Blended pastes composed of slag and fly ash (ratio 50:50) are used with sodium hydroxide and sodium silicate as precursors. Each composition has the same solution to binder ratio (S/B) and the Ms-modulus varies between 1.04 and 1.58. All the experiments were conducted at a constant temperature of 20°C. The physical mechanisms related to the volume change in sealed condition are studied by means of repeated thermal variation using an adapted Autoshrink device, a new testing protocol and by means of isothermal calorimetry tests. From these tests, the autogenous strain, the coefficient of thermal expansion (CTE) and the heat release are determined. It is observed from the results, that an increase of the Ms-modulus causes a decrease of the autogenous shrinkage and the CTE. A linear relationship is observed between the autogenous shrinkage and the heat release by the binder. Thus, the development of the autogenous shrinkage seems to be mainly driven by one major mechanism in case of slag and fly ash paste activated by sodium hydroxide and sodium silicate.