India Soil Sulphate / Aggressive Ground Map
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About sulphate attack
Sulphate ions (SO₄²⁻) in soil or groundwater react with cement hydrates (especially tricalcium aluminate, C₃A) to form ettringite + gypsum, both expansive. The expansion cracks concrete from inside out, exposing rebar and accelerating corrosion. Most severe in saline alkaline belts: Rann of Kutch, Rajasthan saline patches, parts of Punjab/Haryana over-irrigated zones.
Cement choice by class
- Class 1: OPC 33/43, PPC, PSC. Standard mix per IS 456.
- Class 2: OPC 43 with C₃A < 8% (low-alumina) or PPC.
- Class 3: Sulphate-Resistant Cement (SRC, IS 12330). Min cement 350 kg/m³.
- Class 4: SRC + fly ash (25-30%) or GGBS (40-50%). Min 360 kg/m³.
- Class 5: Site-specific mix design — SRC + microsilica + epoxy coating + cathodic protection.
Cross-references
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Frequently asked questions
What is sulphate-resistant cement?
SRC (IS 12330) is a Portland cement with restricted C₃A content (≤ 5%) and limited C₄AF + C₃A. Reduces susceptibility to sulphate attack. Used in foundations + below-ground concrete in saline / sulphate-rich soil. Strength similar to OPC 43; cost 10-20% higher.
How is soil sulphate measured?
Lab test per IS 2720 Part 27 — sulphate as SO₄ (% by mass of dry soil). Classes 1-5 in IS 456 Cl. 8.2.2.4 Table 4. For projects above ₹50 lakh in suspected aggressive zones (Rajasthan, Kutch, Punjab saline pockets, sulphate-bearing rock formations), this test should be in the geotechnical scope.
Is SRC enough or do I need additional measures?
For Class 3 (Severe), SRC alone is adequate. For Class 4-5, combine SRC with supplementary cementitious materials (fly ash 25-30% or GGBS 40-50% — both reduce permeability). For Class 5 industrial or chemically-contaminated soils, also consider epoxy-coated rebar (IS 13620), surface coatings, or cathodic protection.
Sulphate classification is based on regional geology + saline-soil mapping. Hot-spots within nominally 'safe' regions exist (e.g., chemical industry corridors, dried-up salt-pan areas). Always conduct site-specific soil chemical analysis (SO₄ + Cl⁻ + pH) for industrial / commercial projects in suspected zones.