Hydration, strength, and durability of cementitious materials incorporating untreated corn cob ash

Significant research is being conducted to identify alternative sources of supplementary cementitious materials (SCM) worldwide. With the shortage of fly ash, due to the shut-down of several coal-fired power plants worldwide, there is an exigent need to identify sustainable SCMs that can replace fly ash in the concrete industry. This study explores the feasibility of using the ash of corn cob, which is the byproduct of one of the largest agricultural crops in the U.S., in concrete. Untreated corn cob ash (CCA) was prepared and used to replace the cement in concrete at replacement levels of 3% and 20% by mass of cement. The results of this study show that the untreated CCA significantly accelerated cement hydration, likely due to its high potassium oxide content. The results of reactivity testing suggest that the untreated CCA is less reactive than fly ash and that it is closer to an inert material. The concrete made with untreated CCA had significantly lower compressive strengths, lower bulk resistivity, lower formation factor, and higher electrical charge passed than normal concrete and what would typically be expected from the concrete with 3% and 20% replacements of inert materials. The results of this study suggest that untreated CCA is not a promising pozzolanic material, and may even be somewhat harmful to the concrete. A better option for the disposal of the large volumes of such materials could be for low-strength applications, such as fill or blocks. Alternatively, considering the significant variation in corn species and farming regimens, further research and ash treatment could help fine-tune the properties of this product for structural applications.