Answer
In Hawaii's coastal salt air environment, concrete mix water must have a maximum chloride ion content of 500 ppm (parts per million). Chlorides accelerate the corrosion of embedded reinforcing steel by breaking down the passive oxide layer that normally protects it. Limiting chlorides in mix water — combined with using coated rebar and adequate concrete cover — helps protect structural reinforcement from the aggressive marine environment.
Why the Other Options Are Wrong
Option A: 1,000 ppm
1,000 ppm is twice the allowed maximum. At this concentration, chloride-induced corrosion of steel reinforcement would be significantly accelerated, reducing the service life of structures in Hawaii's salt air environment.
Option B: 300 ppm
300 ppm is more restrictive than required and may be used for extremely aggressive marine submersion environments, but 500 ppm is the standard maximum for salt air (atmospheric) exposure.
Option D: 1,500 ppm
1,500 ppm greatly exceeds the allowable limit. Water with this chloride level would be considered unsuitable for concrete mixing in corrosion-sensitive environments without significant mitigation measures.
Memory Technique
500 ppm = '5 hundred for the sea.' Hawaii's 500-mile stretch of ocean surrounds every building — 500 ppm is the ceiling before salt starts eating steel. Think: '500 ppm keeps the steel from rusting in Hawaii's 500-mile ocean ring.'
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A contractor is installing hurricane straps rated at 1,500 pounds each. If the calculated uplift force on a rafter is 3,200 pounds, how many straps are required with a 2.0 safety factor?
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