Towards a New Approach in Designing High-Strength Concrete: Challenges in Replacing Three-Fourth of Natural Fine Aggregate with Coal Bottom Ash

Globally, thermal power plants produce about 780 million tonnes of coal ash, of which Asia alone accounts for 66% of this share. India, the third-largest coal ash producer, generated 226 million metric tonnes in 2019. Conserving natural resources and promoting viable alternatives are priorities that contribute to achieving sustainable development goals. This study aims to assess the fresh and hardened properties of high-strength concrete, in which 75% of natural fine aggregate (NFA) is supplemented with coal bottom ash (CBA). This study assessed ultrasonic pulse velocity and compressive strength at 3, 7, 28, 56, and 90 days using 100 mm cube specimens, split tensile and flexural strength at 7 and 28 days with 150 mm dia. × 300 mm height cylindrical specimens and 500×100×100 mm beam specimens, respectively. A minimum of three samples are tested in each group per test, and the average values are recorded. The findings reveal promising outcomes for using high-volume CBA as a feasible alternative to NFA. The concrete exhibited commendable early-age hardened properties with a 28-day compressive strength of 79.73 MPa, flexural strength of 7.2 MPa, and split tensile strength of 3.25 MPa, supporting the suitability of CBA in high-strength applications. The higher water absorption of CBA due to its porous structure may have led to a higher slump value. However, it's important to note that a higher slump value meant that the slump was a collapse pattern, and the mix also showed significant bleeding, segregation, and a longer setting time, which presents a considerable challenge when attempting to incorporate higher volumes of CBA into concrete.