Industrial civilization causes huge carbon emissions, accelerates climate change, and hinders the sustainable development of human society. The construction industry causes about 40% of annual global anthropogenic carbon emissions, within which the massive construction of concrete structures alone accounts for more than 10% of the global emissions. China's national goals for carbon peaking, neutrality, and the low-carbon development consensus call for the low-carbon design theory of concrete structures in the construction industry. Starting from the scientific issues with the concrete structure-environment symbiotic system, this paper clarifies the indicators, design methods and tuning means of low-carbon structural design, aiming to lay a foundation and provide suggestions for the development of low-carbon design, and promote the sustainable development of concrete industry. By briefly reviewing the history of the concrete industry, we illustrate the trend of low-carbon transitions, for which it is urgently needed to shift the perspective of structural design from only centering on human needs to meeting the sustainable needs of the integrated system of concrete structures and environments. Based on the characteristics of carbon emissions and uptake of concrete structures, the significance of regulating concrete structures' net embodied carbon emissions for climate change mitigation is clarified. Further, to cope with climate change, we put forward the scientific issues and design requirements for the concrete structure-environment symbiotic system. To facilitate the sustainable development of the concrete structure-environment symbiotic system, we focus the low-carbon design method on the quantitative characterization of structure-environment dynamic coupling. The structural sustainability indicator is established to simultaneously reflect the structural reliability and carbon emission level of concrete structures. Further, we sort out relevant evaluation and design methods into the evolution of low-carbon design from the structural reliability design considering sustainability to the sustainability design characterized by a bidirectional perspective, which means the design methodology has developed from the reliability guarantee of qualitative low-carbon strategies facing climate change to quantitative carbon emission target guarantee in the form of conditional probability control, which ensures both low-carbon emissions and reliable service performance during the life cycle of concrete structures under climate change. Further, in order to assist the low-carbon design regulation, we put forward the carbon emission-based 3R(+C) principles, i.e., carbon reduction, carbon reuse, and carbon recycling, to construct a low-carbon design technology system with superimposable carbon emission reduction benefits among categories. Typical low-carbon technologies for concrete structures are classified following the three principles according to their main emission reduction advantages, i.e., embodied carbon reduction in material production, embodied carbon allocation by construction mode transition, and carbon uptake with a developed end-of-life management system, and their emission reduction potential and promotion prospects are explored. A lot of future work is needed for the innovative development and promotion of low-carbon design of concrete structures, which includes clarifying the carbon emission benchmarks and goals for the concrete industry, strengthening the identification and management of failure risks and possible failure consequences under climate change, enriching and improving available low-carbon design technologies, and developing codes and software for integrated low-carbon design.
