Effect of Waste Tire Crumb Rubber on The Marshall Characteristics of Asphalt Concrete Wearing Course (AC-WC)

Abstract

Road infrastructure performance, particularly in Asphalt Concrete Wearing Course (AC- WC), often declines prematurely due to repeated traffic loading and environmental exposure. This study quantitatively evaluates the effect of waste tire crumb rubber as an aggregate additive on the Marshall characteristics and volumetric properties of AC-WC mixtures. Laboratory experiments were conducted using crumb rubber contents of 0%, 1%, 2%, and 3% by total aggregate weight with 60/70 penetration grade asphalt. The results indicate a non-linear relationship between crumb rubber content and mixture performance. Marshall stability increased from the control mixture (0%) to the optimum at 2%, exceeding the minimum specification requirement of 800 kg, before decreasing at 3% due to reduced particle interlocking. Flow values showed a consistent increase with crumb rubber addition, indicating enhanced flexibility, with values approaching the upper specification limits at higher contents. Consequently, the Marshall Quotient (MQ) exhibited a decreasing trend, reflecting a transition from stiff to more elastic behavior. Volumetric parameters, including VIM (within 3–5%), VMA (>15%), and VFB (>65%), satisfied specification limits at 0–2% crumb rubber but began to deviate at 3% content due to increased voids and reduced density. The optimum crumb rubber content was determined to be 2%, providing the best balance between stability, flexibility, and volumetric performance. These findings confirm that crumb rubber improves AC-WC performance while offering a sustainable solution for recycling waste tires in pavement engineering.