|A life cycle assessment includes the mining of all raw materials used for building materials as well as fuel for heating and cooling. (PCA No. 14895)|
An LCA of a building includes environmental effects due to:
Extraction of materials and fuel used for energy;
Manufacture of building components;
Transportation of materials and components;
Assembly and construction;
Operation, including energy consumption, maintenance, repair, and renovations;
Demolition, disposal, recycling, and reuse of the building at the end of its functional or useful life. A full set of effects includes land use, resource use, climate change, health effects, acidification, and toxicity.
An LCA involves a time-consuming manipulation of large quantities of data. A model such as SimaPro (PRé Consultants, Amersfoot, the Netherlands) provides data for common materials and options for selecting LCA impacts. All models require a separate analysis of annual heating, cooling, and other occupant loads using a program such as DOE2.1e or EnergyPlus. This requires separate expertise than that of most LCA practitioners but is necessary for an accurate assessment of environmental impacts.
An LCI is the first stage of a LCA. An LCI accounts for all the individual environmental flows to and from a product throughout its life cycle. It consists of the materials and energy needed to make and use a product and the emissions to air, land, and water associated with making and using that product. PCA publishes reports with life cycle inventory (LCI) data on cement and concrete.
Several organizations have proposed how an LCA should be conducted. Organizations such as the International Organization for Standardization (ISO), the Society of Environmental Toxicology and Chemistry (SETAC), and the U.S. Environmental Protection Agency, have documented standard procedures for conducting an LCA. These procedures are generally consistent with each other; they are all scientific, transparent, and repeatable.
What is the Benefit of Concrete in an LCA?
|Life cycle costs and LCA include the impacts of heating and cooling a building throughout its life.|
Concrete’s thermal mass, combined with the optimal amount of insulation, saves energy over the life of a building, and reduces environmental impacts.
When comparing construction alternatives, an LCA provides a level playing field. An LCA is based on a consistent methodology applied across all products and at all stages of their production, transport, use, and disposal or recycling at end of life. A number of published articles espouse the sustainability of one building product over another based on a few selected metrics instead of a full life cycle assessment (LCA). For instance, some articles representing themselves as LCA studies use only the metrics of embodied energy or embodied CO2 emissions. These comparisons are flawed because they only consider limited metrics and do not cover a full life cycle assessment of the product or building. A full LCA includes the effects of energy use and associated emissions over the life of the product or structure, such as climate change, acidification, materials acquisition, and human health effects.
To get the most useful information out of an LCA, concrete should be considered in context of its end-use, such as in a building. Studies show that the most significant environmental impacts in a building are not from construction products but from the production and use of natural gas and electricity for building operations such as heating, ventilating, cooling, and lighting. The embodied energy of the construction products is approximately equal to 4 years of operational energy use. Stated another way, the operational energy during the life of the building is 85 to 95% of the total energy. A full LCA with an appropriate service life shows the benefits of using optimal amounts of insulation, thermal mass, orientation, and other energy saving features.
What is an LCI Boundary?
The usefulness of an LCA or LCI depends on where the boundaries of a product are drawn. A common approach is to consider all the environmental flows from cradle-to-gate. For example, the system boundary in Fig. 2 shows the most significant processes for ready mixed concrete operations. It includes all of the inputs and outputs associated with producing concrete—from extracting raw materials to producing ready mixed concrete. The system boundary includes the upstream profile of manufacturing cement, as well as quarrying and processing aggregates, and transporting cement, fly ash, and aggregates to the concrete plant. Energy and emissions associated with transporting the primary materials from their source to the concrete plant are also included in the boundary. However, in this case, it does not include upstream profiles of fuel, electricity, water, or supplementary cementitious materials.
An upstream profile can be thought of as a separate LCI that is itself an ingredient to a product. For example, the upstream profile of cement is essentially an LCI of cement, which can be imported into an LCI of concrete. The LCI of concrete itself can then be imported into an LCI of a product, such as an office building.
LCIs of materials generally do not consider embodied energy and emissions associated with construction of manufacturing plant equipment and buildings, nor the heating and cooling of such buildings. This is generally acceptable if their materials, embodied energy, and associated emissions account for less than 1% of those in the process being studied. For example, SETAC guidelines indicate that inputs to a process do not need to be included in an LCI if (i) they are less than 1% of the total mass of the processed materials or product; (ii) they do not contribute significantly to a toxic emission; and (iii) they do not have a significant associated energy consumption.
What is BEES?
BEES is the acronym for Building for Environmental and Economic Sustainability, a software tool developed by the National Institute of Standards and Technology (NIST). BEES combines a partial life cycle assessment and life cycle cost for building and construction materials into one tool. Results are presented in terms of life cycle assessment impacts, costs, or a combination of both. BEES strives to assist the architect, engineer, or purchaser choose a product that balances environmental and economic performance, thus finding cost-effective solutions for protecting the environment. BEES is limited to materials and cannot be used to combine materials into a building or building component. BEES includes resource extraction, manufacturing, maintenance, repair, and disposal. Since it is for materials and not buildings, it does not explicitly include the heating and cooling during the life of a building. BEES development was partially sponsored by the U.S. EPA Environmentally Preferable Purchasing (EPP) Program, a part of Executive Order 13101, "Greening the Government Through Waste Prevention, Recycling, and Federal Acquisition."
Concrete beams, columns, walls, floor slabs, and pavements can be analyzed using BEES. Variations in cement content are considered by selecting different 28-day compressive strengths of the concrete elements. Replacements for portland cement, such as fly ash, slag cement, silica fume, and limestone are also provided as options. In addition to concrete elements, BEES includes materials for roof sheathing, wall finishes, insulation, and floor coverings.
BEES uses the SETAC method of classification and characterization. These six life cycle assessment impact categories are used by BEES:
Indoor air quality is not often used by others as a life cycle assessment impact category, but is used by BEES in an effort to assess human health issues.
Default values for the relative weighting of the impact categories are provided in BEES based on work by others in the life cycle assessment arena; however these relative weightings can be changed by the user. The default proportion of the economic versus the environmental criteria is 50% each, and can also be changed by the user. The user may view results for each inventory flow, impact category, and overall environmental or economic score. BEES results can also be presented by life cycle stages: raw materials, manufacturing, transportation, use, and end of life.
What is ATHENA?
ATHENATM is a life cycle assessment software tool for comparing materials and systems. Walls, roofs, and floors constructed of concrete, steel, or wood can be compared individually or as part of a building. Manufacturers and architects can use ATHENA to establish a benchmark life cycle assessment for a given product or system and then determine the impact of changes to the benchmark. ATHENA includes environmental inputs and outputs from resource extraction, manufacturing, transportation, construction, maintenance, replacement, demolition, and disposal. It does not include operational energy such as heating and cooling during the life of the building. ATHENA calculates the life cycle inventory by accounting for (1.) energy, water, and materials use, and (2.) emissions to air, land, and water. ATHENA then performs a life cycle impact assessment using these six life cycle assessment impact indicators:
Natural resource use
Global warming potential
Pollutants to air
Pollutants to water
Caution should be used when evaluating products based on any set of impact indicators because impact categories are not equivalent and as such cannot be equally weighted.
What is SimaPro
The Dutch company PRé Consultants is a leader in developing tools for life cycle assessment. They created and continue to develop SimaPro, the most widely used life cycle assessment tool. SimaPro can be used to perform detailed and robust life cycle assessments of materials, components, buildings, and processes. It contains a large database of products and processes and seven comprehensive, widely-accepted impact assessment methods.
The user can either build up a product or process from scratch using the databases supplied with SimaPro, or the LCI of an existing product or process can be augmented with upstream and downstream profiles for other processes to determine a life cycle assessment. The impact assessment methods can be utilized to determine the impacts of materials, energy use, and pollutants. For example, upstream profiles can be the energy sources or extraction of raw materials. Downstream profiles can be other manufacturing steps used to make a final product. Table 1 provides the impact categories for three life cycle impact assessment methods in SimaPro.
For buildings, the user must input fuel and electricity energy for building operations such as heating, cooling, ventilation, and lights, and then import the appropriate upstream profiles.
The PCA LCA studies of houses incorporate U.S data for cement and concrete into SimaPro to determine environmental impacts.
References and ResourcesWebsites:
|Table 1 Impact categories for three life cycle impact assessment methods in SimaPro.|
ATHENA Sustainable Materials Institute www.ATHENAsmi.ca
Building for Environmental and Economic Sustainability (BEES) www.bfrl.nist.gov/oae/software/bees
International Organization for Standardization (ISO) www.iso.org
National Institute of Standards and Technology (NIST) www.nist.gov
Society of Environmental Toxicology and Chemistry (SETAC) www.setac.org
U.S. Environmental Protection Agency (EPA) www.epa.gov
Available for free:
Marceau and VanGeem, “Life Cycle Assessment of an Insulating Concrete Form House
Compared to a Wood Frame House,” PCA SN 2571, 2002.
Marceau and VanGeem, “Life Cycle Assessment of a Concrete Masonry House Compared to a Wood Frame House,” PCA SN 2572, 2002.
Guggemos and Horvath, “Comparison of Environmental Effects of Steel and Concrete Framed Buildings,” ASCE Journal of Infrastructure Systems, June 2005.
Amelio and VanGeem, “Life Cycle Cost Literature Survey and Database for Concrete,” SN 2484, 2000.
Available for a fee:
Concrete: Sustainability and Life Cycle, PCA CD033, 2003. [contains over 31 reports, articles, and presentations; most on life cycle cost, LCI, and LCA]