Proportioning the dosage of Ground Calcium Carbonates (GCC) in cementitious materials, beyond current normative levels, is one of the most promising ways towards sustainability of mortar and concrete technology. Performance parameters such as the water/binder ratio do not represent the very significant benefits in terms of mechanical performances, of clinker replacement by GCC in mixes with water/cement ratios in the range of that for normal concretes used in construction (0.4 to 0.6). Alternative parameters such as the water/fines ratio proved to be reliable indicator of performances for Ultra High-Performance Fiber Reinforced Concretes. This concept needs to be further extended to normal concretes, on a scientific basis. With this aim in view, mortar mixes with a similar water/cement ratio of 0.5 and progressive replacement of sand by GCC with water/fines ratios as low as 0.2 were studied. The packing density of the cement and GCC was determined by means of wet packing measurements using the mixing power method. The Compressible Interaction Packing Model from Fennis was generalized to multiple polydisperse components and used to predict the packing density of the mixes. The rheology at fresh state of the mixes was put into perspective with the packing density, water film thickness and sand packing factor to define reliable indicators of performances at fresh states. Finally, the compressive strength of the mixes at 1 and 28 days was related to the efficiency coefficient of the GCC used.