Shear Strength Behavior of Tire Shred-Dune Sand Admixtures

Abstract

A Master of Science thesis in Civil Engineering by Abrar Ahmad entitled, “Shear Strength Behavior of Tire Shred-Dune Sand Admixtures”, submitted in July 2025. Thesis advisor is Dr. Magdi El-Emam. Soft copy is available (Thesis, Completion Certificate, Approval Signatures, and AUS Archives Consent Form).The use of construction and demolition waste in geotechnical applications has emerged as an effective and sustainable approach to enhancing soil performance while reducing environmental impact. Recycled Concrete Aggregate (RCA) has demonstrated significant potential as a soil stabiliser, improving shear strength properties, bearing capacity, and overall soil performance. Despite the widespread availability of dune sand in the UAE, its use in geotechnical engineering is often limited due to its inadequate shear strength and poor gradation. Mechanically stabilized due to sand with RCA reinforcement could be a potentially suitable backfill material for many civil infrastructures. Although several studies have investigated the application of recycled aggregates in soil stabilisation, there is still a lack of agreement about the optimum RCA content and particle size to improve shear strength. This study aims to examine the shear strength characteristics of RCA-dune sand mixes with varying RCA concentrations and particle sizes, and to identify the optimal mix configuration for backfill applications. The main soil parameters were peak and residual shear strength, internal friction angle, stiffness (G₅₀), and ductility. Three RCA gradations (5–10 mm, 10–20 mm, and a 50:50 blend of both sizes) were utilised to evaluate 52 samples with RCA content of 10%, 20%, 30%, and 40% by weight using a specially made large-scale direct shear (LSDS) equipment. Experiments were performed under initial normal stress of 20, 40, 60, and 100 kPa. The findings indicated that the incorporation of RCA substantially enhanced the shear strength of dune sand, with maximum strength improvements reaching 157% relative to pure dune sand. The 10–20 mm RCA at 30% composition yielded the maximum shear strength and internal friction angle of 59.01°, while the peak residual friction angle of 45.2° was recorded at the same composition. Nevertheless, stiffness often decreased beyond 30% RCA due to increased voids and particle segregation. These findings offer significant insights into the possibility of utilising RCA as a dune sand stabiliser in arid regions such as the UAE and support the wider implementation of sustainable construction techniques.College of EngineeringDepartment of Civil EngineeringMaster of Science in Civil Engineering (MSCE