Performance Evaluation of Crumb Rubber Modified Bituminous Concrete Using Marshall Mix Design: A Sustainable Pavement Engineering Approach

The accelerating generation of waste tires, exceeding one billion end-of-life tires annually worldwide, poses critical environmental and public health challenges. This study investigates the performance of crumb rubber (CR) derived from waste tires as a modifier in 60/70-grade bituminous concrete produced by the wet process. Crumb rubber was incorporated at 2%–14% by weight of bitumen. Standard characterization tests, including penetration, softening point, ductility, and flash/fire point, were conducted on conventional bitumen; penetration, softening point, and ductility were repeated for all modified samples. Marshall Mix Design was performed at a constant Optimum Bitumen Content (OBC) of 4.5%, established for the conventional mix and held fixed to isolate the effect of rubber content. The optimum rubber content was 10%, yielding a Marshall stability of 1042.5 kg, an 84% improvement over the conventional mix, while meeting all specification limits. The original laboratory investigation was conducted at Wah Engineering College (2013–2017); this paper's contribution is to re-examine those results against the current 2025–2026 global CRMB literature — including AI-driven optimization, nanotechnology integration, damping performance, and circular economy policy — and to interpret them specifically within Pakistan's developing-economy pavement and waste-management context. This paper presents crumb rubber modified bitumen as a technically sound, cost-effective, and environmentally sustainable option for flexible pavement construction in developing economies, while acknowledging the study's laboratory-scale limitations. Rethinking The Barriers to The Development of Green Buildings in The Global South: A Study from Ghana Matthew Kwaw Somiah1*, Frederick Owusu Danso2, Isaac Yaw Manu3, Jeriscot Henry Quayson4 , Benjamin Kodjo Aidoo5, and Michael Kofi Biney6 1,3,5,6 Faculty of Built and Natural Environment, Takoradi Technical University, Ghana 1, Faculty of Engineering and Built Environment, University of Johannesburg, South Africa 1, Faculty of Engineering, Built Environment, and Information Technology, Walter Sisulu University, East London,