# Granular Material Development Applied in an Experimental Section for Civil Engineering Purposes
## Materials and Methods
### Methods
The leaching behavior depends on the following variables: leachate composition (e.g., pH), method and time of contact, and liquid-to-solid (L/S) ratio [33]. Batch tests are widely used for compliance testing because of the low costs, simple design and low duration [31]. The contact time of 24 h is too short for some metals to reach equilibrium, resulting in an underestimation of metal(loid) solubility [32]. The batch test represents the process of mixing a solid mass into groundwater so as to confirm the effect of this process of groundwater [34]. Nevertheless, the main disadvantage of the batch test is that the provided information is limited, as it only offers a single result in terms of L/S ratio, which does not reflect real-world conditions [31]. On the other hand, percolation column tests better simulate the field conditions and are appropriate to assess the long-term release of chemical constituents from the soil into water and groundwater. The percolation column tests resemble the process of the percolation/seepage of water into a soil structure to examine the effect of leachate on the environment [34]. Besides, the column percolation leaching tests simulate the time-dependent percolation behavior of solids in surface waters and groundwater. Even though column percolation tests are laboratory assays, they simulate natural conditions closer than any other test, and provide more robust results than the batch tests [30]. The advantages of the percolation column test over a batch test are related to the high initial concentrations of the percolates at low L/S ratios and the time-dependent release of the chemicals (necessary for the prediction of leaching behavior under field conditions). However, percolation column tests are more expensive, and more labor and effort is needed compared to batch tests [31]. Therefore, while the static batch tests offer information about the cumulative mobilized mass of pollutant, the percolation column tests are more representative of source term behavior [35], but are also time-consuming [31]. Percolation column tests approximate better to leaching processes under field conditions, and thus are more suitable for prediction purposes [33]. As stated elsewhere [36], column and batch leaching tests are of increasing importance for the recycling of waste materials, especially in the context of the recent Waste Framework Directive. They show that the L/S ratio is a convenient normalization parameter to compare different dynamic leaching tests [35]. Besides, it is important to highlight that the L/S ratio is a proper parameter for comparing between both tests, as it is shown that the leaching behavior is independent of the duration and the physical dimensions of the leaching test. It is usual that when characterizing the leaching behavior of a material using different dynamic leaching tests, the results obtained are different in terms of the metals concentrations released (mg/kg) [37]. Nevertheless, their order of magnitude and their relative significance depends on the type of L/S contact (which in the dynamic leaching tests and the percolation column tests is the same). Usually, the physico-chemical mechanisms governing pollutant release are identical, although they can present different values on the leaching time scale and in the different tests performed [37]. Apart from the laboratory assays, realistic impact simulations for leaching behavior must consider the physico-chemical characteristics of the metals studied. To sum up, both percolation and batch tests can be used for characterization or compliance [33]. Considering that all the rain percolates, an extrapolation of the time can be predicted for the experimental section, simulating a road subbase layer over real years, considering the four following parameters: (i) 200 m\({}^{2}\) surface and 0.2 m thick, (ii) an average rainfall in the area over the last 14 years of 584 L-m\({}^{-2}\).year\({}^{-1}\), (iii) a volume of the column of 589 cm\({}^{3}\), (iv) and 10 L-kg\({}^{-1}\).