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 method. Also the granular properties, different void fraction states of packing and distribution moduli q of the modified Andreasen and Andersen (A&A) curve are analyzed and compared using a mix design tool. In this way, a deformation coefficient is derived from the spread-flow test, which correlates with the value of the computed specific surface area (SSA) based on measured particle size distribution (PSD) and intrinsic density of the individual silica samples. Similar correlations with equal accuracy are found with a computed SSA using the BET method. Finally, the thickness of a constant water layer (24.8 nm) around the powder particles is computed for all silica samples at the onset of flowing. The granular analysis demonstrated that it is possible to decrease the water demand of cement paste with addition of nano particles when the grading of the powders follows the modified A&A curve with a q = 0.5 (similar to Fuller curve) and the concentration of nano particles is less than 5% bwoc. The results allow for predicting the flow behavior of paste only based on the knowledge of the powder’s SSA, either determined by computation or by BET measurements.
Quercia Bianchi, G., Hüsken, G., & Brouwers, H. J. H. (2012). Water demand of amorphous nano silica and their impact on the workability of cement paste. Cement and Concrete Research, 42(2), 344-357. https://doi.org/10.1016/j.cemconres.2011.10.008