## 3 Results and Discussion
### Mass  
Mass loss (or wear) of material was strongly correlated (R\({}^{2}\) = 0.99) with the amount of energy introduced (mechanical work) to the material. However, the same amount of introduced energy in two different machines did not result in a similar amount of wear (Figure 6). This was expected, given the power (energy introduction rate) differences of the two systems (in Watts (J/s)). If comparing the two machines, we can say that, in given conditions, the micro-Deval is a low-energy machine with an energy introduction rate (power) of 5.7 J/s. On the other hand, the Los Angeles machine is a high-energy machine with an energy introduction rate (power) of around 9.5 J/s in the first cycle and 7.7 J/s in the fifth cycle. Power decreased with cycles due to the considerable mass loss, which was absent in experiments in the micro-Deval. The Los Angeles machine in the setup used had between 35% and 67% more power than the micro-Deval, resulting in an almost 10 times higher mass loss (for the same introduced energy). Surely, the selected sieve size determining the mass loss fraction influenced the results of the Los Angeles tests. However, if the selected size of 0.63 mm (as described in the section \"Abrasion in Los Angeles Machine\") was replaced by a larger one, e.g., 1.0 mm, the mass loss values increased by only between 0.7% and 1.3% per cycle (known from the sieve analysis). This accounts for about 50% of the standard deviation (between three tested samples) of the mass loss results on the 0.63 sieve. Comparable results were found in annular flume experiments, described in [PERSON] et al. [2]. In that study, mean abrasion rates were found to be higher at higher flows--resulting in higher pebble velocities. Similarly, it was found that in degradation tests with variable rotational speeds, the wear of material increased with an increase in the rotational speeds of tumbling machines (for tests in the Slake durability apparatus and micro-Deval machine). [PERSON] et al. [42] explained that this increase in rotational speeds represents  
Figure 5: Power draw measurements results for (**a**) micro-Deval abrasion tests; (**b**) Los Angeles abrasion tests. Figure 6: Input energy of abrasion tests—cumulative mass loss of material plot (from micro-Deval test marked blue, from Los Angeles test marked orange). an increase in energy in the environment. If the rotational speed of the machine is increased, in the same experimental setting, it contributes to the greater power of the system. Similar conclusions can be drawn from the results found in a study by [PERSON] [43]. In a series of tumbling experiments, the increased rotational speeds resulted in higher mass loss of the samples. With the sample mixtures of the same properties, this could be attributed to the higher energies resulting from the increased speed. Additionally, in a series of micro-Deval and Los Angeles tests presented by [PERSON] et al. [44], Los Angeles tests resulted in higher mass loss compared to the micro-Deval mass loss for all of the lithotypes tested. In a study comparing aggregate properties, [PERSON] and [PERSON] [45] found no link between Los Angeles and micro-Deval values. If the mass loss was brought down to the travelling distances (without knowing the real travelling distances), which are often determined as 60% of the circumference of the mill multiplied by the number of rotations (e.g., [46; 47]), we yet again observed two very different results for the two machines used, with the same ratios, as when relating mass loss to energy. One of the possible solutions might be to introduce a coefficient related to the power of the system to the abrasion loss equations. By transforming mass loss (%) to \"specific mass loss\" (Equation (14)), we could obtain two almost overlapping curves. To transform mass loss data to specific mass loss (i.e., mass loss per power per unit mass), we had to multiply the values of the mass loss by coefficient (\(P^{*}m_{0}\))\({}^{-1}\) (Equation (15)).