SULFATE RESISTANT CONCRETE

MECHANISMS OF SULFATE ATTACK

Ettringite FormationReaction of Sodium sulfate with calcium

aluminate hydrateReaction of Magnesium sulfate with

calcium aluminate hydrate

Gypsum FormationReaction of sodium sulfate with calcium

hydroxide In aqueous conditions: Reactions of

calcium sulfate with calcium aluminate hydrate

Magnesium sulfate attacks calcium silicate hydrate

MANIFESTATION OF SULFATE ATTACK

• Loss in strength• Expansion • Surface spalling• Mass loss• Disintegration

AFFECTED AREAS

Structures in marine environment

Areas where soil and ground water have high sulfate contents

Chemical and Mining Industries

MAJOR PARAMETERS

1. Use of Type II or V cement.2. Reduce water/cement ratio.3. Minimize binder content.4. Replace cement with

supplementary cementitious material.

5. Provide air entrainment.6. Adequate compaction and

curing.

SUPPLEMENTARY CEMENTITIOUS MATERIAL

• Fly ash• Silica Fumes• Blast furnace slag

Fly Ash

Chemically binds free lime in cementitious compounds

Reduces concrete permeabilityReduces the amount of reactive

aluminates (tricalcium aluminate)

ACI 232.2R-96 (Use of Fly Ash in Concrete) reports that fly ash with CaO content less than 15% will generally improve sulfate resistance.

DEGREE OF RESISTANCE

• Type V Cement + Fly Ash• Type II Cement + Fly Ash• Type V Cement• Type II Cement• Type I Cement + Fly Ash• Type I Cement

SILICA FUMES

Decreases concrete permeabilitySilica fume chemically binds

some of the free calcium hydroxide in the paste preventing future reaction with sulfates.

ACI 234 states that silica fume concrete has good resistance to sodium sulfate attack but does not work as well against magnesium sulfate.

SRC vs TRADITIONAL CONCRETE

AUSTRALIAN STANDARDS

AS 3735 Supplementsulfate levels exceed 2000 ppm in

groundwater :

min. cement content: 320 kg/m3

max. water–cement ratio: 0.5

AS 3972

FULLY BURIED

cement content: 335 kg/m3

water–cement ratio: 0.5

PARTIALLY BURIED

cement content: 415 kg/m3

water–cement ratio: 0.4

Australian Standard 3972

• BENEFITS:– Minimize the corrosion of

reinforced steel– Provides high level of concrete

performance– Increased workability and

pumpability– Improved later-age concrete

strength