V3I10P36

Immersion-Based Durability Assessment of Hybrid Quarry Dust-Plantain Leaf Ash Asphalt Concrete for Flexible Pavements

Amadi P. N.^1*, Oba A. L.²

Abstract

Moisture-induced damage remains one of the principal causes of premature distress in flexible pavements, particularly where rainfall is heavy and drainage is poor. This study examined the Marshall stability and moisture resistance of asphalt concrete in which quarry dust (QD) and plantain leaf ash (PLA), an agricultural waste ash, were introduced by replacement. Gravel, sand and bitumen (penetration 63.3, softening point 51.1 °C) were obtained from local dealers in Mile 3 market, Port Harcourt, and Marshall mix design gave an optimum binder content of 5.4% for the control mix. Mixes containing 0 to 10% QD combined with 0 to 10% PLA were compacted with 75 blows per face and tested for Marshall stability. The 10% QD series, which gave the highest stability at every PLA level, was then immersed in water for 1 to 5 days, and the Retained Strength Index (RSI), First Durability Index (FDI) and Second Durability Index (SDI) were determined. Stability increased with QD content in every PLA series and peaked at 42.2 kN for 10% QD without PLA, 18.5% above the control (35.6 kN). PLA reduced stability at every QD level, by 24.2% at 10% QD and 10% PLA. After five days of immersion, RSI fell from 77.5% for the PLA-free mix to 72.0% for the 10% PLA mix, while cumulative strength loss rose from 22.5 to 28.0 percentage points. Strength loss was fastest between the third and fourth day in every mix. Second-order polynomial regression described the RSI-time trends well (R² of 0.96 to 0.99), whereas FDI and SDI trends were only explained. Within the tested range, QD alone improved stability, whereas PLA reduced both stability and resistance to prolonged immersion, with 2 to 4% PLA being the least harmful. QD is therefore supported as a strength-enhancing filler, while PLA will need processing or a lower dosage before use in wet-climate pavements.

Keywords:

Asphalt concrete; moisture damage; agricultural waste ash; retained strength index; durability index; mineral filler