Influence of limestone on the hydration of ternary slag cement

The hydration kinetics, microstructure and pore solution composition of ternary slag-limestone cements have been investigated. Commercial CEM I 52.5 R was blended with slag and limestone; maintaining a clinker to SCM ratio of 50:50 with up to 20% slag replaced by limestone. The sulphate content was maintained at 3% in all composite systems. Hydration was followed by a combination of isothermal calorimetry, chemical shrinkage, scanning electron microscopy, and thermogravimetric analysis. The hydration of slag was followed by the implementation of QXRD/PONKCS method. The accuracy of the calibrated PONKCS phase was assessed on slag and corundum mixes of varying ratios, at different w/s ratios. Thus, the method was used to analyse hydrated cements without dehydrating the specimens. The results show that the presence of limestone enhanced both clinker and slag hydration. The pore volume and pore solution chemistry were further examined to clarify to the synergistic effects. The nucleation effects account for enhanced clinker hydration while the space available for hydrate growth plus lowering of the aluminium concentration in the pore solution led to the improved slag hydration.