## 4 Experimental Results
### Leading Characteristics of GRMs  
Tires are largely composed of carbon black, vulcanized rubber, rubberized fabric containing reinforcing textile cords, antioxidants, silica, pigments, process and extender oils, accelerators, and steel wire [4] and may contain petroleum residues acquired through use [44]. In this study, due to the recycled rubber's proposed use in geotechnical applications, clarification was needed to understand whether and to what extent metals and inorganics could leach into the environment. This is to ensure that there are no negative, long-term impacts to the environment. Factors expected to affect the rate and concentration of tire leachate include the rubber particle size and content, contact time, and the aquatic or soil environments [6]. Within this scope, in this feasibility study, six pilot 28-day batch leaching tests were conducted on GRMs with \(VRC\) = 40% that were placed in deionized water (additional tests on GRMs with \(VRC\) = 0, 10, 25% are in progress and the results will be presented elsewhere). Samples were taken on days 0, 1, 2, 4, 7, 10, 14, 17, 21, 25, and 28 to track leaching characteristics, which were determined by ICP-MS analyses. The metals and organics tested for included aluminum (Al), arsenic (As), calcium (Ca), cadmium (Cd), cobalt (Co), chromium (Cr), copper (Cu), iron (Fe), potassium (K), magnesium (Mg), manganese (Mn), phosphorus (P), lead (Pb), sodium (Na), nickel (Ni), and zinc (Zn). Note that pH, conductivity, and TOC analyses were also performed and the details are reported in [PERSON] et al. [7]. Table 3 summarizes the total average mass of predominant constituents leached for G-RL and G-RS mixtures, while Table 4 provides the maximum concentrations of all the tested elements. It is expected that the Ca, K, and Na contents are attributed to the gravel and the Zn and Mg to the tires. As an example, Zn concentrations measured during the entire 28-day leaching test period are reported in Figure 11.  
The test results were compared to New Zealand Drinking Water Standards [45] and New Zealand Landfill Waste Acceptance Criteria [46] for class A and B leachability concentration limits. Class A landfills \"provide a degree of redundancy for leachate containment\" to \"reduce the potential for adverse environmental effects\" whereas class B landfills do not have such controls. Guideline values for Zn, Mn, Fe, and Al were exceeded. These values mean that there is an increased discoloration, taste, and staining risk. From a practical viewpoint, these results highlighted that the leachate from smaller tire particles (G-RS) had a higher content of metals, implying that particle size and surface area influence the concentration of elements in GRM leachate. Additionally, the concentration of Zn in G-RS tests exceeded the leachability limit for class B landfills. Hence, G-RS mixtures would need to undergo pre-treatment if used in geotechnical works. \begin{table}
\begin{tabular}{l c c c c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**GRMs**} & \multicolumn{10}{c}{**Maximum Concentration (mg/L)**} \\ \cline{2-13}  & **Al** & **As** & **Ca** & **Cd** & **Co** & **Cr** & **Cu** & **Fe** & **K** & **Mg** & **Mn** & **P** & **Pb** & **Na** & **Ni** & **Zn** \\ \hline G-RL & 0.05 & 0.00 & 4.25 & 0.00 & 0.00 & 0.00 & 0.01 & 0.05 & 1.07 & 0.37 & 0.03 & 0.01 & 0.00 & 1.46 & 0.00 & 0.45 \\ G-RS & 0.03 & 0.00 & 15.0 & 0.00 & 0.01 & 0.00 & 0.00 & 0.02 & 1.58 & 1.08 & 0.08 & 0.01 & 0.00 & 1.61 & 0.00 & 1.76 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Maximum concentration of leachate elements obtained by ICP-MS analyses (average values from three tests). \begin{table}
\begin{tabular}{l c c c c c c c c} \hline \hline \multirow{2}{*}{**GRMs**} & \multicolumn{10}{c}{**Total Mass (mg)**} \\ \cline{2-10}  & **Ca** & **Na** & **K** & **Zn** & **Mg** & **Others** \\ \hline G-RL (\(VRC\) = 40\%) & 117 & 48 & 27 & 16 & 10 & \textless{}2 \\ G-RS (\(VRC\) = 40\%) & 424 & 55 & 55 & 57 & 28 & \textless{}2 \\ \hline \hline \end{tabular}
\end{table}