Optimizing cold bitumen emulsion mixtures with waste coal bottom ash: a performance-based study

In light of growing environmental concerns and the need for sustainable construction practices, incorporating waste materials like coal bottom ash (CBA) into cold bitumen emulsion mixtures (CBEM) offers a promising alternative to traditional hot mix asphalt (HMA), which demands higher energy and natural resource consumption. This study aims to develop a novel CBEM for binder courses by partially replacing the filler (cement) with CBA in proportions ranging from 0 to 50%. Mechanical performance was evaluated through tests such as Marshall stability, indirect tensile strength (ITS), resilient modulus (ITSM), flow number, and durability. A comparative analysis was conducted with conventional HMA and standard CBEM (NCBEM). The results show that CBEMs with up to 30% CBA substitution achieved optimal performance, with a notable increase in Marshall stability, comparable flow, and ITS values to HMA. Higher CBA content also enhanced resilient modulus and rutting resistance, with CBEM-50CBA showing 42% higher durability than HMA. Microscopic analysis (FESEM) indicated increased formation of cementitious compounds, particularly C-S-H gels, contributing to these improvements. The optimal CBA substitution level for binder layer applications was 30%, offering a sustainable and efficient solution for pavement construction.