India Soil Sulphate / Aggressive Ground Map

Soil sulphate exposure classification per IS 456:2000 Cl. 8.2.2.4 + Table 4. Five classes from Class 1 (< 0.2% SO₄, no special spec) to Class 5 (> 2.0% SO₄, site-specific design). Drives cement type (Sulphate-Resistant Cement per IS 12330), water-cement ratio, and concrete grade.
128
class-1
47
class-2
19
class-3
3
class-4
0
class-5
Class 1 · Low (< 0.2% SO₄) · Class 1
Class 2 · Moderate (0.2–0.5% SO₄) · Class 2
Class 3 · Severe (0.5–1.0% SO₄) · Class 3
Class 4 · Very Severe (1.0–2.0% SO₄) · Class 4
Class 5 · Extreme (> 2.0% SO₄) · Class 5
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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

Source IS / IRC / NBC standards

IS 456:2000Cl. 8.2.2.4 sulphate exposure classificationIS 12269OPC 53 — when SRC unavailableIS 1489PPC — fly ash improves sulphate resistance

Related maps

Coastal ExposureCoastal saline soils often overlap with sulphateSoil BearingFoundation type + sulphate-resistant concreteGroundwaterSaline groundwater = aggressive ground

Calculators & tools

Mix DesignIS 10262 — adjust for sulphate-resistant cementFooting DesignSulphate-resistant foundation concrete

Articles & guides

Types of CementOPC vs PPC vs PSC vs SRCConcrete GradesWhen to use M30 / M35 for severe exposure

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.

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