Effect of different types of fly ash on the properties of concrete mixtures: A comparative study

Abstract

In the pursuit of enhancing the durability and sustainability of reinforced concrete structures, the incorporation of supplementary cementitious materials (SCMs) such as fly ash (FA) is advantageous, as it allows for the augmentation of concrete properties in both its fresh and hardened states. Nevertheless, it is acknowledged that the performance of concrete can be influenced to a certain extent by the specific properties of the FA utilized. This study investigates the effects of incorporating five different types of FA as a 25% replacement for ordinary Portland cement on the physical, mechanical, and microstructural properties of concrete mixtures, with a focus on enhancing the durability and sustainability of reinforced concrete structures. Pozzolanic activity was assessed at both 28 and 180 days. At 28 days, a reduction in portlandite content ranging from 14.5% to 22.6% was observed in all FA-containing samples, indicating the early activation of pozzolanic reactions. This reduction increased to 30.4%–33.9% by 180 days, confirming that pozzolanic activity intensified over time. Additionally, the incorporation of FA increased both the initial and final setting times by 15%–30%, which can be attributed to its reduced reactivity at early ages and the dilution effect from cement replacement. While the compressive strength of FA-containing samples was lower than that of control samples at early ages, by 180 days, the strength of the FA-modified cementitious composites reached acceptable levels for various applications. The inclusion of FA not only improves the sustainability of concrete by reducing cement consumption but also promotes the recycling of industrial waste, addressing environmental concerns. Despite variations in the chemical and physical properties of the different FA sources, no significant differences were observed in their impact on portlandite content and mechanical properties, suggesting that FA from different regions can be reliably used in construction without compromising performance. These findings support the broader use of FA in sustainable construction practices and contribute to a global understanding of its variability.