Durability of slag cement containing fired by-pass cement dust

The use of granulated slag cement is increasing worldwide because it needs less energy and low cost for production. When granulated slag is mixed with water at room temperature usually no or less hydration products are formed. This is ascribed to the formation of an acidic film, as a small amount of calcium ions is released into the solution. In the presence of lime, reaction occurs as the lime breaks into the silica framework of the slag. The fired by-pass cement dust acts as an alkaline activator for the granulated slag in this investigation. The Portland cement clinker was substituted with equal amount of fired bypass cement dust in slag cement. The durability of the hardened cement pastes was followed in either 4% MgSO 4 or 4% MgCl 2 solution up to one year. The results revealed that the calcination of by-pass cement dust at 1300°C for 2 hrs decreases the alkalis, chlorides whereas the sulphates remain nearly constant in the fired samples. The change in the compressive strength after one year in MgSO 4 solution was - 8.20, + 8.44, 11.25 and 10.20 % for OPC, Ml, M2, and M3 respectively. It can be said that M2 with 20 % by-pass cement dust has the highest compressive strength after one year. Also, the granulated slag cement as well as this with fired by-pass cement dust is more durable in 4% MgCl 2 than OPC pastes.