349 Performance requirement design and mix proportion optimization of cemented backfill materials are adopted to achieve carbon-reduced tier. MICP is applied to achieve lowcarbon tier. Carbon dioxide mineralization and sequestration are integrated in to backfill material to achieve carbon-negative tier. A life cycle performance design methodology for cemented backfill materials is established. A multi-objective mix proportion optimization method based on the SobolNSGA-III algorithm is formulated based on design results of pipeline transportability, selfstability time, and mechanical properties. Microbial cemented backfill materials are developed. The mechanical properties and key factors of both "mixing-type" and injection-type microbial backfill materials are investigated. The consolidation mechanism is elucidated, revealing that CaCO3 crystals generated within the material effectively fill the internal pores and cement adjacent particles together. High-porosity carbon-negative backfill materials and microbial carbon-negative cemented backfill materials are successfully developed. Their mechanical and carbonation properties are systematically evaluated, and the carbonation-cementation mechanism is revealed. The uniaxial compressive strength of the microbial carbon-negative materials reaches 3.28 MPa, with a carbonation rate of up to 2.45%. ACKNOWLEDGEMENTS Sincere gratitude is expressed to the team led by Professor Xiaohui Cheng at Tsinghua University for assistance with microbial experiments. Appreciation is also extended to all experts and scholars who provided support to this study. This work was supported by the National Natural Science Foundation of China (Grant Nos. 52474162, 52274149) and the Deep Earth Probe and Mineral Resources Exploration-National Science and Technology Major Project (No. 2024ZD1003905). REFERENCES Chen Q., Zhu L., Wang Y., Chen J., Qi C., (2022). The carbon uptake and mechanical property of cemented paste backfill carbonation curing for low concentration of CO2. Science of the Total Environment. 852: 158516. Deng X., Li Y., Liu H., Zhao Y., Yang Y., Xu X., Cheng X., Wit B.d., (2021). Examining energy consumption and carbon emissions of microbial induced carbonate precipitation using the life cycle assessment method. Sustainability. 13, 4856. Deng X., Yuan Z., Li Y., Liu H., Feng J., Wit B.d., (2020). Experimental study on the mechanical properties of microbial mixed backfill. Construction and Building Materials. 265, 120643.
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