Effect of Ultrafine Granulated Blast Furnace Slag on the Strength Development of Portland Cement Mortar

The current study evaluated the effects of ultrafine granulated blast furnace slag (GBFS) on the compressive strength development of Portland cement mortar. The previous studies have investigated the effects of ultrafine slag (UFS) with sizes of around 3–5 μm on the concrete performance. Despite the great potential of smaller size GBFS particles to enhance the concrete performance, such effects are not clearly known. In this study, UFS particles with sizes of around 1 and 0.6 μm were prepared using a planetary ball mill. UFS was then used to replace Portland cement by 5, 10, and 15 wt.% in preparing mortar specimens. The compressive strength of the specimens was measured at different ages. Isothermal calorimetry was also used to provide insight into the strength development mechanisms of specimens. The results showed that UFS powders significantly increased the 1-d and 3-d compressive strength of mortar specimens by up to 46 and 52%, respectively. The compressive strength increase was proportional to the replacement level of Portland cement with UFS powders. Compared to the 1 μm UFS, only a minor enhancement in 1-day compressive strength of the specimens containing 0.6 μm UFS was observed. The 28-day compressive strength of all specimens was similar regardless of their UFS content. The isothermal calorimetry results showed that the UFS powders increased the early hydration rate of Portland cement. A preliminary analysis of energy consumption of UFS preparation showed that partial replacement of Portland cement with UFS could result in cementitious binders with less GHG emission.