The influence of silica fume, nano silica and mixing method on the strength and durability of concrete

The present work was accomplished to investigate silica fume (SF) and nano silica (NS) effects on the compressive strength (fcu28) of concrete made by cement contents (CC) of 300, 400, 500 and 600 kg/m3. Two NS types having purity of 89% (Type I) and 99% (Type II) were partially replaced CC by the percentages of 1.5% and 3%. The influence of replacing cement by 5% and 10% SF was also studied. Nano silica was mixed by two techniques, mechanically and by ultrasonic device. The influence of SF, NS and CC on fcu28 and water absorption (WA) was found. The obtained results indicated that fcu28 increased and WA% reduced by replacing part of CC by either NS or SF. For both of NS types, the enhancement ratio in fcu28 was higher when replacing cement by 1.5% NS compared to replacement ratio of 3% and both ratios recorded greater values of compressive strength when compared to that without NS. At 1.5% NS ratio, fcu28 increased by about 14.81% for type I and by 41.33 for type II while at 3% NS, the enhancement ratios were 5.86% for type I and 35.46 for type II respectively. Mixing Type I NS by ultrasonic mixing method recorded higher values for fcu28 as compared to those recorded by the mechanical method.