Pretreatment of corn stover ash to improve its effectiveness as a supplementary cementitious material in concrete

This paper investigates the feasibility of using corn stover ash (CSA) as supplementary cementitious material to replace cement in concrete. Three types of CSA -- water-washed, acid-washed, and untreated burned corn stover -- were produced, and the influence of the pretreatment regimens on the physical and chemical properties of the produced ashes are evaluated. Moreover, the influence of CSA on the hydration kinetics of cement pastes, and compressive strength and bulk electrical resistivity of concrete specimens is discussed. The results of this study show that pretreating the corn stover before combustion increases the SiO₂ content of the ash, and reduces the Cl and K₂O contents, the loss on ignition, and the median particle size. The results also show that the pretreated CSA is more reactive and can accelerate the cement hydration process. Both acid- and water-washed CSA increase the strength and bulk electrical resistivity of concrete at later ages. Incorporating untreated CSA in the concrete mixture, on the other hand, reduces the compressive strength and bulk electrical resistivity of the concrete, due to the negative impacts of deleterious agents (such as high ash alkali contents) on the cement hydration process. While further work is needed, pretreated CSA could potentially be used as a novel supplementary cementitious material in concrete.