Carbon Emissions Reduction Based Equilibrium Models Of Construction Materials Production-Supply And Their Applications

During the process of population growth and urban expansion,China’s construction industry has gone through booming development.A large number of infrastructure and residential projects are being built,and the demand for cement,steel,concrete,and other construction materials has also expanded rapidly.However,the production and supply of construction materials are carbon-intensive and energy-consuming activities and construction-related industries have become one of the key fields for energy conservation and emission reduction in our country.Following the path of green,low-carbon and sustainable development is always the core concept of Chinese government for long-term development.Currently,as the people’s requirements for air quality and ecological environment increasing,the low-carbon development of the construction industry has become an important means to promote the construction of ecological civilization as well as a part of building a beautiful China.Therefore,it is urgent to conduct environmental protection management and take an action for energy-saving and emission reduction in the construction industry.Moreover,the emission reduction in the production and supply of construction materials is an indispensable link for achieving energy conservation and emission reduction in construction-related fields.A scientific and reasonable construction material production-supply emission reduction plan must fully consider the coordination,systematization,interactivity,and uncertainty during the decision-making process.Coordination:There are differences in the production and supply of construction materials under the two different construction modes of on-site and off-site.Therefore,it is necessary to comprehensively consider the government’s policy influence on construction materials suppliers and the coordination mechanism in the procurement and transportation of corresponding materials when satisfying the needs for projects.Systematization:There are many decision-making participants,such as the regional government,building material suppliers,and the construction enterprise.The regional government aims at formulating carbon emission reduction policies while the construction enterprise considers the procurement of construction materials.Besides,the suppliers make production plans considering their operational conditions.Therefore,the building material production and supply plans are made under the guidance of local government and the construction enterprise’s procurement plans are also influenced by the relevant carbon emission reduction policies to minimize enterprise’s total costs.Interactivity:In the entire carbon emission reduction plan for the production and supply of construction materials,the government,suppliers or enterprises at different levels will inevitably influence each other when optimizing their own goals,and these decision-making objectives may even conflict with each other.If the regional government aims to mitigate carbon emissions or to promote the development of prefabricated buildings in its regional construction industry,the government tends to give more initial carbon allowances to low-carbon production suppliers or suppliers that produce more prefabricated materials,which will also have impacts on the economic profits for carbon-intensive suppliers,and this may cause conflicts between the government and construction suppliers.Uncertainty:The solutions to the problems of construction materials production-emission reduction are affected by various aspects such as natural conditions,market changes,economic environment,etc.For example,the fluctuations in procurement prices,changes in demand,and site investment costs would impact the optimization of total project cost.In summary,it can be seen that the interactivity,coordination,integration,and uncertainty are four essential factors in the decision-making process for the carbon emission reduction optimization in the construction production and supply planning.Combined with above problems during the carbon-economy production and supply planning and review for the existing literature,this thesis uses multi-objective programming theory,bi-level programming theory,dynamic programming theory,fuzzy theory,and optimization algorithms as the main research tools to focus on carboneconomy equilibrium in construction materials production and supply.The research is conducted from the micro and macro perspectives in terms of decision-making system framework,operation management,optimization,and policy discussions.There are six chapters in the thesis.The first part gives a brief introduction on the research background of carbon emission reduction study and policies on construction materials production-supply planning,as well as the literature review at home and abroad,then the main research content is proposed.The second chapter gives basic description for relevant theories,including the basic knowledge of multi-objective programming theory,bi-level theory,dynamic programming theory,fuzzy theory,and optimization algorithms.The third,fourth,and fifth chapters explain researches on the carbon-economy equilibrium management of construction materials production-supply planning from three perspectives,they are also the three main research subjects for this thesis.The research framework are formed by the following parts:the carbon-economy equilibrium method for traditional cast-in-place construction materials production and supply planning,the dynamic supply planning of prefabricated construction materials and collaborative supply planning of hybrid construction materials for carbon reduction and economic development.Finally,the sixth chapter summarizes the total research work,puts forward the innovation and follow-up research points.The following is an overview of the three research subjects.For the carbon-economy equilibrium method for traditional cast-in-place construction materials production and supply planning issues,the local construction materials production and supply of traditional cast-in-place buildings are optimized from the perspective of the government.First,through the carbon quota allocation mechanism,the decision-making relationship between relevant stakeholders(government and construction materials suppliers)is fully considered to limit the carbon emission of suppliers’ material production.Under the requirement of government,the construction enterprise has to switch its procurement strategy and procure more lowcarbon materials,which promotes the low-carbon production of construction materials in turn.Combined with the theory of leader-follower game,production-supply equilibrium planning under the carbon quota allocation mechanism belongs to a bi-level programming problem.In the decision-making process,not only the decision-making conflicts between the government and the enterprise but also the relationship between practitioners in the construction industry is considered.In the carbon-economy balance leader-follower model,the upper-level decision-maker is the government with its objective to minimize total carbon emissions;the lower-level decision-makers are construction company and construction materials suppliers,among which suppliers are in a competitive relationship,therefore each supplier makes decisions based on its production conditions to maximize the economic benefits of material procurement orders The construction company and the suppliers belong to the same subordinate level,but there is no competitive relationship.The two need to coordinate with each other and the objective of the construction company is to minimize the total operational cost.Fuzzy variables are used to describe the uncertainty in the decision-making environment,and mixed expected value operators are adopted to process them into an equivalent global model.Then,according to the characteristics of the bi-level model,an improved particle swarm algorithm was designed to solve the NP-hard model.By modifying the iterative formula of the particle swarm algorithm and introducing an interactive solution mechanism,the improved algorithm can obtain a better search range the calculation stability.The model and algorithm are then applied to the calculation examples of construction materials production and transportation of a large-scale construction project,the result discussion mainly analyzes the suppliers and construction company’s carbon emission and economy performance under the control of different emission reduction policies.In addition,through extended discussion,the effectiveness and universality of the model and algorithm are verified.Finally,some management recommendations are given.The prefabricated construction materials based carbon emission reduction dynamic supply planning problem is considered by the overall decision-makers to make centralized optimization decisions.First,according to the construction characteristics of prefabricated construction projects,the entire prefabricated construction supply process is divided into a multi-stage centralized decision-making process.The first part of the decision is the choice of suppliers.the construction company purchases raw materials for prefabricated components from different suppliers and transports them to the factory;the second part of the decision is to transport the finished prefabricated components from the factory to the project site for assembly and construction.The two stages involve the production,procurement,manufacturing of construction materials,which including relevant decision-making activities such as operation,transportation,and inventory.Then,a two-stage dynamic multi-objective optimization model was established to minimize the total cost and carbon emissions.Considering that the optimization objectives of the decision-making system are economic cost and environmental protection,the carbon emission objective is dealt with as a constraint.As a result,the multi-objective model can be considered as a corresponding singleobjective model.Also,the uncertain fuzzy variables that are used to describe the decision-making environment are converted into the expected values with the expected value operator,obtaining a clear and equivalent model.Then,according to the characteristics of the dynamic model,a particle swarm algorithm based on dynamic programming was designed and applied in the prefabricated component supply planning of a local off-site residential project,and a group satisfactory equilibrium results are achieved in the calculation example.Through different emission reduction scenarios,the construction scheme,and various operational costs analyses and discussions,the effectiveness and practicability of the proposed methods(dynamic optimization model and dynamic particle swarm algorithm)are verified and relevant management suggestions are summarized.The mixed construction materials based coordinated supply equilibrium planning considers the carbon emission reduction problem of the production and transportation of construction materials in the coordinated supply plan of off-site construction and stick-built construction.In terms of the government’s carbon quota system,the collaborative supply planning of traditional stick-built and prefabricated construction methods is analyzed.First,the government adopts different levels of carbon emission reduction policies for different construction material suppliers,aiming to encourage suppliers to carry out low-carbon production.Meanwhile,the government requires the usage of prefabricated materials in projects to guarantee that the proportion of prefabricated materials are satisfied to promote the development of off-site construction.In this leader-follower game model,the government that allocates carbon allowances and controls the proportion of prefabricated materials is the upper decision-maker,while the suppliers under the collaborative supply plan are the subordinate(lower)decisionmakers.The decision of the upper-level government aims to achieve carbon emission mitigation and optimize procurement and transportation costs by adjusting the level of total carbon allowances,formulating emission quota allocation,and prefabricated material procurement schemes;Meantime,the suppliers try to maximize economic profits by adjusting the production output of on-site and off-site materials and obtaining procurement orders under the constraints of the carbon allocation mechanism.So as to process the model and obtain a global equilibrium solution,firstly,the government’s carbon emission reduction target is converted into a constraint with parameter control.Then,through the KKT constraint conversion method,the leader-follower model is transformed into its equivalent single-layer optimization model.Finally,the solution method was applied to a carbon reduction collaborative supply plan example of a prefabricated construction project to prove its effectiveness and practicality.The discussions under different carbon allowance policies and different prefabricated material ratios are given.The results show that the coordinated supply equilibrium plan can meet the objectives of different stakeholders and achieve carbon reduction in the construction materials industry.The research innovations of the thesis are as follows:(1)This paper systematically analyzes the construction materials production and supply planning for carboneconomy equilibrium management.Based on the study of relevant literature,environmental economic theory of carbon emission reduction mechanism,construction production supply management theory,and the background of practical problems,this thesis innovatively proposes the optimization method of construction materials production and supply for different construction modes under carbon quota mechanism.The specific application and analysis are also carried out,which enriches the application research in this field,and has strong practical significance in the research of carbon emission reduction in construction materials production and supply planning.(2)Aiming at the decision-making subjects,decision-making characteristics,and research status of carbon emission reduction system of construction materials production and supply in different construction modes,the corresponding economy-carbon equilibrium model group of bi-level,dynamic and mixed collaborative supply planning is established.In the bi-level model of traditional cast-in-place construction production and supply planning,the two sorts of followers are characterized with different features and decision rules and the leader’s carbon mitigation regulation conflicts with two sorts of followers.A triangle decision structure is then formulated and the economic-carbon equilibrium relationship for construction materials production and supply planning is described from three different decision-maker dimensions.In the dynamic production and supply model of prefabricated onstruction materials,the process of prefabrication and assembly is considered based on two-stage optimization.In the mixed collaborative production and supply planning,the coordinated supply of cast-in-place and prefabricated onstruction materials in the project and the government’s policy regulation of prefabricated building materials are comprehensively considered.Finally,a systematic and scientific management system has been formed dominated by the government and followed with relevant enterprises.(3)According to the different models in the background of corresponding research problems,optimization algorithms are designed to solve these problems.The optimization algorithms with interactive scheme improve the expression process of the model solutions and the update mechanism in the calculation process,which reduces the calculation cost and improve the robustness.The application results show that the proposed methodology can effectively solve the related equilibrium problems of carbon emission reduction of construction materials production and supply planning,and can serve as a reference for relevant decision-makers.