Sustainability of buildings made of steel

transcript

Françoise Labory, Olivier Vassart, Louis-Guy Cajot ArcelorMittal R&D, Esch-sur-Alzette, Luxembourg

Abstract:

This paper treats questions on sustainability concerning environmental issues that have implements on the use of steel in the construction sector. The impact of construction on sustainability issues is investigated. The overall objective of this paper is to outline the opportunities for steel in the construction industry with respect to environmental sustainability. Some challenges are also noted.

1. Introduction

1.1 Summary of benefits

Steel construction means using steel as the building’s main framing material. Steel is also common in the building envelope (walls, roofing), fasteners, building services, substructures and concrete reinforcement. Compared to today’s average construction practice, modern steel construction can offer:

� Material efficiency - resulting in e.g. less natural resource usage, less transports, less emissions and less energy usage,

� Ultra-high recyclability - resulting in e.g. less natural resource usage, less waste, less energy and less emissions,

� Quality and durability – resulting in sustainability favours,

� Dry construction – resulting in less health hazards, less waste, less energy usage and less emissions.

1.2 Sustainability and construction

Sustainability includes environmental, economic and social concerns for achieving a long-lasting development of the society. Sustainability of Construction here comprises the major health and environmental aspects related to the life cycles of all types of buildings. A building’s life cycle includes production, use and deconstruction, and the underlying activities and material and energy flows which generate inevitable influence on the planet – good and bad. The choice of building material as to framing has been considered as of minor interest as to the social aspect of sustainability. Therefore social aspects are not included in this paper.

The construction sector is a core economy in many countries, which employs about 7% of the EU work force and generates revenues of approximately € 1 000 billion in EU answering to almost 10% of GDP (FIEC). Construction means welfare, security for individuals and businesses, growth and investments for the future.

The use of the buildings and all construction related activities generate more than 40% of all CO2 (carbon dioxide) emissions, use about 40% of the produced energy and consume more than 40% of the material resources used in the society. These estimations might differ slightly between European countries. The global governmental intention, except the US, is to reduce the CO2 emissions by an average 5% over the next 5 years (until 2012), and some experts claim that the reduction must be 50% over 50 years in order to avoid large-scale climate changes.

The usage of energy during the building’s service state, called operational energy, is one of the most important sustainability issues for the construction sector. Energy primarily affects the environment due to the production and distribution of electricity and water for heating and cooling. The thermal performance and overall energy efficiency have an effect on the economical and environmental performance of the building, and thereby it’s competitiveness. Some frames of thermal performance are set in national Building Regulations.

Construction needs much material input: as natural resources and as recycled material. Materials primarily affect the environment through the refining processes from raw materials to building components, and also by transports. Natural resources are not infinite, and recycling leads in most cases to improved environmental performance. The construction sector generates an enormous amount of waste (estimated >500 kg/capita, year in Sweden), and the demands for improved recycling are increasing. Therefore, in many countries the sustainability focus is on recyclability.

Sustainable construction does not have to mean new big investments or inventing new materials, just to use “the right materials in the right combinations in the right place”. Sustainability improvements will often generate economical benefits, e.g. lower costs for heating and maintenance, goodwill and market advantages, and also a future world where we can live. The World Business Council for Sustainable Development stated that “Business can benefit from pursuing sustainability in two ways: By generating top line growth through innovation and new markets, and by driving cost efficiencies”. The benefit for man and environment is high quality survival.

2. Specification of key issues

The disturbing influences on the exterior environment can be divided into embracing environmental effects, that all are regarded significant for ecological balances, for human life-quality and on the long term for human survival. Here six main environmental effects under surveillance are:

• Global warming, • Acidification, • Eutrophication, • Ozone layer depletion, • Toxicity, • Resource depletion.

Many different kinds of industrial, human and natural activities contribute to these effects, positively or negatively, which means that we are all able to affect the environmental future today. The major steel construction - and most industry - issues of environmental concern are:

o Energy use in production (embodied energy) o Energy use in service (operational energy) o Transportation o Use of raw materials and water o Emission of harmful substances o CO2 Emissions o Recycling and reuse o Waste treatment and land use o Indoor environment

The differences in sustainability focus can be significant between various types of buildings, and the following relationships between these issues and the building’s life-cycle are to be distinguished for residential, commercial and industrial steel buildings.

2.1 Embodied energy

The production of 1 kg of finished steel product for constructional usage demands about 18.6 MJ/kg of energy in average, including all processes and energy types (Worldwide average). Compared to a 50-year life cycle of a multi-storey steel building, the production of all embedded steel components contributes to less than 2% of the total energy usage.

As only 10-30% of the steel building is steel, the origin of the building’s embodied energy is mainly in the cement production, the lime refining for gypsum boards, iron reduction by coke and electric arc processes for scrap melting.

While making new steel, about 70% of the constructional steel’s embodied energy can be saved. About half of the embodied energy in combustible products will be reused for heating and other purposes.

2.2 Operational energy

The operational phase includes 85-95% of the life-cycle energy usage of a multi-storey building. The framework itself has insignificant influence on the operational energy, but the thermal efficiency of the building envelope in combination with adapted building services is important. Small insulation improvements can have big influence on the total energy usage.

Steel systems in exterior walls can be very efficient if used correctly. Light-gauge steel framing combined with thermal insulation, wind stopper, moisture shield and optional surfaces can be given a U-value down below 0,15 W/m2,K (= R > 7). Modern technology shows that metal framing can be designed to have a prime performance concerning thermal performance. National building regulations set the heat flow limitations for different types of buildings.

The national differences are of course significant depending on the climatic conditions, and the operational energy is directly related to the type of activity within the building. Furthermore, especially in office buildings energy is also used for cooling. In industrial buildings heating is often at a low level as processes might produce heat or as indoor temperature requirements are low.

2.3 Transports

Combustion of fossil fuels is the activity having most influence on the mentioned environmental effects. All heavy transports, except for electrified trains supported by electricity from ‘carbon free’ power plants, emit CO2, NOX, SOX, HC and other pollutants, and use finite fossil resources. Construction transports are today dominated by trucks, and the increasing international trade causes more and longer transports.

Steel structures are light and material efficient, and in most cases fabricated off-site. Therefore there is less weight to transport, a minimum of waste to move to recycling or deposit, and the instant erection and low degree of in-situ production makes the logistics very efficient. The accurate design and shape stability of steel profiles also result in a minimum of constructional waste. Though, the disadvantage of a high degree of prefabrication may be additional transports between production site and construction site.

2.4 Raw materials and water

All new construction needs material, much material. Virgin materials from nature are needed when recycled material not exist in necessary amounts or quality. The virgin materials needed for steel construction are mainly metal ores, limestone, oil, coal, natural gas and some other minerals. The recycled material input is mainly steel, other metals, plaster, glass and water. Steel construction is unique because of its high degree of recycled content and recyclability, and therefore the need for limited virgin resources is relatively small.

Producing 1 kg steel from ore demands about 2,5 kg of material input. The other 1,5 kg is also being used as by-products or being vaporised. In a modern production plant only about 60 g out of the 2,5 kg are sent to deposit as non-usable waste, which prove another type of excellent material efficiency.

Water is used as cooling media for producing one kg of steel for constructional purposes. Much of this is recycled and cleaned within closed systems. Moreover, in the case of steel construction, the water is used on the production site and not on the construction site. As the steel is mainly fabricated in countries and areas where the water supply is not a major problem, the use of steel profiles for construction, in countries where water reserved are small, is a key issue.

2.5 Emissions

The emissions to air and water related to steel construction are in level with other building systems with same functions and size in a life cycle perspective. Most emissions originate in combustion of organic matter, i.e. process for material production, heating, conversion to usable energy, and also transports. Main airborne emissions are CO2, NOX, SOX and dust, which cause most of the environmental effects. By amount CO2 stands for about 98% of the airborne emissions.

Specifying steel also means that the built in elements not will be released as emissions in the future, as the steel and some other important steel construction materials are fully material recyclable and will not be combusted or deteriorated at a deposit.

Building28%

Transport22%

Deforestation22%

ManufacturingIndustry

� Enhancing product performance is a major task

Use phase represents the most important share

Building28%

Transport22%

Deforestation22%

Building28%

Transport22%

Deforestation22%

� Enhancing product performance is a major task

Use phase represents the most important share

Estimation of global CO2 emissions by end user

2.6 Recycling and reuse

Recycling means using the material again as input for producing new material or as an energy source. Reuse means using the demounted product in another location with or without refurbishment. Steel is unique as construction material because it can be fully recycled over and over again without quality loss. Other construction materials often used in combination with steel with a high degree of material recyclability are plaster, other metals and mineral wool.

The recovery rate of structural steel construction products is today about 95% and increasing, which is maybe the strongest sustainability argument for steel construction. And the structures are durable. More than two billion tonnes of steel in buildings out there is waiting to be recycled in the future. The recycled content can be up to 100% dependant on scrap availability and the demand level; in practice about 15 to 100% is recycled content.

Recycling of steel in electric arc furnaces

Reuse normally offers even greater environmental advantages than recycling. Reuse is not yet that common, but up to 10% of the steel construction products are reused on certain markets. Reused products are e.g. steel frames, cladding components, pedestrian bridges, sheet piling, wall elements, temporary structures and modules.

Steel sheet piles are reused after excavation

2.7 Waste and land-use

The waste issue is primarily directly related to the issues of recycling and raw materials. The large amount of constructional waste is a big problem in some regions where controlled disposal areas are small or non-existing. In severely exploited areas, and in close-urban areas with difficult topography or other unpleasant nature conditions, green land is very attractive for man as well as for nature.

Steel construction handles questions concerning waste and land-use in many ways:

• The high degrees of recyclability, reusability and prefabrication means less waste generation,

• Off-site production means small construction sites,

• Light structures, short construction time and material strength means possible vertical extension of existing buildings, use of developed land and construction on bad soil or in tectonic areas,

• Sites for iron ore extraction are commonly situated under ground and refilled with generated mineral waste,

• By-products from steel production are used in many other applications such as road construction.

2.8 Indoor environment

Europeans tend to spend 90% of their life indoors, and children even more. The building physics is therefore very important for health and well-being. The relationships between indoor environment and human health are very complex. Main issues are moisture, thermal comfort, sound and air quality, and the size of each issue vary between different countries.

The Sick Building Syndrome is a modern “disease” usually caused by water in organic building components in the construction. Steel is not hygroscopic, nor organic, which minimizes the risks of SBS, direct airborne emissions and structural deterioration. The common off-site prefabrication of steel buildings keeps the dry materials also dry assembled. Steel systems for walls and floorings also fulfil high Building Regulation levels on thermal comfort and sound insulation.

3. Regulations on Sustainability

3.1 National Regulations on Sustainability

There are many different activities on the topic sustainability in European countries. The different governments have environmental targets, both for outdoor and indoor environment, which can have an effect on the construction industry. However, these targets are often generally expressed and there are few specific environmental regulations. Environmental issues are integrated in all aspects of the building process and sustainability issues are often dealt with in combination with other topics.

An exception is the explicit regulations on energy performance. An increase of the use of a lifetime perspective can be noted. Efforts, as to national regulations and standards, in the sustainability area concerning building constructions and related activities that might have an effect on the use of steel are:

• Energy conservation: focus on in-use consumption, often expressed as thermal performance of building envelope or CO2 emissions

• Building’s health affection: Focus on health in general and emissions of building materials

• Questions concerning life performance: focus on performance and costs where maintenance is a key issue.

• Waste reduction: focus on minimum recycled content and reduction of waste to deposits

• Land use: focus on limiting over development

• Documentation of sustainability issues: focus on assessment/declaration of construction materials and assessment methods for new and existing buildings

3.2 European Regulations and Directives

An Action Plan, in the context of the Commission’s Communication on the competitiveness of the construction industry (COM/97/539), agreed at a tripartite meeting of representatives of the EC, Member States and the Construction Industry (1999), on a consolidated list of priority actions for improving the competitiveness of the construction industry. One of these actions is entitled:

“to develop a strategy for the use and promotion of

a. environmentally friendly construction materials b. energy efficiency in buildings and c. construction and demolition waste management

in order to contribute to sustainability”

Directives relevant to the topic sustainability as to environmental issues are:

• Council directive 89/106/CE of 21/12/88 on the approximation of laws, regulations and administrative provisions of the Member States relating to construction products (Construction Products Directive).

It concerns essentially construction products, i.e. mechanical resistance and stability, safety in case of fire, hygiene, health and environment, safety in use, protection against noise, energy economy and beat retention.

• Directive 2002/91/EC of the European Parliament Council, on the Energy Performance of Buildings came into force on 4 January 2003.

Legislation in all member states had to be in place by 4 January 2006. EPD (Energy Performance Directive) affects all buildings, both domestic and non-domestic. It demands minimum requirements for the limitation of the energy supply of buildings. For example an energy passport is introduced, which includes the energy efficiency of the envelope and the services. Energy performance of buildings becomes an important aspect of innovative and cost-effective building design.

Energy certification (example UK)

The calculation of energy performance of buildings according to the EPD shall at least cover the following energy flows:

- thermal characteristics of the building envelope incl. air-tightness - heating installation and hot water supply - air-conditioning installation - ventilation and built-in lighting installation - position and orientation of buildings, including outdoor climate - passive solar systems and solar protection.

• Directive 2006/121/CE of the European Parliament and Council concerning the “Registration, Evaluation, Authorisation and restriction of Chemicals” (REACH).

Regulation came into force on 1st of June 2007. The aim is to improve the protection of human health and the environment through the better and earlier identification of the properties of chemical substances. This might have a significant impact on the construction industry.

4. Opportunities for steel

Taken the summary of national regulations on sustainability and the trends in sustainability work, several opportunities for steel can be identified. There are also challenges to be embraced in order to secure a prosperous development as to sustainability issues for steel.

It is also noticed that some of the work in the sustainability area concerning constructions are based on voluntary undertakings or related to financial questions e.g. better insurance conditions and conditions for funding. As well as in regulations as in voluntary undertakings, opportunities and challenges can be identified.

Corresponding to important issues in the sustainability area, as stated in preceding chapter, there are opportunities for steel construction.

4.1 Energy conservation

4.1.a. Opportunities:

• Expose the possibilities of good thermal insulation using steel systems. Using slotted steel studs and/or external insulation or other efficient techniques a building envelope with excellent thermal performance can be achieved. This must be communicated to the actors in the building industry. It is also of great importance to communicate the good performance of steel systems as to thermal bridging.

Lightweight Steel-framed Construction

• Prefabricated units, 3D or 2D, can provide a high quality building envelope with excellent performance as to thermal performance and provide good quality, reducing risk of thermal bridging and lack of air tightness.

• The use a photovoltaic cells can reduce drastically the total energy consumption of the building. One square meter of Arsolar roof cladding (6kg) bears photovoltaic cells that can generates 120 kWh per year. Thus each kilogram of steel helps produce 70MJ of solar electricity each year

Arsolar system from Arval ArcelorMittal Construction

• Thanks to innovative solutions like Cellular beam or Angelina™ beam, it’s possible to reduce the storey height by integrating services within the height of the beam in order to have a building with 8 levels where only 7 levels would be possible with classical solutions. An optimisation of the surface can be done by reducing of about 15% the ratio Volume of the building / net surface of floor and so reduce the global energy consumption.

Integration of all the services in the height of the beam using Angelina™

• Reducing the eight between two storeys, we reduce the surface of the façade and the thermal exchanges between interior and exterior. The direct consequence is a reduction of the energy consumption for heating and cooling.

4.1.b. Challenges:

• There is a challenge to communicate the excellent performance of steel systems today. A lot of problems like thermal performance and thermal bridging are now resolved but the a efforts must be done to promote theses new solutions

• One challenge could be the use of transports on an increasing global market. This should be an issue not only for steel, but for all materials. As to steel it could be a benefit as steel is a lighter material, thus transports have less impact and there is less waste.

4.2 Occupational wellbeing and safety

• Using steel systems, building components with low risk of acquiring problems related to moisture.

• The European procedure for providing structural safety in case of fire. This procedure is quite realistic as it takes account of real fire characteristics and of existing active fire fighting measures. It consists in estimating the real behaviour of a structure subjected to the natural fire which may arise under those real fire conditions. The consideration of real actions leads to real safety and also to optimized economy Thanks to this Natural Fire Safety Concept, it’s possible to design unprotected steel structures able to ensure the stability of building in case of fire. Using this king of design, the protection of the structure by spray material or gypsum board can be avoided.

Unprotected and visible steels structure and protected structure that must be hidden

• Using steel systems, building components with low risk of problems with emissions from materials are achieved.

• Good opportunities of off-site production create building systems with high quality reducing risks of health affection during construction process.

4.2.b. Challenges:

• To communicate the good performance of steel systems as to health and to disseminate the use of the Natural Fire Safety Concept

• To provide industry with information on material as to documentation for buildings and as basis for decision-making.

4.3 Life performance

• An increased lifecycle perspective is advantageous for steel as steel constructions have long life with high quality and flexible solutions. The anticorrosion solutions are really effective (coating, galvanisation, stainless steel)

• To emphasise the low maintenance of different steel constructions.

• Steel enables the use of modular buildings for temporary locations.

Transport Module Small office building

• Steel structures have long design life and the high quality remains

• Steel constructions can give flexibility to the use of the building providing long spans. The use of very large span offer free open spaces that can be adapted for a future use.

Very large open space with integration of all the services

4.3.b. Challenges:

• Composite structures are a challenge as to recyclability. Therefore efforts to design composite systems that can be dismantled in a cost-effective way.

• To provide systems with an architecture and function with no “best before date”.

• Further improvement of coatings.

• To provide industry with information on material as to documentation for buildings and as basis for decision-making.

4.4 Waste reduction

• Prefabrication can significantly reduce waste at building site.

Prefabricated steel elements for multi-storey buildings

• Prefabrication can significantly increase the ability to handle waste in a good way, increasing the possibility to recycle.

• Steel is a very good material as to recycling. There should not be material for deposition.

• Steel products for construction purposes always contain recycled material.

• Larger prefabricated units, i.e. modules, might be reused in other constructions. Especially as to temporary constructions this is a great benefit.

4.4.b. Challenges:

• To increase the use of prefabricated units will enhance the benefits for steel as to waste reduction, thus increase the market for steel.

• To facilitate separation of composite constructions in order to increase the recyclability of these constructions.

4.5 Land Use

• Prefabrication reduces need for space at the building site.

• Waste reduction as waste is reduced by an increased prefabrication. Also a well functioning system for recycling significantly reduces the need for deposits.

• Vertical extension reduces the need for land for e.g. new dwellings.

• Steel is an excellent material to use as to high-rise buildings.

• Low weight constructions enable the use of poor grounds to new buildings.

5. Summary of sustainability issues in different steps of the building process

Important considerations for steel constructions at different steps of the building process can be displayed in a figure. Examples of possible benefits at the different steps are listed.

Design Construction End of Life Use

Benefits as to: Material Efficiency Energy Efficiency Recyclability Flexibility

Benefits as to: Prefabrication High Quality Low Waste Dry Construction

Benefits as to: Durability Maintenance Efficiency Energy Efficiency Flexibility

Benefits as to: Demountability Recyclability Reusability

References

- Achieving Sustainable Construction, Corus Construction Centre, UK (2003)

- Björklund, T. et al, LCA of Building Frame Structures, Chalmers University of Technology, Sweden (1996)

- Construction in figures, FIEC, www.fiec.org, 2005-12-07

- Life Cycle Inventory Study for Steel Products 1999/2000, International Iron and Steel Institute, Belgium (2002)

- Sustainable Steel Construction, The Steel Construction Sector Sustainability Committee, UK (2003)

- Widman, J., Stålet och miljön (The steel and the environment), The Swedish Steel Producers Association, Sweden (2001) [in Swedish]

- ECSC 7215-PP-070, 2001-2004 ULSEB “Steel in Low-rise buildings, a symbiosis of cold formed sections and light rolled profiles”

- ECSC 7210-PA/PB/PC/PD/PE/381, 2002-2005, EURO-BUILD in Steel

- RFS-CR-03017, 2003-2006, EEBIS “Energy Efficient Buildings through Innovative systems in Steel”

Sustainability of buildings made of steel

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