Sulfate Attack on Concrete Foundations: Detection and Prevention

Sulfate attack quietly converts sound concrete to crumbling, expanding mush over years. It is preventable at specification stage and expensive to fix after the fact.

What causes sulfate attack

Sulfate ions in soil or groundwater react with cement hydration products, forming expansive crystals that crack the concrete from within. Made ground (especially with industrial fill), brick rubble, and natural sulfate-bearing clays are the main sources.

UK classification

SANS 50197 / SANS 10100 classifies sulfate exposure DS-1 (lowest) to DS-5 (highest):

• DS-1: Standard concrete, normal cement
• DS-2: Slightly elevated — sulfate-resisting cement recommended
• DS-3: Significant — SRPC or CEM III blast furnace slag
• DS-4/5: Severe — specialist mixes, protective coatings, design considerations

Brownfield sites often classify DS-3 or higher. Soil testing identifies the class.

Symptoms of attack

• White efflorescence on concrete surface
• Surface softening or scaling
• Cracking radiating from corners
• Crumbling concrete that can be scraped with a screwdriver

Prevention at specification

• Site investigation including chemical testing (SANS 3001)
• Specify concrete to appropriate DS-class
• Consider protective membranes on contaminated sites
• Use SRPC, GGBS, or PFA cement blends

Remediation for affected concrete

• Limited damage: cut out and patch with resistant material
• Extensive: encase in protective concrete jacket
• Severe: replace affected sections

When to suspect

• Brownfield or made-ground sites
• Industrial heritage areas (gasworks, brickfields)
• Properties with persistent ground-level damp on concrete elements

MCFAR specifies sulfate-resistant concrete on at-risk sites.

Frequently Asked Questions