Mechanical activation of cement–slag mortars

Although the use of slag has many advantages, the low hydration of slag at early age causes the strength to be low. Hence, its uses are restricted, and should be activated. In this investigation, a mechanical method was used to activate ordinary Portland cement (OPC)-slag mortars (OSM). Fourteen OSMs were made, two of them as control. Three groups of mortars were used. The first group includes both the ground slag and OPC. In the second group ground slag and ungrounded OPC were used, and in the third group ground OPC and ungrounded slag used. For the first group, 7- and 28-day strengths were attained as 65 and 80 MPa, respectively. Finally, the results showed that the optimum strengths attributed to the first group, especially at early ages. All the mix proportions were made for water-binder and sand-binder ratios as 0.33 and 2.25, with 50% level of slag, respectively.

► The highest strength was obtained for the optimum OSM made using both the ground slag and OPC in duration 6 h as 80.1 MPa.
► All the three groups of mortars used showed significant effects on strength improvement, especially at early ages.
► The results obtained proved that the strength loss at later ages was due to “phase separation”.
► It was revealed that the ground slag had greater effect on strength improvement when compared to ground OPC particles.
► Finely ground result in larger surface area, but “agglomeration” is a limitation on the specific surface area.