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With a UK target of 80% carbon dioxide reduction by 2050 and a construction industry target of 15% carbon dioxide reduction by 2012 it is clear that the construction industry is faced with a challenge (Spencer & Clark 2010). Each aspect of the construction industry must be analysed to discover the negative impact construction material selection have on the environment and ways to mitigate these impacts with the use of alternatives.
Aims and Objectives
The construction industry contributes to almost 50% of the CO2 emissions emitted from earth. A core element of this is the materials used in construction from sourcing through to manufacture. Individual engineering projects can be relatively large, and can contribute significantly to the CO2 emissions generated by the construction industry. The key materials which will be looked upon are: - Steel
Steel and concrete are considered the main contributors towards the CO2 emissions used in the construction industry, as they are the two key structural elements used throughout the construction industry. Steel is considered ubiquitous; this chapter reviews the available literature on the main construction materials which contribute to CO2 emissions and discusses the need and possibility of alternatives.
'The greenhouse gas of most relevance to the world steel industry is carbon dioxide (CO2). On average, 1.9 tonnes of CO2 are emitted for every tonne of steel produced. According to the International Energy Agency, the iron and steel industry accounts for approximately 4-5% of total world CO2 emissions' (World Steel Association 2010)
'Producing one tonne of cement, results in the emission of approximately one tonne of CO2, created by fuel combustion and the calcination of raw materials. Cement manufacturing is a source of greenhouse gas emissions, accounting for approximately 7% to 8% of CO2 globally'. (Eco Smart Concrete)
Kyoto Protocol 1997/ Copenhagen Accord 2009
The Kyoto Protocol and Copenhagen Accord are both international agreements between countries, worldwide, to reduce emissions of greenhouse gases which are not managed efficiently. The Kyoto Protocol began in 1997 with a framework of targets for industrialised countries to reduce their green house gases emissions to target levels 5.2%.
'The Annex B emissions target for the United Kingdom and other Party's emissions of greenhouse gases is set at -8% from the base year determine the Party's initial assigned amount 1 for the Kyoto Protocol's five-year first commitment period 2008 - 2012'. (Kyoto Protocol, 2008)
In 2009 the Copenhagen Accord followed on from the Protocol, with targets set for 2020 to combat climate change and help stabilise greenhouse gas concentration in the atmosphere to a more sustainable level to prevent interference with the climate system.
'The EU and its member states are committed to an independent quantified economy wide emissions reduction target of 20% by 2020, compared to the 1990 levels. This target could be increased to 30% under the conditions set out by the European council of December 2009' (Copenhagen Accord, European Commission, 2010)
(Not sure if I should expand on this section and place in the introduction with the history, at the beginning?)
From the Kyoto Protocol numerous techniques have been developed to assist with achieving the set targets of the agreement. BREEAM has been created to aid with the reduction in CO2 emissions; BRE Environmental Assessment Method is used for numerous projects around the world, to assess the environmental impact of a construction, setting standards for best practice for sustainable design. BREEAM UK was first launched in August 2008, with the 2011 version published in March 2011. The report contains the latest guidance, benchmarks and detailed criteria to aid in the design of a project. According to the BREEAM 'New Construction' scheme it states the Key changes to be (BREEAM 2011):
Setting new benchmarks and assessment methodology for energy efficiency and operational Carbon emissions, including benchmarks that encourage the zero carbon hierarchy and reward 'carbon negative' buildings.
Updated approach to assessing and quantifying service life planning, stakeholder participation, life cycle impacts and recycled aggregates.
New and updated reporting requirements of key performance indicators, including building life cycle CO2 emissions, construction and operational water consumption, construction waste volumes and VOC emissions.
CO2 emissions and life cycle impact of materials used is a predominate criterion for the BREEAM assessment, including where the materials are sourced and the management needed for sustainable procurement.
Main materials used in construction - Steel
Eurocodes for Design of steel structures BS EN 1993-1-1
The Eurocodes which aid in the design of Steel structures is Eurocode 3 - BS EN 1993-1-1. This standard acts as a guidance document for design, all parts published as British standard codes with national annexes on 31st March 2010, and has no guidance in relation to CO2 emissions caused by steel suggesting which methods are more environmentally friendly, in comparison to others. The document focuses mainly on structural design, which is one of the most important aspects of the design as failure of a steel structure could have detrimental effects on the area which it is situated and also would have increased CO2 emissions for repairing the damaged structure. The fundamental requirements for the basis of design of Eurocode 3 is
'A structure shall be designed and constructed in such a way that:
With acceptable probability, it will remain fit for the use for which it is required, having due regard to its intended life and its cost, and
With appropriate degrees of reliability, it will sustain all actions and other influences likely to occur during execution and use and have adequate durability in relation to maintenance costs.
The above requirements shall be met by the choice of suitable materials, by appropriate design and detailing and by specifying control procedures for production, construction and use as relevant for the particular project'.
The environmental considerations which are highlighted in Eurocode 3 are: Suitable material, design, detailing, production and construction, but are not discussed in any great detail with no reference made to CO2 emissions.
Eurocodes for design of concrete structures BS EN 1992-1-1
For the use of concrete Eurocode 2 BS EN 1992-1-1 is used for the design of concrete structures, the document also acts as a guide for construction in the same context as Eurocode 3 for steel. The British standard code and national annex were published on 8th December 2005, the document only focuses on the structural design as the same as the design of steel in the Eurocode it states:
'Eurocode 2 applies to the design of buildings and civil engineering works in plain, reinforced and prestressed concrete. It complies with the principles and requirements for the safety and serviceability of structures, the basis of their design and verification that are given in EN 1990: Basis of structural design'.
'Eurocode 2 is only concerned with the requirements for resistance, serviceability, durability and fire resistance of concrete structures. Other requirements, e.g. concerning thermal or sound insulation, are not considered'.
There is no reference throughout the document of consideration towards CO2 emissions, and factors used to reduce emissions created or recycle previously created sections.
Although there is a current demand for the use of more economically friendly materials or alternatives to the current materials used, the standards show that there are no reinforcement from the Eurocodes themselves, to ensure designers are taking into consideration the impact of CO2 emissions.
Findings of standards and guidance documents
Due to the lack on emphasis on CO2 emissions in the official design standards, guidance documents, the authors finds it necessary to breakdown the elements of Steel and concrete beams and analyse literature in relation to CO2 emitted throughout the lifecycle of steel beams and Concrete beams, also to further research into a more sustainable alternative.
Greenhouse gas emissions, life-cycle inventory and cost-efficiency of using laminated wood instead of steel construction. Petersen et al (2002)
Petersen concentrated on global warming with the influence of forestry and the use of timber on the net emissions of green house gases (GHG) becoming of high importance in comparison to steel beams. The aim of the study was to compare the use of glulam beams and steel beams in a project in Norway; by comparing the impact each material has along with cost efficiency.
The process which was considered for both materials is shown below:
Petersen (2002) Steps in the life cycle of beams in laminated wood and beams in steel.
Petersen (2002) for the calculations quantified the energy consumption and GHG emissions from waste handling and manufacturing, whilst equalling the use of energy and emissions from the building use and demolition of steel and glulam are not included.
The results of the test are shown below in figure??
Figure??GHG emissions over the life cycle of beams in laminated wood, Petersen results (2002).
A1 refers to the alternative where the laminated wood is combusted and the energy substitute's energy from oil. A2 refers to combustion where the energy substitutes energy from the present energy production in Norway. A3 is land filling.
Figure?? GHG emissions over the life cycle of steel beams, Petersen results (2002).
E1 is that it is used an average of ore-based and scrap-based steel. E2 is that the steel is produced from ore. F1 is that the steel substitutes other scrap. F2 is that the steel substitutes ore.
Figure? An overview of general input data used in the life-cycle inventory of both glulam and steel, Petersen (2002)
Petersen (2002) concluded the following from this investigation:
That the total energy consumption in manufacturing of steel beams is two to three times higher and the use of fossil fuels 6-12 times higher than in the manufacturing of glulam beams.
The waste handling of both materials can either give or use energy. Therefore, the difference in energy consumption over the life-cycle between steel beams and beams in glulam depends strongly on how the materials are handled after demolition.
Manufacturing of glulam beams causes one-fifth of the green house gas emissions from manufacturing of steel beams.
Load bearing constructions in glulam are normally with a range of ±20% the price of similar solutions in steel, and in the actual case analysed, the glulam solution was cheaper than the steel alternative.
The analysis show that beams in glulam cannot be more than 1-6% more expensive than steel beams.
It is interesting that the use of timber alone has a considerable amount of difference in CO2 emissions omitted in production in comparison to steel beams. This suggests that the area of renewable timber from the source of production may be an area worth investigating further.
Greenhouse gas emissions in building construction: A case study of One Peking in Hong Kong. Hui Yan et al (2009)
Hui Yan (2009) investigated into the construction of Hong Kong's One Peking, producing a case study on the green house gas (GHG) emissions produced in the construction industry in Hong Kong. The aim of the study was to establish a calculation method for GHG emissions in building construction and to apply it to a practical case building in Hong Kong. Hui Yan (2009) found that the construction industry is one of the greatest consumers of resources and raw materials, whom manufacture and transport building materials, along with installing and constructing buildings all accumulates to great quantities of energy and large amounts of greenhouse gases (GHG) being omitted into the atmosphere. Hui Yan (2009) discovered that buildings through their life cycle, including construction, operation and demolition, consume approximately 50% of the total energy demand and contribute almost 50% of the CO2 emissions released to the atmosphere.
Hui Yan (2009) stated that to enable a reasonable calculation to be made the processes behind the construction of a building had to be split into five different sections, having individual calculations for each dedicated subdivision. Which were:-
Ei - Total embodied GHG emissions of all building materials
Eii - Total GHG emissions from fuel combustion of transportation for all building materials
Eiii - Total GHG emissions from fuel combustion of construction equipment
Eiv - Total GHG emissions due to electricity used for construction equipment
Ev - Total GHG emissions from fuel combustion of transportation for construction waste
Figure?? Sources of GHG emissions in the construction of buildings. Hui Yan (2009)
Figure?? Embodied GHG emissions of building materials by specific element, Hui Yan (2009)
Hui Yan (2009) found that the GHG emissions calculated from the construction of One Peking resulted in 98.6%-99.2% of the total GHG emissions came from manufacture and transportation of chosen materials and energy consumption of construction equipment. Wherein 81.6-86.7% was from the embodied GHG emissions of building materials alone, the result indicated that the choice of more sustainable materials can substantially reduce GHG emissions within construction.
Furthermore Hui Yan (2009) calculated that embodied GHG emissions of concrete and reinforced steel account for 93.99-95.11% of those of all building materials from the One Peking project.
The Hui Yan case study clearly shows that in the design stages of a construction the choice of material is vital in terms of CO2 emissions for the life cycle assessment of a building.
Figure?? Clearly shows that in material choice alone concrete and steel a lot more emissions than timber, even though the quantity of timber used was considerably less the impact from both concrete and steel is larger. However Hui Yan (2009) failed to obtain a full scale analysis within the total life cycle analysis of a construction project, this area requires further investigation and research into other processes such as operation, maintenance and demolition of the One Peking construction project.
Variability in energy and carbon dioxide balances of wood and concrete building materials. Gustavsson and Sathre (2005)
Gustavsson and Sathre (2005) conducted a study into the changes in energy and CO2 balances caused by variation of key parameters in the manufacturing of wood and concrete framed building. The aim of the study was to use current knowledge from past experiments and case studies completed, and further the research into CO2 emissions with added variables, by identify factors that have strong control on the energy and CO2 balances resulting from construction material production. Also to determine whether wood framed structures might have higher energy and
CO2 balances than concrete structures.
Factors which Gustavsson and Sathre (2005) proposed for the study, were the CO2 emissions created from fossil fuel production of building materials, the substitution of fossil fuels by biomass residues derived from wood production and the chemical reactions in the production and use of cement.
Figure?? Schematic flow chart of wood materials during the building lifecycle Gustavsson and Sathre (2005)
The parameter variations which Gustavsson and Sathre (2005) encountered, which required to be quantified to conduct the analysis were:-
Cement and concrete aggregate - the varied differentials in terms of the wide-ranging aggregates which can be used.
Recycled steel - The subsequent CO2 difference between production of steel using recycled and the original materials.
Wood drying efficiency - The varied parameters of energy used for kiln drying, dependent of moisture content.
Transportation of materials - The difference in travelling from production, dependant on location.
Carbon intensity of fossil fuel - That fossil fuels have different conversion efficiencies and omit different amounts of CO2.
Gustavsson and Sathre (2005) for the analysis based the study on a four story apartment building containing 16 apartments with a usable floor area of 1190m2. Calculations were made for materials required to construct functionally equivalent versions of the building in terms of a wood frame and a reinforced concrete frame.
Figure?? Contributions to the energy balances (GJ) with production of all materials for the wood and concrete frame structures Gustavsson and Sathre (2005)
Figure?? Contributions to CO2 balances (tC) with production of materials for the wood- and concrete-frame buildings Gustavsson and Sathre (2005)
Gustavsson and Sathre (2005) conducted their study to identify factors that contribute most significantly to the variation of energy and CO2 balances of building material lifecycles, by comparing the energy and CO2 balances of buildings made with wood and concrete frames. Gustavsson and Sathre (2005) found that overall with the inclusion of past literature to support their case that regardless of the variations of different parameters, wood framed structures have lower energy and CO2 balances than the concrete framed structures. Also that the use of wood generally instead of concrete, coupled with the greater integration of wood by-products into energy supply systems, could be an effective means of reducing fossil fuel use and net CO2 emission to the atmosphere However Gustavsson and Sathre (2005) do suggest that for example, if concrete was created using natural gravel instead of using crushed gravel it uses less fossil fuel and omits less CO2. This therefore means if the study was conducted using this concrete it may have had a different outcome.