Integrated Life Cycle Design Of Fly Ash Reinforced Concrete Beam Based On Sustainability

At present,the total number of highway bridges in China has amounted to more than 800,000 and the total length is more than 50 million meters.Concrete bridges deteriorate with time due to complex service condition,environmental condition and possible overloading,and it seriously affects the safety of bridges.The feature of integrated life cycle design of structure is that it can consider the post resulting from the maintenance,detection,repair,etc.of the constructed structure in the design stage.Traditional bridge design methodology which considers the condition of completing the construction of bridges and the construction management system are the key factors of the durability problems of current bridges and being unable to achieve design life of bridges.With the move towards sustainable development comes the need for this approach to be expanded to encompass the life cycle of bridges.Based on the concept of life cyele from planning,design,construction and management of serviee phase to demolishment and recycling of materials and components,a comprehensive approach focusing on design methodology and methods of life cycle based bridge design is developed in the dissertation,in which the sustainability for life cycle based bridge design are included.Concrete is the most widely used construction material of bridges.However,in the process of concrete manufacturing,there are serious problems of resource and energy consumption and environment pollution,especially in the process of cement production,a main constituent of concrete.Every ton of cement manufactured for use in concrete emits 0.73-0.99 ton of the greenhouse gas(GHG)into the atmosphere.Fly ash is the most widely used supplementary cementious material.If part of cement is replaced with fly ash in concrete mix,the cement and clinker content can be reduced resulting in a decreasing environmental impact and a changed mechanical performance and durability of concrete.Most of the existing researches focused on solely investigating the environmental impact of fly ash concrete,or comprehensively considering the relationship between environmental impact and mechanical performance or durability only for one stage.The relevant research on the comprehensively investigation of environmental impact,mechanical performance and durability of fly ash concrete from a perspective of life cycle is deficient.In this paper,from the view of the life cycle of fly ash concrete,i.e.production stage,use stage and operation stage,we analyzed GHG emissions quantitatively,by investigating the effects of mechanical performance and durability on GHG emissions and costs as well.In addition,in consideration of the social impact of fly ash concrete,an indicator named life cycle sustainability value was presented to measure the comprehensive sustainable performance,which providing a new way for sustainability assessment of fly ash concrete.The following works are mainly conducted:(1)By considering the influence of fly ash content on the strength of concrete,the indicator combining environmental impact with compressive strength was proposed to assess the integrated performance of fly ash concrete during its production stage.(2)A nonlinear time-varying reliability model for fly ash concrete beams was established.The durability problem of the application of the fly ash concrete structures is taken into account,and the service life of the concrete structure is counted into the total life cycle evaluation of carbon emissions and costs and the environmental impact and cost analysis model of fly ash concrete beam based on service life was established.(3)In view of the insufficient research on the time effect of carbon emission and cost,this paper focus on three aspects:the continuous effect of carbon emissions,the time value of money and the carbon emission discount considering the time value of money to establish time effect model of carbon emissions and costs of fly ash RC beam.(4)In the sustainable design of beam,it is also necessary to consider the impact of the beam construction,maintenance and custody on the environment,and propose the maintenance optimization sheme required to achieve the sustainable beam.Considering the degree of structural performance degradation,commonly used performance-based reinforcement methods and time-based maintenance methods are considered.The dynamic programming method combined with Monte Carlo simulation was used to optimize the carbon emissions,cost and reliability of the beam structure throughout the life cycle.(5)A life cycle sustainability assessment(LCSA)model based on machenical,environment,economy and society performance was established,and the uncertain analysis of social,economic and environmental weighting factors in the model was also conducted.Finally,a sustainable design method for fly ash concrete beams was established.