Effects of a shrinkage-reducing agent on blast-furnace slag cementitious materials

In recent years, blast-furnace slag (BFS) composite cement, which partially replaces ordinary Portland cement (OPC) with a by-product from the manufacture of iron, has been widely used in civil engineering due to its numerous advantages. Although the mechanical properties and durability of BFS concrete are excellent, there are still some issues that need to be addressed – for example, significant drying shrinkage. To mitigate the drying shrinkage, a shrinkage-reducing agent (SRA) is one important kind of admixture that is usually added to cementitious materials. One type of SRA – non-ionic surfactant – was proven to be capable of mitigating the drying shrinkage of OPC concrete, but whether it is also effective in BFS concrete is still unclear. In this study, the influences of a commercial non-ionic surfactant (Sika® Control-40) on the surface tension, hydration process and pore structure of BFS cement pastes are studied experimentally. Mechanical properties and deformation of both BFS cement paste and concrete are also measured. The test results show that the addition of SRA results in lower compressive and flexural strength, higher porosity and lower hydration rate of BFS cement paste. With the addition of non-ionic surfactant, drying shrinkage of BFS cement paste and concrete is significantly reduced.