Crushed salt will be used as backfill material for openings in a potential high-level nuclear waste (HLW) repository in rock salt. Together with the host rock, the backfill material will provide long-term sealing to isolation of radionuclides. Therefore, the understanding of its behavior and evolution over time is crucial. This paper presents a strategy to improve the predictive quality of constitutive crushed salt models for the long-term safety of an HLW repository. The systematic strategy is developed and applied within the framework of the KOMPASS projects (Czaikowski et al., 2020; Friedenberg et al., 2024) and the currently running MEASURES project (2024–2027). It covers the creation of a reliable experimental database that is subsequently used for model analysis and model development/optimization. The progress of model improvement is indicated by a virtual demonstrator, which represents a generic backfilled drift in rock salt. In its current state, the approach's success is demonstrated by a reduction in bandwidth across the different crushed salt models in the demonstrator results for mean stress at an intermediate porosity range. The work is ongoing, and major achievements will be available at the end of the MEASURES project.