Quantitative Assessment of Aggregate Shape Parameters on Mechanical Properties and Performance of Bituminous Mixtures in Flexible Pavement Applications

Abstract

The geometric characteristics of coarse aggregates significantly influence the mechanical properties and long-term performance of bituminous mixtures used in flexible pavement construction. This study investigates the comprehensive relationship between aggregate shape factors and key performance parameters of bituminous mixes through systematic analysis. The research examines three primary shape indicators - flakiness index, elongation index, and angularity index - and their effects on critical performance measures including Marshall stability, flow value, air voids content, indirect tensile strength, and rutting resistance. A synthetic dataset was generated to analyze performance variations across different aggregate types including crushed stone, natural gravel, and recycled aggregate materials. Statistical analysis techniques including correlation analysis, regression modeling, and comparative studies were employed to establish quantitative relationships between shape characteristics and mix performance. The study utilized advanced visualization methods to present comprehensive data analysis through correlation matrices, multi-panel scatter plots, three-dimensional surface plots, and performance dashboards.

Introduction

The text explores the critical role of aggregate shape characteristics in the performance of flexible pavements, which are layered structures designed to distribute vehicular loads. Flexible pavements, favored for their cost-effectiveness and adaptability, rely heavily on material properties—particularly the shape, size, and texture of aggregates that make up 90–95% of the pavement mix. Despite their importance, geometric attributes like flakiness, elongation, and angularity are often overlooked in design standards, which traditionally emphasize gradation and strength. This can lead to inconsistent pavement performance, especially under heavy traffic or in extreme environments.

To address this gap, the study develops a synthetic dataset using Python and simulates the impact of aggregate geometry on key mix performance metrics such as Marshall Stability, Flow Value, Air Voids, Indirect Tensile Strength (ITS), and Rutting Resistance. Three types of aggregate—Crushed Stone, Natural Gravel, and Recycled Aggregate—are analyzed across various shape factor values. The study uses correlation analysis, scatter plots, and polynomial regression to quantify the relationships between shape indices and pavement performance.

Key findings include:

• Flaky and elongated aggregates (high combined shape factor) increase air voids and flow value but reduce stability, tensile strength, and rutting resistance.

• Angular aggregates improve stability, ITS, and reduce air voids, indicating better interlock and compaction.

• Recycled aggregates perform comparably to crushed stone in some metrics but exhibit higher variability, suggesting they need tighter quality control.

• Natural gravel yields better compaction but lower mechanical strength due to its rounded shape.

The regression models, while showing moderate R² values (0.14–0.21), confirm that aggregate shape factors significantly influence pavement performance and should be integrated into mix design practices. The study highlights the potential of data-driven tools and performance-based specifications to improve the reliability and sustainability of flexible pavements, especially when incorporating alternative aggregate sources.

Conclusion

This research was undertaken to investigate the critical role that aggregate geometric characteristics—specifically flakiness index, elongation index, and angularity index—play in influencing the mechanical and volumetric behavior of bituminous mixtures used in flexible pavement construction. Through the generation of a synthetic yet realistic dataset, supported by regression modeling, statistical correlation analysis, and high-quality visual dashboards, the study provided evidence-based insights into how aggregate shape affects key performance parameters such as Marshall stability, flow value, air voids content, indirect tensile strength (ITS), and rutting resistance. The findings of the research clearly demonstrate that aggregate geometry is not merely a secondary consideration in mix design, but a primary factor that significantly governs pavement performance. High values of flakiness and elongation were consistently associated with reduced Marshall stability, increased air voids, and lower rutting resistance, indicating that poorly shaped particles disrupt the internal structure of the mix, hinder compaction, and compromise load-bearing capacity. In contrast, angularity index showed strong positive correlations with both Marshall stability and ITS, confirming that angular aggregates contribute to improved inter-particle friction, mechanical interlock, and overall mix strength.

References

[1] Hassan, H.M.Z., Wu, K., Huang, W., Chen, S., Zhang, Q., Xie, J. and Cai, X., 2021. Study on the influence of aggregate strength and shape on the performance of asphalt mixture. Construction and Building Materials, 294, p.123599. [2] Cui, P., Xiao, Y., Yan, B., Li, M. and Wu, S., 2018. Morphological characteristics of aggregates and their influence on the performance of asphalt mixture. Construction and Building Materials, 186, pp.303-312. [3] Li, B., Zhang, C., Xiao, P. and Wu, Z., 2019. Evaluation of coarse aggregate morphological characteristics affecting performance of heavy-duty asphalt pavements. Construction and Building Materials, 225, pp.170-181. [4] Kusumawardani, D.M. and Wong, Y.D., 2020. The influence of aggregate shape properties on aggregate packing in porous asphalt mixture (PAM). Construction and Building Materials, 255, p.119379. [5] Aragão, F.T.S., Pazos, A.R.G., da Motta, L.M.G., Kim, Y.R. and do Nascimento, L.A.H., 2016. Effects of morphological characteristics of aggregate particles on the mechanical behavior of bituminous paving mixtures. Construction and Building Materials, 123, pp.444-453. [6] Kleizien?, R., Vaitkus, A. and ?ygas, D., 2016. Influence of asphalt visco-elastic properties on flexible pavement performance. The Baltic Journal of Road and Bridge Engineering, 11(4), pp.313-323. [7] Gong, M., Xiong, Z., Deng, C., Peng, G., Jiang, L. and Hong, J., 2022. Investigation on the impacts of gradation type and compaction level on the pavement performance of semi-flexible pavement mixture. Construction and Building Materials, 324, p.126562. [8] Wang, W., Cheng, Y., Tan, G. and Tao, J., 2018. Analysis of aggregate morphological characteristics for viscoelastic properties of asphalt mixes using simplex lattice design. Materials, 11(10), p.1908. [9] Liu, W., Jiang, Y., Zhao, Z., Du, R. and Li, H., 2022. Material innovation and performance optimization of multi-solid waste-based composite grouting materials for semi-flexible pavements. Case Studies in Construction Materials, 17, p.e01624.

Copyright

Copyright © 2025 Lokesh Kumar, Bhawesh Joshi. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.