Effect of mineral additives on the setting of blended cement by the maturity method

The addition of a mineral additive to Portland cement involves an increase of the setting time allotted to the dilution effect (dilution of the most active ingredient) and to the increase in the necessary water to prepare a normal consistency paste. In this study, ordinary cement was substituted by 5, 15 and 25% of limestone powder, 10, 20 and 30% of natural pozzolan and 10, 30 and 50% of slag. The tests of penetration are carried out every 10 min in order to determine initial and final setting time. The mortar is prepared and preserved at curing temperature of 20, 40 and 60A degrees C. The results are analyzed and quantified by using the maturity method where the effect of each addition appears more explicit. The value of the activation energy calculated at the very early age reveals the state of activity of these mineral additives and their temperature sensitivity. For replacement amounts lower than 15%, the activation energy of the three additives increases at the initial setting and beyond this content a clear difference is observed. At the final setting time, the activation energy remains constant for limestone, increases regularly for slag and increases highly for natural pozzolan with replacement amounts above than 20%.