Influence of Na2SO4 on the Mechanical Properties of High Volume Calcined Clay Pozzolan Cement

Calcined clay pozzolan, the major mineral admixture used in Ghana to partially substitute ordinary Portland cement has gained massive recognition in the local construction industry because of its technical advantages and affordability. The most prominent undesirable property associated with the use of calcined clay pozzolans is slow setting and strength development, especially at early ages. This paper presents a study of the effect of Na2SO4 on the mechanical properties of high volume pozzolan cements. The cements containing 30 wt. %, 40 wt. %, 50 wt. % and 60 wt. % calcined clay pozzolan was activated with 1%, 2%, 3% and 4% Na2SO4. Some physical properties such as Blaine index, specific gravity, water demand and setting times were determined. The chemical compositions of the blended cements were also analyzed. The effect of Na2SO4 on compressive strength of blended cements was determined after 2, 7, 28 and 180 days. Durability studies on activated blended cements in aggressive media were also conducted. Activation with a minimum of 2% Na2SO4 improved the 2 days compressive strength of cement containing 60% calcined clay pozzolan by 66.2% and caused it to behave as Class 32.5N cement, at 28 days. As Na2SO4 dosage increased, compressive strength also increased. The optimum Na2SO4 dosage was 2%. Activated blended cements resisted MgSO4 environment better than unactivated cements.