During construction of a home near an active volcanic area in Hawaii, the contractor encounters sulfur-bearing soil. What special consideration is required for concrete foundations?
Correct Answer
D) Use sulfate-resistant cement and increase cover
Sulfur-bearing volcanic soils can cause sulfate attack on concrete. Sulfate-resistant cement and increased concrete cover are required to prevent deterioration.
Why This Is the Correct Answer
Option D (Use sulfate-resistant cement and increase cover) is correct. Sulfur-bearing volcanic soils produce sulfate compounds that chemically attack standard Portland cement (Type I/II), causing expansive reactions that deteriorate concrete. ACI 318 and building codes require sulfate-resistant cement (Type V or Type II with low C3A content) in high-sulfate exposure conditions. Increasing concrete cover provides additional protection for the reinforcing steel against the aggressive soil chemistry.
Why the Other Options Are Wrong
Option A: Use standard Portland cement with accelerator
Standard Portland cement with accelerator does not address the chemical attack mechanism. Accelerators affect setting time and early strength gain — they provide no resistance to sulfate attack. Using standard cement in sulfate-bearing soil will result in progressive concrete deterioration regardless of any accelerator.
Option B: Install additional drainage systems only
Installing additional drainage systems alone addresses moisture management but not the chemical attack from sulfates in the soil. Even dry sulfate-bearing soil can cause sulfate attack during seasonal wetting. Drainage is a supplementary measure, not the primary solution.
Option C: Apply epoxy coating to all surfaces
Applying epoxy coating to surfaces is a surface-applied protective measure that does not address the bulk concrete mix design. Coatings can be damaged or disbonded during construction, and sulfate attack can penetrate through any gap. The code-required solution is sulfate-resistant cement in the mix itself, not a surface coating.
Memory Technique
Sulfur soil → Sulfate-resistant cement. Match the threat to the solution: if the soil has sulfur/sulfates, the cement must resist sulfates. Type V cement is the go-to sulfate fighter. Think 'S for Sulfate, S for Special cement.'
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