Effect of cement grade and fineness of slag on the early age to medium term properties of binary blends

The hydration and microstructural evolution of cementitious materials are dependent on both the mineralogical and physical attributes of the constituent materials. This paper ascertains the influence of constituent materials’ fineness on hydration and the evolution of mechanical properties of CEM I-slag composite cements. The clinker to supplementary cementitious material ratio was maintained at 50:50 and the sulphate content kept constant in all mixes. Compressive strength development was followed over time, with hydration followed by isothermal calorimetry and chemical shrinkage. Results from these techniques show that, for a given clinker, a more finely ground slag was consistently superior to a coarser slag. Furthermore, calorimetry revealed that the intensity of alite hydration and the secondary peak attributable to participation of aluminates from slag in hydration were also greater when using a finer slag. Finely ground clinker also accelerates slag hydration. The early age strengths in the binary blends were weaker than the control specimens, but this was offset beyond 7 days when using finer slag blends. Blending of higher grade CEM I (52.5R) and fine slag also yielded comparable early age strength to a CEM I- 42.5R mix.