You are constructing a foundation on volcanic soil with high sulfate content. The soil test shows sulfate concentration of 2,800 ppm. What type of cement should be specified?
Correct Answer
D) Type V Portland cement
With sulfate concentration above 2,000 ppm, Type V sulfate-resistant cement is required to prevent sulfate attack on the concrete foundation.
Why This Is the Correct Answer
Type V Portland cement is the highest sulfate-resistant cement classification. It is required when sulfate concentrations exceed 2,000 ppm (or 0.20% water-soluble sulfate in soil). Its very low tricalcium aluminate (C₃A) content — no more than 5% — minimizes the expansive chemical reactions that cause sulfate attack, spalling, and structural deterioration. At 2,800 ppm, Type V is the only appropriate choice.
Why the Other Options Are Wrong
Option A: Type II Portland cement
Type II cement has moderate sulfate resistance (C₃A ≤ 8%) and is appropriate for sulfate exposures in the moderate range (150–1,500 ppm). At 2,800 ppm the exposure is classified as severe, exceeding Type II's design threshold.
Option B: Type I Portland cement
Type I is general-purpose Portland cement with no sulfate resistance provisions. Using Type I in high-sulfate volcanic soil would allow aggressive sulfate attack, causing expansion, cracking, and foundation failure.
Option C: Type III Portland cement
Type III is high-early-strength cement designed for rapid strength gain. It is not a sulfate-resistant formulation and has no special resistance to sulfate attack.
Memory Technique
Think '5 for Survive': Type V cement helps concrete survive severe sulfate attack. The Roman numeral V = Victory over sulfates. Threshold for Type V: above 2,000 ppm.
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