Combined effects of dune sand and recycled tire rubber on bentonite stabilization: mineralogical and microstructural insights

Belgacem Choungache , Abdelhalim Bensaada , Rebih Zaitri , Naas Allout

Abstract

This study investigates the mineralogical and microstructural changes of bentonite treated with dune sand (DS) and recycled tire rubber (RTR), with particular emphasis on reducing the free swell strain of expansive soils. A comprehensive experimental program was conducted, including one dimensional free-swell tests, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The results indicate that partial replacement of bentonite with DS and RTR significantly reduces both the magnitude and rate of free swell strain. The optimum mixture, consisting of 5% RTR and 10% DS, exhibited the lowest swell strain (8.9%) along with a dense and well-integrated microstructure characterized by reduced pore connectivity. XRD analysis revealed increased quartz crystallinity and decreased montmorillonite activity, while SEM observations confirmed enhanced particle interlocking and matrix densification. These findings demonstrate a combined stabilization mechanism, where DS improves granular rigidity and RTR provides elastic confinement, leading to enhanced dimensional stability. The proposed DS–RTR stabilization approach offers a sustainable and effective solution for mitigating swelling in expansive soils used in subgrade and embankment applications.

Key Words

bentonite; dune sand; recycled tire rubber; SEM; swelling; XRD

Address

Belgacem Choungache and Rebih Zaitri — Department of Civil Engineering, Faculty of Technology, University of Djelfa, 17000, Algeria
Abdelhalim Bensaada — Laboratory of Civil Engineering and Protection of the Environment (LCEPE), Department of Civil Engineering, Faculty of Technology, University of Medea, Algeria
Naas Allout — Laboratory of Civil Engineering and Sustainable Development, Department of Civil Engineering, Faculty of Technology, University of Djelfa, 17000, Algeria

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