Comparison of efficiency of colloidal nanosilica and microsilica in cement concrete
  Lincy Varghese, V.V.L.Kanta Rao and Lakshmy Parameswaran
  Supplementary cementitious materials such as flyash, silica fume (microsilica), slag, metakaolin and rice husk ash contain amorphous silica, and they are being increasingly used to enhance the strength, durability and sustainability of concrete. The strength efficiency factor is a parameter which indicates the effectiveness of a mineral admixture when used in concrete, and is generally used in the mix proportioning of concrete containing such admixtures. The present study compares the effects of a synthesized and, industrial by-product siliceous mineral admixtures namely; colloidal nanosilica and microsilica, respectively, on the strength efficiency factor. The colloidal nanosilica and microsilica were characterized by transmission electron microscopy and scanning electron microscopy, respectively. The maximum strength efficiency factor was found to be 5.44 and 3.02 for colloidal nanosilica and microsilica based concretes, respectively at 3% and 7.5% replacement levels, at 28 days. The microstructure of concrete studied through scanning electron microscopy revealed that addition of nanosilica resulted in a highly dense and compact microstructure with finer C-S-H and reduced Ca(OH)2. On the other hand, the partially consumed Ca(OH)2 plies of microsilica based concrete at 90 days indicated a prolonged pozzolanic activity.