An Experimental Investigation of Stone Mastic Asphalt Reinforced with Nanoclay-Modified Sisal Fiber
Résumé
Stone Mastic Asphalt (SMA) is a gap-graded, bituminous mixture with a stone-on-stone skeleton and a high binder content. This composition provides superior load-bearing capacity and rutting resistance. However, the gap-graded nature and high binder content of SMA make it susceptible to binder drain-down. Although natural fibers are considered a sustainable additive for reinforcement, their organic and hydrophilic properties raise concerns about high moisture absorption, which could reduce the long-term durability of SMA. This study examined nanoclay-modified, sisal fiber-reinforced SMA, focusing on volumetric design, moisture resistance, and binder draindown. The materials used include aggregates, sisal fiber, Organically Modified Montmorillonite (OMMT) nanoclay, and Styrene-Butadiene-Styrene (SBS)-modified bitumen. The Superpave procedure was adopted to design an SMA with a nominal maximum aggregate size of 12.5 mm. The optimum binder content that yielded the desired air voids was 6.6%. The sisal fiber content varied from 0% to 0.5% of the total weight of the SMA mixtures. Then, OMMT nanoclay was applied as a modifier to the sisal fiber before it was incorporated into the SMA. Sisal modification was performed at OMMT levels of 0%, 2%, 4%, 6%, and 8%. The optimum sisal fiber content was 0.3%, yielding a Tensile Strength Ratio (TSR) of 85.6% and a draindown of 0.08%. OMMT-modified, sisal-reinforced SMA produced an improved TSR of 96.5% and reduced draindown to 0.05%. These results demonstrate that modifying sisal with nanoclay improves the binder retention and moisture resistance of asphalt mixtures.
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