OPTIMIZING CALCINATION CONDITIONS OF CORN COB ASH FOR PARTIAL REPLACEMENT OF PORTLAND CEMENT IN CONCRETES

Abstract

The use of agro-industrial residues as supplementary cementitious materials contributes to environmental sustainability and optimized resource use in concrete production. This study evaluates the pozzolanic potential of corn cob ash (CCA) produced under different thermal conditions. Corn cobs were calcined at 650 °C, 750 °C, and 850 °C for durations of 2 and 4 hours. The ashes were characterized through physical tests, including specific gravity, fineness, particle size distribution, and loss on ignition, as well as chemical and mineralogical analyses by X-ray fluorescence and X-ray diffraction. CCA calcined at 750 °C for 2 hours exhibited the most favorable properties, with the highest specific gravity (2.87 g/cm³) and a more suitable particle size distribution. This condition resulted in a higher amorphous content, identified by broader halos in XRD patterns, a feature associated with enhanced pozzolanic reactivity. In contrast, ashes calcined at 850 °C showed increased crystallinity and reduced fineness, indicating lower pozzolanic potential. XRF analysis revealed high SiO₂ contents in all ashes, meeting the requirements for pozzolanic materials (SiO₂ + Al₂O₃ + Fe₂O₃ ≥ 73%). Although the ash produced at 750 °C for 2 hours did not fully meet the fineness criterion (<15% retained on the 75 µm sieve), it presented a value close to the acceptable limit (19.9%). Overall, this calcination condition provided the best balance for using CCA as a pozzolanic material.