## 5 Conclusions  
In this paper, the impact of the heterogeneity of aggregates coated with asphalt mortar on their spectra based on ATR-FTIR spectroscopy was mainly carried out. The following conclusions can be drawn based on the research results of this paper:  
* As the characteristic absorption peaks of the aggregates coated with asphalt mortar are the superposition of the respective absorption peaks of the aggregates, mineral powders, and asphalt binders, these components can all contribute to the spectrum of the coated aggregates;
* The spectral shapes and peak positions of aggregates coated with asphalt mortar obtained from the same batch of asphalt mixture fabricated at the same time are very similar across the entire mid-infrared region, and the peak intensities are significantly different, showing that intensities are affected by minor variations in the components due to the heterogeneity of the coated aggregates;
* CV values are high across the entire mid-infrared region, indicating that the original spectral reproducibility of aggregates coated with asphalt mortar with ATR-FTIR spectroscopy is greatly affected by the heterogeneity of the coated aggregates;
* Spectra pretreatment of norm normalization could reduce the CV values for better data quality. As spectral reproducibility is greatly affected by the heterogeneity of the aggregates coated with asphalt mortar, future research will focus on spectra preprocessing, including abnormal spectrum rejection, noise reduction, signal enhancement, and feature selection, to improve the accuracy of qualitative and quantitative analysis. Conceptualization, J.Y. and R.J.; methodology, J.Y., X.Z. (Xinglin Zhou) and M.R. ; software, J.Y. ; validation, J.Y., X.Z. (Xinxing Zhou) and L.L. ; formal analysis, J.Y. and P.Z. ; investigation, J.Y. ; resources, M.R. and X.Z. (Xinxing Zhou); data curation, J.Y. ; writing--original \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline
**Wavenumber** & & & & & & & & & & & & \\ **(cm\({}^{-1}\))** & **712** & **729** & **780** & **873** & **1018** & **1377** & **1419** & **1453** & **1797** & **2851** & **2920** & **2952** \\ \hline MV & 0.0410 & 0.0369 & 0.0316 & 0.0749 & 0.0819 & 0.0698 & 0.0859 & 0.0811 & 0.0060 & 0.0661 & 0.0969 & 0.0468 \\ SD & 0.0364 & 0.0308 & 0.0278 & 0.0507 & 0.0460 & 0.0369 & 0.0437 & 0.0379 & 0.0025 & 0.0260 & 0.0370 & 0.0168 \\ CV (100\%) & 88.5 & 83.2 & 88.1 & 67.6 & 56.1 & 52.7 & 50.9 & 46.7 & 40.9 & 39.2 & 38.2 & 35.8 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: MV, SD, and CV values at 12 characteristic peaks of original spectra. \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline
**Wavenumber** & & & & & & & & & & & \\ **(cm\({}^{-1}\))** & **712** & **729** & **780** & **873** & **1018** & **1377** & **1419** & **1453** & **1797** & **2851** & **2920** & **2952** \\ \hline MV & 0.0149 & 0.0141 & 0.0116 & 0.0302 & 0.0350 & 0.0300 & 0.0372 & 0.0358 & 0.0028 & 0.0302 & 0.0444 & 0.0217 \\ SD & 0.0050 & 0.0044 & 0.0039 & 0.0036 & 0.0025 & 0.0027 & 0.0041 & 0.0037 & 0.0009 & 0.0048 & 0.0078 & 0.0039 \\ CV (100\%) & 33.7 & 31.1 & 33.7 & 12.0 & 7.2 & 9.0 & 11.0 & 10.4 & 31.5 & 15.9 & 17.6 & 18.1 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: MV, SD, and CV values at 12 characteristic peaks of normalized spectra. draft preparation, J.Y., P.Z. and L.L. ; writing--review and editing, J.Y., M.R. and X.Z. ([PERSON]); visualization, L.L. and P.Z. ; supervision, P.Z. and R.J.; project administration, R.J., M.R. and X.Z. ([PERSON]); funding acquisition, X.Z. ([PERSON]) and M.R. All authors have read and agreed to the published version of the manuscript. This work was funded by the project supported by the National Natural Science Foundation of China (52172392, 51827812, 51778509, 52372395), Educational Commission of Hubei Province of China (2021 BAA180), and the Open Fund of Hubei Key Laboratory of Mechanical Transmission and Manufacturing Engineering at Wuhan University of Science and Technology (No. MTMEOF2022B04).