Turning corn straw waste into supplementary cementitious materials: Feasibility, properties and life cycle assessment

Supplementary cementitious materials (SCMs) have been the essential constituents of sustainable, low-carbon cement and concrete products. However, the large consumption is inducing the probable resource shortage of industrial by-products-based SCMs. Thus, this study explored the feasibility of agricultural corn straw waste (CSW) as an SCMs for cement products. A three-step process-pre-treatment, pyrolysis, and milling-was used to convert CSW into corn straw ash (CSA), and its effects on physical and chemical properties were analyzed. The influence of different types and dosages of CSA on the heat of hydration and microstructure of the cement paste, as well as the flowability and compressive strength of the mortar, was also investigated. A life cycle assessment (LCA) was conducted to evaluate the environmental impact of CSA-containing mortars. The results showed that acid-washed CSW pyrolyzed at 600 degrees C for 2 h exhibited excellent pozzolanic activity, with active oxide content close to 90 % and SiO2 content above 70 %. The SiO2 content in CSA increased with higher pyrolysis temperature and duration, with temperature having a greater effect on SiO2 crystallization. The addition of CSA accelerated cement hydration and significantly improved early mortar strength. The LCA results showed that pyrolysis had the greatest environmental impact, followed by milling. The prepared mortar with the addition of 5 wt% CSA is an optimal solution in terms of technical and environmental aspects.