Water demand of amorphous nano silica and its impact on the workability of cement paste

This paper addresses the characterization of six different amorphous silica samples with respect to their application in cement paste. Different mixes are compared and analyzed using the mini spread-flow test. Also the granular properties, different void fraction states of packing and distribution moduli q are analyzed and compared using a mix design tool. A deformation coefficient is derived from the spread-flow test, which correlates with the value of specific surface area computed from the particle size distribution, and intrinsic density of the samples. Finally, the thickness of a constant water layer of 25 nm around the particles is computed at the onset of flowing. The granular analysis demonstrated that it is possible to decrease the water demand of the cement paste when nanoparticles are added and the resulting grading follows the modified Andreasen and Andersen curve (q = 0.5), and the concentration of nano silica is less than 5% bwoc. (C) 2011 Elsevier Ltd. All rights reserved.