Utilization of coal bottom ash from thermal power plants as a cement replacement for building: A promising sustainable practice

Coal bottom ash (CBA) is claimed to carry some pozzolanic qualities that can be stimulated by pre-treatment. This study investigates the feasibility of partially replacing ordinary Portland cement (OPC) with ground CBA to produce CBA-cement paste. A thorough experimental program was designed to explore the effect of the CBA source and particle size, liquid-to-binder ratio (l/b), and superplasticizer (SP) on the 28-day compressive strength of CBA-cement paste. The CBA source with a high SiO₂/Al₂O₃ ratio (approximately 3.6) and CaO content (5.3%) yielded higher compressive strengths. Grinding breaks down the large raw CBA particles and enhances their reactivity with water and pozzolanic character. Specimens with 50% ground CBA attained a 28-day compressive strength of up to 51 MPa at l/b of 0.225. The low pozzolanic nature combined with the porous texture of CBA necessitates the incorporation of a superplasticizer to enhance workability at low l/b. A 28-day strength of 61 MPa was achieved at 30% cement replacement with 150 μm CBA at l/b of 0.25 using 1% SP. In view of this, partial replacement of cement with ground CBA has proven to be a viable and sustainable construction option.