Activation of Algerian slag in mortars

Blastfurnace slag has been widely used as a successful replacement material for Portland cement, and concrete of enhanced qualities can be achieved as a result. Due to the slag’s slow reactivity, however, the early-age mechanical properties may suffer. This paper reports the results of an investigation, carried out at Chlef University (Algeria), using Algerian slag, known to exhibit low reactivity due to its low CaO/SiO2 ratio. The slag was activated mechanically by grinding the slag to 250, 360 and 420 m2/kg Blaine surface area, thermally by curing mortar specimens at 20°, 40° and 60 °C, and chemically by mixing the slag with two alkalis, NaOH and KOH at different concentrations. Samples were tested for compressive strength at the ages of 1, 3, 7, 28 and 90 days. All three methods enhanced the reactivity of the slag. The results indicated that the slag is very sensitive to temperature rise. Increase in fineness resulted in increased strength development and the fineness of the slag must be greater than that of the cement to achieve better performance. Alkali activation of slag results in increased strength development but the strength was lower than that of the control mortar.