## 4 Conclusions  
In this work, the standardised equipment used in rock mechanics for aggregate testing was used for abrasion experiments to evaluate the mass loss and morphological evolution of abraded particles. In fluvial abrasion research experiments, wear of material is usually calculated according to the travelling distance of the abraded material. Here, we assessed abrasion according to the input energies (mechanical work) and powers of two different experimental abrasion setups, one in the micro-Deval apparatus and one in the Los Angeles machine. High-energy abrasion (in the Los Angeles machine) resulted in higher abrasion rates than the ones obtained with low-energy abrasion (in the micro-Deval machine). In general, the investigated particles showed the greatest change in the roundness shape aspect, with a greater change during the low-energy abrasion.  
Our study results suggest that the key to scaling different tumbling abrasion experiments one to another is in the power and energy applied to the material by the chosen setups. By introducing the \"mass loss coefficient\", the measured experimental setup specific mass loss data can be transformed into \"specific mass loss\"--a percental loss of mass per initial mass of the material per power unit. Specific mass loss values are then comparable for the two experimental setups and show a good agreement in relation to input energy. This approach might even be applied to natural streams by taking a fraction of fluvial stream power into consideration, which will be a subject of further investigations--as well as for other fields of applied studies investigating abrasion using tumbling experiments (as discussed in the introduction section). Additionally, because of the novelty of the mass loss coefficient, it should be further investigated in abrasion experiments using different materials and further experimental setups, as well as in rigorous analyses of the experimental abrasion results available in the literature. Last but not least, the different morphological changes resulting from the two experimental setups point to the potential of tracking morphological changes in material for the identification of energy-related conditions of the transportation environment.  
Conceptualization: T.K., M.M.; Methodology: T.K., M.M.; Validation: T.K.; Formal Analysis: T.K.; Investigation: T.K., K.L.; Resources: M.M.; Data Curation: T.K.; Writing--Original Draft: T.K.; Writing--Review and Editing: M.M., K.L., T.K.; Visualization: T.K.; Supervision: M.M.; Funding Acquisition: M.M. All authors have read and agreed to the published version of the manuscript.  
Figure 17: Distribution of angularity values according to size class before tests and after each abrasion cycle in Los Angeles machine, for particles coarser than 20 mm.  
**Funding:** This research was funded by the Slovenian Research Agency, PhD grant of the first author, and research core funding No. P2-0180. The APC was funded by the Slovenian Research Agency.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** The data presented in this study are available on request from the corresponding author.  
**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretations of data; in the writing of the manuscript; or in the decision to publish the results.