By Kyle Kerstiens, ASSOC. AIA, LEED AP
Whenever one looks to improve upon something, a baseline is needed to measure that improvement. When you start a weight loss program, your current weight becomes the baseline you continually measure against.
Our industry wants to spread the word that precast concrete products are sustainable. We also want to refine materials, equipment, processes and practices to become more sustainable. How do we measure improvement? Set a baseline. What is our baseline in terms of our impact on the environment? That’s where a Life Cycle Assessment (LCA) comes in.
What is LCA?
Life cycle assessment is a scientific method of evaluating the environmental impacts of a product over its full life cycle. It is one approach to measuring how sustainable a product really is. For example, a product itself may have little or no environmental impact, but the materials that go into making that product and the manufacturing process itself often have negative impacts. How a product is used can also create negative impacts. And when a product is no longer useful or cannot be maintained cost-effectively, its disposal back into the environment can also have negative impacts.
So a true measure of a product’s environmental impact must consider the full life cycle. Specifically, a cradle-to-grave LCA considers environmental impacts throughout a product’s life cycle from the time raw materials are extracted from the environment to make the product, to the time the product is finally recycled or returned to the environment.
In order to understand precast concrete’s environmental impact, the National Precast Concrete Association commissioned an LCA. This LCA study consists of two phases.
- Phase One addresses cradle-to-construction LCA of above-ground precast concrete products, assemblies and buildings relative to alternative structural and envelope material systems in six North American locations as well as a cradle-to-grave LCA of four underground infrastructure products: manhole, septic tank, utility vault and concrete pipe.
- Phase Two will assess construction-to-grave LCA for aboveground precast concrete products and would focus on building use, occupancy, maintenance and end-of-life for the various building scenarios.
Above Ground product assessment
The above-ground portion of the LCA is based on a functional five-story commercial office building that meets the climate-specific minimum building energy code requirements (R-value) and provides conditioned office space for approximately 130 people. The functional unit includes both the physical building and the service the building provides – that is, conditioned space for occupants. The life of the building is assumed to be 73 years, which is the median life for large commercial buildings.
Each building assembly is treated as a singular entity that meets the minimum building energy code requirements (R-value). As modeled there are three primary structural systems (precast concrete, cast-in-place concrete and steel) and five interchangeable wall envelope systems (curtain wall, brick and steel stud, precast concrete, insulated precast concrete, and insulated precast concrete with brick veneer) making a total of 15 scenarios modeled. The study and model also include six regional climate zone locations and 15 scenarios for a total of 90 scenarios to be modeled.
Underground product assessment
The underground portion of the LCA does not compare values with other materials because when this work was carried out in 2009 and 2010, there was no comparable LCA study of underground products made from other materials.
The USGBC’s LEED rating systems are moving slowly away from their “first cost” building rating system and have begun rethinking the overall life cycle as a factor of sustainability. Currently offered is a LEED pilot credit for an LCA study completed on a project. As rating systems like these and standards by ASTM for Sustainable LCA studies become more prevalent, so will the global understanding that concrete is truly a sustainable material.
So what have we learned from the LCA Study Phase One? Here are some points of interest:
- We can reduce overall concrete energy use by 10% by substituting 20% fly ash in cement.
- With regard to total CO2 footprint (contribution to the atmosphere):
- Raw material manufacturing is the largest contributor (46 to 51%)
- Transportation of the finished product to the construction site adds 14 to 15%
- Plant operations are responsible for 9 to 10% of CO2 emissions
NPCA: industry leader
The important point is that we now have a baseline against which to measure. As the industry continues to implement more sustainable practices, we can take subsequent measurements to demonstrate how far we’ve come. We will be walking the walk, and not just talking the talk.
NPCA will be looking at proposals for Phase Two, and based on recommendations, the Board of Directors will decide whether to proceed. This brings up a significant point: NPCA is leading the construction industry by conducting this study.
The summary of the underground portion of Phase One is available online at www.precast.org in the Members Only section.
For more questions on this or other sustainable topics, please contact NPCA at (800) 366-7731 or via email.