Sulphate Contamination

Sulphate attack, sulphates can be contained in bricks, gypsum, fill or pollution which can attack the cement.  It turns the Tri calcium aluminate(C3A) contained in OPC cement to Tri calcium sulphoaluminate (31H2O) with a near doubling of molecular volume.

This Sulphate attack manifests itself with expansion of the OP cement due to chemical change mentioned above which can cause cracking, heaving and complete failure of the mortar, concrete or floor slab.

Manchester Building and Testing Laboratories can carry out analysis in our laboratories to determine the sulphur trioxide as a percentage of the cement content.

BS 4551 states :- Analysis of cement-based mortar showing a sulphur trioxide to cement content higher than 4 % indicates the possibility of the mortar having been exposed to attack by sulphates.

(NOTE Portland cement (CEM I 42.5 N) based mortars do not normally have a sulphur trioxide to cement content of more than 4 %. For allowable sulphur trioxide contents for other cement designations see BS 197-1.)

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