Evaluation of corn straw ash as supplementary cementitious material: Effect of acid leaching on its pozzolanic activity

The use of biomass ash is an environmentally friendly practice in the search for sustainable construction materials. This study aimed to produce pozzolanic ash from corn straw with a high amorphous silica content, low carbon content, and high specific surface area via controlled acid leaching, two-step burning, and grinding. The effect of pretreating corn straw on the properties of the material was assessed by comparative analysis with corn straw and rice husk ashes produced without acid pretreatment. To this end, characterization data, hydration heat, chemically bound water, and portlandite consumption in pastes, and mortar compressive strength were used to evaluate the pozzolanicity of the ashes. The results indicated that all the ashes exhibited pozzolanic behavior and that the leaching process significantly improved the physical and chemical properties of corn straw ash, with reduction in portlandite content. The calorimetric results showed a change in hydration kinetics with an increase in ash in the cement mixes. Moreover, the compressive strength of leached corn straw ash-based mortars was greater than that of the other mortars, primarily for high levels of cement replacement (20 and 30% by mass).