Crushed aggregate fines for SCC: specific surface and pore size study

Manufactured (crushed) sand with its naturally high filler content can be perfectly suited for SCC production. Aggregate (especially the finest fraction) properties have a large effect on the fresh state properties of SCC. However, the current understanding on how crushed fines affect properties of fresh SCC is limited. To proceed in the understanding of how crushed aggregate fines affect the properties of fresh concrete, characteristics of fines (0-125 μm (0-0.0049 in)) from manufactured and natural sand of 5 different Norwegian rock types, were determined. These included density by water- and helium pycnometry, water absorption, PSD by laser diffraction and sedimentation as well as specific surface by Blaine and N2-BET. The results show that the absorption can take place as high inner surface adsorption due to very fine pores of a few nm width (possibly mica). Difficulties in interpretation of water absorption measurements due to uncertainty about water density in adsorbed state are discussed. We also propose to distinguish between the very high internal BET surface and the much lower external surface of the particles represented by sedimentation- and laser methods. In addition, it is proposed that flaky particle shape can increase apparent external surface measured by sedigraph due to increased sinking time compared to less flaky material.