Synergistic effects of natural fibres and agro-waste ash on the engineering and sustainability of stone-matrix asphalt mixes

This study investigates the use of non-traditional natural fibres, specifically sisal plant fibres (SF) and coconut coir coir fibres (CCF), in Stone Matrix Asphalt (SMA) mixtures. The objective was to evaluate the optimal binder content, assess Marshall properties, and investigate drain-down, indirect tensile strength, fatigue, and rutting characteristics of the SMA mixes. Additionally, the study explores the use of sugarcane bagasse ash (SBA), an agro-waste, as a substitute for Ordinary Portland Cement (OPC), aiming to promote sustainability and waste management optimization. The research identified the optimal SMA mix with a 0.30% fibre dosage and 10% SBA, demonstrating favorable mechanical properties with Marshall stability and tensile strength ratio exceeding 90%, alongside satisfactory rutting and fatigue performance. The results showed that SF and CCF provided comparable, or even superior, performance to traditional cellulose fibres (CF), positioning them as sustainable alternatives for pavement construction. Further, a Life Cycle Cost Analysis (LCCA) was conducted on conventional and modified SMA mixes, revealing substantial long-term economic benefits. Although SMA mixes incurred slightly higher initial costs, their superior durability and reduced maintenance needs resulted in a 13.6% cost reduction for SMA-CCF and 11.1% for SMA-SF over a 20-year period. Environmental assessments confirmed that substituting synthetic fibres and OPC with SF, CCF, and SBA substantially lowered carbon emissions and enhanced sustainability, with reductions in Global Warming Potential of up to 50%. These findings highlight the potential of natural fibres and SBA in reducing costs and environmental impacts, offering a sustainable solution for future pavement construction.