Performance-based durability assessment of concrete containing coal bottom ash as fine aggregate under chloride penetration

Abstract The use of industrial wastes represents an alternative for reducing the consumption of natural aggregates in concrete production. Coal bottom ash (CBA), a byproduct of coal combustion in thermal power plants, has been employed as a partial replacement for fine aggregates due to its particle size being comparable to that of river sand. However, the durability-related performance of CBA concrete still requires further investigation – notably under chloride penetration. This study presents an experimental evaluation of concrete incorporating CBA, both with and without metakaolin (MK). The addition of MK aims to assess its potential in mitigating mechanical losses associated with the use of CBA, as well as to explore possible combined effects resulting from the use of CBA and MK. Concrete mixtures were produced with partial replacement of fine aggregate by CBA at levels of 5%, 10%, 15%, 20%, and 30%. Concrete performance was evaluated based on compressive strength, water absorption, chloride penetration, and electrical resistivity. A probabilistic service life analysis was conducted using chloride migration coefficients obtained from the rapid chloride migration test and the corresponding calculated aging factors. Although the CBA used in this study did not exhibit pozzolanic activity, reductions in chloride diffusivity were observed in concretes containing CBA. This effect may be attributed to physical mechanisms such as improved particle packing and increased pore tortuosity. The findings indicate the feasibility of using CBA in concrete production, representing a sustainable alternative for the management of this industrial byproduct. Notably, the use of 15% CBA demonstrated slightly higher compressive strength values, while a 30% replacement level reduced chloride diffusivity by approximately 60% at 91 days.