The effects of blast-furnace slag and fly ash on the hydration of portland cement

Abstract

In this study, a calorimeter, an ultrasonic tester, an optical microscope, and other pieces of conventional laboratory equipment, such as a Vicat needle, were employed in the investigation of the effect of blast-furnace slag and fly ash on the hydration of fresh cement paste. Test results indicate that a strong relationship exists among the calorimetric curve, the ultrasonic pulse velocity curve, and the penetrative resistance strength curve. A transition zone appearing in the ultrasonic pulse velocity curve corresponds to the period between the end of the dormant period and the deceleration period in the calorimetric curve. In the calorimetric curve during the end of the dormant period, the ultrasonic pulse velocity curve rises rapidly and the penetrative resistance strength curve begins to develop simultaneously. From optical microscopy observations, it is found that CH crystals develop rapidly and contribute to the early strength development of cement paste in the plastic state. The end of the dormant period and the second peak in the calorimetric curve are similar to both the initial and final setting times as measured by the Vicat needle. Although the transition zone of hydration introduced by the blast-furnace slag and fly ash differ slightly, they both appear somewhat later in comparison to that of ordinary portland cement.