Effect of very fine particles on workability and strength of concrete made with dune sand

This paper presents the study on the properties of concrete made with dune sand from Australian desert. With constant water-cement ratio of 0.5, dune sand concrete (DSC) and the corresponding reference samples (concrete made with river sand) were prepared with sand-cement (S/C) ratio ranging from 0.91 to 2.28. In comparison to river sand, dune sand possesses a higher amount of very fine particles (VFPs) with grain size smaller than 175 μm. These VFPs are found to modify the properties of concrete by different mechanisms depending on the level of S/C ratio. At low level of S/C ratio (S/C < 1.41), VFPs can fill the porosities between cement pastes and aggregates and has no negative effect on workability and, the highest slump (105 mm) for DSC was found at S/C ratio of 1.18. Moreover, at low level of S/C ratio, the strength of DSC is comparable or even higher than that of river sand concrete (RSC); the higher strength of DSC can be attributed to the heterogeneous nucleation and pozzolanic effect brought by VFPs which enhances cement hydration. At high level of S/C ratio (S/C > 1.41), excessive VFPs absorb large quantities of water on their surface and lead to the reduction in workability for DSC. As a result, more air bubbles are introduced during compaction, leading to higher air content in DSC compared to RSC. The air bubbles increase porous space in cement paste and thereby reducing the strength of DSC.