Reuse And Sustainability Design Of Concrete Components

The construction of concrete structures is a main source of anthropogenic carbon emissions,and concrete component reuse reduces the demands for new production while reducing waste,which possesses substantial carbon reduction potential.This work focuses on t he whole process of concrete component reuse,including the mechanical analysis of structural deconstruction,the sustainability design of new concrete components,and the reliability assurance for the reuse of old concrete components,aiming to provide a theoretical basis for the safe and low-carbon application of concrete component reuse.The main research contents and novel conclusions are in the following:(1)In order to improve the feasibility of concrete component reuse,structural deconstruction,i.e.,disassembling the components from the original structure piece by piece,is proposed to substitute the conventional destructive demolition.Aiming at both targets of safety and low damage,based on the proposed state dispersion method and spatial segmentation method,the workflow,conditions and difficulties of mechanical analysis on structural deconstruction have been clarified,and the practical tools of conceptual analysis,analytical analysis and numerical simulation have been sorted out.The mechanical analysis on the deconstruction of a simple frame structure has been carried out,where preliminary suggestions on the deconstruction sequence have been obtained.(2)In order to systematically measure the environmental benefit level of concrete component reuse,based on the life cycle assessment(LCA)method,the open-loop and closed-loop evaluation principles have been distinguished respectively for component reuse and material recycling.Besides,a non-linear environmental impact allocation rule is proposed according to the degradation characteristics of concrete components,and thereby the unified system boundary suitable for LCA of both component reuse and material recycling strategies is established.Further,the reutilization design parameters,i.e.,reusable rate and replacement percentage,are introduced for environmental impact quantification and adjustment.The proposed LCA framework is adopted to evaluate the global warming potential(i.e.,equivalent carbon emissions)of a sample concrete structure constructed in Shanghai,and the reusable concrete component and recycled coarse aggregate concrete are taken as typical cases of component reuse and material recycling strategies for design.Results show that the maximal carbon emission reduction of component reuse is 2.8 times that of material recycling for the case study.Due to the accelerated effect of recycled aggregates on concrete carbonation,the emission reduction of the combined application of two strategies will be lower than the linear superposition of the reduction from each strategy applied alone.Further,the resistance-based environmental impact allocation rule is proposed to expand applicable scenarios,and the cooperative game theory has been adopted to justify that the proposed rule could promote the practice of concrete component reuse.(3)In order to promote the simultaneous improvement of the safety and low carbon of concrete structures,sustainability is proposed as a new design target,and its conditional probability formula is established to describe tolerability of the environmental system to the environmental impacts caused by structural construction,under the premise that the structural reliability satisfies the requirement.It is suggested to correlate the structural carbon emission limit and expected climate change scenario in structural analysis.Then,a structure-environment bidirectional influence model is established,which is mediated by structural reliability and carbon emission indicators and driven by the natural laws of climate change and structural performance evolution.Preliminary methods for quantifying the interaction between structural reliability and environmental impacts are proposed to formulate the bidirectional sustainability design.According to the service characteristics of reusable components,a lifespan prediction method based on the capacity reliability for one year is proposed,and combined with the simplified stochastic model for time-dependent capacity under climate change,the calculation method for sustainable probability is established,catering for both reusable and non-reusable structural components.With the Monte Carlo simulation,the proposed sustainability design process is implemented in a numerical example,which shows that the reusable structural concrete component design can simultaneously satisfy the current and future safety and environmental requirements.(4)In order to guarantee the reliable application of low-carbon strategies under climate change,the sustainability-based reliability design method is proposed.Taking the old concrete component to be reused as the design object,the carbonation-induced degradation pattern and in-situ structure and climate data collected are combined to construct a domain-specific machine learning model for reusability identification of old components and carbonation-induced degradation prediction under climate change,and the potential risks of component reuse can be evaluated,which constitutes the sustainability-based reliability design for the reuse of concrete components.The proposed method has been implemented in a case study of reused concrete component design in Guangzhou area.Results confirm that the climate change accelerates carbonation-induced degradation,while the design that ignores climate change underestimates failure probabilities grossly and overestimates the sample component’s maximum service life by up to 22.5 years.The sustainability pathway could alleviate the climate change adaptation needs and improve the reusability of old concrete components.Preliminary design suggestions for sustainability-based reuse design have been put forward following the sensitivity analysis on t he case study.Further,a simplified method is proposed to estimate macro carbon reduction benefits of component reuse in response to the long-term service demands of concrete structures,which proved that by dispelling the reliability concerns on concrete component reuse,the sustainability-based reuse design could facilitate the achievement of the carbon emission reduction target for concrete structures required by the sustainability pathway.This exploratory research theoretically guarantees the safety and low carbon of the whole process of concrete component reuse,and strengthens the efforts on the climate change adaptation and mitigation of concrete structures by t aking the lead in establishing the structural sustainability design methodology,which is expected to promote a virtuous cycle between structural construction and climate change.