Elastic Stiffness and Indirect Tensile Strength Ratio of Palm Kernel Shell Ash–Oyster Shell Ash Modified Asphalt Concrete Under Full Moisture Conditioning

Enyi; Festus Weneka1; Igwe; E. A.1; Otto; C. G.1

doi:10.56201/ijemt.vol.12.no9.2026.pg97.107

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Elastic Stiffness and Indirect Tensile Strength Ratio of Palm Kernel Shell Ash–Oyster Shell Ash Modified Asphalt Concrete Under Full Moisture Conditioning

Enyi, Festus Weneka1, Igwe, E. A.1, Otto, C. G.1

Abstract

Moisture-induced damage is one of the leading causes of premature failure in asphalt pavements, and the search for sustainable filler materials that can delay stripping and stiffness loss remains an active research area. This study evaluates the elastic stiffness and indirect tensile strength ratio of asphalt concrete modified with blends of palm kernel shell ash and oyster shell ash under full moisture conditioning. PKSA and OSA were combined at 0, 2, 4, 6, 8 and 10% by weight of filler in a 6 × 6 matrix, and Marshall specimens were prepared, conditioned by continuous water immersion for 0, 1, 2, 4, 7 and 14 days, and tested for tensile and compressive elastic modulus, indirect tensile strength and ITSR. The unmodified mix recorded a dry tensile elastic modulus of about 0.77 × 103 MPa, rising to a maximum of about 1.14 × 103 MPa at 10% OSA with 0% PKSA, while progressive PKSA addition beyond 2% consistently reduced stiffness at every OSA level. After 14 days of immersion, the tensile modulus of the control mix fell to 0.34 × 103 MPa (a loss of over 50%), whereas the 10% PKSA–OSA blend retained 0.52 × 103 MPa over the same period. The ITSR of the control mix declined from 100% at day 0 to 65.6% at day 14, below the AASHTO T283 minimum of 80% beyond day 2, while the best-performing blend (2% PKSA, 2% OSA) sustained an ITSR of 85.9% after two days and the 10% PKSA–OSA blend recorded the highest 14-day ITSR of 69.7%. These findings confirm that low-to-moderate PKSA– OSA combinations, particularly around 2% PKSA with elevated OSA, measurably delay moisture- induced stiffness and strength loss relative to the unmodified control, supporting their use as sustainable, waste-derived alternatives to conventional mineral fillers in moisture-prone pavement environments.

Keywords

asphalt concrete; palm kernel shell ash; oyster shell ash; moisture damage; elastic modulus; indirect tensile strength ratio

References

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Elastic Stiffness and Indirect Tensile Strength Ratio of Palm Kernel Shell Ash–Oyster Shell Ash Modified Asphalt Concrete Under Full Moisture Conditioning

Abstract

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