You are building a home 500 feet from the ocean in Hawaii. During construction, you discover the soil has a high salt content. What additional foundation protection is required?
Correct Answer
D) Use sulfate-resistant cement and increase concrete cover
High salt content soil requires sulfate-resistant cement to prevent chemical attack and increased concrete cover to protect reinforcement from chloride penetration.
Why This Is the Correct Answer
High salt content in coastal soil presents two distinct chemical threats to concrete foundations: (1) sulfates that chemically attack cement paste, requiring sulfate-resistant cement to prevent expansion and deterioration; and (2) chlorides that penetrate concrete and corrode embedded steel reinforcement, requiring increased concrete cover to slow chloride migration. Addressing both threats together is essential for long-term foundation durability in this environment.
Why the Other Options Are Wrong
Option A: Standard concrete mix is sufficient
Standard concrete mix provides no protection against chemical attack from salts or sulfates. In high-salt coastal soil, standard concrete foundations have a significantly shortened service life due to sulfate attack on the cement matrix and chloride-induced rebar corrosion.
Option B: Apply waterproof membrane only
A waterproof membrane alone addresses moisture intrusion but does not protect against chemical attack from salts already present in the soil. Sulfates and chlorides can migrate through membrane imperfections, and the membrane itself does not make the concrete resistant to these chemicals.
Option C: Install French drain system only
A French drain system manages water drainage but does not address the chemical composition of the soil. Removing water may slightly reduce salt migration, but it does not eliminate sulfate attack on concrete or chloride penetration — and alone it provides no protection for the concrete or reinforcement.
Memory Technique
High salt = two problems = two solutions. 'Salt fights cement (use Type V), salt fights steel (increase cover).' Remember both the cement and the cover must change when salt is high.
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