The effect of ultrahigh volume ultrafine blast furnace slag on the properties of cement pastes

•Ultrahigh volume ultrafine BFS are prepared through wet-milling and dry-separation respectively.•The reaction degree of WS system develop at a faster rate owing to dissolution of ions.•Mixes containing WS can exhibit compressive strength of 43.9 ± 2.3 MPa after 3d of curing. The dosage of blast furnace slag (BFS) in cement is limited on account of relative low reaction rate and low early strength. Improving the early age activity of BFS is the fundamental solution for high volume BFS cementitious materials. Generally, mechanical activation is one of the main techniques to accelerate the early reaction of mineral admixtures. In this study, wet-milling and dry-separation are respectively used to prepare ultrafine BFS to improve its early reactivity. The early hydration characteristics, mechanical property, hydration products of ultrahigh volume BFS cementitious materials are analyzed to assess the efficiency of ultrafine BFS on the properties of BFS cement paste. The results show that the initial and final setting time both gradually decrease as the dry-separation BFS (GS) dosage increases, while the wet-milling BFS (WS) series present the opposite tendency. The electrical resistivity of WS specimens develops at a faster rate than that of GS specimens. Mixes containing WS, at a maximum dosage of 90%, have higher mechanical property than those with GS, resulting in an enhancement of strength. The hydration products mainly include calcium hydroxide, hydrotalcite, hydrotalcite-like phase, calcium carbonate, strätlingite, C-S-H, C-A-S-H, and akermanite.