Abstract
Portland cement is highly energy-consuming, and its CO2 emissions raise environmental concerns in the construction sector. This has prompted the desire for sustainable additional cementitious materials, such as slag and banana leaf ash (BLA). Nevertheless, the current literature primarily deals with their single application, with mixed results. Their interaction in natural fiber-reinforced composites is a poorly investigated area of research, and fiber-matrix contact and behavior are yet to be understood. This study investigated the utilization of ground-granulated blast-furnace slag (GGBS) and banana leaf ash in sustainable cementitious composites reinforced with natural fibers. Two binder systems were developed: cement-GGBS and cement-GGBS–banana-leaf ash. Five natural fibers, namely banana, kenaf, pineapple, sisal, and jute, were incorporated at a volume fraction of 0.5%. This study evaluated the combined effects of these parameters on the mechanical performance and microstructural characteristics of the composites, highlighting the role of the fiber type and supplementary materials in enhancing the composite behavior. The results indicated that pineapple fiber reinforcement significantly enhanced the compressive strength (up to 37.78% at 28 days). The highest compressive strength exhibited by the pineapple and kenaf fibers, particularly at early ages. However, fiber addition increased water absorption, particularly in BLA-based systems. Microstructural analyses confirmed enhanced pozzolanic reactivity, less portlandite, and increased calcium-alumino-silicate-hydrate formation. These changes lead to a denser, more compact, and thermally stable matrix, demonstrating the effectiveness of GGBFS, BLA, and natural fibers in the composite. This study offers valuable insights into creating sustainable and low-carbon cementitious composites using a combination of industrial by-products, agricultural waste ash, and natural fibers while enhancing the mechanical and microstructural properties, ultimately supporting the development and application of environmentally friendly yet resourceefficient construction materials.²