Sulphate Resistant Cement – Composition, Properties, Uses and Advantages.

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Sulphate Resisting Cement is a type of Portland Cement in which the amount of tricalcium aluminate (C3A) is restricted to lower than 5% and (2C 3A +C4AF) lower than 25%, which reduces the formation of sulphate salts. The reduction of sulphate salts lowers the possibility of sulphate attack on the concrete. In this article we study about the composition, properties, characteristics, uses, advantages and disadvantages of sulphate resisting cement.

Composition of Sulphate Resisting Cement

Due to very low range of  tricalcium aluminate in sulphate resisting cement, a very small quantity of calcium aluminate is formed on hydration. The formation of calcium sulpho- aluminates which formed due to reaction of calcium sulpho-aluminates which formed due to reaction of calcium sulphoaluminate and sulphate salts is considerably reduced with use of sulphate resisting cement. The sulphate aluminates are highly expansive in nature and cause maximum damage to the concrete.

Properties of Sulphate Resisting Cement

The properties of sulphate resisting cement are,

Table 1: Properties of sulphate resisting cement

Property	Values
Fineness	280+ or -10 sq m /kg
Setting time
Initial	80 min
Final	240 min
Soundness
Lechatelier (mm)	2 (max)
Autoclave	0.25(max)
Compressive strength
3 days	30 + or - 3
7 days	45 + or - 3
28 days	65 + or - 3
Tri calcium aluminate	0.035
Magnesia	0.02
Loss on ignition	0.02

Characteristics of Sulphate Resisting Cement

1. This cement provides maximum resistance to chloride ions - minimising the risk of corrosion of reinforced steel.
2. It also provides high level of concrete performance and structural integrity in highly aggressive sulphate and acidic environments.
3.  It also has increased workability and pumpability.
4. This cement has significantly improved later-age concrete strengths.

Uses of Sulphate Resisting Cement

Sulphate Resisting Cement is recommended for following type of constructions:

1. Foundations.
2. Piling works.
3. Construction in contact with soils or ground water having more than 0.2% or 0.3 % g/l sulphate salts respectively.
4. Concrete surfaces subjected to alternate wetting and drying such as bridge piers, concrete surface in tidal zone, apron etc.
5. Effluent treatment plans.
6. Chimney, cooling towers.
7. Coastal protective works such as sea walls, break waters, tetrapods etc.
8. Building near seacoast.
9. Chemical industries, water storage, sumps, drainage works.
10. Suitable for underground works where Sulphate is present in the Soil and water.

Advantages of Sulphate Resisting Cement

1. The use of sulphate resisting cement provides excellent protection against the formation of sulpho-aluminates and consequent resistance to concrete against sulphate attack.
2. Very high compressive strength  by economic concrete mix design.
3. Very low heat of  hydration helps to avoid shrinkage cracks.
4. Improves life and durability of structures under aggressive conditions.
5. Improves corrosion resistance of steel by preventing sulphate attack.

Disadvantages of Sulphate Resisting Cement

1. Sulphate resisting cement is not suitable where there is danger of chloride attack. This will cause corrosion of rebar.
2. If both Chlorides and Sulphates are present, Ordinary Portland Cement with C3A between 5 & 8 should be used.
3. Curing process should be done properly with great care for min of 8-10 days.
4. It is not prescribed to use it in marine construction.