An Experimental Investigation of Stone Mastic Asphalt Reinforced with Nanoclay-Modified Sisal Fiber

Godfred Kankam; Kiplagat Chelelgo; M’Tulatia Mungathia

doi:10.48084/etasr.18308

Authors

Godfred Kankam Department of Civil Engineering, Pan African University Institute for Basic Sciences, Technology and Innovation, Kenya
Kiplagat Chelelgo Department of Civil Engineering, Dedan Kimathi University of Technology, Kenya
M’Tulatia Mungathia Department of Civil, Construction and Environmental Engineering, Jomo Kenyatta University of Agriculture and Technology, Kenya

Volume: 16 | Issue: 3 | Pages: 34990-34997 | June 2026 | https://doi.org/10.48084/etasr.18308

Received: 21 February 2026 | Revised: 15 March 2026 | Accepted: 26 March 2026 | Online: 5 April 2026

Corresponding author: Godfred Kankam

Abstract

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.

Keywords:

stone mastic asphalt, organically modified montmorillonite, sisal fiber

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