A Study on Effect of Sulphates on Compressive Strength of Blended Cement Mortar

Sulphate attack is considered one of the major deteriorative problems occurred when the cement based materials, such as concrete, mortars and buildings exposed to the acidic environment. Water borne sulphates react with hydration products of the tri-calcium aluminate (C3A) phase of Portland cement, and with calcium hydroxide (Ca(OH)2) to form an expansive crystalline product called ettringite. Sulphates also cause chemical disintegration of some of the cement hydration products. The present paper focuses on the effect of sulphates on the compressive strength properties of the fly ash blended cement. In this investigation the work is carried out to examine sodium, magnesium, ammonium, ferrous, calcium sulphates particularly affecting the strength parameter which are added in different proportions (2000, 2500 and 3000 mg/l) to cement and its effect is studied on cement mortars at different curing ages (7, 28, 90, 180 days). Deionised water was used for mixing the cement mortar specimens and curing. These properties were compared to the control mortar mixes which were cast using deionised water and with no sulphate concentration. From this investigation, it is observed that, compressive strength values of mortar mixes were reduced at all curing periods with the increase of sulphate concentration for all the combinations of sulphate. These values were lower than those of control mortar mixes. It is concluded that proper preventive measures should be taken against these sulphate attacks to control the deterioration of mortar mixes.