Effect of silica fume on the slag cement containing wet cement dust

The present work aims to study the effect of various amounts of silica fume on the physico-mechanical properties of slag cement with 5\% raw cement dust. Slag cement is substituted by 4, 8 and 12\% silica fume. The results reveal that the increase of silica fume tends to increase the water of consistency. On the other side, 4\% silica fume decreases the setting time (initial and final). 8 and 12\% silica fume tend to lengthen the setting time due to the increase of mixing water. The free lime content increases up to 7 days then decreases far all mixes. As the amount of silica fume increases the free lime content decreases. Also, the combined water content increases with the amount of silica fume. The compressive strength of cement paste decreases with silica fume due to the increase of mixing water.