To measure the degree of reaction of slag in blended pastes, five methods were studied. Selective dissolution and differential scanning calorimetry are shown to be unreliable, SEM-BSE-IA-mapping is time consuming, but does provide good results with a reasonable degree of precision. The difference in cumulative calorimetry and chemical shrinkage curves of slag blends in comparison to blends with inert filler shows potential to isolate the reaction of the slag. These methods have the advantage of being continuous, techniques with good precision, but the absolute heat of hydration, or contribution to chemical shrinkage of any particular slag is not known. Calibration of the calorimetry technique with SEM-BSE-IA-mapping seems to be a promising method to understand and quantify the degree of reaction of slag. (C) 2011 Elsevier Ltd. All rights reserved.