Gradation effects on the mechanical response of crushed stone aggregate

Abstract

A study was conducted to evaluate the effects of varying the gradation of aggregate base course (ABC) on material performance. Five different gradations consistent with a range of common ABC were selected. Experimental trials were performed to classify the materials and assess the performance differences between the five gradations. The gradation was found to affect the behaviour of the aggregate in that coarser gradations gave better strength and resilience values under conditions most similar to those found in the field. From research and experience during the laboratory testing, it was concluded that the coarsest blends became too difficult to realistically work with and they also lacked the stability of the well-graded combinations. It was also observed that as the amount of fines in the specimens exceeded 8–12% by mass, the fines governed the behaviour of the material. Results are interpreted using previously published work on specific surface, ‘ideal’ gradations and micromechanical models for the response of granular materials.

Keywords:

• base course
• gradation
• triaxial testing
• Atterberg limits
• resilient modulus
• shear strength

Acknowledgements

The authors extend sincere appreciation to the authorities of NCDOT for funding this work and for providing assistance with laboratory testing. In particular, the authors wish to express their gratitude to Mr. C.K. Su and Mr. M. Haeri and their staff for their generous help and guidance. The authors would also like to thank Mr. Cary Caruso, Mr. Benjamin Cote, and Mr. Brent Robinson for their assistance in the laboratory work conducted at North Carolina State University's Constructed Facilities Laboratory.

Notes

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Additional information

Notes on contributors

Charles N. Cunningham

1

Akhtar A. Tayebali

2