Preparation and properties of supplementary cementing materials based on recycling of straw solid wastes

This paper is aimed at the problem of reducing carbon emissions of cement and its composites under the Carbon Peaking and Carbon Neutrality Goals. This study used corn straw waste (CSW) as raw material to develop a three-step process of pretreatment-pyrolysis-grinding to prepare a sustainable corn straw ash (CSA) material that can be used as supplementary cementing materials. The study focused on studying the effects of pretreatment methods (untreated, distilled water washing, hydrochloric acid washing), pyrolysis temperature (500℃, 600℃, 700℃) and pyrolysis durations (1 h, 2 h, 3 h) on CSA activity, as well as the effects of different pretreatment types and blending amounts of CSA on the performance of prepared mortars. The experimental results showed that the content of SiO₂ of CSA increased with the enhancement of pyrolysis temperature and duration. And the effect of pyrolysis temperature on SiO₂ crystallization was much greater than that of pyrolysis durations. The incorporation of 5 wt% CSA increased the compressive strength of mortar by 11.7%. The incorporation of over 5 wt% CSA decreased the compressive strength due to the porous structure of CSA. The incorporation of untreated, distilled water washing and hydrochloric acid washing CSA demonstrated caused the C-S-H morphology in the cement matrix to change from honeycomb and fibrous to dense gel. The CSA treated by acid washing and pyrolysis at 600℃ for 2 h showed excellent pozzolanic activity and can be used as good supplementary cementing materials.