Influence of milling parameters on the properties of ground coal bottom ash and its blended cement

Coal bottom ash (CBA), a by-product of the coal thermal power plant, can be classified as pozzolanic material according to ASTM C618. Therefore, it is a suitable supplementary cementitious material (SCM) in concrete. In recent developments, it was established that the pulverization of CBA enhanced the pozzolanic properties. Numerous prior studies on utilising the ground CBA (GCBA) as SCM was conducted by milling CBA in a laboratory ball mill. However, the optimisation of the milling parameters was not investigated to achieve the optimum output rate and quality of GCBA. Hence, the present work is aimed to establish optimised milling parameters for producing high-quality GCBA in a ball mill for use as a constituent binder in binary and ternary blended cement. The raw CBA was pulverised at various retention times, the angular velocity of the mill (in revolution per minute, RPM) and CBA to instantaneous media ratio. The physical and pore properties of the resulting GCBA were characterized by Blaine fineness, laser particle and Bruneur Emmer Teller analysis. Besides, the workability and mechanical strength of mortar made with the GCBA blended cement were also examined. Subsequently, statistical analysis of test results was conducted by analysis of variance (ANOVA). It was observed that the CBA ground for 5 hours (5H-GCBA) exhibited optimum performance in physical and mechanical properties. Subsequently, the 5H-GCBA was pulverised at an angular velocity of 50 – 80 revolutions per minute (RPM) with a CBA to instantaneous media ratio of 1:10 – 2:10. The statistical analysis revealed that the retention time and the angular velocity of mill and CBA to instantaneous media ratio significantly influenced the workability, flexural and compressive strength of GCBA-blended mortar. In conclusion, the blended cement containing GCBA pulverised at 70 RPM with a CBA to instantaneous media ratio of 1.5:10 for 5 hours exhibits optimum performance.